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  • 1.
    Alenius Dahlqvist, Jenny
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Pediatrik.
    Karlsson, Marcus
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Wiklund, Urban
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Hörnsten, Rolf
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Klinisk fysiologi.
    Rydberg, Annika
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Pediatrik.
    Handheld ECG in analysis of arrhythmia and heart rate variability in children with Fontan circulation2014Inngår i: Journal of Electrocardiology, ISSN 0022-0736, E-ISSN 1532-8430, Vol. 47, nr 3, 374-382 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: Our aim was to evaluate the intermittent use of a handheld ECG system for detecting silent arrhythmias and cardiac autonomic dysfunction in children with univentricular hearts. Methods: Twenty-seven patients performed intermittent ECG recordings with handheld devices during a 14-day period. A manual arrhythmia analysis was performed. We analyzed heart rate variability (HRV) using scatter plots of all interbeat intervals (Poincare plots) from the total observation period. Reference values of HRV indices were determined from Holter-ECGs in 41 healthy children. Results: One asymptomatic patient had frequent ventricular extra systoles. Another patient had episodes with supraventricular tachycardia (with concomitant palpitations). Seven patients showed reduced HRV. Conclusions: Asymptomatic arrhythmia was detected in one patient. The proposed method for pooling of intermittent recordings from handheld or similar devices may be used for detection of arrhythmias as well as for cardiac autonomic dysfunction.

  • 2.
    Alenius Dahlqvist, Jenny
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Pediatrik.
    Karlsson, Marcus
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Wiklund, Urban
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Hörnsten, Rolf
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Klinisk fysiologi.
    Strömvall-Larsson, Eva
    Division of Cardiology, Department of Paediatrics, Sahlgrenska University Hospital/Queen Silvia Children’s Hospital, Göteborg University, Göteborg, Sweden.
    Berggren, Håkan
    Division of Cardiothoracic Surgery, Department of Paediatrics, Sahlgrenska University Hospital/Queen Silvia Children’s Hospital, Göteborg University, Göteborg, Sweden.
    Hanseus, Katarina
    Department of Paediatrics, Children’s Hospital, Lund University Hospital, Lund, Sweden.
    Johansson, Sune
    Paediatric Cardiac Surgical Unit, Children’s Hospital, Lund University Hospital, Lund, Sweden.
    Rydberg, Annika
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Pediatrik.
    Heart rate variability in children with fontan circulation: lateral tunnel and extracardiac conduit2012Inngår i: Pediatric Cardiology, ISSN 0172-0643, E-ISSN 1432-1971, Vol. 33, nr 2, 307-315 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The technique in Fontan surgery has developed from the lateral tunnel (LT) toward the extracardiac conduit (EC) used to reduce long-term complications such as atrial arrhythmia and sinus node dysfunction. Heart rate variability (HRV) examines cardiac nervous activity controlling the sinus node. This study aimed to investigate HRV in a cohort of children with univentricular hearts, focusing on the relation between HRV and surgical procedure. For 112 children with Fontan circulation, HRV was analyzed using power spectral analysis. Spectral power was determined in three regions: very-low-frequency (VLF), low-frequency (LF), and high-frequency (HF) regions. Patients were compared with 66 healthy controls subject. Patients with LT were compared with patients who had EC. The children with Fontan circulation showed a significantly reduced HRV including total power (P < 0.0001), VLF (P < 0.0001), LF (P < 0.0001), and HF (P = 0.001) compared with the control subjects. The LT and EC patients did not differ significantly. Reduced HRV was found in both the LT and EC patients. In terms of HRV reduction, EC was not superior to LT.

  • 3. Alrifaiy, Ahmed
    et al.
    Borg, Johan
    Lindahl, Olof A.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Department of Computer Science, Electrical and Space Engineering, Luleå University of Technology; CMTF, Centre for Biomedical Engineering and Physics, Luleå and Umeå, Sweden; Department of Engineering Sciences and Mathematics, Luleå University of Technology.
    Ramser, Kerstin
    A lab-on-a-chip for hypoxic patch clamp measurements combined with optical tweezers and spectroscopy-first investigations of single biological cells2015Inngår i: Biomedical engineering online, ISSN 1475-925X, Vol. 14, 36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The response and the reaction of the brain system to hypoxia is a vital research subject that requires special instrumentation. With this research subject in focus, a new multifunctional lab-on-a-chip (LOC) system with control over the oxygen content for studies on biological cells was developed. The chip was designed to incorporate the patch clamp technique, optical tweezers and absorption spectroscopy. The performance of the LOC was tested by a series of experiments. The oxygen content within the channels of the LOC was monitored by an oxygen sensor and verified by simultaneously studying the oxygenation state of chicken red blood cells (RBCs) with absorption spectra. The chicken RBCs were manipulated optically and steered in three dimensions towards a patch-clamp micropipette in a closed microfluidic channel. The oxygen level within the channels could be changed from a normoxic value of 18% O-2 to an anoxic value of 0.0-0.5% O-2. A time series of 3 experiments were performed, showing that the spectral transfer from the oxygenated to the deoxygenated state occurred after about 227 +/- 1 s and a fully developed deoxygenated spectrum was observed after 298 +/- 1 s, a mean value of 3 experiments. The tightness of the chamber to oxygen diffusion was verified by stopping the flow into the channel system while continuously recording absorption spectra showing an unchanged deoxygenated state during 5400 +/- 2 s. A transfer of the oxygenated absorption spectra was achieved after 426 +/- 1 s when exposing the cell to normoxic buffer. This showed the long time viability of the investigated cells. Successful patching and sealing were established on a trapped RBC and the whole-cell access (Ra) and membrane (Rm) resistances were measured to be 5.033 +/- 0.412 M Omega and 889.7 +/- 1.74 M Omega respectively.

  • 4. Alrifaiy, Ahmed
    et al.
    Lindahl, Olof A
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Ramser, Kerstin
    Polymer-based microfluidic devices for pharmacy, biology and tissue engineering2012Inngår i: Polymers, ISSN 2073-4360, Vol. 4, nr 3, 1349-1398 s.Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    This paper reviews microfluidic technologies with emphasis on applications in the fields of pharmacy, biology, and tissue engineering. Design and fabrication of microfluidic systems are discussed with respect to specific biological concerns, such as biocompatibility and cell viability. Recent applications and developments on genetic analysis, cell culture, cell manipulation, biosensors, pathogen detection systems, diagnostic devices, high-throughput screening and biomaterial synthesis for tissue engineering are presented. The pros and cons of materials like polydimethylsiloxane (PDMS), polymethylmethacrylate (PMMA), polystyrene (PS), polycarbonate (PC), cyclic olefin copolymer (COC), glass, and silicon are discussed in terms of biocompatibility and fabrication aspects. Microfluidic devices are widely used in life sciences. Here, commercialization and research trends of microfluidics as new, easy to use, and cost-effective measurement tools at the cell/tissue level are critically reviewed.

