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  • 1.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Hallberg, Per
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Jóhannesson, Gauti
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Lindén, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Zarrinkoob, Laleh
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Blood flow of ophthalmic artery in healthy individuals determined by phase-contrast magnetic resonance imaging2013Inngår i: Investigative Ophthalmology and Visual Science, ISSN 0146-0404, E-ISSN 1552-5783, Vol. 54, nr 4, s. 2738-2745Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    PURPOSE: Recent development of magnetic resonance imaging (MRI) offers new possibilities to assess ocular blood flow. This prospective study evaluates the feasibility of phase-contrast MRI (PCMRI) to measure flow rate in the ophthalmic artery (OA) and establish reference values in healthy young (HY) and elderly (HE) subjects.

    METHODS: Fifty HY subjects (28 females, 21-30 years of age) and 44 HE (23 females, 64-80 years of age) were scanned on a 3-Tesla MR system. The PCMRI sequence had a spatial resolution of 0.35 mm per pixel, with the measurement plan placed perpendicularly to the OA. Mean flow rate (Qmean), resistive index (RI), and arterial volume pulsatility of OA (ΔVmax) were measured from the flow rate curve. Accuracy of PCMRI measures was investigated using a vessel-phantom mimicking the diameter and the flow rate range of the human OA.

    RESULTS: Flow rate could be assessed in 97% of the OAs. Phantom investigations showed good agreement between the reference and PCMRI measurements with an error of <7%. No statistical difference was found in Qmean between HY and HE individuals (HY: mean ± SD = 10.37 ± 4.45 mL/min; HE: 10.81 ± 5.15 mL/min, P = 0.655). The mean of ΔVmax (HY: 18.70 ± 7.24 μL; HE: 26.27 ± 12.59 μL, P < 0.001) and RI (HY: 0.62 ± 0.08; HE: 0.67 ± 0.1, P = 0.012) were significantly different between HY and HE.

    CONCLUSIONS: This study demonstrated that the flow rate of OA can be quantified using PCMRI. There was an age difference in the pulsatility parameters; however, the mean flow rate appeared independent of age. The primary difference in flow curves between HE and HY was in the relaxation phase of the systolic peak.

  • 2.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Israelsson, Hanna
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Brain ventricular size in healthy elderly: comparison between evans index and volume measurement.2010Inngår i: Neurosurgery, ISSN 0148-396X, E-ISSN 1524-4040, Vol. 67, nr 1, s. 94-99Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: A precise definition of ventricular enlargement is important in the diagnosis of hydrocephalus as well as in assessing central atrophy. The Evans index (EI), a linear ratio between the maximal frontal horn width and the cranium diameter, has been extensively used as an indirect marker of ventricular volume (VV). With modern imaging techniques, brain volume can be directly measured. OBJECTIVE: To determine reference values of intracranial volumes in healthy elderly individuals and to correlate volumes with the EI. METHODS: Magnetic resonance imaging (3 T) was performed in 46 healthy white elderly subjects (mean age +/- standard deviation, 71 +/- 6 years) and in 20 patients (74 +/- 7 years) with large ventricles according to visual inspection. VV, relative VV (RVV), and EI were assessed. Ventricular dilation was defined using VV and EI by a value above the 95th percentile range for healthy elderly individuals. RESULTS: In healthy elderly subjects, we found VV = 37 +/- 18 mL, RVV = 2.47 +/- 1.17%, and EI = 0.281 +/- 0.027. Including the patients, there was a strong correlation between EI and VV (R = 0.94) as well as between EI and RVV (R = 0.95). However, because of a wide 95% prediction interval (VV: +/-45 mL; RVV: +/- 2.54%), EI did not give a sufficiently good estimate of VV and RVV. CONCLUSION: VV (or RVV) and the EI reflect different properties. The exclusive use of EI in clinical studies as a marker of enlarged ventricles should be questioned. We suggest that the definition of dilated ventricles in white elderly individuals be defined as VV >77 mL or RVV >4.96 %. Future studies should compare intracranial volumes with clinical characteristics and prognosis.

  • 3.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Lindqvist, Tomas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Petterson, E
    Warntjes, JBM
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Evaluation of automatic measurement of the intracranial volume based on quantitative MR imaging2012Inngår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 33, nr 10, s. 1951-1956Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND AND PURPOSE: Brain size is commonly described in relation to ICV, whereby accurate assessment of this quantity is fundamental. Recently, an optimized MR sequence (QRAPMASTER) was developed for simultaneous quantification of T1, T2, and proton density. ICV can be measured automatically within minutes from QRAPMASTER outputs and a dedicated software, SyMRI. Automatic estimations of ICV were evaluated against the manual segmentation.

    MATERIALS AND METHODS: In 19 healthy subjects, manual segmentation of ICV was performed by 2 neuroradiologists (Obs1, Obs2) by using QBrain software and conventional T2-weighted images. The automatic segmentation from the QRAPMASTER output was performed by using SyMRI. Manual corrections of the automatic segmentation were performed (corrected-automatic) by Obs1 and Obs2, who were blinded from each other. Finally, the repeatability of the automatic method was evaluated in 6 additional healthy subjects, each having 6 repeated QRAPMASTER scans. The time required to measure ICV was recorded.

    RESULTS: No significant difference was found between reference and automatic (and corrected-automatic) ICV (P > .25). The mean difference between the reference and automatic measurement was -4.84 ± 19.57 mL (or 0.31 ± 1.35%). Mean differences between the reference and the corrected-automatic measurements were -0.47 ± 17.95 mL (-0.01 ± 1.24%) and -1.26 ± 17.68 mL (-0.06 ± 1.22%) for Obs1 and Obs2, respectively. The repeatability errors of the automatic and the corrected-automatic method were <1%. The automatic method required 1 minute 11 seconds (SD = 12 seconds) of processing. Adding manual corrections required another 1 minute 32 seconds (SD = 38 seconds).

    CONCLUSIONS: Automatic and corrected-automatic quantification of ICV showed good agreement with the reference method. SyMRI software provided a fast and reproducible measure of ICV.

  • 4.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Petr, J.
    Wahlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Wirestam, R.
    Zarrinkoob, Laleh
    Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Partial Volume Correction of Cerebral Perfusion Estimates Obtained by Arterial Spin Labeling2015Inngår i: 16th Nordic-Baltic Conference on Biomedical Engineering: 16. NBC & 10. MTD 2014 joint conferences. October 14-16, 2014, Gothenburg, Sweden, 2015, Vol. 48, s. 17-19Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Arterial Spin labeling (ASL) is a fully non-invasive MRI method capable to quantify cerebral perfusion. However, gray (GM) and white matter (WM) ASL perfusions are difficult to assess separately due to limited spatial resolution increasing the partial volume effects (PVE). In the present study, ASL PVE correction was implemented based on a regression algorithm in 22 healthy young men. PVE corrected perfusion of GM and WM were compared to previous studies. PVE-corrected GM perfusion was in agreement with literature values. In general, WM perfusion was higher despite the use of PVE correction.

  • 5.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    MR imaging of brain volumes: evaluation of a fully automatic software2011Inngår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 32, nr 2, s. 408-412Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND AND PURPOSE: Automatic assessment of brain volumes is needed in researchand clinical practice. Manual tracing is still the criterionstandard but is time-consuming. It is important to validatethe automatic tools to avoid the problems of clinical studiesdrawing conclusions on the basis of brain volumes estimatedwith methodologic errors. The objective of this study was toevaluate a new commercially available fully automatic softwarefor MR imaging of brain volume assessment. Automatic and expertmanual brain volumes were compared.

    MATERIALS AND METHODS: MR imaging (3T, axial T2 and FLAIR) was performed in 41 healthyelderly volunteers (mean age, 70 ± 6 years) and 20 patientswith hydrocephalus (mean age, 73 ± 7 years). The softwareQBrain was used to manually and automatically measure the followingbrain volumes: ICV, BTV, VV, and WMHV. The manual method hasbeen previously validated and was used as the reference. Agreementbetween the manual and automatic methods was evaluated by usinglinear regression and Bland-Altman plots.

    RESULTS: There were significant differences between the automatic andmanual methods regarding all volumes. The mean differences wereICV = 49 ± 93 mL (mean ± 2SD, n = 61), BTV = 11± 70 mL, VV = –6 ± 10 mL, and WMHV = 2.4± 9 mL. The automatic calculations of brain volumes tookapproximately 2 minutes per investigation.

    CONCLUSIONS: The automatic tool is promising and provides rapid assessmentof brain volumes. However, the software needs improvement beforeit is incorporated into research or daily use. Manual segmentationremains the reference method.

