umu.sePublikationer
Ändra sökning
Avgränsa sökresultatet
1 - 36 av 36
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 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 imaging2013Ingår i: Investigative Ophthalmology and Visual Science, ISSN 0146-0404, E-ISSN 1552-5783, Vol. 54, nr 4, s. 2738-2745Artikel i tidskrift (Refereegranskat)
    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.2010Ingår i: Neurosurgery, ISSN 0148-396X, E-ISSN 1524-4040, Vol. 67, nr 1, s. 94-99Artikel i tidskrift (Refereegranskat)
    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 imaging2012Ingår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 33, nr 10, s. 1951-1956Artikel i tidskrift (Refereegranskat)
    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 Labeling2015Ingår 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. 17-19Konferensbidrag (Refereegranskat)
    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 software2011Ingår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 32, nr 2, s. 408-412Artikel i tidskrift (Refereegranskat)
    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 Volunteers2015Ingår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 36, nr 10, s. 1816-1821Artikel i tidskrift (Refereegranskat)
    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.
    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.2010Ingår i: Neurosurgery, ISSN 0148-396X, E-ISSN 1524-4040, Vol. 66, nr 6, s. 1050-1057Artikel i tidskrift (Refereegranskat)
    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.

  • 8.
    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:  2011Ingår i: Neurosurgery, ISSN 0148-396X, E-ISSN 1524-4040, Vol. 69, nr 4, s. E1033-E1034Artikel i tidskrift (Refereegranskat)
  • 9.
    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 angiography2016Ingår i: Magnetic Resonance Materials in Physics, Biology and Medicine, ISSN 0968-5243, E-ISSN 1352-8661, Vol. 29, nr 1, s. 39-47Artikel i tidskrift (Refereegranskat)
    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.

  • 10.
    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 Arteries2017Ingår i: Neuroinformatics, ISSN 1539-2791, E-ISSN 1559-0089, Vol. 15, nr 1, s. 101-110Artikel i tidskrift (Refereegranskat)
    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.

  • 11.
    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 MRI2015Ingår i: 16th Nordic-Baltic Conference on Biomedical Engineering / [ed] Henrik Mindedal, Mikael Persson, 2015, Vol. 48, s. 40-43Konferensbidrag (Refereegranskat)
    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%.

  • 12. 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 Rate2017Ingår i: Journal of Alzheimer's Disease, ISSN 1387-2877, E-ISSN 1875-8908, Vol. 58, nr 3, s. 821-828Artikel i tidskrift (Refereegranskat)
    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.

  • 13.
    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 Posture2016Ingår i: Annals of Neurology, ISSN 0364-5134, E-ISSN 1531-8249, Vol. 80, nr 2, s. 269-276Artikel i tidskrift (Refereegranskat)
    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. 

  • 14.
    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 regulation2017Ingår i: Fluids and Barriers of the CNS, ISSN 2045-8118, E-ISSN 2045-8118, Vol. 14, artikel-id 17Artikel i tidskrift (Refereegranskat)
    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.

  • 15.
    Holmlund, Petter
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Johansson, Elias
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Avdelningen för medicin.
    Qvarlander, Sara
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    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, Radiofysik.
    Jugular vein collapse in upright and its relation to intracranial pressure regulation2017Ingår i: Journal of Cerebral Blood Flow and Metabolism, ISSN 0271-678X, E-ISSN 1559-7016, Vol. 37, s. 297-297Artikel i tidskrift (Refereegranskat)
  • 16.
    Israelsson, Hanna
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Ventriculomegaly and balance disturbances in patients with TIA2012Ingår i: Acta Neurologica Scandinavica, ISSN 0001-6314, E-ISSN 1600-0404, Vol. 125, nr 3, s. 163-170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Objectives -  Dilated ventricles and gait disturbances are common in the elderly, and these are also features of the treatable syndrome idiopathic normal pressure hydrocephalus (INPH). Many studies report an association between hypertension, vascular disease and INPH. The objective of this study was to study the frequency of ventriculomegaly, with or without hydrocephalic symptoms, in patients who had suffered from a transitory ischaemic attack (TIA).

    Methods -  Gait, Romberg sign, tandem standing and one-leg stance were consecutively evaluated in elderly >24 h after a TIA. Ventricular size, white matter lesions and atrophy were assessed on computed tomography scans. Exclusion criteria were conditions possibly influencing the balance tests.

    Results -  Seventy-six patients with TIA out of 105 were included. Ventriculomegaly [Evans Index (EI) > 0.30] was observed in 19.7% and very large ventricles (EI > 0.33) in 7.9%. Ventriculomegaly was found in 58% of the patients with a previous 'history of balance or gait disturbance', but only in 12% of those without any prior disturbance (chi-square test; P = 0.0009). Three out of 76 patients with TIA (3.9%) fulfilled both radiological and clinical criteria for 'possible INPH'.

    Conclusion -  Ventriculomegaly is a common finding in elderly. One out of 20 patients with TIA may suffer from INPH, existing before and independent of the TIA diagnosis. Therefore, patients presenting with ventriculomegaly and gait/balance disturbances not attributable to other causes should be referred to a hydrocephalus centre or a neurologist with special interest in INPH.