  • 5.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Hallberg, Per
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Jóhannesson, Gauti
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Lindén, Christina
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik.
    Zarrinkoob, Laleh
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Blood flow of ophthalmic artery in healthy individuals determined by phase-contrast magnetic resonance imaging2013Inngår i: Investigative Ophthalmology and Visual Science, ISSN 0146-0404, Vol. 54, nr 4, 2738-2745 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

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

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

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

  • 6.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Israelsson, Hanna
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Brain ventricular size in healthy elderly: comparison between evans index and volume measurement.2010Inngår i: Neurosurgery, ISSN 0148-396X, E-ISSN 1524-4040, Vol. 67, nr 1, 94-99 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 7.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Lindqvist, Tomas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Petterson, E
    Warntjes, JBM
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Evaluation of automatic measurement of the intracranial volume based on quantitative MR imaging2012Inngår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 33, nr 10, 1951-1956 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

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

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

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

  • 8.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Petr, J.
    Wahlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Wirestam, R.
    Zarrinkoob, Laleh
    Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Partial Volume Correction of Cerebral Perfusion Estimates Obtained by Arterial Spin Labeling2015Inngår i: 16th Nordic-Baltic Conference on Biomedical Engineering: 16. NBC & 10. MTD 2014 joint conferences. October 14-16, 2014, Gothenburg, Sweden, 2015, Vol. 48, 17-19 s.Konferansepaper (Fagfellevurdert)
    Abstract [en]

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

  • 9.
    Ambarki, Khalid
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    MR imaging of brain volumes: evaluation of a fully automatic software2011Inngår i: American Journal of Neuroradiology, ISSN 0195-6108, E-ISSN 1936-959X, Vol. 32, nr 2, 408-412 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

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

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

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

  • 10.
    Andersson, Jonas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Ion recombination in liquid ionization chambers: development of an experimental method to quantify general recombination2013Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    An experimental method (the two-dose-rate method) for the correction of general recombination losses in liquid ionization chambers has been developed and employed in experiments with different liquids and radiation qualities. The method is based on a disassociation of initial and general recombination, since an ionized liquid is simultaneously affected by both of these processes.

    The two-dose-rate method has been compared to an existing method for general recombination correction for liquid ionization chambers, and has been found to be the most robust method presently available.

    The soundness of modelling general recombination in liquids on existing theory for gases has been evaluated, and experiments indicate that the process of general recombination is similar in a gas and a liquid. It is thus reasonable to employ theory for gases in the two-dose-rate method to achieve experimental corrections for general recombination in liquids. There are uncertainties in the disassociation of initial and general recombination in the two-dose-rate method for low applied voltages, where initial recombination has been found to cause deviating results for different liquids and radiation qualities.

    Sensitivity to ambient electric fields has been identified in the microLion liquid ionization chamber (PTW, Germany). Experimental data may thus be perturbed if measurements are conducted in the presence of ambient electric fields, and the sensitivity has been found to increase with an increase in the applied voltage. This can prove to be experimentally limiting since general recombination may be too severe for accurate corrections if the applied voltage is low.

  • 11.
    Andersson, Jonas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Radiation Dosimetry for CBCT – Quality Control and Applied Dosimetry2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The use of Cone Beam CT (CBCT) devices in health care has increased in recent years. Unfortunately, this trend has not been followed by a standardization of dose metrics for Quality Control (QC), or a necessary evolution of applied dosimetry for assessment of patient dose.

    The European Federation of Organisations in Medical Physics (EFOMP) has drafted a report on the property of QC for CBCT devices. The report contains objective, practical and unifying methodology for QC of CBCT used in oral radiology, radiotherapy, interventional radiology and guided surgery. The dose metrics discussed include the Computed Tomography Dose Index (CTDI), Kerma-Area Product (KAP) and detector incident air kerma. The report concludes that KAP-meters are preferable for QC as long as they can be mounted on the X-ray tube housing. Otherwise measurements of detector incident kerma seem to offer a practical solution for QC.

    The European Radiation Dosimetry Group (EURADOS) are preparing a literature review on patient dose from various applications of CBCT, which will in part be included in the EFOMP report. Most studies on patient dose from CBCT examinations and interventional procedures are based on thermoluminescent dosimeter (TLD) measurements in Rando phantoms. While helpful to the community, these studies yield substantial uncertainty when applied in the clinical reality of medical physicists working with justification and optimization. Applied dosimetry for CBCT needs to evolve and adopt recent theoretical advances to allow robust estimates of patient dose.

  • 12.
    Andersson, Jonas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    TG246 On Patient Dose From Diagnostic Radiation: Acceptance Testing and Dose Measurements with CT2014Inngår i: 56th AAPM Annual Meeting and Exhibition 2014, Austin, TX, USA, July 20-24 (2014), 2014Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Radiation dose from diagnostic and interventional use of ionizing radiation continues to be a focus of the regulatory, accreditation and standards organizations in the US and Europe. A Joint AAPM/EFOMP effort has been underway in the past year – having the goal to assist the clinical medical physicist with communicating optional and varied approaches in estimating (and validating) patient dose. In particular, the tools provided by DICOM Radiation Dose Structured Reports, either by themselves or as part of a networked data repository of dose related information are a rich source of actionable information. The tools of the medical physicist have evolved to include using DICOM data in meaningful ways to look at patient dose with respect to imaging practices. In addition to how accurate or reproducible a dose value is (totally necessary and our traditional workspace) it is now being asked how reproducible (patient to patient, device to device) are the delivered doses? Clinical medical physicists are best equipped to assist our radiology and technologist colleagues with this effort. The purpose of this session is to review the efforts of TG246 - bringing forward a summary content of the TG246 Report including specific dose descriptors for CT and Fluoroscopy – particularly in a focus of leveraging the RDSR as a means for monitoring good practices according to the ALARA principle. Additionally, rapidly evolving technologies for more refined dose estimates are now in use. These will be presented as they look to having highly patient specific dose estimates in automated use.

  • 13.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Johansson, Erik
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Tölli, Heikki
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    On the property of measurements with the PTW microLion chamber in continuous beam2012Inngår i: Medical physics (Lancaster), ISSN 0094-2405, Vol. 39, nr 8, 4775-4787 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Purpose: The performance of liquid ionization chambers, which may prove to be useful tools in the field of radiation dosimetry, is based on several chamber and liquid specific characteristics. The present work investigates the performance of the PTW microLion liquid ionization chamber with respect to recombination losses and perturbations from ambient electric fields at various dose rates in continuous beams.

    Methods: In the investigation, experiments were performed using two microLion chambers, containing isooctane (C8H18) and tetramethylsilane (Si(CH3)4) as the sensitive media, and a NACP-02 monitor chamber. An initial activity of approximately 250 GBq 18F was employed as the radiation source in the experiments. The initial dose rate in each measurement series was estimated to 1.0 Gy min-1 by Monte Carlo simulations and the measurements were carried out during the decay of the radioactive source. In the investigation of general recombination losses, employing the two-dose-rate method for continuous beams, the liquid ionization chambers were operated at polarizing voltages 25, 50, 100, 150, 200 and 300 V. Furthermore, measurements were also performed at 500 V polarizing voltage in the investigation of the sensitivity of the microLion chamber to ambient electric fields.

    Results: The measurement results from the liquid ionization chambers, corrected for general recombination losses according to the two-dose-rate method for continuous beams, had a good agreement with the signal to dose linearity from the NACP-02 monitor chamber for general collection efficiencies above 70%. The results also displayed an agreement with the theoretical collection efficiencies according to the Greening theory, except for the liquid ionization chamber containing isooctane operated at 25 V. At lower dose rates, perturbations from ambient electric fields were found in the microLion chamber measurement results. Due to the perturbations, measurement results below an estimated dose rate of 0.2 Gy min-1 were excluded from the present investigation of the general collection efficiency. The perturbations were found to be more pronounced when the chamber polarizing voltage was increased.