  • 6.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Zarrinkoob, Laleh
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Wirestam, R.
    Petr, J.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Accuracy of Parenchymal Cerebral Blood Flow Measurements Using Pseudocontinuous Arterial Spin-Labeling in Healthy Volunteers2015Inngår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 36, nr 10, s. 1816-1821Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND AND PURPOSE: The arterial spin-labeling method for CBF assessment is widely available, but its accuracy is not fully established. We investigated the accuracy of a whole-brain arterial spin-labeling technique for assessing the mean parenchymal CBF and the effect of aging in healthy volunteers. Phase-contrast MR imaging was used as the reference method. MATERIALS AND METHODS: Ninety-two healthy volunteers were included: 49 young (age range, 20-30 years) and 43 elderly (age range, 65-80 years). Arterial spin-labeling parenchymal CBF values were averaged over the whole brain to quantify the mean pCBF(ASL) value. Total. CBF was assessed with phase-contrast MR imaging as the sum of flows in the internal carotid and vertebral arteries, and subsequent division by brain volume returned the pCBF(PCMRI) value. Accuracy was considered as good as that of the reference method if the systematic difference was less than 5 mL/min/100 g of brain tissue and if the 95% confidence intervals were equal to or better than +/- 10 mL/min/100 g. RESULTS: pCBF(ASL) correlated to pCBF(PCMRI) (r = 0.73; P < .001). Significant differences were observed between the pCBF(ASL) and pCBF(PCMRI) values in the young (P = .001) and the elderly (P < .001) volunteers. The systematic differences (mean 2 standard deviations) were -4 +/- 14 mL/min/100 g in the young subjects and 6 +/- 12 mL/min/100 g in the elderly subjects. Young subjects showed higher values than the elderly subjects for pCBF(PCMRI) (young, 57 +/- 8 mL/min/100 g; elderly, 54 +/- 7 mL/min/100 g; P = .05) and pCBF(ASL) (young, 61 +/- 10 mL/min/100 g; elderly, 48 +/- 10 mL/min/100 g; P < .001). CONCLUSIONS: The limits of agreement were too wide for the arterial spin-labeling method to be considered satisfactorily accurate, whereas the systematic overestimation in the young subjects and underestimation in the elderly subjects were close to acceptable. The age-related decrease in parenchymal CBF was augmented in arterial spin-labeling compared with phase-contrast MR imaging.

  • 7.
    Andersson, Kennet
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Manchester, I. R.
    Laurell, Katarina
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Cesarini, K. Giuliana
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Measurement of CSF dynamics with oscillating pressure infusion2013Inngår i: Acta Neurologica Scandinavica, ISSN 0001-6314, E-ISSN 1600-0404, Vol. 128, nr 1, s. 17-23Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Introduction Infusion tests are used to diagnose and select patients with idiopathic normal pressure hydrocephalus (INPH) for shunt surgery. The test characterizes cerebrospinal fluid dynamics and estimates parameters of the cerebrospinal fluid system, the pressure-volume index (PVI) and the outflow conductance (Cout). The Oscillating Pressure Infusion (OPI) method was developed to improve the test and reduce the investigation time. The aim of this study was to evaluate the new OPI method by comparing it with an established reference method. Methods Forty-seven patients (age 71.2 +/- 8.9years) with communicating hydrocephalus underwent a preoperative lumbar infusion investigation with two consecutive infusion protocols, reference (42min) and new (20min), that is, 94 infusion tests in total. The OPI method estimated Cout and PVI simultaneously. A real-time analysis of reliability was applied to investigate the possibility of infusion time reduction. Results The difference in Cout between the methods was 1.2 +/- 1.8l/s/kPa (Rout=-0.8 +/- 3.5mmHg/ml/min), P<0.05, n=47. With the reliability analysis, the preset 20min of active infusion could have been even further reduced for 19 patients to between 10 and 19min. PVI was estimated to 16.1 +/- 6.9ml, n=47. Conclusions The novel Oscillating Pressure Infusion method produced real-time estimates of Cout including estimates of reliability that was in good agreement with the reference method and allows for a reduced and individualized investigation time.

  • 8.
    Andersson, Kennet
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Manchester, Ian R
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Andersson, Nina
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Shiriaev, Anton
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Assessment of cerebrospinal fluid outflow conductance using an adaptive observer-experimental and clinical evaluation2007Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 28, nr 11, s. 1355-1368Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Idiopathic normal pressure hydrocephalus (INPH) patients have a disturbance in the dynamics of the cerebrospinal fluid (CSF) system. The outflow conductance, C, of the CSF system has been suggested to be prognostic for positive outcome after treatment with a CSF shunt. All current methods for estimation of C have drawbacks; these include lack of information on the accuracy and relatively long investigation times. Thus, there is a need for improved methods. To accomplish this, the theoretical framework for a new adaptive observer (OBS) was developed which provides real-time estimation of C. The aim of this study was to evaluate the OBS method and to compare it with the constant pressure infusion (CPI) method. The OBS method was applied to data from infusion investigations performed with the CPI method. These consisted of repeated measurements on an experimental set-up and 30 patients with suspected INPH. There was no significant difference in C between the CPI and the OBS method for the experimental set-up. For the patients there was a significant difference, −0.84 ± 1.25 µl (s kPa)−1, mean ± SD (paired sample t-test, p < 0.05). However, such a difference is within clinically acceptable limits. This encourages further development of this new real-time approach for estimation of the outflow conductance.

  • 9.
    Andersson, Kennet
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Manchester, Ian R
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Eklund, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Real-time estimation of cerebrospinal fluid system parameters via oscillating pressure infusion2010Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 48, nr 11, s. 1123-1131Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Hydrocephalus is related to a disturbed cerebrospinal fluid (CSF) system. For diagnosis, lumbar infusion test are performed to estimate outflow conductance, C (out), and pressure volume index, PVI, of the CSF system. Infusion patterns and analysis methods used in current clinical practice are not optimized. Minimizing the investigation time with sufficient accuracy is of major clinical relevance. The aim of this study was to propose and experimentally evaluate a new method, the oscillating pressure infusion (OPI). The non-linear model of the CSF system was transformed into a linear time invariant system. Using an oscillating pressure pattern and linear system identification methods, C (out) and PVI with confidence intervals, were estimated in real-time. Forty-two OPI and constant pressure infusion (CPI) investigations were performed on an experimental CSF system, designed with PVI = 25.5 ml and variable C (out). The ARX model robustly estimated C (out) (mean C (out,OPI) - C (out,CPI) = 0.08 μl/(s kPa), n = 42, P = 0.68). The Box-Jenkins model proved most reliable for PVI (23.7 ± 2.0 ml, n = 42). The OPI method, with its oscillating pressure pattern and new parameter estimation methods, efficiently estimated C (out) and PVI as well as their confidence intervals in real-time. The results from this experimental study show potential for the OPI method and supports further evaluation in a clinical setting.

  • 10.
    Andersson, Kennet
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Sundström, Nina
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Effect of resting pressure on the estimate of cerebrospinal fluid outflow conductance2011Inngår i: Fluids and barriers of the CNS, ISSN 2045-8118, Vol. 8, nr 1, s. 15-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: A lumbar infusion test is commonly used as a predictive test for patients with normal pressure hydrocephalus and for evaluation of cerebrospinal fluid (CSF) shunt function. Different infusion protocols can be used to estimate the outflow conductance (Cout) or its reciprocal the outflow resistance, (Rout) with or without using the baseline resting pressure, Pr. Both from a basic physiological research and a clinical perspective, it is important to understand the limitations of the model on which infusion tests are based. By estimating Cout using two different analyses, with or without Pr, the limitations could be explored. The aim of this study was to compare the Cout estimates, and investigate what effect Pr had on the results.

    METHODS: Sixty-three patients that underwent a constant pressure infusion protocol as part of their preoperative evaluation for normal pressure hydrocephalus, were included (age 70.3+/-10.8 years (mean +/-SD). The analysis was performed without (Cexcl Pr) and with (Cincl Pr) Pr. The estimates were compared using Bland-Altman plots and paired sample t-tests (p<0.05 considered significant).

    RESULTS: Mean Cout for the 63 patients was: Cexcl Pr = 7.0+/-4.0 (mean +/-SD) ul/(s kPa) and Cincl Pr = 9.1+/-4.3 ul/(s kPa) and Rout was 19.0+/-9.2 and 17.7+/-11.3 mmHg/ml/min, respectively. There was a positive correlation between methods (r=0.79, n=63, p<0.01). The difference, DeltaCout, -2.1+/-2.7 ul/(s kPa) between methods was significant (p<0.01) and DeltaRout was 1.2 +/- 8.8 mmHg/ml/min). The Bland-Altman plot visualized that the variation around the mean difference was similar all through the range of measured values and there was no correlation between DeltaCout and Cout.

    CONCLUSIONS: The difference between Cout estimates, obtained from analyses with or without Pr, needs to be taken into consideration when comparing results from studies using different infusion test protocols. The study suggests variation in CSF formation rate, variation in venous pressure or a pressure dependent Cout as possible causes for the deviation from the CSF absorption model seen in some patients.