  • 17.
    Johannesson, Gauti
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Hallberg, Per
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Ambarki, Khalid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Eklund, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Linden, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Age-dependency of ocular parameters - a cross sectional study of young and old healthy subjects2015Ingår i: Investigative Ophthalmology and Visual Science, ISSN 0146-0404, E-ISSN 1552-5783, Vol. 56, nr 7, artikel-id Meeting Abstract: 116Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Purpose: To investigate aging effect on ocular parameters inkluding intraocular pressure (IOP) measured with different tonometry methods in healthy young (HY) and elderly (HE) subjects.

    Methods: Fifty eyes of 50 HY subjects (28 females, 22-31 years of age) and 43 eyes of 43 HE subjects (22 females, 64-79 years of age) were included. IOP was measured with four tonometry methods in a standardized order: Ocular Response Analyser (ORA), Dynamic Contour Tonometry (DCT), Applanation Resonance Tonometry (ART) and Goldmann Applanation Tonometry (GAT). Other measurements included axial length (AL), central corneal thickness (CCT), corneal curvature (CC), ocular pulse amplitude (OPA) and aqueous humor (aq).

    Results: The mean IOP (HY/HE; mmHg ± standard deviation) was 13.9 ± 2.7/16.4 ± 3.4 with ORA, 15.1 ± 2.1/16.3 ± 3.1 with DCT, 12.3 ± 2.0/13.7 ± 2.8 with GAT and 13.1 ± 2.2/12.1 ± 2.5 with ART. IOP was significantly higher (difference ± standard error) in HE compared to HY measured with ORA (+2.5 mmHg ± 0.6), GAT (+1.4 ± 0.5) and DCT (+1.2 ± 0.6). There was a trend towards lower IOP in HE when measured with ART (-1.0 ± 0.5, p=0.05). There was no difference between HE and HY in CCT, CC, AL or OPA.

    Conclusions: Tonometry methods are affected differently by age. IOP was measured higher in elderly people with ORA, DCT and GAT in this Scandinavian population. This effect was not seen in measurements with ART. Other ocular parameters did not differ between the age groups indicating that these measured parameters are not influenced by age in this population.

  • 18.
    Johannesson, Gauti
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Hallberg, Per
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Ambarki, Khalid
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Eklund, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Linden, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Age-dependency of ocular parameters: a cross sectional study of young and elderly healthy subjects2015Ingår i: Graefe's Archives for Clinical and Experimental Ophthalmology, ISSN 0721-832X, E-ISSN 1435-702X, Vol. 253, nr 11, s. 1979-1983Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To investigate the effect of aging on ocular parameters, including intraocular pressure (IOP), measured with different tonometry methods in healthy young (HY) and healthy elderly (HE) subjects and to study the effect of corneal parameters on tonometry methods. In this prospective, cross-sectional study, fifty eyes of 50 HY subjects (28 females, 22-31 years of age) and 43 eyes of 43 HE subjects (22 females, 64-79) were included. IOP was measured with four tonometry methods in a standardized order: ocular response analyser (ORA), dynamic contour tonometry (DCT), applanation resonance tonometry (ART) and Goldmann applanation tonometry (GAT). Other measurements included axial length (AL), central corneal thickness (CCT), corneal curvature (CC), anterior chamber volume (ACV), corneal hysteresis (CH) and corneal resistance factor (CRF). The mean IOP (HY/HE; mmHg +/- standard deviation (SD)) was 12.2 +/- 2.2/14.1 +/- 3.5 with GAT. IOP was significantly higher (difference +/- standard error) in HE compared to HY measured with an ORA (+3.1 mmHg +/- 0.6), GAT (+1.9 +/- 0.6) and DCT (+1.6 +/- 0.6). No significant difference was found in IOP measured with ART. CH and ACV were significantly lower in HE compared to HY. There was no difference between the groups in CCT, CC, AL or CRF. No tonometry method was dependant on CCT or CC. IOP measured with an ORA and via DCT and GAT was higher in HE compared to HY Swedish subjects, while IOP measured with ART did not differ between the groups. In these homogeneous groups, tonometry methods were independent of CCT and CC.

  • 19.
    Johansson, Elias
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Bahrami, Nazila
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Cerebral microbleeds in idiopathic normal pressure hydrocephalus2016Ingår i: Fluids and Barriers of the CNS, ISSN 2045-8118, E-ISSN 2045-8118, Vol. 13, artikel-id UNSP 4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: A vascular disease could be involved in pathophysiology of normal pressure hydrocephalus (INPH). If so, there should be an association between INPH and cerebral microbleeds (CMB). This study aims to analyze if CMB are associated with INPH.

    Methods: In this case-control study we included 14 patients with INPH (mean age 76 years, 60 % female) and 41 healthy controls (HeCo; mean age 71 years, 60 % female). All were investigated with magnetic resonance imaging (MRI) using a T2*-sequence. The MRI exams were reviewed by two neuroradiologists for the presence of CMBs; the prevalence of findings of two or more CMBs was compared between INPH group and control group. After investigation, INPH patients underwent shunt surgery.

