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  • 1. Adams, D.
    et al.
    Coelho, T.
    Conceicao, E.
    Waddington-Cruz, M.
    Schmidt, H.
    Buades, J.
    Campistol, J. M.
    Pouget, J.
    Berk, J. L.
    Polydefkis, M.
    Ziyadeh, N.
    Partisano, A. M.
    Chen, J.
    Gollob, J.
    Suhr, Ole B.
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine.
    PHASE 2 OPEN-LABEL EXTENSION (OLE) STUDY OF PATISIRAN, AN INVESTIGATIONAL RNA INTERFERENCE (RNAI) THERAPEUTIC FOR THE TREATMENT OF HEREDITARY ATTR AMYLOIDOSIS WITH POLYNEUROPATHY2017In: Value in Health, ISSN 1098-3015, E-ISSN 1524-4733, Vol. 20, no 5, p. A211-A212Article in journal (Other academic)
  • 2.
    Adjeiwaah, Mary
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Quality assurance for magnetic resonance imaging (MRI) in radiotherapy2017Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Magnetic resonance imaging (MRI) utilizes the magnetic properties of tissues to generate image-forming signals. MRI has exquisite soft-tissue contrast and since tumors are mainly soft-tissues, it offers improved delineation of the target volume and nearby organs at risk. The proposed Magnetic Resonance-only Radiotherapy (MR-only RT) work flow allows for the use of MRI as the sole imaging modality in the radiotherapy (RT) treatment planning of cancer. There are, however, issues with geometric distortions inherent with MR image acquisition processes. These distortions result from imperfections in the main magnetic field, nonlinear gradients, as well as field disturbances introduced by the imaged object. In this thesis, we quantified the effect of system related and patient-induced susceptibility geometric distortions on dose distributions for prostate as well as head and neck cancers. Methods to mitigate these distortions were also studied.

    In Study I, mean worst system related residual distortions of 3.19, 2.52 and 2.08 mm at bandwidths (BW) of 122, 244 and 488 Hz/pixel up to a radial distance of 25 cm from a 3T PET/MR scanner was measured with a large field of view (FoV) phantom. Subsequently, we estimated maximum shifts of 5.8, 2.9 and 1.5 mm due to patient-induced susceptibility distortions. VMAT-optimized treatment plans initially performed on distorted CT (dCT) images and recalculated on real CT datasets resulted in a dose difference of less than 0.5%.

     The magnetic susceptibility differences at tissue-metallic,-air and -bone interfaces result in local B0 magnetic field inhomogeneities. The distortion shifts caused by these field inhomogeneities can be reduced by shimming.  Study II aimed to investigate the use of shimming to improve the homogeneity of local  B0 magnetic field which will be beneficial for radiotherapy applications. A shimming simulation based on spherical harmonics modeling was developed. The spinal cord, an organ at risk is surrounded by bone and in close proximity to the lungs may have high susceptibility differences. In this region, mean pixel shifts caused by local B0 field inhomogeneities were reduced from 3.47±1.22 mm to 1.35±0.44 mm and 0.99±0.30 mm using first and second order shimming respectively. This was for a bandwidth of 122 Hz/pixel and an in-plane voxel size of 1×1 mm2.  Also examined in Study II as in Study I was the dosimetric effect of geometric distortions on 21 Head and Neck cancer treatment plans. The dose difference in D50 at the PTV between distorted CT and real CT plans was less than 1.0%.

    In conclusion, the effect of MR geometric distortions on dose plans was small. Generally, we found patient-induced susceptibility distortions were larger compared with residual system distortions at all delineated structures except the external contour. This information will be relevant when setting margins for treatment volumes and organs at risk.  

    The current practice of characterizing MR geometric distortions utilizing spatial accuracy phantoms alone may not be enough for an MR-only radiotherapy workflow. Therefore, measures to mitigate patient-induced susceptibility effects in clinical practice such as patient-specific correction algorithms are needed to complement existing distortion reduction methods such as high acquisition bandwidth and shimming.

  • 3.
    Adjeiwaah, Mary
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Bylund, Mikael
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Lundman, Josef A.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Thellenberg Karlsson, Camilla
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Jonsson, Joakim H.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Nyholm, Tufve
    Umeå University, Faculty of Medicine, Department of Radiation Sciences. Medical Radiation Physics, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
    Quantifying the effect of 3T MRI residual system and patient-induced susceptibility distortions on radiotherapy treatment planning for prostate cancer2018In: International Journal of Radiation Oncology, Biology, Physics, ISSN 0360-3016, E-ISSN 1879-355X, Vol. 100, no 2, p. 317-324Article in journal (Refereed)
    Abstract [en]

    Purpose: To investigate the effect of magnetic resonance system- and patient-induced susceptibility distortions from a 3T scanner on dose distributions for prostate cancers.

    Methods and Materials: Combined displacement fields from the residual system and patient-induced susceptibility distortions were used to distort 17 prostate patient CT images. VMAT dose plans were initially optimized on distorted CT images and the plan parameters transferred to the original patient CT images to calculate a new dose distribution.

    Results: Maximum residual mean distortions of 3.19 mm at a radial distance of 25 cm and maximum mean patient-induced susceptibility shifts of 5.8 mm were found using the lowest bandwidth of 122 Hz per pixel. There was a dose difference of <0.5% between distorted and undistorted treatment plans. The 90% confidence intervals of the mean difference between the dCT and CT treatment plans were all within an equivalence interval of (−0.5, 0.5) for all investigated plan quality measures.

    Conclusions: Patient-induced susceptibility distortions at high field strengths in closed bore magnetic resonance scanners are larger than residual system distortions after using vendor-supplied 3-dimensional correction for the delineated regions studied. However, errors in dose due to disturbed patient outline and shifts caused by patient-induced susceptibility effects are below 0.5%.

  • 4.
    Ahlgren, Ulf
    Umeå University, Faculty of Medicine, Umeå Centre for Molecular Medicine (UCMM).
    Exploring the pancreas with optical projection tomography2012In: Imaging in Medicine, ISSN 1755-5191, Vol. 4, no 1, p. 5-7Article in journal (Refereed)
  • 5.
    Akhtari, Mohammad Mehdi
    Umeå University, Faculty of Science and Technology, Department of Physics. Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    3D Structural similarity check between CT and SCT2014Independent thesis Advanced level (degree of Master (Two Years)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The aim of the current work was to develop and test a method for comparing the geometrical representation of a patient using computed tomography (CT), and CT like images derived from magnetic resonance images (MRI). It would be beneficial to use MRI alone for both target delineation and treatment planning to save time and costs. This was first investigated in Umea university Hospital by introducing substitute computed tomography (SCT) obtained from MRI images and which can be used as CT equivalent information. The data that is used in this report are from five patients with intracranial tumors; A MATLAB code has been developed to compare DDRs based on s-CT data with CT based DRR’s for these five patients.

  • 6.
    Al-Amiry, Bariq
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences.
    Does body mass index affect restoration of femoral offset and leg length and cup positioning after total hip arthroplasty?: A prospective radiological cohort studyIn: Article in journal (Other academic)
  • 7.
    Andersson, Jonas
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics. Norrlands universitetssjukhus.
    Fysik och teknik: konventionell planar röntgen2013In: Nuklearmedicin / [ed] Sven-Ola Hietala, Katrine Åhlström Riklund, Lund: Studentlitteratur AB, 2013, 2, p. 40-46Chapter in book (Other academic)
  • 8.
    Andersson, Jonas
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Ion recombination in liquid ionization chambers: development of an experimental method to quantify general recombination2013Doctoral thesis, comprehensive summary (Other academic)
    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.

  • 9.
    Andersson, Jonas
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    TG246 On Patient Dose From Diagnostic Radiation: Acceptance Testing and Dose Measurements with CT2014In: 56th AAPM Annual Meeting and Exhibition 2014, Austin, TX, USA, July 20-24 (2014), 2014Conference paper (Refereed)
    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.

  • 10.
    Andersson, Jonas
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Kaiser, Franz-Joachim
    Gómez, Faustino
    Jäkel, Oliver
    Pardo-Montero, Juan
    Tölli, Heikki
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    A comparison of different experimental methods for general recombination correction for liquid ionization chambers2012In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, no 21, p. 7161-7175Article in journal (Refereed)
    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.

  • 11.
    Andersson, Jonas
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Tölli, Heikki
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Application of the two-dose-rate method for general recombination correction for liquid ionization chambers in continuous beams2011In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 56, no 2, p. 299-314Article in journal (Refereed)
    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.

  • 12.
    Andersson, Jonas
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Tölli, Heikki
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Modeling ion recombination in liquid ionization chambers: Improvement and analysis of the two-dose-rate method2017In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 44, no 11, p. 5977-5987Article in journal (Refereed)
    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. As 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.