  • 11.
    Andersson, Nina
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Grip, Helena
    Umeå universitet, Medicinska fakulteten, Institutionen för samhällsmedicin och rehabilitering, Sjukgymnastik.
    Lindvall, Peter
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Koskinen, Lars-Owe D
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Brändström, Helge
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Anestesiologi och intensivvård.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Air transport of patients with intracranial air: computer model of pressure effects2003Inngår i: Aviation, Space and Environmental Medicine, ISSN 0095-6562, E-ISSN 1943-4448, Vol. 74, nr 2, s. 138-144Artikkel i tidsskrift (Fagfellevurdert)
  • 12.
    Andersson, Nina
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi. Neurologi.
    Bäcklund, Tomas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Assessment of cerebrospinal fluid outflow conductance using constant-pressure infusion - a method with real time estimation of reliability2005Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 26, nr 6, s. 1137-1148Artikkel i tidsskrift (Fagfellevurdert)
  • 13.
    Andersson, Nina
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Department of Biomedical Engineering and Informatics, Umeå University Hospital.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Department of Biomedical Engineering and Informatics, Umeå University Hospital.
    Dependency of cerebrospinal fluid outflow resistance on intracranial pressure2008Inngår i: Journal of Neurosurgery, ISSN 0022-3085, E-ISSN 1933-0693, Vol. 109, nr 5, s. 918-922Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    OBJECT: The outflow resistance (Rout) of the cerebrospinal fluid (CSF) system has generally been accepted by most investigators as independent of intracranial pressure (ICP), but there are also those claiming that it is not. The general belief is that this question has been investigated numerous times in the past, but few studies have actually been specifically aimed at looking at this relationship, and no study has been able to provide scientific evidence to elucidate fully this fundamental and important issue. The objective of this study was to investigate the relationship between ICP and CSF outflow in 30 patients investigated for idiopathic normal-pressure hydrocephalus. METHODS: Lumbar infusion tests with constant pressure levels were performed, and ICP and corresponding flow were measured on 6 pressure levels for each patient. All data were standardized for comparison. RESULTS: In the range of moderate increases from baseline pressure (approximately 5-12 mm Hg, mean baseline pressure 11.7 mm Hg), the assumption of a pressure-independent Rout was confirmed (p = 0.5). However, when the pressure increment from baseline pressure was larger (approximately 15-22 mm Hg), the relationship had a nonlinear tendency (p < 0.05). CONCLUSIONS: The results of this study support the classic textbook theory of a pressure-independent Rout in the normal ICP range, where the CSF system is commonly operating. However, the theory might have to be questioned in regions where ICP exceeds baseline pressure by too much.

  • 14.
    Andersson, Nina
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Wiklund, Urban
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Adaptive method for assessment of cerebrospinal fluid outflow conductance.2007Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 45, nr 4, s. 337-343Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Outflow conductance (C out) is important for predicting shunt responsiveness in patients with suspected idiopathic adult hydrocephalus syndrome (IAHS). C out is determined by performing an infusion test into the cerebrospinal fluid system, and the reliability of the test is dependent on the measurement time. The objective of this study was to develop an adaptive signal analysis method to reduce the investigation time, by taking the individual intracranial pressure variations of the patient into consideration. The method was evaluated on 28 patients with suspected IAHS. The results from full time investigations (60 min) were compared to the results of the new algorithm. Applying the new adaptive method resulted in a reduction of mean investigation time by 14.3 ± 5.9 min (mean ± SD), p < 0.01. The reduction of reliability in the C out estimation was found clinically negligible. We thus recommend this adaptive method to be used when performing constant pressure infusion tests.

  • 15.
    Arnell, Kai
    et al.
    Department of Paediatric Surgery, University Hospital, Uppsala.
    Koskinen, Lars-Owe D
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurokirurgi.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Eklund, Anders
    Evaluation of Strata NSC and Codman Hakim adjustable cerebrospinal fluid shunts and their corresponding antisiphon devices: laboratory investigation2009Inngår i: Journal of Neurosurgery: Pediatrics, ISSN 1933-0707, E-ISSN 1933-0715, Vol. 3, nr 3, s. 166-172Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    OBJECT: The authors investigated and compared the in vitro characteristics of 2 CSF shunts, the Strata NSC and the Codman Hakim, and their corresponding antisiphon devices (ASDs).

    METHODS: Six new CSF shunts and the corresponding ASDs for each model were tested in an automated, computerized experimental setup based on pressure regulation. Opening pressure accuracy, resistance, sensitivity to abdominal pressure, antisiphon effect, and the influence of different ASD positions were determined.

    RESULTS: In general the shunts performed according to the manufacturers' specifications. However, at the lowest setting, the opening pressure of the Strata NSC was close to 0, and in the Codman Hakim shunt, it was higher than specified. The resistance in the Codman Hakim shunt (5.4 mm Hg/ml/min) was much higher than that in the Strata NSC (3.6 mm Hg/ml/min). Abdominal pressure affected opening pressure in both valves. Positioning the Strata ASD above or below the ventricular catheter tip resulted in higher and lower opening pressures, respectively, than when it was placed in line with the catheter. The positioning of the Codman Hakim ASD did not influence the opening pressure.

    CONCLUSIONS: Both CSF shunts work properly, but at the lowest setting the opening pressure of the Strata NSC was near 0 and in the Codman Hakim it was twice the manufacturer's specifications. The resistance in the Strata NSC was below the normal physiological range, and in the Codman Hakim device it was in the lower range of normal. The ASD did not change the shunt characteristics in the lying position and therefore might not do so in children. If this is the case, then a shunt system with an integrated ASD could be implanted at the first shunt insertion, thus avoiding a second operation and the possibility of infection.

  • 16.
    Behrens, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap. Blekinge Centre of Competence, Blekinge Hospital Karlskrona, Karlskrona, Sweden.
    Eklund, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Elgh, Eva
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Psykiatri.
    Smith, Cynthia
    Williams, Michael A
    Malm, Jan
    A computerized neuropsychological test battery designed for idiopathic normal pressure hydrocephalus2014Inngår i: Fluids and Barriers of the CNS, ISSN 2045-8118, E-ISSN 2045-8118, Vol. 11, artikkel-id 22Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: A tool for standardized and repeated neuropsychological assessments in patients with idiopathic normal pressure hydrocephalus (INPH) is needed. The objective of this study was to develop a computerized neuropsychological test battery designed for INPH and to evaluate its reliability, validity and patient's ability to complete the tests.

    METHODS: Based on a structured review of the literature on neuropsychological testing in INPH, the eight tests most sensitive to the INPH cognitive profile were implemented in a computerized format. The Geriatric Depression Scale (GDS) was also included. Tests were presented on a touch-screen monitor, with animated instructions and speaker sound. The battery was evaluated with the following cohorts: A. Test-retest reliability, 44 healthy elderly; B. Validity against standard pen and pencil testing, 28 patients with various cognitive impairments; C. Ability to complete test battery, defined as completion of at least seven of the eight tests, 40 investigated for INPH.

    RESULTS: A. All except the figure copy test showed good test-retest reliability, r = 0.67-0.90; B. A high correlation was seen between conventional and computerized tests (r = 0.66-0.85) except for delayed recognition and figure copy task; C. Seventy-eight percent completed the computerized battery; Patients diagnosed with INPH (n = 26) performed worse on all tests, including depression score, compared to healthy controls.

    CONCLUSIONS: A new computerized neuropsychological test battery designed for patients with communicating hydrocephalus and INPH was introduced. Its reliability, validity for general cognitive impairment and completion rate for INPH was promising. After exclusion of the figure copy task, the battery is ready for clinical evaluation and as a next step we suggest validation for INPH and a comparison before and after shunt surgery.

    TRIAL REGISTRATION: ClinicalTrials.org NCT01265251.

  • 17.
    Behrens, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Lenfeldt, Niklas
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Koskinen, Lars-Owe
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurokirurgi.
    Transcranial Doppler pulsatility index: not an accurate method to assess intracranial pressure.2010Inngår i: Neurosurgery, ISSN 0148-396X, E-ISSN 1524-4040, Vol. 66, nr 6, s. 1050-1057Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: Transcranial Doppler sonography (TCD) assessment of intracranial blood flow velocity has been suggested to accurately determine intracranial pressure (ICP). OBJECTIVE: We attempted to validate this method in patients with communicating cerebrospinal fluid systems using predetermined pressure levels. METHODS: Ten patients underwent a lumbar infusion test, applying 4 to 5 preset ICP levels. On each level, the pulsatility index (PI) in the middle cerebral artery was determined by measuring the blood flow velocity using TCD. ICP was simultaneously measured with an intraparenchymal sensor. ICP and PI were compared using correlation analysis. For further understanding of the ICP-PI relationship, a mathematical model of the intracranial dynamics was simulated using a computer. RESULTS: The ICP-PI regression equation was based on data from 8 patients. For 2 patients, no audible Doppler signal was obtained. The equation was ICP = 23*PI + 14 (R = 0.22, P < .01, N = 35). The 95% confidence interval for a mean ICP of 20 mm Hg was -3.8 to 43.8 mm Hg. Individually, the regression coefficients varied from 42 to 90 and the offsets from -32 to +3. The mathematical simulations suggest that variations in vessel compliance, autoregulation, and arterial pressure have a serious effect on the ICP-PI relationship. CONCLUSIONS: The in vivo results show that PI is not a reliable predictor of ICP. Mathematical simulations indicate that this is caused by variations in physiological parameters.