    Results: Two or more CMB were detected more frequently in the INPH group compared to HeCo (n = 6, 43 % vs. n = 4, 10 %; p = 0.01). Among the participants where MRI revealed CMB, the number of CMB was higher among the INPH patients than the HeCo (median 8; IQR 2-34 vs. median 1; IQR 1-2; p = 0.005).

    Conclusions: This study supports a vascular component to the pathophysiology of INPH.

  • 20.
    Kristiansen, Martin
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Linden, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Qvarlander, Sara
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Hallberg, Per
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Jóhannesson, Gauti
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Blood flow rate of ophthalmic artery in patients with normal tension glaucoma and healthy controls2018Ingår i: Investigative Ophthalmology and Visual Science, ISSN 0146-0404, E-ISSN 1552-5783, Vol. 59, nr 9Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    Purpose: To determine the blood flow rate of the ophthalmic artery (OA) in patients with Normal Tension Glaucoma (NTG) compared to age-matched healthy controls using phase-contrast magnetic resonance imaging (PCMRI).

    Methods: Seventeen patients with treated NTG (11 female; mean age: 70±9 years) and 16 age-matched healthy controls (10 female; mean age: 71±9 years) underwent PCMRI using a 3-Tesla scanner as well as ophthalmological examinations including visual acuity, Goldmann Applanation Tonometry, Humphrey perimetry and fundoscopy. Ophthalmic blood flow was acquired using a 2D PCMRI sequence set to a spatial resolution of 0.35mm/pixel. Mean flow rate and cross-sectional area was calculated using Segment Software. The eye with the most severe glaucomatous damage classified by visual field index (VFI) was chosen for comparison. The primary outcome was blood flow rate of OA.

    Results: The mean VFI was 41% ± 26 (mean±SD) for the worse NTG eyes. The intraocular pressure was 13.6±2.6 mmHg for NTG eyes and 13.8±2.1 mmHg for control eyes. The blood flow rate in the NTG group was 9.6±3.7 ml/min compared to 11.8±5.5 ml/min in the control group. The area was 1.7±0.3 mm2 and 2.0±0.6 mm2 respectively. No statistical significance was found between NTG and the control group regarding blood flow rate (p=0.07) or OA area (p=0.12).

    Conclusions: Despite OA being an anastomosis between the intracranial and extracranial circulation, possibly generating an eye unrelated variability in blood flow, we found a trend level reduction of approximately 2 ml/min in NTG. The finding warrants blood flow rate analysis of smaller arteries specifically supplying the eye, e.g. the central retinal artery.

  • 21. Marshall-Goebel, Karina
    et al.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Institutionen för klinisk mikrobiologi, Biomedicinsk laboratorievetenskap.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Mulder, Edwin
    Gerlach, Darius
    Bershad, Eric
    Rittweger, Joern
    Effects of short-term exposure to head-down tilt on cerebral hemodynamics: a prospective evaluation of a spaceflight analog using phase-contrast MRI2016Ingår i: Journal of applied physiology, ISSN 8750-7587, E-ISSN 1522-1601, Vol. 120, nr 12, s. 1466-1473Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Alterations in cerebral hemodynamics in microgravity are hypothesized to occur during spaceflight and could be linked to the Visual Impairment and Intracranial Pressure syndrome. Head-down tilt (HDT) is frequently used as a ground-based analog to simulate cephalad fluid shifts in microgravity; however, its effects on cerebral hemodynamics have not been well studied with MRI techniques. Here, we evaluate the effects of 1) various HDT angles on cerebral arterial and venous hemodynamics; and 2) exposure to 1% CO2 during an intermediate HDT angle (-12 degrees) as an additional space-related environmental factor. Blood flow, cross-sectional area (CSA), and blood flow velocity were measured with phase-contrast MRI in the internal jugular veins, as well as the vertebral and internal carotid arteries. Nine healthy male subjects were measured at baseline (supine, 0 degrees) and after 4.5 h of HDT at -6 degrees, -12 degrees (with and without 1% CO2), and -18 degrees. We found a decrease in total arterial blood flow from baseline during all angles of HDT. On the venous side, CSA increased with HDT, and outflow decreased during -12 degrees HDT (P = 0.039). Moreover, the addition of 1% CO2 to -12 degrees HDT caused an increase in total arterial blood flow (P = 0.016) and jugular venous outflow (P = 0.001) compared with -12 degrees HDT with ambient atmosphere. Overall, the results indicate decreased cerebral blood flow during HDT, which may have implications for microgravity-induced cerebral hemodynamic changes.