  • 13.
    Andersson, Kennet
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Suhr, Ole B.
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine.
    Faes, Luca
    Wiklund, Urban
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Directed coherence analysis in patients with severe autonomic dysfunction2014In: 2014 8th conference of the European Study Group on Cardiovascular Oscillations (ESGCO), IEEE conference proceedings, 2014, p. 167-168Conference paper (Refereed)
    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.

  • 14.
    Andersson, Kristina
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Evaluation of uncertainties in sub-volume based image registration: master of science thesis in medical radiation physics2010Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Physicians often utilize different imaging techniques to provide clear, visual information about internal parts of the patient. Since the different imaging modalities give different types of information, the combination of them serves as a powerful tool while determining the diagnosis, planning of treatment or during therapy follow-up. To simplify the interpretation of the image information, image registration is often used. The goal of the registration is to put different images in a common coordinate system. It is essential that the registration between the images is accurate.

    Normalized Mutual Information (NMI) is a metric that quantifies the conformity between images. Even though NMI is a robust method it is often dominated by large structures as the external contour of the patient as well as by the structures of the bones. The prostate is an organ that does not have a fixed position relative to the other organs and host small amounts of image information. The accuracy of the registration is therefore limited with respect to the prostate when using the whole image volume. This master thesis investigates the possibility to restrict the part of the image used for registration to a small volume around the prostate with goal to receive a better registration of the prostate than if full sized images are used.

    A registration program, utilizing NMI, was written and optimized in MatLab. Four Magnetic Resonance (MR) series and one Computed Tomographic (CT) series where taken over the pelvic area of five patients with the diagnosis prostate cancer. The prostate were delineated by a physician. By adding margin to the delineations five different sized Regions of Interest (ROI) where created.  The smallest ROI precisely covered the prostate while the largest covered the whole image. The deviation in Center of Mass (CoM) between the images and the Percentage Volume Overlap (PVO) were calculated and used as a measure of alignment.

    The registrations performed with sub-volumes showed an improvement compared to those that used full-volume while registering a MR image to another MR image. In one third of the cases a 2 cm margin to the prostate is preferable. A 3 cm margin is the most favorable option in another third of the cases. The use of sub-volumes to register MR images to CT series turned out to be unpredictable with poor accuracy.

    Full sized image registration between two MR image pairs has a high precision but, due to the motion of the prostate, poor accuracy. As a result of the high information content in the MR images both high precision as well as high accuracy can be achieved by the use of sub-volume registration. CT images do not contain the same amount of image information around the prostate and the sub-volume based registrations between MR and CT images are hence inconsistent with a low precision.  

  • 15. Andersson, M.
    et al.
    Johansson, Lennart
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Minarik, D.
    Mattsson, S.
    Leide-Svegborn, S.
    Absorbed dose to the urinary bladder wall for different radiopharmaceuticals using dynamic S-values2013In: European Journal of Nuclear Medicine and Molecular Imaging, ISSN 1619-7070, E-ISSN 1619-7089, Vol. 40, no Supplement 2, p. S161-S161Article in journal (Other academic)
  • 16. Andersson, M.
    et al.
    Johansson, Lennart
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Minarik, D.
    Mattsson, S.
    Leide-Svegborn, S.
    An internal radiation dosimetry computer program, IDAC 2.0, for estimation of patient doses from radiopharmaceuticals2014In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 162, no 3, p. 299-305Article in journal (Refereed)
    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.

  • 17. Andersson, M.
    et al.
    Johansson, Lennart
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    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 phantoms2013In: European Journal of Nuclear Medicine and Molecular Imaging, ISSN 1619-7070, E-ISSN 1619-7089, Vol. 40, no Supplement 2, p. S175-S176Article in journal (Other academic)
  • 18. Andersson, Martin
    et al.
    Johansson, Lennart
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Eckerman, Keith
    Mattsson, Sören
    IDAC-Dose 2.1, an internal dosimetry program for diagnostic nuclear medicine based on the ICRP adult reference voxel phantoms2017In: EJNMMI Research, ISSN 2191-219X, E-ISSN 2191-219X, Vol. 7, article id 88Article in journal (Refereed)
    Abstract [en]

    Background: To date, the estimated radiation-absorbed dose to organs and tissues in patients undergoing diagnostic examinations in nuclear medicine is derived via calculations based on models of the human body and the biokinetic behaviour of the radiopharmaceutical. An internal dosimetry computer program, IDAC-Dose2.1, was developed based on the International Commission on Radiological Protection (ICRP)-specific absorbed fractions and computational framework of internal dose assessment given for reference adults in ICRP Publication 133. The program uses the radionuclide decay database of ICRP Publication 107 and considers 83 different source regions irradiating 47 target tissues, defining the effective dose as presented in ICRP Publications 60 and 103. The computer program was validated against another ICRP dosimetry program, Dose and Risk Calculation (DCAL), that employs the same computational framework in evaluation of occupational and environmental intakes of radionuclides. IDAC-Dose2.1 has a sub-module for absorbed dose calculations in spherical structures of different volumes and composition; this sub-module is intended for absorbed dose estimates in radiopharmaceutical therapy. For nine specific alpha emitters, the absorbed dose contribution from their decay products is also included in the committed absorbed dose calculations. Results: The absorbed doses and effective dose of I-131-iodide determined by IDAC-Dose2.1 were validated against the dosimetry program DCAL, showing identical results. IDAC-Dose2.1 was used to calculate absorbed doses for intravenously administered F-18-FDG and orally administered Tc-99m-pertechnetate and I-131-iodide, three frequently used radiopharmaceuticals. Using the tissue weighting factors from ICRP Publication 103, the effective dose per administered activity was estimated to be 0.016 mSv/MBq for F-18-FDG, 0.014 mSv/MBq for Tc-99m-pertechnetate, and 16 mSv/MBq for I-131-iodide. Conclusions: The internal dosimetry program IDAC-Dose2.1 was developed and applied to three radiopharmaceuticals for validation against DCAL and to generate improved absorbed dose estimations for diagnostic nuclear medicine using specific absorbed fraction values of the ICRP computational voxel phantoms. The sub-module for absorbed dose calculations in spherical structures 1 mm to 9 cm in diameter and different tissue composition was included to broaden the clinical usefulness of the program. The IDAC-Dose2.1 program is free software for research and available for download at http://www.idac-dose.org.

  • 19. Andersson, Martin
    et al.
    Johansson, Lennart
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Mattsson, Sören
    Minarik, David
    Leide-Svegborn, Sigrid
    Organ doses and effective dose for five pet radiopharmaceuticals2016In: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 169, no 1-4, p. 253-258Article in journal (Refereed)
    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.

  • 20.
    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 University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    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 wall2014In: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 59, no 9, p. 2173-2182Article in journal (Refereed)
    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.

  • 21.
    Andersson, Nina
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Malm, Jan
    Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Neurology.
    Wiklund, Urban
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Eklund, Anders
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Adaptive method for assessment of cerebrospinal fluid outflow conductance.2007In: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 45, no 4, p. 337-343Article in journal (Refereed)
    Abstract [en]

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

  • 22.
    Arvidsson, Peder
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics. Umeå University, Faculty of Science and Technology, Department of Physics.
    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 credits / 30 HE creditsStudent thesis
  • 23.
    Axelsson, Jan
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    PET/MR ur fysikerns perspektiv2015Conference paper (Other academic)
  • 24. Bailey, D. L.
    et al.
    Pichler, B. J.
    Gueckel, B.
    Antoch, G.
    Barthel, H.
    Bhujwalla, Z. M.
    Biskup, S.
    Biswal, S.
    Bitzer, M.
    Boellaard, R.
    Braren, R. F.
    Brendle, C.
    Brindle, K.
    Chiti, A.
    la Fougere, C.
    Gillies, R.
    Goh, V.
    Goyen, M.
    Hacker, M.
    Heukamp, L.
    Knudsen, G. M.
    Krackhardt, A. M.
    Law, I.
    Morris, J. C.
    Nikolaou, K.
    Nuyts, J.
    Ordonez, A. A.
    Pantel, K.
    Quick, H. H.
    Riklund, Katrine
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Sabri, O.
    Sattler, B.
    Troost, E. G. C.
    Zaiss, M.
    Zender, L.
    Beyer, Thomas
    Combined PET/MRI: Global Warming-Summary Report of the 6th International Workshop on PET/MRI, March 27-29, 2017, Tubingen, Germany2018In: Molecular Imaging and Biology, ISSN 1536-1632, E-ISSN 1860-2002, Vol. 20, no 1, p. 4-20Article, review/survey (Refereed)
    Abstract [en]