    Conclusions: By using the two-dose-rate method for continuous beams, comparable corrected ionization currents from experiments in low- and medium energy photon beams can be achieved. However, the valid range of general collection efficiencies has been found to vary in a comparison between experiments performed in continuous beams of 120 kVp x-ray, and the present investigation of 511 keV annihilation photons. At very high dose rates in continuous beams, there are presently no methods that can be used to correct for general recombination losses and at low dose rates the microLion chamber may be perturbed by ambient electric fields. Increasing the chamber polarizing voltage, which diminishes the general recombination effect, was found to increase the microLion chamber sensitivity to ambient electric fields. Prudence is thus advised when employing the microLion chamber in radiation dosimetry, as ambient electric fields of the strength observed in the present work may be found in many common situations. Due to uncertainties in the theoretical basis for recombination losses in liquids, further studies on the underlying theories for the initial and general recombination effect are needed if liquid ionization chambers are to become a viable option in high precision radiation dosimetry.

  • 14.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Kaiser, Franz-Joachim
    Gómez, Faustino
    Jäkel, Oliver
    Pardo-Montero, Juan
    Tölli, Heikki
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    A comparison of different experimental methods for general recombination correction for liquid ionization chambers2012Inngår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, nr 21, 7161-7175 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Radiation dosimetry of highly modulated dose distributions requires a detector with a high spatial resolution. Liquid filled ionization chambers (LICs) have the potential to become a valuable tool for the characterization of such radiation fields. However, the effect of an increased recombination of the charge carriers, as compared to using air as the sensitive medium has to be corrected for. Due to the presence of initial recombination in LICs, the correction for general recombination losses is more complicated than for air-filled ionization chambers. In the present work, recently published experimental methods for general recombination correction for LICs are compared and investigated for both pulsed and continuous beams. The experimental methods are all based on one of two approaches, either measurements at two different dose rates (two-dose-rate methods), or measurements at three different LIC polarizing voltages (three-voltage methods). In a comparison with the two-dose-rate methods, the three-voltage methods fail to achieve accurate corrections in several instances, predominantly at low polarizing voltages and dose rates. However, for continuous beams in the range of polarizing voltages recommended by the manufacturer of the LICs used, the agreement between the different methods is generally within the experimental uncertainties. For pulsed beams, the agreement between the methods is poor. The inaccuracies found in the results from the three-voltage methods are associated with numerical difficulties in solving the resulting equation systems, which also make these methods sensitive to small variations in the experimental data. These issues are more pronounced for the case of pulsed beams. Furthermore, the results suggest that the theoretical modelling of initial recombination used in the three-voltage methods may be a contributing factor to the deviating results observed.

  • 15.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Pavlicek, William
    Patient organ dose with computed tomography - a review of present methodology and DICOM information: executive summary of the joint report of AAPM task group 246 and EFOMP2016Inngår i: ECR 2016 Book of Abstracts, 2016, Vol. 7, nr 1, B0303Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Purpose: The justification and optimisation of medical imaging employing ionizing radiation have been intensely discussed in recent years, particularly for computed tomography (CT). A key point in this discussion is the estimation of patient dose, which commonly employs radiation output metrics developed for quality assurance and no patient specific information. Such patient dose estimates are of limited value, and more refined methods needs to be promoted and provided to the community.

    Methods and Materials: AAPM Task Group 246 was formed in 2013, and in a joint venture with EFOMP charged with summarizing present methodology and DICOM information available for estimating patient dose with computed tomography.

    Results: The Joint Report of AAPM Task Group 246 and EFOMP is a comprehensive resource for the clinical medical physicist. The possibilities of patient specific dosimetry from the Computed Tomography Dose Index (CTDIvol), to the Size-Specific Dose Estimates (SSDE) and advanced Monte Carlo methods are discussed together with available DICOM information, as well as practical examples on how patient dose estimates can be achieved. The report also summarizes important factors contributing to the uncertainty in patient dose estimates and gives examples of achievable confidence intervals.

    Conclusion: The SSDE and Monte Carlo methods can together with detailed scanner, examination and patient specific DICOM information offer refined estimates of patient dose for justification and optimisation of CT examinations. Given the present robustness of available methods AAPM Task Group 246 and EFOMP recommend that all reports of patient dose should be accompanied by estimates of the associated uncertainty.

  • 16.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin.
    Sjöström, Lars-Göran
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin.
    Karlsson, Marcus
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Wiklund, Urban
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Hultin, Magnus
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Anestesiologi och intensivvård.
    Karpe, Fredrik
    Olsson, Tommy
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin.
    Dysregulation of subcutaneous adipose tissue blood flow in overweight postmenopausal women2010Inngår i: Menopause: The Journal of the North American Menopause, ISSN 1072-3714, E-ISSN 1530-0374, Vol. 17, nr 2, 365-371 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    OBJECTIVE:: A putative link between abdominal obesity and metabolic-vascular complications after menopause may be due to a decreased adipose tissue blood flow (ATBF). The present work aimed to analyze possible changes in ATBF with being overweight and menopausal and its putative link to endothelial dysfunction and autonomic nervous system balance.

    METHODS:: Forty-three healthy women were classified into four groups according to weight and menopause status. The ATBF was measured by xenon washout while fasting and after oral glucose intake. The nitric oxide synthase inhibitor asymmetric dimethylarginine was used as a marker of endothelial function and heart rate variability-estimated autonomic nervous system activity.

    RESULTS:: Fasting ATBF was decreased in both overweight groups (P = 0.044 and P = 0.048) versus normal-weight premenopausal women. Normal-weight and overweight postmenopausal women exhibited lower maximum ATBF compared with normal-weight premenopausal women (P = 0.015 and P = 0.001, respectively), and overweight postmenopausal women exhibited lower maximum ATBF compared with normal-weight postmenopausal women (P = 0.003). A negative correlation was found between fasting ATBF and asymmetric dimethylarginine (P = 0.015), whereas maximum ATBF was negatively associated with sympathetic-parasympathetic nervous system balance (ratio of the power of the low frequency to the power of the high frequency; P = 0.002).

    CONCLUSIONS:: Loss of ATBF flexibility in overweight postmenopausal women may contribute to the metabolic dysfunction seen in this group of women.

  • 17.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Tölli, Heikki
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    A study of recombination losses in liquid ionization chambersManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    In the present work, recombination losses in liquid ionization chambers are studied by employing theories derived for gas-filled ionization chambers. A new and robust approximate relation for the general collection efficiency is derived, which is theoretically and experimentally investigated alongside existing theory. Ionized liquids can be strongly affected by both initial and general recombination, and these effects have therefore been disassociated by the two-dose-rate method in order to evaluate the soundness of modelling recombination losses in liquids according to theories for gases, where initial recombination is negligible. The results indicate that liquids and gases have very similar general recombination characteristics, where liquids mimic the behaviour expected in gases. However, it is shown that the disassociation of initial and general recombination in the two-dose-rate method is not trivial since initial recombination depends on the spatial variation of the collecting electric field, which in turn is employed to describe the general collection efficiency. The problem of initial recombination in liquids is also shown to be further complicated by a dependence on the radiation quality, as well as the type of liquid employed as the sensitive media.