  • 22.
    Qvarlander, Sara
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Ambarki, Khalid
    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).
    Jacobsson, Johan
    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, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Cerebrospinal fluid and blood flow patterns in idiopathic normal pressure hydrocephalus2017Ingår i: Acta Neurologica Scandinavica, ISSN 0001-6314, E-ISSN 1600-0404, Vol. 135, nr 5, s. 576-584Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Objectives: Increased aqueduct cerebrospinal fluid (CSF) flow pulsatility and, recently, a reversed CSF flow in the aqueduct have been suggested as hallmarks of idiopathic normal pressure hydrocephalus (INPH). However, these findings have not been adequately confirmed. Our objective was to investigate the flow of blood and CSF in INPH, as compared to healthy elderly, in order to clarify which flow parameters are related to the INPH pathophysiology.

    Materials and Methods: Sixteen INPH patients (73 years) and 35 healthy subjects (72 years) underwent phase-contrast magnetic resonance imaging (MRI). Measurements included aqueduct and cervical CSF flow, total arterial inflow (tCBF; i.e. carotid + vertebral arteries), and internal jugular vein flow. Flow pulsatility, net flow, and flow delays were compared (multiple linear regression, correcting for sex and age).

    Results: Aqueduct stroke volume was higher in INPH than healthy (148±95 vs 90±50 mL, P<.05). Net aqueduct CSF flow was similar in magnitude and direction. The cervical CSF stroke volume was lower (P<.05). The internal carotid artery net flow was lower in INPH (P<.05), although tCBF was not. No differences were found in internal jugular vein flow or flow delays.

    Conclusions: The typical flow of blood and CSF in INPH was mainly characterized by increased CSF pulsatility in the aqueduct and reduced cervical CSF pulsatility. The direction of mean net aqueduct CSF flow was from the third to the fourth ventricle. Our findings may reflect the altered distribution of intracranial CSF volume in INPH, although the causality of these relationships is unclear.

  • 23.
    Qvarlander, Sara
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Jacobsson, Johan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    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.
    Differences in cerebral blood flow and CSF flow between INPH and healthy elderlyManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Idiopathic normal pressure hydrocephalus (INPH) is linked to disturbance of the CSF circulation, though the exact nature of the disturbance is not clarified. Phase contrast magnetic resonance imaging (PC-MRI) allows for measurement of local CSF and blood flows, and has been applied in hydrocephalus to demonstrate changes in both cerebral blood flow and aqueduct CSF flow. Many of these studies have, however been based on small numbers of subjects, or poorly defined selection criteria. This study therefore aimed to confirm if cerebral blood flow and CSF flow between compartments differed between INPH subjects and healthy elderly.

    Forty-three healthy elderly and 22 patients diagnosed with INPH according to the INPH guidelines were investigated with PC-MRI measurements of cerebral arterial inflow (CBF) and internal jugular venous outflow, cervical CSF flow, and aqueduct CSF flow. Both net flows, pulsatile aspects of flow, and delays between flow waveforms were analysed.

    Pulsatility in the aqueduct flow was significantly higher in INPH than healthy elderly (aqueduct stroke volume: 189±184 vs. 86±46 ml, p<0.01). There was larger variation in aqueduct net flow in INPH (SD: 1.31 vs. 0.25 ml/min), but the mean net flow did not differ. Cerebral blood flow and internal jugular vein flow showed no significant differences between the groups, though there was a trend toward lower CBF in the diastolic phase and higher CBF pulsatility index. No differences were found in flow delays.

    In conclusion, cerebral in- and outflow of blood, and cervical CSF flow were similar in healthy elderly and INPH subjects. Aqueduct flow showed higher pulsatility in INPH, but there was no general reversal of the direction of aqueduct net flow. 

  • 24.
    Schrauben, Eric
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Wisconsin, USA.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Department of Radiology, University of Wisconsin – Madison, Madison, Wisconsin, USA.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Spaak, Erik
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Wieben, Oliver
    University of Wisconsin – Madison, Madison, Wisconsin, USA.
    Eklund, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Fast 4D flow MRI intracranial segmentation and quantification in tortuous arteries2015Ingår i: Journal of Magnetic Resonance Imaging, ISSN 1053-1807, E-ISSN 1522-2586, Vol. 42, nr 5, s. 1458-1464Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    PurposeTo describe, validate, and implement a centerline processing scheme (CPS) for semiautomated segmentation and quantification in carotid siphons of healthy subjects. 4D flow MRI enables blood flow measurement in all major cerebral arteries with one scan. Clinical translational hurdles are time demanding postprocessing and user-dependence induced variability during analysis. Materials and MethodsA CPS for 4D flow data was developed to automatically separate cerebral artery trees. Flow parameters were quantified at planes along the centerline oriented perpendicular to the vessel path. At 3T, validation against 2D phase-contrast (PC) magnetic resonance imaging (MRI) and 4D flow manual processing was performed on an intracranial flow phantom for constant flow, while pulsatile flow validation was performed in the internal carotid artery (ICA) of 10 healthy volunteers. The CPS and 4D manual processing times were measured and compared. Flow and area measurements were also demonstrated along the length of the ICA siphon. ResultsPhantom measurements for area and flow were highly correlated between the CPS and 2D measurements (area: R=0.95, flow: R=0.94), while in vivo waveforms were highly correlated (R=0.93). Processing time was reduced by a factor of 4.6 compared with manual processing. Whole ICA measurements revealed a significantly decreased area in the most distal segment of the carotid siphon (P=0.0017), with flow unchanged (P=0.84). ConclusionThis study exhibits fast semiautomated analysis of intracranial 4D flow MRI. Internal consistency was shown through flow conservation along the tortuous ICA siphon, which is typically difficult to assess. J. Magn. Reson. Imaging 2015;42:1458-1464.