  • 18.
    Behrens, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Lenfeldt, Niklas
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Koskinen, Lars-Owe D
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurokirurgi.
    Intracranial Pressure and Pulsatility Index:  2011Inngår i: Neurosurgery, ISSN 0148-396X, E-ISSN 1524-4040, Vol. 69, nr 4, s. E1033-E1034Artikkel i tidsskrift (Fagfellevurdert)
  • 19.
    Behrens, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Lenfeldt, Niklas
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Qvarlander, Sara
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Koskinen, Lars-Owe
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Are intracranial pressure wave amplitudes measurable through lumbar puncture?2013Inngår i: Acta Neurologica Scandinavica, ISSN 0001-6314, E-ISSN 1600-0404, Vol. 127, nr 4, s. 233-241Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

     Objective The aim of this study was to investigate whether pulsations measured in the brain correspond to those measured in lumbar space, and subsequently whether lumbar punctures could replace invasive recordings. Methods In ten patients with normal pressure hydrocephalus, simultaneous recordings of the intracranial pressure (ICP; intraparenchymal) and lumbar pressure (LP; cerebrospinal fluid pressure) were performed. During registration, pressure was altered between resting pressure and 45mmHg using an infusion test. Data were analyzed regarding pulsations (i.e., amplitudes). Also, the pressure sensors were compared in a bench test. Results The correlation between intracranial and lumbar amplitudes was 0.98. At resting pressure, and moderately elevated ICP, intracranial pulse amplitudes exceeded that of lumbar space with about 0.9mmHg. At the highest ICP, the difference changed to 0.2mmHg. The bench test showed that the agreement of sensor readings was good at resting pressure, but reduced at higher amplitudes. Conclusions Compared to intracranial registrations, amplitudes measured through lumbar puncture were slightly attenuated. The bench test showed that differences were not attributable to dissimilarities of the sensor systems. A lumbar pressure amplitude measurement is an alternative to ICP recording, but the thresholds for what should be interpreted as elevated amplitudes need to be adjusted.

  • 20.
    Dunås, Tora
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Holmgren, Madelene
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Accuracy of blood flow assessment in cerebral arteries with 4D flow MRI: Evaluation with three segmentation methods2019Inngår i: Journal of Magnetic Resonance Imaging, ISSN 1053-1807, E-ISSN 1522-2586, Vol. 50, nr 2, s. 511-518Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Accelerated 4D flow MRI allows for high‐resolution velocity measurements with whole‐brain coverage. Such scans are increasingly used to calculate flow rates of individual arteries in the vascular tree, but detailed information about the accuracy and precision in relation to different postprocessing options is lacking.

    Purpose: To evaluate and optimize three proposed segmentation methods and determine the accuracy of in vivo 4D flow MRI blood flow rate assessments in major cerebral arteries, with high‐resolution 2D PCMRI as a reference.

    Study Type: Prospective.

    Subjects: Thirty‐five subjects (20 women, 79 ± 5 years, range 70–91 years).

    Field Strength/Sequence: 4D flow MRI with PC‐VIPR and 2D PCMRI acquired with a 3 T scanner.

    Assessment: We compared blood flow rates measured with 4D flow MRI, to the reference, in nine main cerebral arteries. Lumen segmentation in the 4D flow MRI was performed with k‐means clustering using four different input datasets, and with two types of thresholding methods. The threshold was defined as a percentage of the maximum intensity value in the complex difference image. Local and global thresholding approaches were used, with evaluated thresholds from 6–26%.

    Statistical Tests: Paired t‐test, F‐test, linear correlation (P < 0.05 was considered significant) along with intraclass correlation (ICC).

    Results: With the thresholding methods, the lowest average flow difference was obtained for 20% local (0.02 ± 15.0 ml/min, ICC = 0.97, n = 310) or 10% global (0.08 ± 17.3 ml/min, ICC = 0.97, n = 310) thresholding with a significant lower standard deviation for local (F‐test, P = 0.01). For all clustering methods, we found a large systematic underestimation of flow compared with 2D PCMRI (16.1–22.3 ml/min).

    Data Conclusion: A locally adapted threshold value gives a more stable result compared with a globally fixed threshold. 4D flow with the proposed segmentation method has the potential to become a useful reliable clinical tool for assessment of blood flow in the major cerebral arteries.

    Level of Evidence: 2

    Technical Efficacy: Stage 2

  • 21.
    Dunås, Tora
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Zarrinkoob, Laleh
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Automatic labeling of cerebral arteries in magnetic resonance angiography2016Inngår i: Magnetic Resonance Materials in Physics, Biology and Medicine, ISSN 0968-5243, E-ISSN 1352-8661, Vol. 29, nr 1, s. 39-47Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In order to introduce 4D flow magnetic resonance imaging (MRI) as a standard clinical instrument for studying the cerebrovascular system, new and faster postprocessing tools are necessary. The objective of this study was to construct and evaluate a method for automatic identification of individual cerebral arteries in a 4D flow MRI angiogram. Forty-six elderly individuals were investigated with 4D flow MRI. Fourteen main cerebral arteries were manually labeled and used to create a probabilistic atlas. An automatic atlas-based artery identification method (AAIM) was developed based on vascular-branch extraction and the atlas was used for identification. The method was evaluated by comparing automatic with manual identification in 4D flow MRI angiograms from 67 additional elderly individuals. Overall accuracy was 93 %, and internal carotid artery and middle cerebral artery labeling was 100 % accurate. Smaller and more distal arteries had lower accuracy; for posterior communicating arteries and vertebral arteries, accuracy was 70 and 89 %, respectively. The AAIM enabled fast and fully automatic labeling of the main cerebral arteries. AAIM functionality provides the basis for creating an automatic and powerful method to analyze arterial cerebral blood flow in clinical routine.

  • 22.
    Dunås, Tora
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Zarrinkoob, Laleh
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    A Stereotactic Probabilistic Atlas for the Major Cerebral Arteries2017Inngår i: Neuroinformatics, ISSN 1539-2791, E-ISSN 1559-0089, Vol. 15, nr 1, s. 101-110Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Improved whole brain angiographic and velocity-sensitive MRI is pushing the boundaries of noninvasively obtained cerebral vascular flow information. The complexity of the information contained in such datasets calls for automated algorithms and pipelines, thus reducing the need of manual analyses by trained radiologists. The objective of this work was to lay the foundation for such automated pipelining by constructing and evaluating a probabilistic atlas describing the shape and location of the major cerebral arteries. Specifically, we investigated how the implementation of a non-linear normalization into Montreal Neurological Institute (MNI) space improved the alignment of individual arterial branches. In a population-based cohort of 167 subjects, age 64-68 years, we performed 4D flow MRI with whole brain volumetric coverage, yielding both angiographic and anatomical data. For each subject, sixteen cerebral arteries were manually labeled to construct the atlas. Angiographic data were normalized to MNI space using both rigid-body and non-linear transformations obtained from anatomical images. The alignment of arterial branches was significantly improved by the non-linear normalization (p < 0.001). Validation of the atlas was based on its applicability in automatic arterial labeling. A leave-one-out validation scheme revealed a labeling accuracy of 96 %. Arterial labeling was also performed in a separate clinical sample (n = 10) with an accuracy of 92.5 %. In conclusion, using non-linear spatial normalization we constructed an artery-specific probabilistic atlas, useful for cerebral arterial labeling.

  • 23.
    Dunås, Tora
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Zarrinkoob, Laleh
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Ambarki, Khalid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Towards Automatic Identification of Cerebral Arteries in 4D Flow MRI2015Inngår i: 16th Nordic-Baltic Conference on Biomedical Engineering / [ed] Henrik Mindedal, Mikael Persson, 2015, Vol. 48, s. 40-43Konferansepaper (Fagfellevurdert)
    Abstract [en]

    4D flow MRI is a powerful imaging technique which provides an angiographic image with information about blood flow in a large volume, time resolved over the cardiac cycle, in a short imaging time. This study aims to develop an automatic method for identification of cerebral arteries. The proposed method is based on an atlas of twelve arteries, developed from 4D flow MRI of 25 subjects. The atlas was constructed by normalizing all images to MNI-space, manually identifying the arteries and creating an average over the volume. The identification is done by extracting a vascular skeleton from the image, transforming it to MNI-space, labeling it with the atlas and transforming it back to subject space. The method was evaluated on a pilot cohort of 8 subjects. The rate of correctly identified arteries was 97%.

  • 24.
    Dunås, Tora
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå Universitet.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Zarrinkoob, Laleh
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    4D flow MRI: automatic assessment of blood flow in cerebral arteries2019Inngår i: Biomedical Physics & Engineering Express, ISSN 2057-1976, Vol. 5, nr 1, artikkel-id 015003Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objective: With a 10-minute 4D flow MRI scan, the distribution of blood flow to individual arteries throughout the brain can be analyzed. This technique has potential to become a biomarker for treatment decisions, and to predict prognosis after stroke. To efficiently analyze and model the large dataset in clinical practice, automatization is needed. We hypothesized that identification of selected arterial regions using an atlas with a priori probability information on their spatial distribution can provide standardized measurements of blood flow in the main cerebral arteries.

    Approach: A new method for automatic placement of measurement locations in 4D flow MRI was developed based on an existing atlas-based method for arterial labeling, by defining specific regions of interest within the corresponding arterial atlas. The suggested method was evaluated on 38 subjects with carotid artery stenosis, by comparing measurements of blood flow rate at automatically selected locations to reference measurements at manually selected locations.

    Main results: Automatic and reference measurement ranged from 10 to 580 ml min−1 and were highly correlated (r = 0.99) with a mean flow difference of 0.61 ± 10.7 ml min−1 (p = 0.21). Out of the 559 arterial segments in the manual reference, 489 were correctly labeled, yielding a sensitivity of 88%, a specificity of 85%, and a labeling accuracy of 87%.