    The 6th annual meeting to address key issues in positron emission tomography (PET)/magnetic resonance imaging (MRI) was held again in Tubingen, Germany, from March 27 to 29, 2017. Over three days of invited plenary lectures, round table discussions and dialogue board deliberations, participants critically assessed the current state of PET/MRI, both clinically and as a research tool, and attempted to chart future directions. The meeting addressed the use of PET/MRI and workflows in oncology, neurosciences, infection, inflammation and chronic pain syndromes, as well as deeper discussions about how best to characterise the tumour microenvironment, optimise the complementary information available from PET and MRI, and how advanced data mining and bioinformatics, as well as information from liquid biomarkers (circulating tumour cells and nucleic acids) and pathology, can be integrated to give a more complete characterisation of disease phenotype. Some issues that have dominated previous meetings, such as the accuracy of MR-based attenuation correction (AC) of the PET scan, were finally put to rest as having been adequately addressed for the majority of clinical situations. Likewise, the ability to standardise PET systems for use in multicentre trials was confirmed, thus removing a perceived barrier to larger clinical imaging trials. The meeting openly questioned whether PET/MRI should, in all cases, be used as a whole-body imaging modality or whether in many circumstances it would best be employed to give an in-depth study of previously identified disease in a single organ or region. The meeting concluded that there is still much work to be done in the integration of data from different fields and in developing a common language for all stakeholders involved. In addition, the participants advocated joint training and education for individuals who engage in routine PET/MRI. It was agreed that PET/MRI can enhance our understanding of normal and disrupted biology, and we are in a position to describe the in vivo nature of disease processes, metabolism, evolution of cancer and the monitoring of response to pharmacological interventions and therapies. As such, PET/MRI is a key to advancing medicine and patient care.

  • 25. Bailey, D. L.
    et al.
    Pichler, B. J.
    Gueckel, B.
    Barthel, H.
    Beer, A. J.
    Botnar, R.
    Gillies, R.
    Goh, V.
    Gotthardt, M.
    Hicks, R. J.
    Lanzenberger, R.
    la Fougere, C.
    Lentschig, M.
    Nekolla, S. G.
    Niederdraenk, T.
    Nikolaou, K.
    Nuyts, J.
    Olego, D.
    Åhlstrom Riklund, Katrine
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Diagnostic Radiology.
    Signore, A.
    Schaefers, M.
    Sossi, V.
    Suminski, M.
    Veit-Haibach, P.
    Umutlu, L.
    Wissmeyer, M.
    Beyer, T.
    Combined PET/MRI: from Status Quo to Status Go. Summary Report of the Fifth International Workshop on PET/MR Imaging; February 15-19, 2016; Tubingen, Germany2016In: Molecular Imaging and Biology, ISSN 1536-1632, E-ISSN 1860-2002, Vol. 18, no 5, p. 637-650Article in journal (Refereed)
    Abstract [en]

    This article provides a collaborative perspective of the discussions and conclusions from the fifth international workshop of combined positron emission tomorgraphy (PET)/magnetic resonance imaging (MRI) that was held in Tubingen, Germany, from February 15 to 19, 2016. Specifically, we summarise the second part of the workshop made up of invited presentations from active researchers in the field of PET/MRI and associated fields augmented by round table discussions and dialogue boards with specific topics. This year, this included practical advice as to possible approaches to moving PET/MRI into clinical routine, the use of PET/MRI in brain receptor imaging, in assessing cardiovascular diseases, cancer, infection, and inflammatory diseases. To address perceived challenges still remaining to innovatively integrate PET and MRI system technologies, a dedicated round table session brought together key representatives from industry and academia who were engaged with either the conceptualisation or early adoption of hybrid PET/MRI systems. Discussions during the workshop highlighted that emerging unique applications of PET/MRI such as the ability to provide multi-parametric quantitative and visual information which will enable not only overall disease detection but also disease characterisation would eventually be regarded as compelling arguments for the adoption of PET/MR. However, as indicated by previous workshops, evidence in favour of this observation is only growing slowly, mainly due to the ongoing inability to pool data cohorts from independent trials as well as different systems and sites. The participants emphasised that moving from status quo to status go entails the need to adopt standardised imaging procedures and the readiness to act together prospectively across multiple PET/MRI sites and vendors.

  • 26. Baste, Valborg
    et al.
    Hansson Mild, Kjell
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Moen, Bente E
    Radiofrequency exposure on fast patrol boats in the Royal Norwegian Navy-an approach to a dose assessment.2010In: Bioelectromagnetics, ISSN 0197-8462, E-ISSN 1521-186X, Vol. 31, no 5, p. 350-360Article in journal (Refereed)
    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.

  • 27.
    Bayisa, Fekadu L.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Liu, Xijia
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Garpebring, Anders
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Yu, Jun
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Computed Tomography Image Estimation by Statistical Learning MethodsManuscript (preprint) (Other academic)
    Abstract [en]

    There is increasing interest in computed tomography (CT) image estimations from magnetic resonance (MR) images. The estimated CT images canbe utilised for attenuation correction, patient positioning, and dose planningin diagnostic and radiotherapy workflows. This study presents a statisticallearning method for CT image estimation. We have used predefined tissuetype information in a Gaussian mixture model to explore the estimation.The performance of our method was evaluated using cross-validation on realdata. In comparison with the existing model-based CT image estimationmethods, the proposed method has improved the estimation, particularly inbone tissues. Evaluation of our method shows that it is a promising methodto generate CT image substitutes for the implementation of fully MR-basedradiotherapy and PET/MRI applications.

  • 28.
    Bayisa, Fekadu Lemessa
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Statistical methods in medical image estimation and sparse signal recovery2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis presents work on methods for the estimation of computed tomography (CT) images from magnetic resonance (MR) images for a number of diagnostic and therapeutic workflows. The study also demonstrates sparse signal recovery method, which is an intermediate method for magnetic resonance image reconstruction. The thesis consists of four articles. The first three articles are concerned with developing statistical methods for the estimation of CT images from MR images. We formulated spatial and non-spatial models for CT image estimation from MR images, where the spatial models include hidden Markov model (HMM) and hidden Markov random field model (HMRF) while the non-spatial models incorporate Gaussian mixture model (GMM) and skewed-Gaussian mixture model (SGMM). The statistical models are estimated via a maximum likelihood approach using the EM-algorithm in GMM and SGMM, the EM gradient algorithm in HMRF and the Baum–Welch algorithm in HMM. We have also examined CT image estimation using GMM and supervised statistical learning methods. The performance of the models is evaluated using cross-validation on real data. Comparing CT image estimation performance of the models, we have observed that GMM combined with supervised statistical learning method has the best performance, especially on bone tissues. The fourth article deals with a sparse modeling in signal recovery. Using spike and slab priors on the signal, we formulated a sparse signal recovery problem and developed an adaptive algorithm for sparse signal recovery. The developed algorithm has better performance than the recent iterative convex refinement (ICR) algorithm. The methods introduced in this work are contributions to the lattice process and signal processing literature. The results are an input for the research on replacing CT images by synthetic or pseudo-CT images, and for an efficient way of recovering sparse signal.

  • 29. Berglund, Johan
    et al.
    Skorpil, Mikael
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Diagnostic Radiology.
    Multi-scale graph-cut algorithm for efficient water-fat separation2017In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 78, no 3, p. 941-949Article in journal (Refereed)
    Abstract [en]

    PURPOSE: To improve the accuracy and robustness to noise in water-fat separation by unifying the multiscale and graph cut based approaches to B0 -correction.

    METHODS: A previously proposed water-fat separation algorithm that corrects for B0 field inhomogeneity in 3D by a single quadratic pseudo-Boolean optimization (QPBO) graph cut was incorporated into a multi-scale framework, where field map solutions are propagated from coarse to fine scales for voxels that are not resolved by the graph cut. The accuracy of the single-scale and multi-scale QPBO algorithms was evaluated against benchmark reference datasets. The robustness to noise was evaluated by adding noise to the input data prior to water-fat separation.

    RESULTS: Both algorithms achieved the highest accuracy when compared with seven previously published methods, while computation times were acceptable for implementation in clinical routine. The multi-scale algorithm was more robust to noise than the single-scale algorithm, while causing only a small increase (+10%) of the reconstruction time.

    CONCLUSION: The proposed 3D multi-scale QPBO algorithm offers accurate water-fat separation, robustness to noise, and fast reconstruction. The software implementation is freely available to the research community. Magn Reson Med, 2016. © 2016 International Society for Magnetic Resonance in Medicine.