  • 25.
    Sundström, Peter
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Ambarki, Khalid
    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.
    Venous and cerebrospinal fluid flow in multiple sclerosis. A case-control study.2010Ingår i: Annals of Neurology, ISSN 0364-5134, E-ISSN 1531-8249, Vol. 68, nr 2, s. 255-259Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The prevailing view on multiple sclerosis etiopathogenesis has been challenged by the suggested new entity chronic cerebrospinal venous insufficiency. To test this hypothesis, we studied 21 relapsing-remitting multiple sclerosis cases and 20 healthy controls with phase-contrast magnetic resonance imaging. In addition, in multiple sclerosis cases we performed contrast-enhanced magnetic resonance angiography. We found no differences regarding internal jugular venous outflow, aqueductal cerebrospinal fluid flow, or the presence of internal jugular blood reflux. Three of 21 cases had internal jugular vein stenoses. In conclusion, we found no evidence confirming the suggested vascular multiple sclerosis hypothesis.

  • 26.
    Vågberg, Mattias
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Lindqvist, Thomas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Svenningsson, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Brain parenchymal fraction in an age-stratified healthy population: determined by MRI using manual segmentation and three automated segmentation methods2016Ingår i: Journal of neuroradiology, ISSN 0150-9861, E-ISSN 1773-0406, Vol. 43, nr 6, s. 384-391Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND AND PURPOSE: Brain atrophy is a prominent feature in many neurodegenerative diseases, such as multiple sclerosis, but age-related decrease of brain volume occurs regardless of pathological neurodegeneration. Changes in brain volume can be described by use of the brain parenchymal fraction (BPF), most often defined as the ratio of total brain parenchyma to total intracranial space. The BPF is of interest both in research and in clinical practice. To be able to properly interpret this variable, the normal range of BPF must be known. The objective of this study is to present normal values for BPF, stratified by age, and compare manual BPF measurement to three automated methods. MATERIALS AND METHODS: The BPFs of 106 healthy individuals aged 21 to 85 years were determined by the automated segmentation methods SyMap, VBM8 and SPM12. In a subgroup of 54 randomly selected individuals, the BPF was also determined by manual segmentation. RESULTS: The median (IQR) BPFs of the whole study population were 0.857 (0.064), 0.819 (0.028) and 0.784 (0.073) determined by SyMap, VBM8 and SPM12, respectively. The BPF decreased with increasing age. The correlation coefficients between manual segmentation and SyMap, VBM8 and SPM12 were 0.93 (P<0.001), 0.77 (P<0.001) and 0.56 (P<0.001), respectively. CONCLUSIONS: There was a clear relationship between increasing age and decreasing BPF. Knowledge of the range of normal BPF in relation to age group will help in the interpretation of BPF data. The automated segmentation methods displayed varying degrees of similarity to the manual reference, with SyMap being the most similar.

  • 27.
    Vågberg, Mattias
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Lindqvist, T.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi. Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Warntjes, J. B. M.
    Sundström, Peter
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Svenningsson, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Automated Determination of Brain Parenchymal Fraction in Multiple Sclerosis2013Ingår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 34, nr 3, s. 498-504Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND AND PURPOSE: Brain atrophy is a manifestation of tissue damage in MS. Reduction in brain parenchymal fraction is an accepted marker of brain atrophy. In this study, the approach of synthetic tissue mapping was applied, in which brain parenchymal fraction was automatically calculated based on absolute quantification of the tissue relaxation rates R1 and R2 and the proton attenuation. MATERIALS AND METHODS: The BPF values of 99 patients with MS and 35 control subjects were determined by using SyMap and tested in relationship to clinical variables. A subset of 5 patients with MS and 5 control subjects were also analyzed with a manual segmentation technique as a reference. Reproducibility of SyMap was assessed in a separate group of 6 healthy subjects, each scanned 6 consecutive times. RESULTS: Patients with MS had significantly lower BPF (0.852 0.0041, mean +/- SE) compared with control subjects (0.890 +/- 0.0040). Significant linear relationships between BPF and age, disease duration, and Expanded Disability Status Scale scores were observed (P < .001). A strong correlation existed between SyMap and the reference method (r = 0.96; P < .001) with no significant difference in mean BPF. Coefficient of variation of repeated SyMap BPF measurements was 0.45%. Scan time was <6 minutes, and postprocessing time was <2 minutes. CONCLUSIONS: SyMap is a valid and reproducible method for determining BPF in MS within a clinically acceptable scan time and postprocessing time. Results are highly congruent with those described using other methods and show high agreement with the manual reference method.