    Significance: This study confirms that atlas-based labeling of 4D flow MRI data is suitable for efficient flow quantification in the major cerebral arteries. The suggested method improves the feasibility of analyzing cerebral 4D flow data, and fills a gap necessary for implementation in clinical use.

  • 25. Edsbagge, Mikael
    et al.
    Andreasson, Ulf
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Wikkelsø, Carsten
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Blennow, Kaj
    Zetterberg, Henrik
    Tullberg, Mats
    Alzheimer's Disease-Associated Cerebrospinal Fluid (CSF) Biomarkers do not Correlate with CSF Volumes or CSF Production Rate2017Inngår i: Journal of Alzheimer's Disease, ISSN 1387-2877, E-ISSN 1875-8908, Vol. 58, nr 3, s. 821-828Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Neuropathologically, Alzheimer's disease (AD) is characterized by accumulation of a 42 amino acid peptide called amyloid-beta (A beta(42)) in extracellular senile plaques together with intraneuronal inclusions of hyperphosphorylated tau protein in neurofibrillary tangles and neuronal degeneration. These changes are reflected in the cerebrospinal fluid (CSF), the volumes and production rates of which vary considerably between individuals, by reduced concentration of A beta(42), increased concentration of phosphorylated tau (P-tau) protein, and increased concentration of total tau (T-tau) protein, respectively. Objective: To examine the outstanding question if CSF concentrations of AD associated biomarkers are influenced by variations in CSF volumes, CSF production rate, and intracranial pressure in healthy individuals. Methods: CSF concentrations of A beta(42), P-tau, and T-tau, as well as a number of other AD-related CSF biomarkers were analyzed together with intracranial subarachnoid, ventricular, and spinal CSF volumes, as assessed by magnetic resonance imaging volumetric measurements, and CSF production rate in 19 cognitively normal healthy subjects (mean age 70.6, SD 3.6 years). Results: Negative correlations were seen between the concentrations of three CSF biomarkers (albumin ratio, A beta(38), and A beta(40)), and ventricular CSF volume, but apart from this finding, no significant correlations were observed. Conclusion: These results speak against inter-individual variations in CSF volume and production rate as important confounds in the AD biomarker research field.

  • 26. Eklund, A
    et al.
    Ågren Wilsson, A
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Andersson, N
    Bergenheim, AT
    Koskinen, LO
    Malm, J
    Two computerized methods used to analyze intracranial pressure B waves: comparison with traditional visual interpretation2001Inngår i: Journal of Neurosurgery, ISSN 0022-3085, E-ISSN 1933-0693, Vol. 94, nr 3, s. 392-396Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    OBJECT: Slow and rhythmic oscillations in intracranial pressure (ICP), also known as B waves, have been claimed to be one of the best preoperative predictive factors in idiopathic adult hydrocephalus syndrome (IAHS). Definitions of B waves vary widely, and previously reported results must be treated with caution. The aims of the present study were to develop a definition of B waves, to develop a method to estimate the B-wave content in an ICP recording by using computer algorithms, and to validate these procedures by comparison with the traditional visual interpretation. METHODS: In eight patients with IAHS, ICP was continuously monitored for approximately 20 hours. The ICP B-wave activity as a percentage of total monitoring time (B%) was estimated by using visual estimation according to the definition given by Lundberg, and also by using two computer algorithms (Methods I and II). In Method I each individual wave was classified as a B wave or not, whereas Method II was used to estimate the B-wave content by evaluating the B-wave power in 10-minute blocks of ICP recordings. CONCLUSIONS: The two computerized algorithms produced similar results. However, with the amplitude set to 1 mm Hg, Method I yielded the highest correlation with the visual analysis (r = 0.74). At least 5 hours of monitoring time was needed for an acceptable approximation of the B% in an overnight ICP recording. The advantages of using modern technology in the analysis of B-wave content of ICP are obvious and these methods should be used in future studies.

  • 27.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Resonator sensor technique for medical use: an intraocular pressure measurement system2002Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In the work of this doctoral dissertation a new resonator sensor technique, first presented in 1989, has been further developed and evaluated with focus on technical characteristics and applications within the medical field.

    In a first part a catheter-type tactile sensor using the resonator sensor technique was evaluated in a silicone model and applied to human prostate in vitro. The main finding was that different histological compositions of prostate tissue correlated with the frequency shift, .fS, of the resonator sensor and that the common property was the hardness of the tissue. The results indicated that hardness of the prostate tissue, and maybe hardness of human tissue in general, can be expressed according to a cone penetration standard (DIN ISO 2137) and that the hardness can be measured with this tactile sensor system. The tissue hardness application for the resonator sensor technique has to be further developed and evaluated in a larger study. The study also produced results that has led to the basic understanding of the resonator sensor system. One important result was that .fS of the sensor system was related to the contact area between sensor and sample. This indicated that the resonance sensor could be used for contact area measurement.

    In a second part, containing three studies, the area-sensing capability from the first study was utilised in the development and evaluation of the applanation resonator sensor (ARS) for measurement of intraocular pressure (IOP). For the purpose of evaluating IOP-tonometers, an in vitro pig-eye model was developed, and it was shown that a saline column connected to the vitreous chamber could be used successfully to induce variations in IOP.

    A ARS sensor with a flat contact surface was applied onto the cornea with constant force and .fS was measured. A mathematical model based on the Imbert-Fick law and the assumption that .fS was linearly related to contact area was proposed and verified with a convincing result. IOP measured with the ARS correlated well (r=0.92, n=360) with the IOP elicited by a saline column.

    The ARS in a constant-force arrangement was evaluated on healthy human subjects in vivo. The results verified the sensor principle but revealed a nonnegligible source of error in off-centre positioning between the sensor and cornea. The sensor probe was redesigned and evaluated in the in vitro model. The new probe, with a spherical contact surface against the eye reduced the sensitivity to off-centre positioning. It was also shown that a .fS normalisation procedure could reduce the between-eye differences.

    The ARS method for IOP measurement was further developed using combined continuous force and area measurement during the dynamic phase when the sensor initially contacts the cornea. A force sensor was included with the resonator sensor in one probe. Evaluation was performed with the in vitro pig-eye model. The hypothesis was that the IOP could be deduced from the differential change of force and area during that phase. The study showed good accuracy and good reproducibility with a correlation of r=0.994 (n=414) between measured pressure in the vitreous chamber and IOP according to the ARS. Measurement time was short, 77 ms after initial contact. Problems with inter-eye differences and low resolution at high pressures were reduced. The ARS method is the first to combine simultaneous, continuous sampling of both parameters included in the applanation principle. Consequently, there is a potential for reducing errors in the clinical IOP tonometry.

  • 28.
    Eklund, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Bergh, A
    Lindahl, O A
    A catheter tactile sensor for measuring hardness of soft tissue: measurement in a silicone model and in an in vitro human prostate model.1999Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 37, nr 5, s. 618-24Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Tissue hardness is related to tissue composition, and this is often changed by disease. It is therefore of interest to measure the hardness in an objective and non-invasive way. A tactile sensor based on a vibrating piezoelectric ceramic element in a feedback loop is described. When the sensor touches an object it produces a frequency shift related to the hardness of the object. The aim of this study was to develop an in vitro hardness measurement method using a catheter type version of the sensor. The method was evaluated in an established silicone tissue model and on human prostate tissue in vitro. A linear relationship was found with a high degree of explanation (R2 = 0.98) between a cone penetration hardness standard (DIN ISO 2137) applied to the silicone model and the corresponding frequency shift. The results from measurements on a human prostate tissue sample, fixed with formalin, showed that the relative hardness measured with the tactile sensor correlated (R = -0.96, p < 0.001, N = 60) with the proposed hardness related to the histological composition of the prostate tissue. The results indicated that hardness of prostate tissue, and maybe hardness of human tissue in general, can be expressed according to the cone penetration standard and that the hardness can be measured with this tactile sensory system. These findings hold the promise of further development of a non-invasive tool for hardness measurement in a clinical situation.

  • 29.
    Eklund, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Bäcklund, T
    Lindahl, O A
    A resonator sensor for measurement of intraocular pressure--evaluation in an in vitro pig-eye model.2000Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 21, nr 3, s. 355-67Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Intraocular pressure (IOP) measurement is performed routinely at every eye clinic. High IOP, which can be a sign of glaucoma, can lead to degeneration of the retina and can cause blindness. In this study we developed a resonator sensor for IOP measurement based on an oscillator consisting of a piezoelectric element made of lead zirconate titanate, a flat contact piece of nylon and a feedback circuit. The aim of this study was to evaluate the new sensor's ability to determine lOP in an in vitro pig-eye model. Six eyes from four pigs were removed and fixed in agar. They were then pressurized by a saline column (10-35 cm H2O) through a cannula inserted into the vitreous chamber. The IOP was measured with the resonator sensor applied to cornea. An Alcon applanation pneumatonometer and a standard Viggo-Spectramed pressure sensor connected to the saline column were used as references. The IOP as measured with the resonator sensor correlated well with the pressure elicited by the saline column for individual eyes (r = 0.96-0.99, n = 60) and for all eyes (r = 0.92, n = 360). The correlation between the resonance sensor and the pneumatonometer was r = 0.92 (n = 360). The pneumatonometer also showed a good correlation with the saline column (r = 0.98, n = 360). We conclude that our in vitro pig-eye model made it possible to induce reproducible variation in IOP, and measurement of that pressure with the newly developed resonator sensor gave very promising results for development of a clinically applicable IOP tonometer with unique properties.

