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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 universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin.
    PHASE 2 OPEN-LABEL EXTENSION (OLE) STUDY OF PATISIRAN, AN INVESTIGATIONAL RNA INTERFERENCE (RNAI) THERAPEUTIC FOR THE TREATMENT OF HEREDITARY ATTR AMYLOIDOSIS WITH POLYNEUROPATHY2017Ingår i: Value in Health, ISSN 1098-3015, E-ISSN 1524-4733, Vol. 20, nr 5, s. A211-A212Artikel i tidskrift (Övrigt vetenskapligt)
  • 2.
    Adjeiwaah, Mary
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Quality assurance for magnetic resonance imaging (MRI) in radiotherapy2017Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    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 universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Bylund, Mikael
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Lundman, Josef A.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Söderström, Karin
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Zackrisson, Björn
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Jonsson, Joakim H.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Garpebring, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Nyholm, Tufve
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Dosimetric Impact of MRI Distortions: A Study on Head and Neck Cancers2019Ingår i: International Journal of Radiation Oncology, Biology, Physics, ISSN 0360-3016, E-ISSN 1879-355X, Vol. 103, nr 4, s. 994-1003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose: To evaluate the effect of magnetic resonance (MR) imaging (MRI) geometric distortions on head and neck radiation therapy treatment planning (RTP) for an MRI-only RTP. We also assessed the potential benefits of patient-specific shimming to reduce the magnitude of MR distortions for a 3-T scanner.

    Methods and Materials: Using an in-house Matlab algorithm, shimming within entire imaging volumes and user-defined regions of interest were simulated. We deformed 21 patient computed tomography (CT) images with MR distortion fields (gradient nonlinearity and patient-induced susceptibility effects) to create distorted CT (dCT) images using bandwidths of 122 and 488 Hz/mm at 3 T. Field parameters from volumetric modulated arc therapy plans initially optimized on dCT data sets were transferred to CT data to compute a new plan. Both plans were compared to determine the impact of distortions on dose distributions.

    Results: Shimming across entire patient volumes decreased the percentage of voxels with distortions of more than 2 mm from 15.4% to 2.0%. Using the user-defined region of interest (ROI) shimming strategy, (here the Planning target volume (PTV) was the chosen ROI volume) led to increased geometric for volumes outside the PTV, as such voxels within the spinal cord with geometric shifts above 2 mm increased from 11.5% to 32.3%. The worst phantom-measured residual system distortions after 3-dimensional gradient nonlinearity correction within a radial distance of 200 mm from the isocenter was 2.17 mm. For all patients, voxels with distortion shifts of more than 2 mm resulting from patient-induced susceptibility effects were 15.4% and 0.0% using bandwidths of 122 Hz/mm and 488 Hz/mm at 3 T. Dose differences between dCT and CT treatment plans in D-50 at the planning target volume were 0.4% +/- 0.6% and 0.3% +/- 0.5% at 122 and 488 Hz/mm, respectively.

    Conclusions: The overall effect of MRI geometric distortions on data used for RTP was minimal. Shimming over entire imaging volumes decreased distortions, but user-defined subvolume shimming introduced significant errors in nearby organs and should probably be avoided.

  • 4.
    Adjeiwaah, Mary
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Bylund, Mikael
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Lundman, Josef A.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Thellenberg Karlsson, Camilla
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Jonsson, Joakim H.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Nyholm, Tufve
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. 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 cancer2018Ingår i: International Journal of Radiation Oncology, Biology, Physics, ISSN 0360-3016, E-ISSN 1879-355X, Vol. 100, nr 2, s. 317-324Artikel i tidskrift (Refereegranskat)
    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%.

  • 5.
    Ahlgren, Ulf
    Umeå universitet, Medicinska fakulteten, Umeå centrum för molekylär medicin (UCMM).
    Exploring the pancreas with optical projection tomography2012Ingår i: Imaging in Medicine, ISSN 1755-5191, Vol. 4, nr 1, s. 5-7Artikel i tidskrift (Refereegranskat)
  • 6.
    Akhtari, Mohammad Mehdi
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik. Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    3D Structural similarity check between CT and SCT2014Självständigt arbete på avancerad nivå (masterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    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.