  • 18.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Tölli, Heikki
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Application of the two-dose-rate method for general recombination correction for liquid ionization chambers in continuous beams2011Inngår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 56, nr 2, 299-314 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A method to correct for the general recombination losses for liquid ionization chambers in continuous beams has been developed. The proposed method has been derived from Greening's theory for continuous beams and is based on measuring the signal from a liquid ionization chamber and an air filled monitor ionization chamber at two different dose rates. The method has been tested with two plane parallel liquid ionization chambers in a continuous radiation x-ray beam with a tube voltage of 120 kV and with dose rates between 2 and 13 Gy min-1. The liquids used as sensitive media in the chambers were isooctane (C8H18) and tetramethylsilane (Si(CH3)4). The general recombination effect was studied using chamber polarizing voltages of 100, 300, 500, 700 and 900 V for both liquids. The relative standard deviation of the results for the collection efficiency with respect to general recombination was found to be a maximum of 0.7 % for isooctance and 2.4 % for tetramethylsilane. The results are in excellent agreement with Greening's theory for collection efficiencies over 90 %. The measured and corrected signals from the liquid ionization chambers used in this work are in very good agreement with the air filled monitor chambers with respect to signal to dose linearity.

  • 19.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Tölli, Heikki
    Modeling ion recombination in liquid ionization chambers - Improvement and analysis of the two-dose-rate method.2017Inngår i: Medical physics, ISSN 2473-4209Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    PURPOSE: The use of liquid ionization chambers can provide useful information to endeavors with radiation dosimetry for highly modulated beams. Liquid ionization chambers may be particularly suitable for computed tomography applications where conventional ionization chambers do not present a high enough sensitivity for the spatial resolution required to characterize common X-ray beams. Due to the sensitivity, which leads to high charge densities, liquid ionization chambers can suffer from large recombination losses leading to degradation in signal to dose rate linearity. To solve this problem, a two-dose-rate method for general recombination correction has been proposed for liquid ionization chambers. However, the valid range of recombination losses that the method can accurately account for has been found to vary depending on radiation quality. The present work provides an in-depth analysis of the performance of the two-dose-rate method. Furthermore, the soundness of applying gas theory to liquids is investigated by using the two-dose-rate method.

    METHODS: In the present work the two-dose-rate method for general recombination correction of liquid ionization chambers used in continuous beams is studied by employing theory for gas-filled ionization chambers. An approximate relation for the general collection efficiency containing a material specific parameter that is traceable to liquids has been derived for theoretical and experimental investigation alongside existing theory. Furthermore, the disassociation between initial and general recombination in the method is analyzed both theoretically and experimentally.

    RESULTS: The results indicate that liquids and gases share general recombination characteristics, where the liquids investigated (isooctane and tetramethylsilane) to a large extent mimic the behavior theoretically expected in gases. Furthermore, it is shown that the disassociation between initial and general recombination in the two-dose-rate method is an approximation that depends on the relation between initial recombination and the collecting electric field strength at the dose rates used.

    CONCLUSIONS: Due to the approximation used to separate initial and general recombination the valid range of collection efficiencies for the two-dose-rate method will not only depend on the model used to describe general recombination but also on the type of liquid and radiation beam quality. Since there is no robust theory for initial recombination in liquids to apply, the valid range of general collection efficiencies for the two-dose-rate method should be experimentally evaluated for each radiation dosimetry application. This article is protected by copyright. All rights reserved.

  • 20.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Tölli, Heikki
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    The Use of Liquid Ionization Chambers in Radiation Dosimetry2012Inngår i: World Congress on Medical Physics and Biomedical Engineering May 26-31, 2012 Beijing, China / [ed] Mian Long, Springer, 2012Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Liquid ionization chambers (LICs) have found applications in many fields in radiation dosimetry, e.g. IMRT, hadron therapy, brachytherapy and computed tomography. The wide range of applications is made possible due to the high sensitivity of LICs, allowing them to be manufactured with small physical dimensions of the chamber body and the effective measurement volume. Furthermore, the commonly used liquids (such as isooctane) have radiation absorption characteristics similar to water, introducing only small fluence perturbation effects as compared to conventional dosimeters. The small dimension of the effective measurement volume is beneficial for the quantification of radiation beams with steep gradients, while retaining a high measurement signal with good statistical properties. However, the interpretation of measurement results is not straight-forward due to several factors influencing their performance. Here, the main problems are recombination effects and particle type- and energy dependence, which may cause severe non-linear effects. The loss of measurement signal in LICs is due to both initial and general recombination. In the present work it is shown that the general recombination effect can be treated with in a similar manner as for air-filled ionization chambers, while there are currently no theories that adequately describe the initial recombination effect for LICs. Furthermore, the relationship between energy dependence and recombination losses in LICs are evaluated at different radiation qualities. Recently developed methods for the correction of general recombination losses in LICs are discussed and their validity evaluated.

  • 21.
    Andersson, Kennet
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Assessment of cerebrospinal fluid system dynamics: novel infusion protocol, mathematical modelling and parameter estimation for hydrocephalus investigations2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Patients with idiopathic normal pressure hydrocephalus (INPH) have a disturbance in the cerebrospinal fluid (CSF) system. The treatment is neurosurgical – a shunt is placed in the CSF system. The infusion test is used to assess CSF system dynamics and to aid in the selection of patients that will benefit from shunt surgery. The infusion test can be divided into three parts: a mathematical model, an infusion protocol and a parameter estimation method. A non-linear differential equation is used to mathematically describe the CSF system, where two important parameters are the outflow conductance (Cout) and the Pressure Volume Index (PVI). These are used both for clinical and research purposes. The analysis methods for the non-linear CSF system have limited the infusion protocols of presently used infusion investigations. They come with disadvantages such as long investigation time, no estimation of PVI and no measure of the reliability of the estimates.

    The aim of this dissertation was to develop and evaluate novel methods for infusion protocols, mathematical modelling and parameter estimation methods for assessment of CSF system dynamics.

    The infusion protocols and parameter estimation methods in current use, constant pressure infusion (CPI), constant infusion and bolus infusion, were investigated. The estimates of Cout were compared, both on an experimental set-up and on 20 INPH patients. The results showed that the bolus method produced a significantly higher Cout than the other methods. The study suggested a method with continuous infusion for estimating Cout and emphasized that standardization of Cout measurement is necessary.

    The non-linear model of the CSF system was further developed. The ability to model physiological variations that affect the CSF system was incorporated into the model and it was transformed into a linear time-invariant system. This enabled the use of methods developed for identification of such systems. The underlying model for CSF absorption was discussed and the effect of baseline resting pressure (Pr) in the analysis on the estimation of Cout was explored using two different analyses, with and without Pr.

    A novel infusion protocol with an oscillating pressure pattern was introduced. This protocol was theoretically better suited for the CSF system characteristics. Three new parameter estimation methods were developed. The adaptive observer was developed from the original non-linear model of the CSF system and estimated Cout in real time. The prediction error method (PEM) and the robust simulation error (RSE) method were based on the transformed linear system, and they estimated both Cout and PVI with confidence intervals in real time. Both the oscillating pressure pattern and the reference CPI protocol were performed on an experimental set-up of the CSF system and on 47 hydrocephalus patients. The parameter estimation methods were applied to the data, and the RSE method produced estimates of Cout that were in good agreement with the reference method and allowed for an individualized and considerably reduced investigation time.

    In summary, current methods have been investigated and a novel approach for assessment of CSF system dynamics has been presented. The Oscillating Pressure Infusion method, which includes a new infusion protocol, a further developed mathematical model and new parameter estimation methods has resulted in an improved way to perform infusion investigations and should be used when assessing CSF system dynamics. The advantages of the new approach are the pressure-regulated infusion protocol, simultaneous estimation of Cout and PVI and estimates of reliability that allow for an individualized investigation time.