  • 28.
    Wåhlin, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Alperin, Noam
    Department of Radiology, University of Miami, Miami, Florida.
    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 craniospinal pressure-volume indices2010Ingår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 31, nr 9, s. 1645-1650Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    BACKGROUND AND PURPOSE: The PVI(CC) of the craniospinal compartment defines the shape of the pressure-volume curve and determines the damping of cyclic arterial pulsations. Despite no reports of direct measurements of the PVI(CC) among healthy elderly, it is believed that a change away from adequate accommodation of cardiac-related pulsations may be a pathophysiologic mechanism seen in neurodegenerative disorders such as Alzheimer disease and idiopathic normal pressure hydrocephalus. In this study, blood and CSF flow measurements are combined with lumbar CSF infusion measurements to assess the craniospinal PVI(CC) and its distribution of cranial and spinal compartments in healthy elderly.

    MATERIALS AND METHODS: Thirty-seven healthy elderly were included (60-82 years of age). The cyclic arterial volume change and the resulting shift of CSF to the spinal compartment were quantified by PC-MR imaging. In addition, each subject underwent a lumbar CSF infusion test in which the magnitude of cardiac-related pulsations in intracranial pressure was quantified. Finally, the PVI was calculated by using a mathematic model.

    RESULTS: After excluding 2 extreme values, the craniospinal PVI(CC) was calculated to a mean of 9.8 ± 2.7 mL and the estimated average 95% confidence interval of individual measurements was ± 9%. The average intracranial and spinal contributions to the overall compliance were 65% and 35% respectively (n = 35).

    CONCLUSIONS: Combining lumbar CSF infusion and PC-MR imaging proved feasible and robust for assessment of the craniospinal PVI(CC). This study produced normative values and showed that the major compensatory contribution was located intracranially.

  • 29.
    Wåhlin, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    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.
    In healthy elderly the volumes of several brain regions are related to pulsatility in cerebral arteries and cerebrospinal fluidManuskript (preprint) (Övrigt vetenskapligt)
  • 30.
    Wåhlin, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Institutionen för medicinsk kemi och biofysik.
    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, Institutionen för medicinsk kemi och biofysik.
    Intracranial pulsatility is associated with regional brain volume in elderly individuals2014Ingår i: Neurobiology of Aging, ISSN 0197-4580, E-ISSN 1558-1497, Vol. 35, nr 2, s. 365-372Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Excessive intracranial pulsatility is thought to damage the cerebral microcirculation, causing cognitive decline in elderly individuals. We investigated relationships between brain structure and measures related to intracranial pulsatility among healthy elderly. Thirty-seven stroke-free, non-demented individuals (62-82 years of age) were included. We assessed brain structure, invasively measured cerebrospinal fluid (CSF) pulse pressure, and magnetic resonance-quantified arterial and CSF flow pulsatility, as well as arterial pulse pressure. Using both multivariate partial least squares and ordinary regression analyses, we identified a significant pattern of negative relationships between the volume of several brain regions and measures of intracranial pulsatility. The strongest relationships concerned the temporal lobe cortex and hippocampus. These findings were also coherent with observations of positive relationships between intracranial pulsatility and ventricular volume. In conclusion, elderly subjects with high intracranial pulsatility display smaller brain volume and larger ventricles, supporting the notion that excessive cerebral arterial pulsatility harms the brain. This calls for research investigating altered intracranial cardiac-related pulsatile stress as a potential risk factor that may cause or worsen the prognosis in subjects developing cognitive impairment and dementia.

  • 31.
    Wåhlin, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Wieben, O
    Johnson, KM
    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).
    Measuring pulsatile flow in cerebral arteries using 4D phase-contrast magnetic resonance imaging2013Ingår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 34, nr 9, s. 1740-1745Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    BACKGROUND AND PURPOSE: 4D PCMRI can be used to quantify pulsatile hemodynamics in multiple cerebral arteries. The aim of this study was to compare 4D PCMRI and 2D PCMRI for assessments of pulsatile hemodynamics in major cerebral arteries. MATERIALS AND METHODS: We scanned the internal carotid artery, the anterior cerebral artery, the basilar artery, and the middle cerebral artery in 10 subjects with a single 4D and multiple 2D PCMRI acquisitions by use of a 3T system and a 32-channel head coil. We assessed the agreement regarding net flow and the volume of arterial pulsatility (V) for all vessels. RESULTS: 2D and 4D PCMRI produced highly correlated results, with r = 0.86 and r = 0.95 for V and net flow, respectively (n = 69 vessels). These values increased to r = 0.93 and r = 0.97, respectively, during investigation of a subset of measurements with <5% variation in heart rate between the 4D and 2D acquisition (n = 31 vessels). Significant differences were found for ICA and MCA net flow (P = .004 and P < .001, respectively) and MCA V (P = .006). However, these differences were attenuated and no longer significant when the subset with stable heart rate (n = 31 vessels) was analyzed. CONCLUSIONS: 4D PCMRI provides a powerful methodology to measure pulsatility of the larger cerebral arteries from a single acquisition. A large part of differences between measurements was attributed to physiologic variations. The results were consistent with 2D PCMRI.