  • 30.
    Eklund, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Bäcklund, Tomas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Henein, Michael Y
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Kardiologi. Heart centrum, Umeå universitet.
    Natural angioplasty as a mechanical effect of exercise2013Inngår i: International Journal of Cardiology, ISSN 0167-5273, E-ISSN 1874-1754, Vol. 168, nr 3, s. 3083-3085Artikkel i tidsskrift (Fagfellevurdert)
  • 31.
    Eklund, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk biovetenskap.
    Hallberg, Per
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Lindén, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Lindahl, Olof A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    An applanation resonator sensor for measuring intraocular pressure using combined continuous force and area measurement2003Inngår i: Investigative Ophthalmology and Visual Science, ISSN 0146-0404, E-ISSN 1552-5783, Vol. 44, nr 7, s. 3017-3024Artikkel i tidsskrift (Fagfellevurdert)
  • 32.
    Eklund, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Jóhannesson, Gauti
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Johansson, Elias
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Farmakologi.
    Holmlund, Petter
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Qvarlander, Sara
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Koskinen, Lars-Owe D.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Farmakologi.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    The Pressure Difference between Eye and Brain Changes with Posture2016Inngår i: Annals of Neurology, ISSN 0364-5134, E-ISSN 1531-8249, Vol. 80, nr 2, s. 269-276Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objective: The discovery of a posture-dependent effect on the difference between intraocular pressure (IOP) and intracranial pressure (ICP) at the level of lamina cribrosa could have important implications for understanding glaucoma and idiopathic intracranial hypertension and could help explain visual impairments in astronauts exposed to microgravity. The aim of this study was to determine the postural influence on the difference between simultaneously measured ICP and IOP.

    Methods: Eleven healthy adult volunteers (age = 46 ± 10 years) were investigated with simultaneous ICP, assessed through lumbar puncture, and IOP measurements when supine, sitting, and in 9° head-down tilt (HDT). The trans–lamina cribrosa pressure difference (TLCPD) was calculated as the difference between the IOP and ICP. To estimate the pressures at the lamina cribrosa, geometrical distances were estimated from magnetic resonance imaging and used to adjust for hydrostatic effects.

    Results: The TLCPD (in millimeters of mercury) between IOP and ICP was 12.3 ± 2.2 for supine, 19.8 ± 4.6 for sitting, and 6.6 ± 2.5 for HDT. The expected 24-hour average TLCPD on earth—assuming 8 hours supine and 16 hours upright—was estimated to be 17.3mmHg. By removing the hydrostatic effects on pressure, a corresponding 24-hour average TLCPD in microgravity environment was simulated to be 6.7mmHg.

    Interpretation: We provide a possible physiological explanation for how microgravity can cause symptoms similar to those seen in patients with elevated ICP. The observed posture dependency of TLCPD also implies that assessment of the difference between IOP and ICP in upright position may offer new understanding of the pathophysiology of idiopathic intracranial hypertension and glaucoma. 

  • 33.
    Eklund, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Koskinen, Lars-Owe D
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurokirurgi.
    Williams, Michael A
    Luciano, Mark G
    Dombrowski, Stephen M
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Hydrodynamics of the CertasTM programmable valve for the treatment of hydrocephalus2012Inngår i: Fluids and barriers of the CNS, ISSN 2045-8118, Vol. 9, nr 1, s. 12-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: The new CertasTM shunt for the treatment of hydrocephalus has seven standard pressure settings that according to the manufacturer range from 36 to 238 mmH2O, and an additional "Virtual Off" setting with an opening pressure >400 mmH2O. Information on actual pressure response and reliability of shunt performance is important in clinical application, especially the "Virtual Off" setting as a non-surgical replacement for shunt ligation. The objective of this study was to evaluate the in-vitro hydrodynamic performance of the CertasTM shunt.

    METHODS: Six new CertasTM shunts with proximal and distal catheters were tested with an automated, computerized test system that raised the pressure from zero to a maximum pressure and back to zero at each valve setting. Opening pressure and flow resistance were determined.

    RESULTS: For settings 1-7 the measured opening pressure range was 26 to 247 mmH2O, and the mean change in opening pressure for a one-step adjustment was between 33 and 38 mmH2O. For setting 8 ("Virtual Off") the measured mean opening pressure was 494 +/- 34 mmH2O (range 451 to 556 mmH2O). The mean outflow resistance was 7.0 mmHg/ml/min (outflow conductance 17.9 ul/s/kPa).

    CONCLUSIONS: The six shunts had similar characteristics and closely matched the manufacturer's specifications for opening pressure at settings 1-7. The opening pressure for the "Virtual Off" setting was nearly 500 mmH2O, which is 100 mmH2O higher than the manufacturer's specification of ">400" and should be functionally off for most patients with communicating hydrocephalus. Clinical studies are needed to evaluate if the CSF dynamic profile persists after implantation in patients.

  • 34.
    Eklund, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Koskinen, L-O D
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurokirurgi.
    Malm, J
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Features of the Sinushunt and its influence on the cerebrospinal fluid system2004Inngår i: J Neurol Neurosurg Psychiatry, ISSN 0022-3050, Vol. 75, nr 8, s. 1156-1159Artikkel i tidsskrift (Fagfellevurdert)
    Abstract
  • 35.
    Eklund, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Lindén, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap.
    Bäcklund, Tomas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Andersson, Britt M
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Lindahl, Olof A
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Evaluation of applanation resonator sensors for intra-ocular pressure measurement: results from clinical and in vitro studies.2003Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 41, nr 2, s. 190-197Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Glaucoma is an eye disease that, in its most common form, is characterised by high intra-ocular pressure (IOP), reduced visual field and optic nerve damage. For diagnostic purposes and for follow-up after treatment, it is important to have simple and reliable methods for measuring IOP. Recently, an applanation resonator sensor (ARS) for measuring IOP was introduced and evaluated using an in vitro pig-eye model. In the present study, the first clinical evaluation of the same probe has been carried out, with experiments in vivo on human eyes. There was a low but significant correlation between IOP(ARS) and the IOP measured with a Goldmann applanation tonometer (r = 0.40, p = 0.001, n = 72). However, off-centre positioning of the sensor against the cornea caused a non-negligible source of error. The sensor probe was redesigned to have a spherical, instead of flat, contact surface against the eye and was evaluated in the in vitro model. The new probe showed reduced sensitivity to off-centre positioning, with a decrease in relative deviation from 89% to 11% (1 mm radius). For normalised data, linear regression between IOP(ARS) and direct IOP measurement in the vitreous chamber showed a correlation of r = 0.97 (p < 0.001, n = 108) and a standard deviation for the residuals of SD < or = 2.18 mm Hg (n = 108). It was concluded that a spherical contact surface should be preferred and that further development towards a clinical instrument should focus on probe design and signal analysis.

  • 36.
    Eklund, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Lundkvist, B
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Koskinen, L-O D
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurokirurgi.
    Malm, J
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Infusion technique can be used to distinguish between dysfunction of a hydrocephalus shunt system and a progressive dementia.2004Inngår i: Med Biol Eng Comput, ISSN 0140-0118, Vol. 42, nr 5, s. 644-649Artikkel i tidsskrift (Fagfellevurdert)
    Abstract
  • 37.
    Eklund, Anders
    et al.
    Umeå universitet, Medicinsk fakultet, Strålningsvetenskaper.
    Smielewski, Peter
    Chambers, Iain
    Alperin, Noam
    Malm, Jan
    Umeå universitet, Medicinsk fakultet, Farmakologi och klinisk neurovetenskap, Neurologi.
    Czosnyka, Marek
    Marmarou, Anthony
    Assessment of cerebrospinal fluid outflow resistance.2007Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 45, nr 8, s. 719-735Artikkel i tidsskrift (Fagfellevurdert)
  • 38.
    Ekman, Urban
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB). Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap. Department of Neurobiology, Care Sciences and Society, Karolinska Institutet, Stockholm, Sweden.
    Fordell, Helena
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Eriksson, Johan
    Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB).
    Lenfeldt, Niklas
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Increase of frontal neuronal activity in chronic neglect after training in virtual reality2018Inngår i: Acta Neurologica Scandinavica, ISSN 0001-6314, E-ISSN 1600-0404, Vol. 138, nr 4, s. 284-292Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives: A third of patients with stroke acquire spatial neglect associated with poor rehabilitation outcome. New effective rehabilitation interventions are needed. Scanning training combined with multisensory stimulation to enhance the rehabilitation effect is suggested. In accordance, we have designed a virtual-reality based scanning training that combines visual, audio and sensori-motor stimulation called RehAtt((R)). Effects were shown in behavioural tests and activity of daily living. Here, we use fMRI to evaluate the change in brain activity during Posners Cuing Task (attention task) after RehAtt((R)) intervention, in patients with chronic neglect.

    Methods: Twelve patients (mean age=72.7years, SD=6.1) with chronic neglect (persistent symptoms >6months) performed the interventions 3 times/wk during 5weeks, in total 15hours. Training effects on brain activity were evaluated using fMRI task-evoked responses during the Posners cuing task before and after the intervention.