  • 22.
    Andersson, Kennet
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Novel infusion method for measurement of CSF dynamicsManuskript (preprint) (Annet vitenskapelig)
  • 23.
    Andersson, Kennet
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Manchester, I. R.
    Laurell, Katarina
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Cesarini, K. Giuliana
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Measurement of CSF dynamics with oscillating pressure infusion2013Inngår i: Acta Neurologica Scandinavica, ISSN 0001-6314, E-ISSN 1600-0404, Vol. 128, nr 1, 17-23 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 24.
    Andersson, Kennet
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Manchester, Ian R
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Andersson, Nina
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Shiriaev, Anton
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Assessment of cerebrospinal fluid outflow conductance using an adaptive observer-experimental and clinical evaluation2007Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 28, nr 11, 1355-1368 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 25.
    Andersson, Kennet
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Manchester, Ian R
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för tillämpad fysik och elektronik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Eklund, Anders
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Real-time estimation of cerebrospinal fluid system parameters via oscillating pressure infusion2010Inngår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 48, nr 11, 1123-1131 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 26.
    Andersson, Kennet
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Suhr, Ole B.
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin.
    Faes, Luca
    Wiklund, Urban
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Directed coherence analysis in patients with severe autonomic dysfunction2014Inngår i: 2014 8th conference of the European Study Group on Cardiovascular Oscillations (ESGCO), IEEE conference proceedings, 2014, 167-168 s.Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Many different approaches have been applied to analyse the coupling between cardiovascular signals. This study evaluated the use of directed coherence, based on multivariate autoregressive modelling, for analysis of cardiovascular signals in patients with transthyretin amyloidosis, a rare disease where severe autonomic dysfunction is common.

  • 27.
    Andersson, Kennet
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Sundström, Nina
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Effect of resting pressure on the estimate of cerebrospinal fluid outflow conductance2011Inngår i: Fluids and barriers of the CNS, ISSN 2045-8118, Vol. 8, nr 1, 15- s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

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

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

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

  • 28. Andersson, M.
    et al.
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Minarik, D.
    Mattsson, S.
    Leide-Svegborn, S.
    Absorbed dose to the urinary bladder wall for different radiopharmaceuticals using dynamic S-values2013Inngår i: European Journal of Nuclear Medicine and Molecular Imaging, ISSN 1619-7070, E-ISSN 1619-7089, Vol. 40, nr Supplement 2, S161-S161 s.Artikkel i tidsskrift (Annet vitenskapelig)
  • 29. Andersson, M.
    et al.
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Minarik, D.
    Mattsson, S.
    Leide-Svegborn, S.
    An internal radiation dosimetry computer program, IDAC 2.0, for estimation of patient doses from radiopharmaceuticals2014Inngår i: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 162, nr 3, 299-305 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The internal dosimetry computer program internal dose assessment by computer (IDAC) for calculations of absorbed doses to organs and tissues as well as effective doses to patients from examinations with radiopharmaceuticals has been developed. The new version, IDAC2.0, incorporates the International Commission on Radiation Protection (ICRP)/ICRU computational adult male and female voxel phantoms and decay data from the ICRP publication 107. Instead of only 25 source and target regions, calculation can now be made with 63 source regions to 73 target regions. The major advantage of having the new phantom is that the calculations of the effective doses can be made with the latest tissue weighting factors of ICRP publication 103. IDAC2.0 uses the ICRP human alimentary tract (HAT) model for orally administrated activity and for excretion through the gastrointestinal tract and effective doses have been recalculated for radiopharmaceuticals that are orally administered. The results of the program are consistent with published data using the same specific absorption fractions and also compared with published data from the same computational phantoms but with segmentation of organs leading to another set of specific absorption fractions. The effective dose is recalculated for all the 34 radiopharmaceuticals that are administered orally and has been published by the ICRP. Using the new HAT model, new tissue weighting factors and the new adult computational voxel phantoms lead to an average effective dose of half of its earlier estimated value. The reduction mainly depends on electron transport simulations to walled organs and the transition from the stylised phantom with unrealistic interorgan distances to more realistic voxel phantoms.

  • 30. Andersson, M.
    et al.
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Minarik, D.
    Mattsson, S.
    Leide-Svegborn, S.
    IDAC2.0 a new generation of internal dosimetric calculations for diagnostic examinations in nuclear medicine using the adult ICRP/ICRU reference computational voxel phantoms2013Inngår i: European Journal of Nuclear Medicine and Molecular Imaging, ISSN 1619-7070, E-ISSN 1619-7089, Vol. 40, nr Supplement 2, S175-S176 s.Artikkel i tidsskrift (Annet vitenskapelig)
  • 31. Andersson, Martin
    et al.
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Mattsson, Sören
    Minarik, David
    Leide-Svegborn, Sigrid
    Organ doses and effective dose for five pet radiopharmaceuticals2016Inngår i: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 169, nr 1-4, 253-258 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Diagnostic investigations with positron-emitting radiopharmaceuticals are dominated by 18F-fluorodeoxyglucose (18F-FDG), but other radiopharmaceuticals are also commercially available or under development. Five of them, which are all clinically important, are 18F-fluoride, 18F-fluoroethyltyrosine (18F-FET), 18F-deoxyfluorothymidine (18F-FLT), 18F-fluorocholine (18F-choline) and 11C-raclopride. To estimate the potential risk of stochastic effects (mainly lethal cancer) to a population, organ doses and effective dose values were updated for all five radiopharmaceuticals. Dose calculations were performed using the computer program IDAC2.0, which bases its calculations on the ICRP/ICRU adult reference voxel phantoms and the tissue weighting factors from ICRP publication 103. The biokinetic models were taken from ICRP publication 128. For organ doses, there are substantial changes. The only significant change in effective dose compared with previous estimations was a 46 % reduction for 18F-fluoride. The estimated effective dose in mSv MBq−1 was 1.5E−02 for 18F-FET, 1.5E−02 for 18F-FLT, 2.0E−02 for 18F-choline, 9.0E−03 for 18F-fluoride and 4.4E−03 for 11C-raclopride.

  • 32.
    Andersson, Martin
    et al.
    Medical Radiation Physics, Department of Clinical Sciences Malmö, Lund University, Skåne University Hospital, Malmö, Sweden .
    Minarik, David
    Medical Radiation Physics, Department of Clinical Sciences Malmö, Lund University, Skåne University Hospital, Malmö, Sweden .
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Mattsson, Soren
    Medical Radiation Physics, Department of Clinical Sciences Malmö, Lund University, Skåne University Hospital, Malmö, Sweden .
    Leide-Svegborn, Sigrid
    Medical Radiation Physics, Department of Clinical Sciences Malmö, Lund University, Skåne University Hospital, Malmö, Sweden .
    Improved estimates of the radiation absorbed dose to the urinary bladder wall2014Inngår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 59, nr 9, 2173-2182 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Specific absorbed fractions (SAFs) have been calculated as a function of the content in the urinary bladder in order to allow more realistic calculations of the absorbed dose to the bladder wall. The SAFs were calculated using the urinary bladder anatomy from the ICRP male and female adult reference computational phantoms. The urinary bladder and its content were approximated by a sphere with a wall of constant mass, where the thickness of the wall depended on the amount of urine in the bladder. SAFs were calculated for males and females with 17 different urinary bladder volumes from 10 to 800 mL, using the Monte Carlo computer program MCNP5, at 25 energies of mono-energetic photons and electrons ranging from 10 KeV to 10 MeV. The decay was assumed to be homogeneously distributed in the urinary bladder content and the urinary bladder wall, and the mean absorbed dose to the urinary bladder wall was calculated. The Monte Carlo simulations were validated against measurements made with thermoluminescent dosimeters. The SAFs obtained for a urine volume of 200 mL were compared to the values calculated for the urinary bladder wall using the adult reference computational phantoms. The mean absorbed dose to the urinary wall from F-18-FDG was found to be 77 mu Gy/MBq formales and 86 mu Gy/MBq for females, while for (99)mTc-DTPA the mean absorbed doses were 80 mu Gy/MBq for males and 86 mu Gy/MBq for females. Compared to calculations using a constant value of the SAF from the adult reference computational phantoms, the mean absorbed doses to the bladder wall were 60% higher for F-18-FDG and 30% higher for (99)mTc-DTPA using the new SAFs.