  • 32.
    Wåhlin, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Hauksson, Jón
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Phase contrast MRI quantification of pulsatile volumes of brain arteries, veins, and cerebrospinal fluids compartments: repeatability and physiological interactions2012Ingår i: Journal of Magnetic Resonance Imaging, ISSN 1053-1807, E-ISSN 1522-2586, Vol. 35, nr 5, s. 1055-1062Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    PURPOSE: To study measurement repeatability and physiological determinants on measurement stability for phase contrast MRI (PC-MRI) measurements of cyclic volume changes (ΔV) of brain arteries, veins, and cerebrospinal fluid (CSF) compartments.

    MATERIALS AND METHODS: Total cerebral blood flow (tCBF), total internal jugular flow (tJBF) and spinal CSF flow at C2-C3 level and CSF in the aqueduct was measured using five repetitions in 20 healthy subjects. After subtracting net flow, waveforms were integrated to calculate ΔV of arterial, venous, and cerebrospinal fluid compartments. The intraclass correlation coefficient (ICC) was used to measure repeatability. Systematic errors were investigated by a series of phantom measurements.

    RESULTS: For ΔV calculated from tCBF, tJBF and both CSF waveforms, the ICC was ≥0.85. ΔV from the tCBF waveform decreased linearly between repetitions (P = 0.012). Summed CSF and venous volume being shifted out from the cranium was correlated with ΔV calculated from the tCBF waveform (r = 0.75; P < 0.001). Systematic errors increased at resolutions <4 pixels per diameter.

    CONCLUSION: Repeatability of ΔV calculated from tCBF, tJBF, and CSF waveforms allows useful interpretations. The subject's time in the MR system and imaging resolution should be considered when interpreting volume changes. Summed CSF and venous volume changes was associated with arterial volume changes.

    J. Magn. Reson. Imaging 2011;. © 2011 Wiley Periodicals, Inc.

  • 33.
    Zarrinkoob, Laleh
    et al.
    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.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Carlberg, Bo
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Aging alters the dampening of pulsatile blood flow in cerebral arteries2016Ingår i: Journal of Cerebral Blood Flow and Metabolism, ISSN 0271-678X, E-ISSN 1559-7016, Vol. 36, nr 9, s. 1519-1527Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Excessive pulsatile flow caused by aortic stiffness is thought to be a contributing factor for several cerebrovascular diseases. The main purpose of this study was to describe the dampening of the pulsatile flow from the proximal to the distal cerebral arteries, the effect of aging and sex, and its correlation to aortic stiffness. Forty-five healthy elderly (mean age 71 years) and 49 healthy young (mean age 25 years) were included. Phase-contrast magnetic resonance imaging was used for measuring blood flow pulsatility index and dampening factor (proximal artery pulsatility index/distal artery pulsatility index) in 21 cerebral and extra-cerebral arteries. Aortic stiffness was measured as aortic pulse wave velocity. Cerebral arterial pulsatility index increased due to aging and this was more pronounced in distal segments of cerebral arteries. There was no difference in pulsatility index between women and men. Dampening of pulsatility index was observed in all cerebral arteries in both age groups but was significantly higher in young subjects than in elderly. Pulse wave velocity was not correlated with cerebral arterial pulsatility index. The increased pulsatile flow in elderly together with reduced dampening supports the pulse wave encephalopathy theory, since it implies that a higher pulsatile flow is reaching distal arterial segments in older subjects.

  • 34.
    Zarrinkoob, Laleh
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Ambarki, Khalid
    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, Radiofysik. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Blood flow distribution in cerebral arteries2015Ingår i: Journal of Cerebral Blood Flow and Metabolism, ISSN 0271-678X, E-ISSN 1559-7016, Vol. 35, nr 4, s. 648-654Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-resolution phase-contrast magnetic resonance imaging can now assess flow in proximal and distal cerebral arteries. The aim of this study was to describe how total cerebral blood flow (tCBF) is distributed into the vascular tree with regard to age, sex and anatomic variations. Forty-nine healthy young (mean 25 years) and 45 elderly (mean 71 years) individuals were included. Blood flow rate (BFR) in 21 intra-and extracerebral arteries was measured. Total cerebral blood flow was defined as BFR in the internal carotid plus vertebral arteries and mean cerebral perfusion as tCBF/brain volume. Carotid/vertebral distribution was 72%/28% and was not related to age, sex, or brain volume. Total cerebral blood flow (717 +/- 123 mL/min) was distributed to each side as follows: middle cerebral artery (MCA), 21%; distal MCA, 6%; anterior cerebral artery (ACA), 12%, distal ACA, 4%; ophthalmic artery, 2%; posterior cerebral artery (PCA), 8%; and 20% to basilar artery. Deviating distributions were observed in subjects with 'fetal' PCA. Blood flow rate in cerebral arteries decreased with increasing age (P < 0.05) but not in extracerebral arteries. Mean cerebral perfusion was higher in women (women: 61 +/- 8; men: 55 +/- 6 mL/min/100 mL, P < 0.001). The study describes a new method to outline the flow profile of the cerebral vascular tree, including reference values, and should be used for grading the collateral flow system.