    Results: Patients improved their performance in the Posner fMRI task. In addition, patients increased their task-evoked brain activity after the VR interventions in an extended network including pre-frontal and temporal cortex during attentional cueing, but showed no training effects during target presentations.

    Conclusions: The current pilot study demonstrates that a novel multisensory VR intervention has the potential to benefit patients with chronic neglect in respect of behaviour and brain changes. Specifically, the fMRI results show that strategic processes (top-down control during attentional cuing) were enhanced by the intervention. The findings increase knowledge of the plasticity processes underlying positive rehabilitation effects from RehAtt((R)) in chronic neglect.

  • 39.
    el Azazi, Mildred
    et al.
    S:t Erik, Stockholm.
    Wang, Ling
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Wachtmeister, Lillemor
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Background light adaptation of the retinal neuronal adaptive system. II. Dynamic effects2004Inngår i: Documenta Ophthalmologica, ISSN 0012-4486, Vol. 109, nr 2, s. 201-213Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dynamic effects of continuous exposure to light on the neuronal adaptive system of the retina, as indicated by the oscillatory response (OPs) of the electroretinogram (ERG) were studied in the albino rat. Digitally filtered OPs and the a- and b-waves of the corneal ERG were simultaneously recorded in dark adaptation, during continuous light adaptation to four levels of background light (BGL) changing in steps of two log units from 1.43 x 10(-6) cd/m2, referred to as 'low and high scotopic, low and high mesopic' levels. Exposed to 'high scotopic' BGL the total oscillatory response (SOP) significantly enhanced within the first minute, whereas the amplitudes of the a- and b-waves were unaffected. In 'low mesopic' BGL the SOP increased within the first minute, whereas the a- and b-waves significantly decreased. 'High mesopic' BGL instantaneously and profoundly reduced both the SOP and the slow potentials. The individual OPs changed in amplitudes mainly within the first minute of BGL. In general, the earlier OPs (O1 and O2) reacted more to the two 'scotopic' BGL levels, whereas the later OPs (O3 and 04) were more affected by the relatively brighter two 'mesopic' conditions. In conclusion, the rapid increase of the OPs within the first minute of 'high scotopic' and 'low mesopic' BGL exposure may represent a rudimentary light adaptational effect in the rod-dominated rat retina. These findings also suggest that the neuronal adaptive mechanism of the retina seems to be a robust system, probably attaining preservation of visual abilities in the rat on exposure to light.

  • 40.
    Farahmand, Dan
    et al.
    Hydrocephalus Research Unit, Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
    Qvarlander, Sara
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Wikkelsö, Carsten
    Hydrocephalus Research Unit, Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Tisell, Magnus
    Hydrocephalus Research Unit, Institute of Neuroscience and Physiology, The Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden.
    Intracranial pressure in hydrocephalus: impact of shunt adjustments and body positions2015Inngår i: Journal of Neurology, Neurosurgery and Psychiatry, ISSN 0022-3050, E-ISSN 1468-330X, Vol. 86, nr 2, s. 222-228Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background The association between intracranial pressure (ICP) and different shunt valve opening pressures in relation to body positions is fundamental for understanding the physiological function of the shunt.

    Objective To analyse the ICP and ICP wave amplitude (AMP) at different shunt settings and body positions in patients with hydrocephalus.

    Methods In this prospective study 15 patients with communicating hydrocephalus were implanted with a ligated adjustable ventriculoperitoneal shunt. They also received a portable intraparenchymatous ICP-monitoring device. Postoperative ICP and AMP were recorded with the patients in three different body positions (supine, sitting and walking) and with the shunt ligated and open at high, medium and low valve settings. In each patient 12 10 min segments were coded, blinded and analysed for mean ICP and mean AMP using an automated computer algorithm.

    Results Mean ICP and mean AMP were lower at all three valve settings compared with the ligated shunt state (p<0.001). Overall, when compared with the supine position, mean ICP was 11.5 +/- 1.1 (mean +/- SD) mm Hg lower when sitting and 10.5 +/- 1.1 mm Hg lower when walking (p<0.001). Mean ICP was overall 1.1 mm Hg higher (p=0.042) when walking compared with sitting. The maximal adjustability difference (highest vs lowest valve setting) was 4.4 mm Hg.

    Conclusions Changing from a supine to an upright position reduced ICP while AMP only increased at trend level. Lowering of the shunt valve opening pressure decreased ICP and AMP but the difference in mean ICP in vivo between the highest and lowest opening pressures was less than half that previously observed in vitro.

  • 41.
    Fordell, Helena
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Bodin, Kenneth
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för datavetenskap. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Högpresterande beräkningscentrum norr (HPC2N).
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    RehAtt – scanning training for neglect enhanced by multi-sensory stimulation in Virtual Reality2016Inngår i: Topics in Stroke Rehabilitation, ISSN 1074-9357, E-ISSN 1945-5119, Vol. 23, nr 3, s. 191-199Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: There is a lack of effective treatment for neglect. We have developed a new training method, RehAtt (TM). The objective of this study was to determine whether RehAtt (TM) improves spatial attention in chronic neglect after stroke. Methods: RehAtt (TM) consists of a computer with monitor, 3D glasses, and a force feedback interface (Robotic pen) giving sensory motor activation to the contra-lesional arm. The software combines visual scanning training with multi-sensory stimulation in 3D virtual reality (VR) game environment. Fifteen stroke patients with chronic neglect (duration > 6 month) had repeated baseline evaluations to confirm stability of symptoms. There were no test-retest effects for any of the tests. Thereafter, all patients trained 15 h in RehAtt (TM) (3 x 1 h for 5 weeks). A neglect test battery and Catherine Bergego Scale, CBS, were used to assess behavioral outcome after intervention. CBS was also used at a 6-month follow-up. Results: Using repeated measurement analysis improvements due to the training were found for Star cancellation test (p = 0.006), Baking tray task (p < 0.001), and Extinction test (p = 0.05). In the Posner task improvements were seen fewer missed targets (p = 0.024). CBS showed improvements in activities of daily life immediately after training (p < 0.01). After 6 months the patients still reported improvement in CBS. Conclusion: RehAtt (TM) is a new concept for rehabilitation of neglect. Training with the VR-method improved spatial attention and showed transfer to improved spatial attention in activities of daily living in chronic neglect. Our results are promising and merit further studies.

  • 42. Gehlen, Manuel
    et al.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Kurtcuoglu, Vartan
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Schmid Daners, Marianne
    Comparison of anti-siphon devices: how do they affect CSF dynamics in supine and upright posture?2017Inngår i: Acta Neurochirurgica, ISSN 0001-6268, E-ISSN 0942-0940, Vol. 159, nr 8, s. 1389-1397Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    BACKGROUND: Three different types of anti-siphon devices (ASDs) have been developed to counteract siphoning-induced overdrainage in upright posture. However, it is not known how the different ASDs affect CSF dynamics under the complex pressure environment seen in clinic due to postural changes. We investigated which ASDs can avoid overdrainage in upright posture best without leading to CSF accumulation.

    METHODS: Three shunts each of the types Codman Hakim with SiphonGuard (flow-regulated), Miethke miniNAV with proSA (gravitational), and Medtronic Delta (membrane controlled) were tested. The shunts were compared on a novel in vitro setup that actively emulates the physiology of a shunted patient. This testing method allows determining the CSF drainage rates, resulting CSF volume, and intracranial pressure in the supine, sitting, and standing posture.

    RESULTS: The flow-regulated ASDs avoided increased drainage by closing their primary flow path when drainage exceeded 1.39 ± 0.42 mL/min. However, with intraperitoneal pressure increased in standing posture, we observed reopening of the ASD in 3 out of 18 experiment repetitions. The adjustable gravitational ASDs allow independent opening pressures in horizontal and vertical orientation, but they did not provide constant drainage in upright posture (0.37 ± 0.03 mL/min and 0.26 ± 0.03 mL/min in sitting and standing posture, respectively). Consequently, adaptation to the individual patient is critical. The membrane-controlled ASDs stopped drainage in upright posture. This eliminates the risk of overdrainage, but leads to CSF accumulation up to the volume observed without shunting when the patient is upright.

    CONCLUSIONS: While all tested ASDs reduced overdrainage, their actual performance will depend on a patient's specific needs because of the large variation in the way the ASDs influence CSF dynamics: while the flow-regulated shunts provide continuous drainage in upright posture, the gravitational ASDs allow and require additional adaptation, and the membrane-controlled ASDs show robust siphon prevention by a total stop of drainage.