  • 30.
    Berthon, Beatrice
    et al.
    Wales Research and Diagnostic PET Imaging Centre, Cardiff University, Cardiff, UK.
    Häggström, Ida
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Apte, Aditya
    Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA.
    Beattie, Bradley J.
    Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA.
    Kirov, Assen S.
    Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA.
    Humm, John L.
    Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA.
    Marshall, Christopher
    Wales Research and Diagnostic PET Imaging Centre, Cardiff University, Cardiff, UK.
    Spezi, Emiliano
    School of Engineering, Cardiff University, Cardiff, Wales, UK.
    Larsson, Anne
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Schmidtlein, C. Ross
    Department of Medical Physics, Memorial Sloan Kettering Cancer Center, New York, USA.
    PETSTEP: generation of synthetic PET lesions for fast evaluation of segmentation methods2015In: Physica medica (Testo stampato), ISSN 1120-1797, E-ISSN 1724-191X, Vol. 31, no 8, p. 969-980Article in journal (Refereed)
    Abstract [en]

    Purpose: This work describes PETSTEP (PET Simulator of Tracers via Emission Projection): a faster and more accessible alternative to Monte Carlo (MC) simulation generating realistic PET images, for studies assessing image features and segmentation techniques.

    Methods: PETSTEP was implemented within Matlab as open source software. It allows generating threedimensional PET images from PET/CT data or synthetic CT and PET maps, with user-drawn lesions and user-set acquisition and reconstruction parameters. PETSTEP was used to reproduce images of the NEMA body phantom acquired on a GE Discovery 690 PET/CT scanner, and simulated with MC for the GE Discovery LS scanner, and to generate realistic Head and Neck scans. Finally the sensitivity (S) and Positive Predictive Value (PPV) of three automatic segmentation methods were compared when applied to the scanner-acquired and PETSTEP-simulated NEMA images.

    Results: PETSTEP produced 3D phantom and clinical images within 4 and 6 min respectively on a single core 2.7 GHz computer. PETSTEP images of the NEMA phantom had mean intensities within 2% of the scanner-acquired image for both background and largest insert, and 16% larger background Full Width at Half Maximum. Similar results were obtained when comparing PETSTEP images to MC simulated data. The S and PPV obtained with simulated phantom images were statistically significantly lower than for the original images, but led to the same conclusions with respect to the evaluated segmentation methods.

    Conclusions: PETSTEP allows fast simulation of synthetic images reproducing scanner-acquired PET data and shows great promise for the evaluation of PET segmentation methods.

  • 31.
    Boman, Kurt
    et al.
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine. Research Unit, Department of Medicine, Skellefteå.
    Olofsson, Mona
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine. Research Unit, Department of Medicine, Skellefteå.
    Berggren, Peter
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine. Primary Health Care Center, Storuman.
    Sengupta, Partho P.
    Narula, Jagat
    Robot-Assisted Remote Echocardiographic Examination and Teleconsultation: A Randomized Comparison of Time to Diagnosis With Standard of Care Referral Approach2014In: JACC Cardiovascular Imaging, ISSN 1936-878X, E-ISSN 1876-7591, Vol. 7, no 8, p. 799-803Article in journal (Refereed)
    Abstract [en]

    The strategy using cardiological consultation in addition to the robot-assisted remote echocardiography at a distance was tested in a prospective, randomized open-Label trial to evaluate its feasibility and to define its clinical value in a rural area. The present study involved 1 primary healthcare center in the north of Sweden, 135 miles from the hospital where the echocardiograms and the cardiology teleconsultation were performed tong distance in real time. Nineteen patients were randomized to remote consultation and imaging, and 19 to the standard of care consultation. The total process time was significantly reduced in the former arm (median 114 days vs. 26.5 days; p < 0.001). The time from randomization until attaining a specialist consultation was also significantly reduced (p < 0.001). The patients satisfaction was reassuring; they considered that the remote consultation strategy offered an increased rapidity of diagnosis and the likelihood of receiving faster management compared with the standard of care at the primary healthcare center. 

  • 32.
    Boraxbekk, Carl-Johan
    et al.
    Umeå University, Faculty of Social Sciences, Centre for Demographic and Ageing Research (CEDAR). Umeå University, Faculty of Medicine, Umeå Centre for Functional Brain Imaging (UFBI).
    Salami, Alireza
    Umeå University, Faculty of Medicine, Umeå Centre for Functional Brain Imaging (UFBI). Aging Research Center (ARC), Karolinska Institute, Stockholm, Sweden.
    Wåhlin, Anders
    Umeå University, Faculty of Medicine, Umeå Centre for Functional Brain Imaging (UFBI). Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Nyberg, Lars
    Umeå University, Faculty of Medicine, Umeå Centre for Functional Brain Imaging (UFBI). Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology. Umeå University, Faculty of Medicine, Department of Radiation Sciences, Diagnostic Radiology.
    Physical activity over a decade modifies age-related decline in perfusion, gray matter volume, and functional connectivity of the posterior default mode network: a multimodal approach2016In: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 131, p. 133-141Article in journal (Refereed)
    Abstract [en]

    One step toward healthy brain aging may be to entertain a physically active lifestyle. Studies investigating physical activity effects on brain integrity have, however, mainly been based on single brain markers, and few used a multimodal imaging approach. In the present study, we used cohort data from the Betula study to examine the relationships between scores reflecting current and accumulated physical activity and brain health. More specifically, we first examined if physical activity scores modulated negative effects of age on seven resting state networks previously identified by Salami, Pudas, and Nyberg (2014). The results revealed that one of the most age-sensitive RSN was positively altered by physical activity, namely, the posterior default-mode network involving the posterior cingulate cortex (PCC). Second, within this physical activity-sensitive RSN, we further analyzed the association between physical activity and gray matter (GM) volumes, white matter integrity, and cerebral perfusion using linear regression models. Regions within the identified DMN displayed larger GM volumes and stronger perfusion in relation to both current and 10-years accumulated scores of physical activity. No associations of physical activity and white matter integrity were observed. Collectively, our findings demonstrate strengthened PCC–cortical connectivity within the DMN, larger PCC GM volume, and higher PCC perfusion as a function of physical activity. In turn, these findings may provide insights into the mechanisms of how long-term regular exercise can contribute to healthy brain aging.

  • 33.
    Boson, Jonas
    Umeå University, Faculty of Medicine, Radiation Sciences, Radiation Physics.
    Improving accuracy of in situ gamma-ray spectrometry2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Gamma-ray spectrometry measurements performed on site, or “in situ”, is a widely used and powerful method that can be employed both to identify and quantify ground deposited radionuclides. The purpose of this thesis is to improve the calibration of high purity germanium (HPGe) detectors for in situ measurements, and calculate the combined uncertainty and potential systematic effects.

    An improved semi-empirical calibration method is presented, based on a novel expression for the intrinsic detector efficiency that includes both the energy and angular response of the detector. A three-layer model for the description of the depth distribution of the radionuclide and the soil density is proposed. The combined uncertainty of intrinsic detector efficiency calibrations and in situ measurements according to the proposed method was estimated. The uncertainty in the intrinsic detector efficiency was found to be 5.1 and 8.1% (coverage factor k=1, i.e. for a confidence interval of about 68%), for the two detectors calibrated. These numbers were, however, at a later stage reduced to 3.7 and 4.2%, using a revised expression for the intrinsic detector efficiency.

    For in situ measurements, the combined standard uncertainty was found to be 15-20% (k=1), based on the original expression for the intrinsic detector efficiency. Monte Carlo models of the two detectors were created and Monte Carlo calculated values for intrinsic detector efficiency were compared with experimental data. As a discrepancy was found, a thorough investigation of the detector response was performed. Scanning of the detector surface with a collimated 59.5 keV photon beam revealed the detector response to be highly irregular over the detector surface. It was concluded that the efficiency deficit of the detector could most likely be attributed to an increase in dead layer thickness compared with manufacturer supplied data. The thickness of the dead layer was estimated to be 1.5-1.9 mm, whereas the nominal value was 0.7 mm. Radiographs of the detectors were produced that provided valuable information about the physical dimensions of the germanium crystal, as well as its actual location within the detector housing.

    The Monte Carlo models were employed to calculate in situ measurement efficiencies for measurements of 137Cs deposition from the Chernobyl fallout. Results from the Monte Carlo simulations were compared both with the semi-empirical method and with soil sample data, and satisfactory agreement was confirmed. It was then proceeded to employ the Monte Carlo model to calculate the effect on in situ measurement results by two influencing parameters: ground curvature and activity in trees. Neither of these parameters was found to influence the result by more than about 25%. This deviation is comparable with the measurement uncertainty, and should not deter from measurements in such terrain.