  • 33.
    Andersson, Nina
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi. Neurologi.
    Bäcklund, Tomas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Assessment of cerebrospinal fluid outflow conductance using constant-pressure infusion - a method with real time estimation of reliability2005Inngår i: Physiological Measurement, ISSN 0967-3334, E-ISSN 1361-6579, Vol. 26, nr 6, 1137-1148 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 34.
    Andersson, Nina
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Department of Biomedical Engineering and Informatics, Umeå University Hospital.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Department of Biomedical Engineering and Informatics, Umeå University Hospital.
    Dependency of cerebrospinal fluid outflow resistance on intracranial pressure2008Inngår i: Journal of Neurosurgery, ISSN 0022-3085, Vol. 109, nr 5, 918-922 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 35. Antoni, Gunnar
    et al.
    Lubberink, Mark
    Estrada, Sergio
    Axelsson, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Carlson, Kristina
    Lindsjö, Lars
    Kero, Tanja
    Långström, Bengt
    Granstam, Sven-Olof
    Rosengren, Sara
    Vedin, Ola
    Wassberg, Cecilia
    Wikstrom, Gerhard
    Westermark, Per
    Sörensen, Jens
    In Vivo Visualization of Amyloid Deposits in the Heart with C-11-PIB and PET2013Inngår i: Journal of Nuclear Medicine, ISSN 0161-5505, E-ISSN 1535-5667, Vol. 54, nr 2, 213-220 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Cardiac amyloidosis is a differential diagnosis in heart failure and is associated with high mortality. There is currently no noninvasive imaging test available for specific diagnosis. N-[methyl-C-11]2-(4'-methylamino-phenyl)-6-hydroxybenzothiazole (C-11-PIB) PET is used in the evaluation of brain amyloidosis. We evaluated the potential use of C-11-PIB PET in systemic amyloidosis affecting the heart. Methods: Patients (n = 10) diagnosed with systemic amyloidosis-including heart involvement of either monoclonal immunoglobulin light-chain (AL) or transthyretin (ATTR) type- and healthy volunteers (n = 5) were investigated with PET/CT using C-11-PIB to study cardiac amyloid deposits and with C-11-acetate to measure myocardial blood flow to study the impact of global and regional perfusion on PIB retention. Results: Myocardial C-11-PIB uptake was visually evident in all patients 15-25 min after injection and was not seen in any volunteer. A significant difference in C-11-PIB retention in the heart between patients and healthy controls was found. The data indicate that myocardial amyloid deposits in patients diagnosed with systemic amyloidosis could be visualized with C-11-PIB. No correlation between C-11-PIB retention index and myocardial blood flow as measured with C-11-acetate was found on the global level, whereas a positive correlation on the segmental level was seen in a single patient. Conclusion: C-11-PIB and PET could be a method to study systemic amyloidosis of type AL and ATTR affecting the heart and should be investigated further both as a diagnostic tool and as a noninvasive method for treatment follow-up.

  • 36.
    Anåker, Anna
    et al.
    Falun, Sweden.
    Nilsson, Maria
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Epidemiologi och global hälsa.
    Holmner, Åsa
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Elf, Marie
    Falun, Sweden.
    Nurses' perceptions of climate and environmental issues: a qualitative study2015Inngår i: Journal of Advanced Nursing, ISSN 0309-2402, E-ISSN 1365-2648, Vol. 71, nr 8, 1883-1891 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    AIM: The aim of this study was to explore nurses' perceptions of climate and environmental issues and examine how nurses perceive their role in contributing to the process of sustainable development.

    BACKGROUND: Climate change and its implications for human health represent an increasingly important issue for the healthcare sector. According to the International Council of Nurses Code of Ethics, nurses have a responsibility to be involved and support climate change mitigation and adaptation to protect human health.

    DESIGN: This is a descriptive, explorative qualitative study.

    METHODS: Nurses (n = 18) were recruited from hospitals, primary care and emergency medical services; eight participated in semi-structured, in-depth individual interviews and 10 participated in two focus groups. Data were collected from April-October 2013 in Sweden; interviews were transcribed verbatim and analysed using content analysis.

    RESULTS: Two main themes were identified from the interviews: (i) an incongruence between climate and environmental issues and nurses' daily work; and (ii) public health work is regarded as a health co-benefit of climate change mitigation. While being green is not the primary task in a lifesaving, hectic and economically challenging context, nurses' perceived their profession as entailing responsibility, opportunities and a sense of individual commitment to influence the environment in a positive direction.

    CONCLUSIONS: This study argues there is a need for increased awareness of issues and methods that are crucial for the healthcare sector to respond to climate change. Efforts to develop interventions should explore how nurses should be able to contribute to the healthcare sector's preparedness for and contributions to sustainable development.

  • 37.
    Arvidsson, Peder
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Implementation and Evaluation of Volumetric Modulated Arc Therapy at the Radiation Therapy Department at The University Hospital of Umeå.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
  • 38.
    Asklund, Thomas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Onkologi.
    Nyholm, Tufve
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Garpebring, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Hauksson, Jon
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Brynolfsson, Patrik
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Karlsson, Mikael
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Henriksson, Roger
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Onkologi.
    Evaluation of advanced MR techniques for development of early biomarkers for treatment efficacy in malignant brain tumors2010Konferansepaper (Fagfellevurdert)
  • 39.
    Axelsson, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Imlook4d: introducing an extendable research 4d analysis software2014Inngår i: XII Turku PET Symposium, 24-27 May 2014, Turku, Finland: the symposium of Nordic Association for Clinical Physics (NACP), 2014, 63-63 s.Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Imlook4d (http://www.dicom-port.com) is a free Matlab based graphical user interface (GUI) tool useful for static, dynamic and gated PET studies.  It supports reading and writing DICOM, Nifti, Analyze, ECAT.  The DICOM reader is orders of magnitude faster than the Matlab imaging toolbox.  Imlook4d requires no additional Matlab toolboxes.

    The main benefit with imlook4d is that it is easily extendable with scripts, accessing exported variables such as the image matrix (4D) and a region-of-interest (ROI) matrix.  Scripts are available via a menu in the imlook4d GUI, and can be used to manipulate the image-matrix and ROI data.  There is also a menu option to export and import these variables to the Matlab workspace for interactive manipulation, useful for one-off fixes or for script development.  There are presently about 30 scripts in categories such as ROI, Matrix, Header info etc.  There is also direct export to ImageJ [1] and import back from ImageJ, thus giving access to all tools available within ImageJ.

    Imlook4d has a built in volume-of-interest editor, with a brush tool for quick interactive ROI delineation, and via scripts, different ways of thresholding ROIs from parts of the image.  Time activity data is saved to a tab-delimited text file.

    The principal-component (PC) based Hotelling filter is an integrated part of the program, which allows for interactive noise reduction without loss of quantitation [2].  A typical work flow for a dynamic data set is to turn on the filter for ROI delineation, and then there is the choice of turning it off for export of time-activity data.  Also the PC images can be used to draw ROIs on, which under some circumstances gives enhanced contrast.

    Calculation of parametric pharmacokinetic modelling images can be performed interactively, calculated slice by slice as the user scrolls through the volume.  Reference models for Patlak, Logan and Averaged Simple Flow Model [3]  applied on 15O-water are implemented, and it is relatively easy to implement other kinetic models.  Similarly, scripts have been developed for regional Patlak and Logan models on ROI data.

    [1] Rasband, WS, ImageJ, U. S. National Institutes of Health, Bethesda, Maryland, USA, http://imagej.nih.gov/ij/, 1997-2014

    [2] Axelsson J, Sörensen J, The 2D Hotelling filter - a quantitative noise-reducing principal-component filter for dynamic PET data, with applications in patient dose reduction. BMC Med Phys. 2013 Apr 10;13:1. doi: 10.1186/1756-6649-13-1.

    [3] Yoshida, K, Mullani, N and Gould KL, Coronary Flow and Flow Reserve by PET Simplified for Clinical Applications Using Rubidium-82 or Nitrogen-13-Ammonia, J Nucl Med 1996; 37:1701-1712

    Figure 1.  The imlook4d GUI with the user SCRIPTS menu selected.  The group of ROI scripts was further selected.  In the underlying image, a rough ROI is created.  

  • 40.
    Axelsson, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    PET/MR ur fysikerns perspektiv2015Konferansepaper (Annet vitenskapelig)
  • 41.
    Axelsson, Jan
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Sörensen, Jens
    PET-center, Department of Radiology, Oncology and Radiation Sciences, Uppsala University, Uppsala, Sweden.
    The 2D Hotelling filter: a quantitativenoise-reducing principal-component filter fordynamic PET data, with applications in patientdose reduction2013Inngår i: BMC Medical Physics, ISSN 1756-6649, Vol. 13, nr 1Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: In this paper we apply the principal-component analysis filter (Hotelling filter) to reduce noise fromdynamic positron-emission tomography (PET) patient data, for a number of different radio-tracer molecules. Wefurthermore show how preprocessing images with this filter improves parametric images created from suchdynamic sequence.We use zero-mean unit variance normalization, prior to performing a Hotelling filter on the slices of a dynamictime-series. The Scree-plot technique was used to determine which principal components to be rejected in thefilter process. This filter was applied to [11C]-acetate on heart and head-neck tumors, [18F]-FDG on liver tumors andbrain, and [11C]-Raclopride on brain. Simulations of blood and tissue regions with noise properties matched to realPET data, was used to analyze how quantitation and resolution is affected by the Hotelling filter. Summing varyingparts of a 90-frame [18F]-FDG brain scan, we created 9-frame dynamic scans with image statistics comparable to 20MBq, 60 MBq and 200 MBq injected activity. Hotelling filter performed on slices (2D) and on volumes (3D) werecompared.Results: The 2D Hotelling filter reduces noise in the tissue uptake drastically, so that it becomes simple to manuallypick out regions-of-interest from noisy data. 2D Hotelling filter introduces less bias than 3D Hotelling filter in focalRaclopride uptake. Simulations show that the Hotelling filter is sensitive to typical blood peak in PET prior to tissueuptake have commenced, introducing a negative bias in early tissue uptake. Quantitation on real dynamic data isreliable. Two examples clearly show that pre-filtering the dynamic sequence with the Hotelling filter prior toPatlak-slope calculations gives clearly improved parametric image quality. We also show that a dramatic dosereduction can be achieved for Patlak slope images without changing image quality or quantitation.Conclusions: The 2D Hotelling-filtering of dynamic PET data is a computer-efficient method that gives visuallyimproved differentiation of different tissues, which we have observed improve manual or automated regionof-interest delineation of dynamic data. Parametric Patlak images on Hotelling-filtered data display improved clarity,compared to non-filtered Patlak slope images without measurable loss of quantitation, and allow a dramaticdecrease in patient injected dose.

  • 42.
    Backlund, Tomas
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Frankel, Jennifer
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Israelsson, Hanna
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap. Vrinnevi Hospital, Norrköping, Sweden.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Sundström, Nina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Trunk sway in idiopathic normal pressure hydrocephalus: quantitative assessment in clinical practice2017Inngår i: Gait & Posture, ISSN 0966-6362, E-ISSN 1879-2219, Vol. 54, 62-70 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Background: In diagnosis and treatment of patients with idiopathic normal pressure hydrocephalus (iNPH), there is need for clinically applicable, quantitative assessment of balance and gait. Using a body worn gyroscopic system, the aim of this study was to assess postural stability of iNPH patients in standing, walking and during sensory deprivation before and after cerebrospinal fluid (CSF) drainage and surgery. A comparison was performed between healthy elderly (HE) and patients with various types of hydrocephalus (ventriculomegaly (VM)). Methods: Trunk sway was measured in 31 iNPH patients, 22 VM patients and 58 HE. Measurements were performed at baseline in all subjects, after CSF drainage in both patient groups and after shunt surgery in the iNPH group. Results: Preoperatively, the iNPH patients had significantly higher trunk sway compared to HE, specifically for the standing tasks (p < 0.001). Compared to VM, iNPH patients had significantly lower sway velocity during gait in three of four cases on firm support (p < 0.05). Sway velocity improved after CSF drainage and in forward-backward direction after surgery (p < 0.01). Compared to HE both patient groups demonstrated less reliance on visual input to maintain stable posture. Conclusions: INPH patients had reduced postural stability compared to HE, particularly during standing, and for differentiation between iNPH and VM patients sway velocity during gait is a promising parameter. A reversible reduction of visual incorporation during standing was also seen. Thus, the gyroscopic system quantitatively assessed postural deficits in iNPH, making it a potentially useful tool for aiding in future diagnoses, choices of treatment and clinical follow-up. 

  • 43.
    Bahar Gogani, Jalil
    et al.
    Umeå universitet, Medicinsk fakultet, Strålningsvetenskaper, Radiofysik.
    Hägglund, Peter
    Umeå universitet, Medicinsk fakultet, Strålningsvetenskaper, Radiofysik.
    Wickman, Göran
    Umeå universitet, Medicinsk fakultet, Strålningsvetenskaper, Radiofysik.
    Assessment of correlated dose and sensitivity profiles on a multi-slice CT scanner2005Inngår i: Radiat Prot Dosimetry, ISSN 0144-8420, Vol. 114, nr 1-3, 332-336 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 44. Baste, Valborg
    et al.
    Hansson Mild, Kjell
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Moen, Bente E
    Radiofrequency exposure on fast patrol boats in the Royal Norwegian Navy-an approach to a dose assessment.2010Inngår i: Bioelectromagnetics, ISSN 0197-8462, E-ISSN 1521-186X, Vol. 31, nr 5, 350-360 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Epidemiological studies related to radiofrequency (RF) electromagnetic fields (EMF) have mainly used crude proxies for exposure, such as job titles, distance to, or use of different equipment emitting RF EMF. The Royal Norwegian Navy (RNoN) has measured RF field emitted from high-frequency antennas and radars on several spots where the crew would most likely be located aboard fast patrol boats (FPB). These boats are small, with short distance between the crew and the equipment emitting RF field. We have described the measured RF exposure aboard FPB and suggested different methods for calculations of total exposure and annual dose. Linear and spatial average in addition to percentage of ICNIRP and squared deviation of ICNIRP has been used. The methods will form the basis of a job exposure matrix where relative differences in exposure between groups of crew members can be used in further epidemiological studies of reproductive health. Bioelectromagnetics, 2010. (c) 2010 Wiley-Liss, Inc.

  • 45. Baste, Valborg
    et al.
    Moen, Bente E
    Oftedal, Gunnhild
    Strand, Leif Age
    Bjørge, Line
    Hansson Mild, Kjell
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Pregnancy outcomes after paternal radiofrequency field exposure aboard fast patrol boats2012Inngår i: Journal of Occupational and Environmental Medicine, ISSN 1076-2752, E-ISSN 1536-5948, Vol. 54, nr 4, 431-438 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Objectives: To investigate adverse reproductive outcomes among male employees in the Royal Norwegian Navy exposed to radiofrequency electromagnetic fields aboard fast patrol boats.

    Methods: Cohort study of Royal Norwegian Navy servicemen linked to the Medical Birth Registry of Norway, including singleton offspring born between 1967 and 2008 (n = 37,920). Exposure during the last 3 months before conception (acute) and exposure more than 3 months before conception (nonacute) were analyzed.

    Results: Perinatal mortality and preeclampsia increased after service aboard fast patrol boats during an acute period and also after increased estimated radiofrequency exposure during an acute period, compared with service aboard other vessels. No associations were found between nonacute exposure and any of the reproductive outcomes.

    Conclusions: Paternal work aboard fast patrol boats during an acute period was associated with perinatal mortality and preeclampsia, but the cause is not clear.

  • 46.
    Beckman Rehnman, Jeannette
    Umeå universitet, Medicinska fakulteten, Institutionen för klinisk vetenskap, Oftalmiatrik. Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    New methods to evaluate the effect of conventional and modified crosslinking treatment for keratoconus2015Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Background: Today corneal crosslinking with ultraviolet-A photoactivation of riboflavin is an established method to halt the progression of keratoconus. In some cases, when the refractive errors are large and the visual acuity is low, conventional corneal crosslinking may not be sufficient. In these cases it would be desirable with a treatment that both halts the progression and also reduces the refractive errors and improves the quality of vision.

    Aims:  The aims of this thesis were to determine whether mechanical compression of the cornea during corneal crosslinking for keratoconus using a sutured rigid contact lens could improve the optical and visual outcomes of the treatment, and also to find methods to evaluate the effect of different corneal crosslinking treatment regimens.

    Methods: In a prospective, open, randomized case-control study, 60 eyes of 43 patients with progressive keratoconus, aged 18-28 years, planned for routine corneal crosslinking, and a corresponding age- and sex-matched control group was included. The patients were randomized to conventional corneal crosslinking (CXL; n=30) or corneal crosslinking with mechanical compression of the cornea during the treatment (CRXL; n=30).

    Biomicroscopy, autorefractometry, best spectacle corrected visual acuity, axial length measurement, Pentacam® HR Scheimpflug photography, pachymetry, intraocular pressure measurements and corneal biomechanical assessments were performed before treatment (baseline) and at 1 month and 6 months after the treatment.

    One of the articles evaluated and compared the optical and visual outcomes between CXL and CRXL, while the other three articles focused on methods to evaluate treatment effects. In Paper I, the corneal light scattering was manually quantified from Scheimpflug images throughout the corneal thickness at 8 measurements points, 0.0 to 3.0 mm from the corneal centre, in patients treated with CXL. In Paper IV the corneal densitometry (light scattering) was measured with the Pentacam® HR software, in 4 circular zones around the corneal apex and at 3 different depths of the corneal stroma, in both CXL and CRXL treated corneas. Paper III quantified the biomechanical effects of CXL in vivo.

    Results: Corneal light scattering after CXL showed distinctive spatial and temporal profiles and Applanation Resonance Tonometry (ART) -technology demonstrated an increased corneal hysteresis 1 and 6 months after CXL. When comparing the refractive and structural results after CXL and CRXL, CRXL failed to flatten the cornea, and the treatment did not show any benefits to conventional CXL treatment, some variables even indicated an inferior effect. Accordingly, the increase in corneal densitometry was also less pronounced after CRXL.

    Conclusions: Analysis of corneal light scattering/densitometry shows tissue changes at the expected treatment location, and may be a relevant variable in evaluating the crosslinking effect. ART -technology is an in vivo method with the potential to assess the increased corneal hysteresis after CXL treatment. By refining the method, ARTmay become a useful tool in the future. Unfortunately, CRXL does not improve the optical and visual outcomes after corneal crosslinking. Possibly, stronger crosslinking would be necessary to stabilize the cornea in a flattened position.

  • 47.
    Behrens, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Lenfeldt, Niklas
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Koskinen, Lars-Owe
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurokirurgi.
    Transcranial Doppler pulsatility index: not an accurate method to assess intracranial pressure.2010Inngår i: Neurosurgery, ISSN 0148-396X, E-ISSN 1524-4040, Vol. 66, nr 6, 1050-1057 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 48.
    Behrens, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Lenfeldt, Niklas
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Ambarki, Khalid
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Centrum för medicinsk teknik och fysik (CMTF).
    Koskinen, Lars-Owe D
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurokirurgi.
    Intracranial Pressure and Pulsatility Index:  2011Inngår i: Neurosurgery, ISSN 0148-396X, E-ISSN 1524-4040, Vol. 69, nr 4, E1033-E1034 s.Artikkel i tidsskrift (Fagfellevurdert)
  • 49.
    Behrens, Anders
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Lenfeldt, Niklas
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Qvarlander, Sara
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Koskinen, Lars-Owe
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Are intracranial pressure wave amplitudes measurable through lumbar puncture?2013Inngår i: Acta Neurologica Scandinavica, ISSN 0001-6314, E-ISSN 1600-0404, Vol. 127, nr 4, 233-241 s.Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 50.
    Benedek, Hunor
    et al.
    Skåne University Hospital, Lund, Sweden.
    Isacsson, Ulf
    Uppsala University Hospital, Uppsala, Sweden .
    Olevik-Dunder, Maria
    Karolinska University Hospital, Stockholm, Sweden.
    Westermark, Mathias
    Karolinska University Hospital, Stockholm, Sweden.
    Hållström, Per
    Gävle Hospital, Gavle, Swe.
    Olofsson, Jörgen
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Gustafsson, Magnus
    Sahlgrenska University Hospital, Göteborg, Sweden.
    Strategies for quality assurance of intensity modulated radiation therapy2015Inngår i: 8TH INTERNATIONAL CONFERENCE ON 3D RADIATION DOSIMETRY (IC3DDOSE), Institute of Physics (IOP), 2015, Vol. 573, 012015- s., 012015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In late 2011 The Swedish Society of Radiation Physics formed a working group to concentrate on the Quality Assurance of modern radiation therapy techniques. The given task was to identify and summarise the different QA strategies in Sweden and also the international recommendations. This was used to formulate recommendations for practical guidelines within Sweden. In this paper a brief summery of the group's work is presented. All the Swedish radiation therapy centres do a pre treatment verification measurement as QA for every new IMRT and VMAT plan. Physicists do it and they believe it to be time consuming. A general standpoint from all the centres was that new guidelines and legislation is needed to allow QA that does not require a measurement. Based on various international publications and recommendations the working group has presented two strategies, one where all new plans are checked through measurement and one where no measurement is needed. The measurement-based strategy is basically the same as the one used today with an extended machine QA part. The other presented strategy is process oriented where all the different parts of the treatment chain are checked separately. The final report can be found in Swedish on http://www.radiofysik.org.

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