  • 43. Hallberg, Per
    et al.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Bäcklund, Tomas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Lindén, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Clinical evaluation of applanation resonance tonometry: a comparison with Goldmann applanation tonometry.2007Inngår i: Journal of glaucoma, ISSN 1057-0829, E-ISSN 1536-481X, Vol. 16, nr 1, s. 88-93Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    PURPOSE: The purpose of this study was to calibrate and evaluate the precision of the new applanation resonance tonometry (ART) in a clinical study designed in accordance with the International Standard Organization's requirements. METHODS: This was a prospective, randomized, single-center study, where healthy volunteers and patients participated. A total of 153 eyes were divided into 3 groups with respect to their intraocular pressure (IOP) at screening: <16 mm Hg, 16 to 23 mm Hg, and >23 mm Hg. IOP was measured with Goldmann applanation tonometry (GAT) as reference method and by ART in both a biomicroscope (ARTBiom) and a handheld (ARTHand) setup with a 10-minutes pause between methods. The mean of 6 readings was regarded as one measurement value. RESULTS: Mean age of the subjects was 59 years (range 20 to 87 y). GAT showed a mean IOP of 20.0 mm Hg (range 8.5 to 43.5 mm Hg, n=153). The precision was 2.07 mm Hg for ARTBiom and 2.50 mm Hg for ARTHand, with a significant dependency for age as compared with GAT. Measurement order produced a decreasing IOP with a mean of 2.3 mm Hg between the first and last method. CONCLUSIONS: The precision obtained in both ARTBiom and ARTHand was within the limits set by the International Standard Organization standards for tonometers. The standardized procedure and the stability of the biomicroscope setup resulted in a slightly better precision as compared with the handheld setup. Despite a 10-minutes pause between measurements, the order was a significant factor, possibly because the patients were more apprehensive at the first measurement.

  • 44.
    Hallberg, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Santala, Kenneth
    Koskela, Timo
    Lindahl, Olof A.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Lindén, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Underestimation of intraocular pressure after photorefractive keratectomy - a biomechanical analysisArtikkel i tidsskrift (Fagfellevurdert)
  • 45. Hallberg, Per
    et al.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Santala, Kenneth
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Koskela, Timo
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Lindahl, Olof
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Lindén, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Underestimation of intraocular pressure after photorefractive keratectomy: a biomechanical analysis2006Inngår i: Med Biol Eng Comput, Vol. 44, s. 609-168Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Excimer laser surgery, to correct corneal refraction, induces changes in corneal thickness and curvature. Both factors can cause measurement errors when determining intraocular pressure (IOP). This study evaluates effects of photorefractive keratectomy (PRK) on IOP measurements, using Goldmann applanation tonometry (GAT) and Applanation resonance tonometry (ART), in an in vitro model. Six porcine eyes was enucleated and pressurised to a constant IOP=30 mmHg. After removal of the epithelium, the eyes were PRK-treated for a total of 25 dioptres. The measured IOP decreased 13.2 mmHg for GAT and 9.0 mmHg for ART. The total underestimation by GAT was larger than for ART, and a part of the ART underestimation (3.5 mmHg) was assigned to sensitivity to the change in corneal surface structure resulting from the removal of epithelium. The flat contact probe of GAT, as compared with the convex tip of ART, provided explanation for the difference in IOP measurement error after PRK.

  • 46.
    Hallberg, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Lindén, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Bäcklund, Tomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Symmetric sensor for applanation resonance tonometry of the eye2006Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 44, nr 1-2, s. 54-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Applanation resonance tonometry (ART) has been shown in a number of studies to be useful for measuring intraocular pressure (IOP). Data from in vitro laboratory bench testing, where the sensor was carefully centralised onto the cornea, has been very consistent with good precision in the determination of IOP. However, in a clinical study the unavoidable off-centre placement of the sensor against the cornea resulted in a reduced precision. The aim of this study was to evaluate a new design of the sensor with a symmetric sensor probe and a contact piece with a larger diameter. Two in vitro porcine eye experimental set-ups were used. One bench-based for examining position dependence and one biomicroscope-based set-up, simulating a clinical setting, for evaluating IOP(ART) precision at seven different pressure levels (1040 mmHg), set by connecting a saline column to the vitreous chamber. The reference IOP was recorded using a pressure transducer. There was no significant difference between four positions 1 mm off centre and the one centre position. The precision of the ART as compared with the reference pressure was +/- 1.03 mmHg (SD, n = 42). The design improvement has enhanced the precision of the ART in the biomicroscope set-up to be in parity with bench test results from a set-up using perfect positioning. This indicates that off-centre positioning was no longer a major contributor to the deviations in measured IOP. The precision was well within the limits set by ISO standard for eye tonometers. Therefore, a larger in vivo study on human eyes with the ART should be performed.

  • 47.
    Hallberg, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Lindén, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Lindahl, Olof A.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Bäcklund, Tomas
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Eklund, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Applanation resonance tonometry for intraocular pressure in humans2004Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 25, nr 4, s. 1053-1065Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Glaucoma is a group of diseases associated with optic nerve damage and loss of visual field. The aetiology is not completely understood, but one of the major risk factors is elevated intraocular pressure (IOP). Reliable methods for measuring the IOP are therefore important. The aim of the study was to investigate the ability of the applanation resonance tonometry (ART) system, based on continuous force and area recording, to measure IOP in humans. Both the phase of initial indentation (IOPIndentation) and the phase when the sensor was removed (IOPRemoval) from the cornea were analysed. The Goldmann applanation tonometry (GAT) was used as reference method. The study included 24 healthy volunteers with normal IOP and 24 patients with elevated IOP. The correlation and standard deviation (SD) between IOPIndentation and IOPGAT was R = 0.92 (p < 0.001), SD = 3.6 mmHg, n = 104, and between IOPRemoval and IOPGAT R = 0.94 (p < 0.001), SD = 3.1 mmHg, n = 104. In conclusion, resonance sensor technology has made it possible to introduce a new multi-point method for measuring IOP, and the method is relevant for measuring IOP in humans. The study indicates that with further development towards elimination of position dependence, the ART has the potential to become a useful clinical instrument for IOP measurement.

  • 48.
    Hallberg, Per
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Santala, Kenneth
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Lindén, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Lindahl, Olof A
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Comparison of Goldmann applanation and applanation resonance tonometry in a biomicroscope-based in vitro porcine eye model2006Inngår i: J Med Eng Technol, ISSN 0309-1902, Vol. 30, nr 6, s. 345-352Artikkel i tidsskrift (Fagfellevurdert)
  • 49.
    Holmlund, Petter
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Koskinen, Lars-Owe D.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Johansson, Elias
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Sundström, Nina
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Qvarlander, Sara
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Venous collapse regulates intracranial pressure in upright body positions2018Inngår i: American Journal of Physiology. Regulatory Integrative and Comparative Physiology, ISSN 0363-6119, E-ISSN 1522-1490, Vol. 314, nr 3, s. R377-R385Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Recent interest in intracranial pressure (ICP) in the upright posture has revealed that the mechanisms regulating postural changes in ICP are not fully understood. We have suggested an explanatory model where the postural changes in ICP depend on well-established hydrostatic effects in the venous system and where these effects are interrupted by collapse of the internal jugular veins (IJVs) in more upright positions. The aim of this study was to investigate this relationship by simultaneous invasive measurements of ICP, venous pressure and IJV collapse in healthy volunteers. ICP (monitored via the lumbar route), central venous pressure (PICC-line) and IJV cross-sectional area (ultrasound) were measured in 11 healthy volunteers (47±10 years) in seven positions, from supine to sitting (0°-69°). Venous pressure and anatomical distances were used to predict ICP in accordance with the explanatory model, and IJV area was used to assess IJV collapse. The hypothesis was tested by comparing measured ICP to predicted ICP. Our model accurately described the general behavior of the observed postural ICP changes (mean difference: -0.03±2.7 mmHg). No difference was found between predicted and measured ICP for any tilt-angle (p-values: 0.65 - 0.94). The results support the hypothesis that postural ICP changes are governed by hydrostatic effects in the venous system and IJV collapse. This improved understanding of the postural ICP regulation may have important implications for the development of better treatments for neurological and neurosurgical conditions affecting ICP.

  • 50.
    Holmlund, Petter
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Johansson, Elias
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Qvarlander, Sara
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Koskinen, Lars-Owe D.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Human jugular vein collapse in the upright posture: implications for postural intracranial pressure regulation2017Inngår i: Fluids and Barriers of the CNS, ISSN 2045-8118, E-ISSN 2045-8118, Vol. 14, artikkel-id 17Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Intracranial pressure (ICP) is directly related to cranial dural venous pressure (P-dural). In the upright posture, P-dural is affected by the collapse of the internal jugular veins (IJVs) but this regulation of the venous pressure has not been fully understood. A potential biomechanical description of this regulation involves a transmission of surrounding atmospheric pressure to the internal venous pressure of the collapsed IJVs. This can be accomplished if hydrostatic effects are cancelled by the viscous losses in these collapsed veins, resulting in specific IJV cross-sectional areas that can be predicted from flow velocity and vessel inclination. Methods: We evaluated this potential mechanism in vivo by comparing predicted area to measured IJV area in healthy subjects. Seventeen healthy volunteers (age 45 +/- 9 years) were examined using ultrasound to assess IJV area and flow velocity. Ultrasound measurements were performed in supine and sitting positions. Results: IJV area was 94.5 mm(2) in supine and decreased to 6.5 +/- 5.1 mm(2) in sitting position, which agreed with the predicted IJV area of 8.7 +/- 5.2 mm(2) (equivalence limit +/- 5 mm(2), one-sided t tests, p = 0.03, 33 IJVs). Conclusions: The agreement between predicted and measured IJV area in sitting supports the occurrence of a hydrostatic-viscous pressure balance in the IJVs, which would result in a constant pressure segment in these collapsed veins, corresponding to a zero transmural pressure. This balance could thus serve as the mechanism by which collapse of the IJVs regulates P-dural and consequently ICP in the upright posture.

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