  • 34. Brown, J
    et al.
    Jacobs, R
    Levring Jäghagen, Eva
    Umeå University, Faculty of Medicine, Department of Odontology, School of Dentistry.
    Lindh, C
    Baksi, G
    Schulze, D
    Schulze, R
    Basic training requirements for the use of dental CBCT by dentists: a position paper prepared by the European Academy of DentoMaxilloFacial Radiology2014In: Dento-Maxillo-Facial Radiology, ISSN 0250-832X, E-ISSN 1476-542X, Vol. 43, no 1, article id 20130291Article in journal (Refereed)
    Abstract [en]

    Cone beam CT (CBCT) is a relatively new imaging modality, which is now widely available to dentists for examining hard tissues in the dental and maxillofacial regions. CBCT gives a three-dimensional depiction of anatomy and pathology, which is similar to medical CT and uses doses generally higher than those used in conventional dental imaging. The European Academy of DentoMaxilloFacial Radiology recognizes that dentists receive training in two-dimensional dental imaging as undergraduates, but most of them have received little or no training in the application and interpretation of cross-sectional three-dimensional imaging. This document identifies the roles of dentists involved in the use of CBCT, examines the training requirements for the justification, acquisition and interpretation of CBCT imaging and makes recommendations for further training of dentists in Europe who intend to be involved in any aspect of CBCT imaging. Two levels of training are recognized. Level 1 is intended to train dentists who prescribe CBCT imaging, such that they may request appropriately and understand the resultant reported images. Level 2 is intended to train to a more advanced level and covers the understanding and skills needed to justify, carry out and interpret a CBCT examination. These recommendations are not intended to create specialists in CBCT imaging but to offer guidance on the training of all dentists to enable the safe use of CBCT in the dentoalveolar region.

  • 35.
    Bryndahl, Fredrik
    Umeå University, Faculty of Medicine, Department of Odontology, Oral and Maxillofacial Radiology.
    Temporomandibular joint disk displacement and subsequent adverse mandibular growth: a radiographic, histologic and biomolecular experimental study2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The mandibular condyles represent important growth sites within the facial skeleton. Condylar growth is not a pacemaker of mandibular development, but it provides regional adaptive growth that is of considerable clinical significance, as the condyle’s upward and backward growth movement regulates the anteriorly and inferiorly directed displacement of the mandible as a whole.

    Orthopedic problems of the temporomandibular joint (TMJ), such as displacement of the TMJ disk, are common in the adolescent population. Clinical studies of mandibular asymmetry and mandibular retrognathia in adults as well as in children and adolescents, have reported an association with coexisting non-reducing displacement of the TMJ disk without identifying the cause and effect. Through experimental studies causality has been established, and unilateral affliction during growth has been shown to retard ipsilateral mandibular development with facial asymmetry as the sequel. It was hypothesized that bilateral non-reducing TMJ disk displacement during growth would impair mandibular development bilaterally, resulting in mandibular retrognathia. TMJ disk displacement has repeatedly been demonstrated to induce histological reactions of the condylar cartilage. An additional assumption was therefore that a non-deranged TMJ disk function is crucial for the maintenance of the growing condyle’s biophysical environment, and that a connection ought to exist between the amount of condylar cartilage changes caused by TMJ disk displacement and the amount of subsequent adverse mandibular growth. It was also hypothesized that non-reducing displacement of the TMJ disk in growing individuals would result in qualitative and quantitative changes of the condylar subchondral bone.

    An improved experimental cephalometric method was developed in order to optimize the reliability of longitudinal radiographic evaluation of fast growing small animals. Bilateral non-reducing TMJ disk displacement was surgically created in ten growing New Zealand White rabbits, with ten additional rabbits serving as a sham operated control group. The amount and direction of craniofacial growth was followed over time in serial cephalograms, aided by tantalum implants in the jaws. The study period was chosen to correspond to childhood and adolescence in man. The assessed growth of each side of the mandible was correlated to the histological feature of ipsilateral condylar cartilage at the end of the growth period. The amount and composition of subchondral bone from three regions of interest in the condyle, and the expression of local growth factors in the adjacent condylar cartilage was evaluated.

    The results verified that bilateral non-reducing TMJ disk displacement retarded mandibular growth bilaterally; the extent corresponding to mandibular retrognathia in man. Displacement of the TMJ disk during the growth period induced condylar cartilage adaptive reactions that were associated with both an adverse amount and direction of mandibular growth, manifesting in a retrognathic mandibular growth pattern. Growth impairment fluctuated over time, with the most striking retardation occurring during periods of increased general growth, implying a local growth reduction explicitly counteracting general hormonal growth acceleration. A significant decrease of the total amount of subchondral bone, in spite of a general increase of new bone formation in the experimental condyles, pointed to a reparative compensation for an extensive resorption of subchondral bone due to displacement of the TMJ disk, but not to the extent that normal growth would be maintained. These results constitute an explanation for the adverse mandibular development following non-reducing TMJ disk displacement in growing individuals.

    This project has shown that non-reducing displacement of the TMJ disk during growth has significant consequences on facial development. The findings strongly advocate early and accurate diagnosis and treatment of TMJ disk displacement in the adolescent population, thereby presumably reducing the need for future orthodontic and surgical craniofacial corrective therapy. The results furthermore enhance the need for full appraisal of TMJ disk function in the adolescent population during orthodontic functional therapy, as the condylar cartilage and subchondral bone reactions to a concomitantly displaced non-reducing TMJ disk must be expected to interfere with the intended growth stimulating treatment. The findings of intact articular layers in spite of gross histological and morphological soft and hard tissue changes as a sequel to TMJ disk displacement in growing individuals, implicate a clinical risk of false positive radiographic diagnosis of degenerative changes of the TMJ in children and adolescents.

  • 36.
    Bryndahl, Fredrik
    et al.
    Umeå University, Faculty of Medicine, Department of Odontology, Oral and Maxillofacial Radiology.
    Warfvinge, G
    Eriksson, L
    Isberg, A
    Cartilage changes link retrognathic mandibular growth to TMJ disc displacement in a rabbit model2011In: International Journal of Oral and Maxillofacial Surgery, ISSN 0901-5027, E-ISSN 1399-0020, Vol. 40, no 6, p. 621-627Article in journal (Refereed)
    Abstract [en]

    Recent experimental research demonstrated that non-reducing temporomandibular joint (TMJ) disc displacement in growing rabbits impaired mandibular growth. TMJ disc displacement is also shown to induce histological changes of the condylar cartilage. The authors hypothesized that the severity of these changes would correlate to the magnitude of mandibular growth. Bilateral non-reducing TMJ disc displacement was surgically created in 10 growing New Zealand White rabbits. Ten additional rabbits constituted a sham operated control group. Aided by tantalum implants, growth was cephalometrically determined for each mandibular side during a period equivalent to childhood and adolescence in man. At the end of the growth period, histologically classified cartilage features were correlated with the assessed ipsilateral mandibular growth. Non-reducing displacement of the TMJ disc during the growth period induced histological reactions of the condylar cartilage in the rabbit model. The severity of cartilage changes was inversely correlated to the magnitude and the direction of mandibular growth, which resulted in a retrognathic growth pattern.

  • 37.
    Brynolfsson, Patrik
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Applications of statistical methods in quantitative magnetic resonance imaging2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Magnetic resonance imaging, MRI, offers a vast range of imaging methods that can be employed in the characterization of tumors. MRI is generally used in a qualitative way, where radiologists interpret the images for e.g. diagnosis, follow ups, or assessment of treatment response. In the past decade, there has been an increasing interest for quantitative imaging, which give repeatable measurements of the anatomy. Quantitative imaging allows for objective analysis of the images, which are grounded in physical properties of the underlying tissues. The aim of this thesis was to improve quantitative measurements of Dynamic contrast enhanced MRI (DCE-MRI), and the texture analysis of diffusion weighted MRI (DW-MRI).

    DCE-MRI measures perfusion, which is the delivery of blood, oxygen and nutrients to the tissues. The exam involves continuously imaging the region of interest, e.g. a tumor, while injecting a contrast agent (CA) in the blood stream. By analyzing how fast and how much CA leaks out into the tissues, the cell density and the permeability of the capillaries can be estimated. Tumors often have an irregular and broken vasculature, and DCE-MRI can aid in tumor grading or treatment assessment. One step is crucial when performing DCE-MRI analysis, the quantification of CA in the tissue. The CA concentration is difficult to measure accurately due to uncertainties in the imaging, properties of the CA, and physiology of the patient. Paper I, the possibility of using two aspects of the MRI data, phase and magnitude, for improved CA quantification, is explored. We found that the combination of phase and magnitude information improved the CA quantification in regions with high CA concentration, and was more advantageous for high field strength scanners.

    DW-MRI measures the diffusion of water in and between cells, which reflects the cell density and structure of the tissue. The structure of a tumor can give insights into the prognosis of the disease. Tumors are heterogeneous, both genetically and in the distribution of cells, and tumors with high intratumoral heterogeneity have poorer prognosis. This heterogeneity can be measured using texture analysis. In 1973, Haralick et al. presented a texture analysis method using a gray level co-occurrence matrix, GLCM, to gauge the spatial distribution of gray levels in the image. This method of assessing texture in images has been successfully applied in many areas of research, from satellite images to medical applications. Texture analysis in treatment outcome assessment is studied in Paper II, where we showed that texture can distinguish between groups of patients with different survival times, in images acquired prior to treatment start.

    However, this type of texture analysis is not inherently quantitative in the way it is calculated today. This was studied in Paper III, where we investigated how texture features were affected by five parameters related to image acquisition and pre-processing. We found that the texture feature values were dependent on the choice of these imaging and preprocessing parameters. In Paper IV, a novel method for calculating Haralick texture features was presented, which makes the texture features asymptotically invariant to the size of the GLCM. This method allows for comparison of textures between images that have been analyzed in different ways.

    In conclusion, the work in this thesis has been aimed at improving quantitative analysis of tumors using MRI and texture analysis.

  • 38.
    Brynolfsson, Patrik
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Axelsson, Jan
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Holmberg, August
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Jonsson, Joakim
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Goldhaber, David
    Jian, Yiqiang
    Illerstam, Fredrik
    Engström, Mathias
    Zackrisson, Björn
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Nyholm, Tufve
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Technical note: adapting a GE SIGNA PET/MR scanner for radiotherapy2018In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 45, no 8, p. 3546-3550Article in journal (Refereed)
    Abstract [en]

    Purpose: Simultaneous collection of PET and MR data for radiotherapy purposes are useful for, for example, target definition and dose escalations. However, a prerequisite for using PET/MR in the radiotherapy workflow is the ability to image the patient in treatment position. The aim of this work was to adapt a GE SIGNA PET/MR scanner to image patients for radiotherapy treatment planning and evaluate the impact on signal-to-noise (SNR) of the MR images, and the accuracy of the PET attenuation correction. Method: A flat tabletop and a coil holder were developed to image patients in the treatment position, avoid patient contour deformation, and facilitate attenuation correction of flex coils. Attenuation corrections for the developed hardware and an anterior array flex coil were also measured and implemented to the PET/MR system to minimize PET quantitation errors. The reduction of SNR in the MR images due to the added distance between the coils and the patient was evaluated using a large homogenous saline-doped water phantom, and the activity quantitation errors in PET imaging were evaluated with and without the developed attenuation corrections. Result: We showed that the activity quantitation errors in PET imaging were within ±5% when correcting for attenuation of the flat tabletop, coil holder, and flex coil. The SNR of the MRI images were reduced to 74% using the tabletop, and 66% using the tabletop and coil holders. Conclusion: We present a tabletop and coil holder for an anterior array coil to be used with a GE SIGNA PET/MR scanner, for scanning patients in the radiotherapy work flow. Implementing attenuation correction of the added hardware from the radiotherapy setup leads to acceptable PET image quantitation. The drop in SNR in MR images may require adjustment of the imaging protocols.

  • 39.
    Brynolfsson, Patrik
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Nilsson, David
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Torheim, Turid
    Asklund, Thomas
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
    Thellenberg Karlsson, Camilla
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Oncology.
    Trygg, Johan
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Nyholm, Tufve
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Garpebring, Anders
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Haralick texture features from apparent diffusion coefficient (ADC) MRI images depend on imaging and pre-processing parameters2017In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, article id 4041Article in journal (Refereed)
    Abstract [en]

    In recent years, texture analysis of medical images has become increasingly popular in studies investigating diagnosis, classification and treatment response assessment of cancerous disease. Despite numerous applications in oncology and medical imaging in general, there is no consensus regarding texture analysis workflow, or reporting of parameter settings crucial for replication of results. The aim of this study was to assess how sensitive Haralick texture features of apparent diffusion coefficient (ADC) MR images are to changes in five parameters related to image acquisition and pre-processing: noise, resolution, how the ADC map is constructed, the choice of quantization method, and the number of gray levels in the quantized image. We found that noise, resolution, choice of quantization method and the number of gray levels in the quantized images had a significant influence on most texture features, and that the effect size varied between different features. Different methods for constructing the ADC maps did not have an impact on any texture feature. Based on our results, we recommend using images with similar resolutions and noise levels, using one quantization method, and the same number of gray levels in all quantized images, to make meaningful comparisons of texture feature results between different subjects.

  • 40.
    Brynolfsson, Patrik
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Yu, Jun
    Umeå University, Faculty of Science and Technology, Department of Mathematics and Mathematical Statistics.
    Wirestam, Ronnie
    Lund University.
    Karlsson, Mikael
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Garpebring, Anders
    Umeå University, Faculty of Medicine, Department of Radiation Sciences. CJ Gorter Center for High Field MRI, Leiden University Medical Center, Leiden, Netherlands.
    Combining phase and magnitude information for contrast agent quantification in dynamic contrast-enhanced MRI using statistical modeling2015In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 74, no 4, p. 1156-1164Article in journal (Refereed)
    Abstract [en]

    Purpose: The purpose of this study was to investigate, using simulations, a method for improved contrast agent (CA) quantification in DCE-MRI.

    Methods: We developed a maximum likelihood estimator that combines the phase signal in the DCE-MRI image series with an additional CA estimate, e.g. the estimate obtained from magnitude data. A number of simulations were performed to investigate the ability of the estimator to reduce bias and noise in CA estimates. Noise levels ranging from that of a body coil to that of a dedicated head coil were investigated at both 1.5T and 3T.

    Results: Using the proposed method, the root mean squared error in the bolus peak was reduced from 2.24 to 0.11 mM in the vessels and 0.16 to 0.08 mM in the tumor rim for a noise level equivalent of a 12-channel head coil at 3T. No improvements were seen for tissues with small CA uptake, such as white matter.

    Conclusion: Phase information reduces errors in the estimated CA concentrations. A larger phase response from higher field strengths or higher CA concentrations yielded better results. Issues such as background phase drift need to be addressed before this method can be applied in vivo.

  • 41.
    Brändström, Helge
    et al.
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Anaesthesiology.
    Sundelin, Anna
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Anaesthesiology.
    Hoseason, Daniela
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Anaesthesiology.
    Sundström, Nina
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Birgander, Richard
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Diagnostic Radiology.
    Johansson, Göran
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Anaesthesiology.
    Winsö, Ola
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Anaesthesiology.
    Koskinen, Lars-Owe
    Umeå University, Faculty of Medicine, Department of Pharmacology and Clinical Neuroscience, Clinical Neuroscience.
    Haney, Michael
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Anaesthesiology.
    Risk for intracranial pressure increase related to enclosed air in post-craniotomy patients during air ambulance transport: a retrospective cohort study with simulation2017In: Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine, ISSN 1757-7241, E-ISSN 1757-7241, Vol. 25, article id 50Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Post-craniotomy intracranial air can be present in patients scheduled for air ambulance transport to their home hospital. We aimed to assess risk for in-flight intracranial pressure (ICP) increases related to observed intracranial air volumes, hypothetical sea level pre-transport ICP, and different potential flight levels and cabin pressures. METHODS: A cohort of consecutive subdural hematoma evacuation patients from one University Medical Centre was assessed with post-operative intracranial air volume measurements by computed tomography. Intracranial pressure changes related to estimated intracranial air volume effects of changing atmospheric pressure (simulating flight and cabin pressure changes up to 8000 ft) were simulated using an established model for intracranial pressure and volume relations. RESULTS: Approximately one third of the cohort had post-operative intracranial air. Of these, approximately one third had intracranial air volumes less than 11 ml. The simulation estimated that the expected changes in intracranial pressure during 'flight' would not result in intracranial hypertension. For intracranial air volumes above 11 ml, the simulation suggested that it was possible that intracranial hypertension could develop 'inflight' related to cabin pressure drop. Depending on the pre-flight intracranial pressure and air volume, this could occur quite early during the assent phase in the flight profile. DISCUSSION: These findings support the idea that there should be radiographic verification of the presence or absence of intracranial air after craniotomy for patients planned for long distance air transport. CONCLUSIONS: Very small amounts of air are clinically inconsequential. Otherwise, air transport with maintained ground-level cabin pressure should be a priority for these patients.

  • 42.
    Byenfeldt, Marie
    Umeå University, Faculty of Medicine, Department of Nursing.
    Ultraljuds-baserad shear wave elastografi- En kvantitativ studie av faktorer som kan påverka tillförlitligheten i mätresultatet vid gradering av leverfibros2016Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Aim: The aim of this study was to investigate factors that may affect the reliability of measurement result with ultrasound-based shear wave elastography, when scoring liver fibrosis, among patients with chronic liver disease.

    Background: Chronic liver disease may develop liver fibrosis, and in worst cases cancer of the liver. Today, there is antiviral treatment and among the non-invasive methods that have been developed to score liver fibrosis, there is ultrasound-based shear wave elastography. This new method started in 2014 at Östersunds Hospital x-ray department and in cases when the measurements result does not correlate with the clinical findings, problems emerge.

    Design: The study has been performed as a descriptive quantitative study with retrospective design, at the level of Master’s degree in the radiography science at Umeå University.

    Method: Measurements from 132 individuals, which have been examined with Philips iU22 ElastPQ shear wave elastography, was analyzed.  The measurements was divided into two groups, using the inter quartile range as a cut-off; obtaining one study group and one control group. Logistic regression analysis has been performed to investigate the relationship to either group.

    Results: The following factors showed significant correlation to less accurate measurement result: age, the length of disease, steatosis, antiviral-and/or cardiovasckular medicine, AST och ALT and distance between probe surface and liver capsule. With bivariate regression analysis the significant findings were: age (p=0.002), the disease length (p=0.039), steatosis (p=0.001), antivirale- and/or cardiovascular medicine (p=0.045), AST (p=0.001), ALT (p=0.038) and distance between probe surface and liver capsule (p=0.000). Using the multivariate regression analysis the following significant findings remained: antivirale- and/or cardiovascular medicine (p=0.049) and increased distance between probe surface and liver capsule (p=0.003).

    Conclusion: When scoring liver fibrosis with the method ultrasound-based shear wave elastography, and the distance between probe surface and liver capsule are increased, the measurements may, according to the study´s main finding, imply less accurate measurements result. The patient may for that reason advantageously lie in left decubitus position during the examination, to obtain decreased distance to the liver capsule. There is still need for further research of variables that may affect the reliability of measurement result and which quality parameters that should be used for liver elastography with ARFI technology.

  • 43.
    Byenfeldt, Marie
    et al.
    Umeå University, Faculty of Medicine, Department of Nursing.
    Elvin, Anders
    Fransson, Per
    Umeå University, Faculty of Medicine, Department of Nursing.
    On patient related factors and their impact on ultrasound-based shear wave elastography of the liver2018In: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 44, no 8, p. 1606-1615Article in journal (Refereed)
    Abstract [en]

    The aim of the study was to investigate patient-related factors associated with either reliable or poorly reliable measurement results of ultrasound-based shear wave elastography (SWE) of the liver. A total of 188 patients were analyzed prospectively with binary logistic regression using the interquartile range/median as cutoff to define two groups based on reliable and poorly reliable SWE results. SWE results correlated significantly with liver biopsy. Factors associated with reliable SWE results (i.e., no negative impact on measurements) were age, sex, cirrhosis, antiviral and/or cardiovascular medication, smoking habits and body mass index. Factors associated with poorly reliable SWE results were increased skin-to-liver capsule distance (odds ratio = 3.08, 95% confidence interval: 1.70-5.60) and steatosis (odds ratio =2.89, 95% confidence interval: 1.33-6.28). These findings indicate that the interquartile range/median as a quality parameter is useful in avoiding poorly reliable SWE results. How best to examine patients with increased skin-to-liver capsule distance is a matter of some controversy, as the incidences of obesity, diabetes and metabolic syndrome are increasing worldwide; however, our results indicate that reliable SWE results can be obtained in this group of patients by using ultrasound-based SWE. (Email: marie.byenfeldt@umu.se, Marie.byenfeldt@aleris.se ) 

  • 44.
    Bylund, Sara
    et al.
    Umeå University, Faculty of Medicine, Department of Nursing.
    Sundén, Anna
    Umeå University, Faculty of Medicine, Department of Nursing.
    Magnetfältstyrkans betydelse för personer med multipel skleros eller kliniskt isolerat syndrom: en litteraturstudie2016Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Title: The importance of magnetic field strength for people with multiple sclerosis or clinically isolated syndrome - a literature study. Background: Multiple sclerosis (MS) is an autoimmune demyelinating disease of the central nervous system debuting mostly in young adults. MS is diagnosed based on clinical and radiological findings according to the McDonald criteria where no requirements are placed on which field strength that should be used. Magnetic resonance imaging (MRI) scanners with higher field strengths are however becoming more common. Objective: To investigate whether higher field strength (Tesla, T) gave better detection of lesions at MRI examinations of people with MS or clinically isolated syndrome. Methods: In this literature study searches were made in the databases PubMed, Web of Science and Scopus between the 8th and 11th of March 2016. Ten quantitative articles were examined and analyzed to finally be compiled under the results. Results: The results are presented under four main headings and twelve sub- headings. The main headings are the differences between field strengths, field strength and anatomical regions, field strength and pulse sequences and artifacts and image quality. Conclusion: 3T and 7T are better than 1,5T and 7T is usually better than 3T at detecting lesions. However other aspects need to be taken into account because many parameters come into play during MRI examinations. Further studies regarding optimization of pulse sequences and field strength and patients’ experiences of ultrahigh field strength are recommended, among others. 

  • 45.
    Byström, Björn
    et al.
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine. Örnsköldsvik Hospital.
    Lindqvist, Per
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine.
    Henein, Michael
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine.
    The right ventricle: knowing what is right2008In: The International Journal of Cardiovascular Imaging, ISSN 1569-5794, E-ISSN 1875-8312, Vol. 24, no 7, p. 701-702Article in journal (Refereed)
  • 46.
    Byström, Sara
    et al.
    Umeå University, Faculty of Medicine, Department of Nursing.
    Olofsson, Linn
    Umeå University, Faculty of Medicine, Department of Nursing.
    Skillnader och likheter mellan magnetresonanstomografi och datortomografi vid undersökning av barns hjärnor: En litteraturstudie2014Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    Skillnader och likheter mellan magnetresonanstomografi och datortomografi vid undersökning av barns hjärnor

    - En litteraturstudie

     

     

    Sara Byström

    Linn Olofsson

     

    Vårterminen 2014

    Självständigt arbete, 15 hp

    Röntgensjuksköterskeprogrammet, 180 hp

    Handledare: Ulf Isaksson, Universitetslektor, Institutionen för omvårdnad

    Abstrakt

    Bakgrund: Användandet av magnetresonanstomografi och datortomografi har ökat under åren. Det finns skillnader och likheter mellan dessa som bör finnas i åtanke vid val av undersökningsmetod. En magnetresonanstomografi är den bästa undersökningen för att se mjukvävnadskontraster. Datortomografens korta undersökningstid och dess lättillgängliget gör den kostnadseffektiv. En skillnad är att patienten utsätts för joniserande strålning vid en datortomografiundersökning, även om den är lättillgänglig och kostnadseffektiv gör den också skada. Barn är extra strålkänsliga och nyttan med att utföra undersökningen måste vägas mot riskerna. Syfte: Belysa skillnader och likheter mellan magnetresonanstomografi och datortomografi vid undersökning av barns hjärnor vid tre olika tillstånd. Metod: Tolv kvantitativa vetenskapliga artiklar granskades och analyserades av författarna. Artiklarna söktes fram via databaserna CINAHL, EBSCOhost, Pubmed samt med hjälp av manuell sökning. Resultat: Resultatet visade att både magnetresonanstomografi och datortomografi är ett radiologiskt verktyg för avbildning av barns hjärnor. Magnetresonanstomografi visade på bättre bilddiagnostik, dessutom utsätter magnetresonanstomografi inte patienten för joniserande strålning. Användandet av sedering visad sig dock vara frekventare vid magnetresonanstomografiundersökningar. Konklusion: Vid huvudtrauma, huvudvärk och krampanfall var magnetresonanstomografi den undersöknings metod att föredra. Den korta undersökningstiden för datortomografen visade sig kunna vara livsavgörande och en stor fördel vid akuta huvudtrauman.

    Nyckelord: MR, DT, barn, skillnad, likhet

     

     

     

     

     

     

     

    Abstract

    Background: The utilization of magnetic resonance imaging and computed tomography has increased over the years. There are differences and similarities between these imaging techniques that should be considered when selecting method of examination. Magnetic resonance imaging is the technique to prefer to view the soft tissue contrast. The short examination time and the accessibility make the computed tomography cost-effective. Although, one difference is that the patient is exposed to ionizing radiation during a computed tomography scan that may lead to harmful effects. Children are particularly sensitive to radiation exposure and the benefits of performing the examination must be weighed against the risks. Aim: Illuminate differences and similarities between magnetic resonance imaging and computed tomography in the examination of children’s brains for three different conditions. Method: Twelve quantitative scientific articles were reviewed and analyzed. Searched was done in the databases CINAHL, EBSCOhost, Pubmed and by manual search. Results: The results showed that both magnetic resonance imaging and computed tomography is a radiological tool for imaging of children’s brains. Magnetic resonance imaging showed better diagnostic imaging. Additionally this method does not expose the patient to ionizing radiation. Sedation shows to be more frequently used during a magnetic resonance examination. Conclusion: Magnetic resonance imaging was the method to prefer when examining head trauma, headache and seizures. The short examination time for computed tomography proved to be life changing and a great benefit for acute head trauma.

  • 47. Bäcklund, J
    et al.
    Clewett Dahl, E
    Skorpil, Mikael
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Is CT indicated in diagnosing sacroiliac joint degeneration?2017In: Clinical Radiology, ISSN 0009-9260, E-ISSN 1365-229X, Vol. 72, article id S0009-9260(17)30107-1Article in journal (Refereed)
    Abstract [en]

    AIM: To assess the value of computed tomography (CT) in the diagnosis of symptomatic sacroiliac (SI) joint degeneration.

    MATERIALS AND METHODS: CT images from 123 patients with clinically diagnosed SI joint pain were compared to age- and gender-matched controls without chronic back pain or previous back surgery. Degeneration was graded assessing joint space narrowing, osteophytes, subchondral sclerosis, cysts, and vacuum phenomena.

    RESULTS: The mean total score for the patients was 9.6 and for the controls 9.7 (p=0.77). A subgroup analysis of the mean score for the SI joints that were subjected to surgery was 4.3, compared to 4.8 in the conservatively treated SI joints in the patient group (p=0.23) and 4.8 for all SI joints in the control group (p=0.25). For patients with unilateral left-sided pain (n=40), the mean score for the left side was 5.2 and for the right side 4.9 (p=0.49). For patients with right-sided pain (n=41), the mean score for the right side was 4.8 and the left side 4.7 (p=0.55).

    CONCLUSION: The prevalence of SI joint degeneration on CT is equal in symptomatic and non-symptomatic individuals. This study indicates that the value of CT is limited, but further studies are needed to establish if CT has a place in diagnosing SI joint degeneration.

  • 48.
    Börlin, Emma
    et al.
    Umeå University, Faculty of Medicine, Department of Nursing.
    Randleff, Jessica
    Umeå University, Faculty of Medicine, Department of Nursing.
    Biverkningar vid administrering av gadoliniumkontrastmedel vid MRT-undersökningar2015Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Bakgrund: Inom röntgenverksamhet används kontrastmedel som ett hjälpmedel för att påvisa skillnader mellan vävnader i kroppen. Gadoliniumbaserade kontrastmedel används till större delen vid MR undersökningar. Biverkningar anses ovanliga, men de förekommer och kan innebära allvarliga konsekvenser. Röntgensjuksköterskor behöver kunskap om dessa biverkningar för att kunna ge en patientsäker vård.  Syfte: Studien har således som syfte att undersöka biverkningar som kan uppstå vid administrering av gadoliniumkontrastmedel vid MRT undersökningar. Metod: En litteraturstudie med artikelsökningar i tre databaser PubMed, CinAhl samt Scopus. Tolv kvantitativa artiklar användes och bearbetades till att bilda kategorier och underkategorier genom innehållsanalys. Resultat: Utifrån artiklarna bildades kategorin Cirkulationssystem och luftvägar med underkategorier hjärtpåverkan och andningsproblem, kategorin Mag- tarmkanalen och bukorgan med underkategorier GI-systemet samt njurar, urinvägar och lever, kategorin Ändrade sinnesförnimmelser med underkategorier ögat, förnimmelser från smak och lukt, hudpåverkan och temperaturförnimmelser samt kategorin Påverkan av kommunicerbarhet och obehag med underkategorier medvetandepåverkan och obehagsupplevelse. Konklusion: De allvarligaste biverkningarna involverade hjärtpåverkan, andningsproblem, njurproblem samt medvetandepåverkan. De vanligaste biverkningarna förknippades med GI-systemet, Hudreaktioner och Obehagsupplevelser. Eftersom biverkningar var otroligt sällsynta vid administrering av Gadoliniumkontrastmedel finns det risk att vårdpersonal inte känner till biverkningarna och därmed inte är uppmärksamma.

  • 49. Christensen, Jeppe Brage
    et al.
    Tolli, Heikki
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Bassler, Niels
    A general algorithm for calculation of recombination losses in ionization chambers exposed to ion beams2016In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 43, no 10Article in journal (Refereed)
    Abstract [en]

    Purpose: Dosimetry with ionization chambers in clinical ion beams for radiation therapy requires correction for recombination effects. However, common radiation protocols discriminate between initial and general recombination and provide no universal correction method for the presence of both recombination types in ion beams of charged particles heavier than protons. The advent of multiple field optimization in ion beams, allowing for complex patterns of dose delivery in both temporal and spatial domains, results in new challenges for recombination correction where the resulting recombination depends on the plan delivered. Here, the authors present the open source code IonTracks version 1.0, where the combined initial and general recombination effects in principle can be predicted for any ion beam with arbitrary particle-energy spectrum and temporal structure. Methods: IonTracks uses track structure theory to distribute the charge carriers in ion tracks. The charge carrier movements are governed by a pair of coupled differential equations, based on fundamental physical properties as charge carrier drift, diffusion, and recombination, which are solved numerically while the initial and general charge carrier recombination is computed. A space charge screening of the electric field is taken into account and the algorithm furthermore allows an inclusion of a free-electron component. Results: The algorithm is numerically stable and in accordance with experimentally validated theories for initial recombination in heavy ion tracks and general recombination in a proton beam. Conclusions: Given IonTracks' ability to handle arbitrary inputs, IonTracks can in principle be applied to any complex particle field in the spatial and temporal domain. IonTracks is validated against the Jaffe's and Boag's theory of recombination in pulsed beams of multiple ion species. IonTracks is able to calculate the correction factor for initial and general recombination losses in parallel-plate ionization chambers. Even if only few experimental data on recombination effects in ionization chambers are available today, the universal concept of IonTracks is not limited to the ions investigated here. Future experimental investigations of recombination in pulsed and possibly also continuous ion beams may be conducted with IonTracks, which ultimately may lead to a more precise prediction of recombination factors in complex radiation fields. 

  • 50.
    Cole, Frida
    et al.
    Umeå University, Faculty of Medicine, Department of Nursing.
    Öberg, Julia
    Umeå University, Faculty of Medicine, Department of Nursing.
    Åldersbedömningar baserat på undersökningar med datortomografi och magnetisk resonanstomografi av mediala nyckelbensepifysen2016Independent thesis Basic level (professional degree), 10 credits / 15 HE creditsStudent thesis
    Abstract [sv]

    Titel: Åldersbedömningar baserat på undersökningar med datortomografi och magnetisk resonanstomografi av mediala nyckelbensepifysen.

    Bakgrund: Barn och ungdomar som flytt från krig saknar ofta offentliga handlingar. Dessa individer kan därför erbjudas en medicinsk åldersbedömning. I asylprocesser spelar åldern 18 år en stor roll och vid åldersbedömningar av dessa individer rekommenderar Study Group on Forensic Age Diagnostics en röntgenundersökning av nyckelbenen.

    Syfte: Syftet med denna litteraturstudie var att beskriva åldersvariationerna inom nyckelbenets olika utvecklingssteg vid undersökning med datortomografi respektive magnetisk resonanstomografi vid åldersbedömmande processer.

    Metod: En litteraturstudie genomfördes med 11 artiklar med kvantitativ ansats. Artiklarnas resultat granskades, analyserades och sammanställdes.

    Resultat: Åldersvariationerna inom utvecklingsstegen varierade i större och mindre grad dock tycktes det inte föreligga några större skillnader mellan modaliteterna. Överlappen mellan utvecklingsstegen tenderade att vara större för MRT än för DT. Resultaten visade ett positivt samband mellan kronologisk ålder och utvecklingsstegen samt att medelåldern generellt ökade med utvecklingsstegen.

    Konklusion: Det förekom stora åldersvariationer inom utvecklingsstegen samt stora överlapp mellan utvecklingsstegen vilket indikerade på precisionsproblem och osäkerheter, för både DT och MRT. Sett till den kliniska tillgängligheten, kostnader, tid, smidighet och upplevelser för patienten tyder DT på att vara en bättre metod än MRT.

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