  • 35.
    Zarrinkoob, Laleh
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap. Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap.
    Wåhlin, 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).
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    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).
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap.
    Blood flow lateralization and collateral compensatory mechanisms in patients with carotid artery stenosis2019Ingår i: Stroke, ISSN 0039-2499, E-ISSN 1524-4628, Vol. 50, nr 5, s. 1081-1088Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background and Purpose: Four-dimensional phase-contrast magnetic resonance imaging enables quantification of blood flow rate (BFR; mL/min) in multiple cerebral arteries simultaneously, making it a promising technique for hemodynamic investigation in patients with stroke. The aim of this study was to quantify the hemodynamic disturbance and the compensatory pattern of collateral flow in patients with symptomatic carotid stenosis.

    Methods: Thirty-eight patients (mean, 72 years; 27 men) with symptomatic carotid stenosis (>/=50%) or occlusion were investigated using 4-dimensional phase-contrast magnetic resonance imaging. For each patient, BFR was measured in 19 arteries/locations. The ipsilateral side to the symptomatic carotid stenosis was compared with the contralateral side.

    Results: Internal carotid artery BFR was lower on the ipsilateral side (134+/-87 versus 261+/-95 mL/min; P<0.001). BFR in anterior cerebral artery (A1 segment) was lower on ipsilateral side (35+/-58 versus 119+/-72 mL/min; P<0.001). Anterior cerebral artery territory bilaterally was primarily supplied by contralateral internal carotid artery. The ipsilateral internal carotid artery mainly supplied the ipsilateral middle cerebral artery (MCA) territory. MCA was also supplied by a reversed BFR found in the ophthalmic and the posterior communicating artery routes on the ipsilateral side (-5+/-28 versus 10+/-28 mL/min, P=0.001, and -2+/-12 versus 6+/-6 mL/min, P=0.03, respectively). Despite these compensations, BFR in MCA was lower on the ipsilateral side, and this laterality was more pronounced in patients with severe carotid stenosis (>/=70%). Although comparing ipsilateral MCA BFR between stenosis groups (<70% and >/=70%), there was no difference ( P=0.95).

    Conclusions: With a novel approach using 4-dimensional phase-contrast magnetic resonance imaging, we could simultaneously quantify and rank the importance of collateral routes in patients with carotid stenosis. An important observation was that contralateral internal carotid artery mainly secured the bilateral anterior cerebral artery territory. Because of the collateral recruitment, compromised BFR in MCA is not necessarily related to the degree of carotid stenosis. These findings highlight the importance of simultaneous investigation of the hemodynamics of the entire cerebral arterial tree.

  • 36.
    Zarrinkoob, Laleh
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Medicinska fakulteten, Institutionen för klinisk mikrobiologi, Biomedicinsk laboratorievetenskap. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Quantification and mapping of cerebral hemodynamics before and after carotid endarterectomy: a 4D PCMRI studyManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Background and purpose: A carotid stenosis can have a profound impact on the cerebral hemodynamics that cannot be inferred from the degree of stenosis by itself. We aimed to quantify and map the distribution of blood flow rate (BFR) in cerebral arteries before and after carotid endarterectomy (CEA), using four-dimensional phase-contrast magnetic resonance imaging (4D PCMRI).

    Methods: Nineteen patients (71±6 years, 2 women) with symptomatic carotid stenosis (≥50%)undergoing CEA were investigated using 4D PCMRI before and after surgery. BFR was measured in 17 cerebral arteries and in the ophthalmic arteries (OA). Collateral recruitment through the anterior and posterior communicating arteries, OA and the leptomeningeal arterial route was identified and quantified. BFR laterality was described as contralateral BFR minus ipsilateral BFR in paired arteries.

    Results: Total cerebral blood flow increased by 15% (p<0.01) after CEA. On the ipsilateral side, increased BFR was found after CEA in internal carotid artery (ICA) (246±62mL/min vs. 135±80mL/min; p<0.001), anterior cerebral artery (87±mL/min vs. 38±58mL/min; p<0.01) and middle cerebral artery (MCA) (149±43mL/min vs. 119±34mL/min; p<0.01), resulting in a postoperative BFR distribution without signs of laterality. In patients with preoperatively recruited collaterals (n=9), BFR laterality was found in MCA before, but not after, CEA (p<0.01). This laterality was not found in patients without collateral recruitment (n=10) (p=0.2). The degree of stenosis did not differ between the groups with vs. without collateral recruitment (p=0.85). 

    Conclusion: 4D PCMRI is a useful technique to quantify cerebral hemodynamic changes seen in patients with carotid stenosis before and after CEA. MCA laterality, seen in patients with collateral recruitment before CEA, pointed towards a hemodynamic disturbance in MCA territory for those patients. This study introduces a new and non-invasive way to evaluate cerebral hemodynamics due to carotid stenosis prior to and after CEA.

1 - 36 av 36
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf