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Träfflista för sökning "WFRF:(Magnusson P) ;pers:(Magnusson Peter)"

Sökning: WFRF:(Magnusson P) > Magnusson Peter

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1.
  • Bäck, Sven, et al. (författare)
  • Ferrous sulphate gel dosimetry and MRI for proton beam dose measurements
  • 1999
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 1361-6560 .- 0031-9155. ; 44:8, s. 1983-1996
  • Tidskriftsartikel (refereegranskat)abstract
    • Ferrous sulphate gel dosimetry has the potential for measurement of absorbed dose distributions in proton therapy. The chemical properties of the gel are altered according to the radiation dose and these changes can be evaluated in three dimensions using MRI. The purpose of this work was to investigate the properties of a ferrous gel used with clinical proton beams. The gel was irradiated with both monoenergetic and range-modulated proton beams. It was then evaluated using MRI. The depth dose by means of the 1/T1 distribution was studied and compared with data from a plane-parallel plate ionization chamber. 1/T1 was shown to be proportional to the dose at a mean proton energy of approximately 90 MeV. The dose response was no different from that obtained using photon beams. However, on normalization at the entrance, the relative 1/T1 at the Bragg peak was 15-20% lower than the corresponding ionization chamber data for the monoenergetic proton beam. Better agreement was found for the modulated beam, but with significant differences close to the distal edge of the 1/T1 distribution. The change in sensitivity with depth was explained by means of a linear energy transfer dependence. This property was further studied using Monte Carlo methods.
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2.
  • Bäck, Sven, et al. (författare)
  • Improvements in absorbed dose measurements for external radiation therapy using ferrous dosimeter gel and MR imaging (FeMRI)
  • 1998
  • Ingår i: Physics in Medicine and Biology. - : IOP Publishing. - 0031-9155 .- 1361-6560. ; 43, s. 261-
  • Tidskriftsartikel (refereegranskat)abstract
    • A ferrous gel, based on ferrous (Fe) sulphate and agarose, was used with a clinical magnetic resonance imaging (MRI) scanner to obtain relative dose distribution data from therapeutic photon and electron beams. The FeMRI gel was scanned using a new MRI acquisition protocol optimized for T1 measurements. Thorough comparisons with silicon semiconductor detector and ionization chamber measurements, as well as with Monte Carlo calculations, were performed in order to quantify the improvements obtained using FeMRI for dose estimations. Most of the relative doses measured with FeMRI were within 2% of the doses measured with other methods. The larger discrepancies (2-4%) found at shallow depths are discussed. The uncertainty in relative dose measurements using FeMRI was significantly improved compared with previously reported results (5-10%, one standard deviation, 1 SD), and is today between 1.6% and 3.3% (depending on dose level, 2 SD). This corresponds to an improvement in the minimum detectable dose (3 SD above background) from approximately 2 Gy to better than 0.6 Gy. The results obtained in this study emphasize the importance of obtaining basic FeMRI dose data before the method is extended to complicated treatment regimes.
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3.
  • Haraldsson, P, et al. (författare)
  • Dose response characteristics and basic dose distribution data for a polymerization-based dosemeter gel evaluated using MR
  • 2000
  • Ingår i: British Journal of Radiology. - : British Institute of Radiology. - 0007-1285 .- 1748-880X. ; 73:865, s. 58-65
  • Tidskriftsartikel (refereegranskat)abstract
    • A safe and reproducible mixing procedure for the manufacture of a polymerization-based dosemeter gel evaluated using MRI (PoMRI) is presented. The dose response, obtained by irradiating gel-filled vials with absorbed doses in the interval 0-20 Gy and evaluated with respect to 1/T2, was found to be linear in the interval 0-8 Gy, with a sensitivity of 0.211 s-1Gy-1 (r2 = 0.998) at 1.5 T. Evaluation of the same set of vials with respect to 1/T1 gave a sensitivity of 0.018 s-1Gy-1 (r2 = 0.960). PoMRI and diode data were compared for standard photon and electron treatment beams. A deviation of less than 3% was found between the two methods for central depth dose curves as well as dose profiles (2 mm for electrons in the steep dose gradient regions). The importance of the method used for background correction for the reliability of the results was also evaluated. Barex (with a wall thickness of 1.5 mm) was investigated for use as phantom material and found to be favourable compared with glass. The results obtained in this study show that PoMRI has excellent potential as a 3D detector.
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4.
  • Mulders, Peter C.R., et al. (författare)
  • Structural changes induced by electroconvulsive therapy are associated with clinical outcome
  • 2020
  • Ingår i: Brain Stimulation. - : Elsevier BV. - 1935-861X. ; 13:3, s. 696-704
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Electroconvulsive therapy (ECT) is the most effective treatment option for major depressive disorder, so understanding whether its clinical effect relates to structural brain changes is vital for current and future antidepressant research. Objective: To determine whether clinical response to ECT is related to structural volumetric changes in the brain as measured by structural magnetic resonance imaging (MRI) and, if so, which regions are related to this clinical effect. We also determine whether a similar model can be used to identify regions associated with electrode placement (unilateral versus bilateral ECT). Methods: Longitudinal MRI and clinical data (Hamilton Depression Rating Scale) was collected from 10 sites as part of the Global ECT-MRI research collaboration (GEMRIC). From 192 subjects, relative changes in 80 (sub)cortical areas were used as potential features for classifying treatment response. We used recursive feature elimination to extract relevant features, which were subsequently used to train a linear classifier. As a validation, the same was done for electrode placement. We report accuracy as well as the structural coefficients of regions included in the discriminative spatial patterns obtained. Results: A pattern of structural changes in cortical midline, striatal and lateral prefrontal areas discriminates responders from non-responders (75% accuracy, p < 0.001) while left-sided mediotemporal changes discriminate unilateral from bilateral electrode placement (81% accuracy, p < 0.001). Conclusions: The identification of a multivariate discriminative pattern shows that structural change is relevant for clinical response to ECT, but this pattern does not include mediotemporal regions that have been the focus of electroconvulsive therapy research so far.
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