  • 7. Akram, Harith
    et al.
    Hariz, Marwan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Zrinzo, Ludvic
    Connectivity derived thalamic segmentation: Separating myth from reality2019Ingår i: NeuroImage: Clinical, ISSN 0353-8842, E-ISSN 2213-1582, Vol. 22, artikel-id UNSP 101758Artikel i tidskrift (Refereegranskat)
  • 8.
    Al-Amiry, Bariq
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap.
    Does body mass index affect restoration of femoral offset and leg length and cup positioning after total hip arthroplasty?: A prospective radiological cohort studyIngår i: Artikel i tidskrift (Övrigt vetenskapligt)
  • 9.
    Andersson, Jonas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Norrlands universitetssjukhus.
    Fysik och teknik: konventionell planar röntgen2013Ingår i: Nuklearmedicin / [ed] Sven-Ola Hietala, Katrine Åhlström Riklund, Lund: Studentlitteratur AB, 2013, 2, s. 40-46Kapitel i bok, del av antologi (Övrigt vetenskapligt)
  • 10.
    Andersson, Jonas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Ion recombination in liquid ionization chambers: development of an experimental method to quantify general recombination2013Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

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

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

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

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

  • 11.
    Andersson, Jonas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    TG246 On Patient Dose From Diagnostic Radiation: Acceptance Testing and Dose Measurements with CT2014Ingår i: 56th AAPM Annual Meeting and Exhibition 2014, Austin, TX, USA, July 20-24 (2014), 2014Konferensbidrag (Refereegranskat)
    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.

  • 12.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Kaiser, Franz-Joachim
    Gómez, Faustino
    Jäkel, Oliver
    Pardo-Montero, Juan
    Tölli, Heikki
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    A comparison of different experimental methods for general recombination correction for liquid ionization chambers2012Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 57, nr 21, s. 7161-7175Artikel i tidskrift (Refereegranskat)
    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.

  • 13.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Tölli, Heikki
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Application of the two-dose-rate method for general recombination correction for liquid ionization chambers in continuous beams2011Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 56, nr 2, s. 299-314Artikel i tidskrift (Refereegranskat)
    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.

  • 14.
    Andersson, Jonas
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Tölli, Heikki
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Modeling ion recombination in liquid ionization chambers: Improvement and analysis of the two-dose-rate method2017Ingår i: Medical physics (Lancaster), ISSN 0094-2405, Vol. 44, nr 11, s. 5977-5987Artikel i tidskrift (Refereegranskat)
    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.

  • 15.
    Andersson, Kennet
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Suhr, Ole B.
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin.
    Faes, Luca
    Wiklund, Urban
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Directed coherence analysis in patients with severe autonomic dysfunction2014Ingår i: 2014 8th conference of the European Study Group on Cardiovascular Oscillations (ESGCO), IEEE conference proceedings, 2014, s. 167-168Konferensbidrag (Refereegranskat)
    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.

  • 16.
    Andersson, Kristina
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Evaluation of uncertainties in sub-volume based image registration: master of science thesis in medical radiation physics2010Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    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.  

  • 17. Andersson, M.
    et al.
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Minarik, D.
    Mattsson, S.
    Leide-Svegborn, S.
    Absorbed dose to the urinary bladder wall for different radiopharmaceuticals using dynamic S-values2013Ingår i: European Journal of Nuclear Medicine and Molecular Imaging, ISSN 1619-7070, E-ISSN 1619-7089, Vol. 40, nr Supplement 2, s. S161-S161Artikel i tidskrift (Övrigt vetenskapligt)
  • 18. Andersson, M.
    et al.
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Minarik, D.
    Mattsson, S.
    Leide-Svegborn, S.
    An internal radiation dosimetry computer program, IDAC 2.0, for estimation of patient doses from radiopharmaceuticals2014Ingår i: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 162, nr 3, s. 299-305Artikel i tidskrift (Refereegranskat)
    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.

  • 19. Andersson, M.
    et al.
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Minarik, D.
    Mattsson, S.
    Leide-Svegborn, S.
    IDAC2.0 a new generation of internal dosimetric calculations for diagnostic examinations in nuclear medicine using the adult ICRP/ICRU reference computational voxel phantoms2013Ingår i: European Journal of Nuclear Medicine and Molecular Imaging, ISSN 1619-7070, E-ISSN 1619-7089, Vol. 40, nr Supplement 2, s. S175-S176Artikel i tidskrift (Övrigt vetenskapligt)
  • 20. Andersson, Martin
    et al.
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Eckerman, Keith
    Mattsson, Sören
    IDAC-Dose 2.1, an internal dosimetry program for diagnostic nuclear medicine based on the ICRP adult reference voxel phantoms2017Ingår i: EJNMMI Research, ISSN 2191-219X, E-ISSN 2191-219X, Vol. 7, artikel-id 88Artikel i tidskrift (Refereegranskat)
    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.

  • 21. Andersson, Martin
    et al.
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Mattsson, Sören
    Minarik, David
    Leide-Svegborn, Sigrid
    Organ doses and effective dose for five pet radiopharmaceuticals2016Ingår i: Radiation Protection Dosimetry, ISSN 0144-8420, E-ISSN 1742-3406, Vol. 169, nr 1-4, s. 253-258Artikel i tidskrift (Refereegranskat)
    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.

  • 22.
    Andersson, Martin
    et al.
    Medical Radiation Physics, Department of Clinical Sciences Malmö, Lund University, Skåne University Hospital, Malmö, Sweden .
    Minarik, David
    Medical Radiation Physics, Department of Clinical Sciences Malmö, Lund University, Skåne University Hospital, Malmö, Sweden .
    Johansson, Lennart
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Mattsson, Soren
    Medical Radiation Physics, Department of Clinical Sciences Malmö, Lund University, Skåne University Hospital, Malmö, Sweden .
    Leide-Svegborn, Sigrid
    Medical Radiation Physics, Department of Clinical Sciences Malmö, Lund University, Skåne University Hospital, Malmö, Sweden .
    Improved estimates of the radiation absorbed dose to the urinary bladder wall2014Ingår i: Physics in Medicine and Biology, ISSN 0031-9155, E-ISSN 1361-6560, Vol. 59, nr 9, s. 2173-2182Artikel i tidskrift (Refereegranskat)
    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.

  • 23.
    Andersson, Nina
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Malm, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Neurologi.
    Wiklund, Urban
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Eklund, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Adaptive method for assessment of cerebrospinal fluid outflow conductance.2007Ingår i: Medical and Biological Engineering and Computing, ISSN 0140-0118, E-ISSN 1741-0444, Vol. 45, nr 4, s. 337-343Artikel i tidskrift (Refereegranskat)
    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.

  • 24.
    Arteaga-Marrero, Natalia
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. Department of Physics and Technology, University of Bergen, Bergen, Norway.
    Mainou-Gomez, Jose F.
    Rygh, Cecilie Brekke
    Lutay, Nataliya
    Roehrich, Dieter
    Reed, Rolf K.
    Olsen, Dag R.
    Radiation treatment monitoring with DCE-US in CWR22 prostate tumor xenografts2019Ingår i: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 60, nr 6, s. 788-797Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Background: Longitudinal monitoring of potential radiotherapy treatment effects can be determined by dynamic contrast-enhanced ultrasound (DCE-US).

    Purpose: To assess functional parameters by means of DCE-US in a murine subcutaneous model of human prostate cancer, and their relationship to dose deposition and time-frame after treatment. A special focus has been placed to evaluate the vascular heterogeneity of the tumor and on the most suitable data analysis approach that reflects this heterogeneity.

    Material and Methods: In vivo DCE-US was acquired 24 h and 48 h after radiation treatment with a single dose of 7.5 Gy and 10 Gy, respectively. Tumor vasculature was characterized pixelwise using the Brix pharmacokinetic analysis of the time-intensity curves.

    Results: Longitudinal changes were detected (P < 0.001) at 24 h and 48 h after treatment. At 48 h, the eliminating rate constant of the contrast agent from the plasma, kel, was correlated (P ≤ 0.05) positively with microvessel density (MVD; rτ = 0.7) and negatively with necrosis (rτ = –0.6) for the treated group. Furthermore, Akep, a parameter related to transcapillary transport properties, was also correlated to MVD (rτ = 0.6, P ≤ 0.05).

    Conclusion: DCE-US has been shown to detect vascular changes at a very early stage after radiotherapy, which is a great advantage since DCE-US is non-invasive, available at most hospitals, and is low in cost compared to other techniques used in clinical practice.

  • 25.
    Arvidsson, Peder
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik. Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för fysik.
    Implementation and Evaluation of Volumetric Modulated Arc Therapy at the Radiation Therapy Department at The University Hospital of Umeå.2011Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 26.
    Axelsson, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    PET/MR ur fysikerns perspektiv2015Konferensbidrag (Övrigt vetenskapligt)
  • 27. 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 universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    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, Germany2018Ingår i: Molecular Imaging and Biology, ISSN 1536-1632, E-ISSN 1860-2002, Vol. 20, nr 1, s. 4-20Artikel, forskningsöversikt (Refereegranskat)
    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.

  • 28. 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 universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    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, Germany2016Ingår i: Molecular Imaging and Biology, ISSN 1536-1632, E-ISSN 1860-2002, Vol. 18, nr 5, s. 637-650Artikel i tidskrift (Refereegranskat)
    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.

  • 29. Baste, Valborg
    et al.
    Hansson Mild, Kjell
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Moen, Bente E
    Radiofrequency exposure on fast patrol boats in the Royal Norwegian Navy-an approach to a dose assessment.2010Ingår i: Bioelectromagnetics, ISSN 0197-8462, E-ISSN 1521-186X, Vol. 31, nr 5, s. 350-360Artikel i tidskrift (Refereegranskat)
    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.

  • 30.
    Bayisa, Fekadu L.
    et al.
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Liu, Xijia
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Garpebring, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Yu, Jun
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Computed Tomography Image Estimation by Statistical Learning MethodsManuskript (preprint) (Övrigt vetenskapligt)
    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.

  • 31.
    Bayisa, Fekadu Lemessa
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Statistical methods in medical image estimation and sparse signal recovery2018Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Denna avhandling presenterar arbete kring metoder för skattning av datortomografibilder (CT) från magnetiska resonanstomografibilder (MR) för ett antal diagnostiska och terapeutiska arbetsflöden. Studien demonstrerar även en metod för gles signalrekonstruktion, vilket är en mellanliggande metod för rekonstruktion av MR-bilder. Avhandlingen består av fyra artiklar. De tre första artiklarna handlar om att utveckla statistiska metoder för uppskattning av CT-bilder från MR-bilder. Här formuleras rumsliga och icke-rumsliga modeller för skattning av CT-bilder från MR-bilder, där de rumsliga modellerna inkluderar dolda Markov-modeller (HMM) och dolda Markov-slumpfältmodeller (HMRF), medan de icke-rumsliga modellerna består av Gaussiska mix-modeller (GMM) och skeva Gaussiska mixmodeller (SGMM). De statistiska modellerna skattas via en maximum-likelihoodansats, där EM-algoritmen används för GMM och SGMM, EM-gradientalgoritmen för HMRF samt Baum-Welch-algoritmen för HMM. Vi har även undersökt CTbildskattning med hjälp av GMM och övervakade statistiska inlärningsmetoder. Modellernas prestanda har utvärderats med hjälp av korsvalidering på faktiska data. Genom att jämföra prestandan hos modellernas CT-bildskattningar har vi observerat att GMM kombinerat med övervakad statistisk inlärning har den bästa prestandan, i synnerhet ifråga om benvävnad. Den fjärde artikeln behandlar en gles modellering inom signalrekonstruktion. Med hjälp av så kallade ”spike and slab priors” för signalen formulerade vi ett glest signalrekonstruktionsproblem och utvecklade en adaptiv algoritm för gles signalrekonstruktion. Den utvecklade algoritmen har bättre prestanda än den nyligen föreslagna iterativ konvex förfining (ICR)-algoritmen. De metoder som introducerats i detta arbete är bidrag till litteraturen inom så kallade ”lattice-processer” och signalbehandling. Resultaten levererar ett bidrag till forskningen kring ersättandet av CT-bilder med syntetiska eller pseudo-CTbilder, samt till effektiv gles signalrekonstruktion.

  • 32. Becker, Nina
    et al.
    Kalpouzos, Grégoria
    Salami, Alireza
    Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Umeå universitet, Medicinska fakulteten, Wallenberg centrum för molekylär medicin vid Umeå universitet (WCMM). Aging Research Center, Karolinska Institutet and Stockholm University, Stockholm, Sweden.
    Laukka, Erika J.
    Brehmer, Yvonne
    Structure-function associations of successful associative encoding2019Ingår i: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 201, artikel-id 116020Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Functional magnetic resonance imaging (MRI) studies have demonstrated a critical role of hippocampus and inferior frontal gyrus (IFG) in associative memory. Similarly, evidence from structural MRI studies suggests a relationship between gray-matter volume in these regions and associative memory. However, how brain volume and activity relate to each other during associative-memory formation remains unclear. Here, we used joint independent component analysis (jICA) to examine how gray-matter volume and brain activity would be associated during associative encoding, especially in medial-temporal lobe (MTL) and IFG. T1-weighted images were collected from 27 young adults, and functional MRI was employed during intentional encoding of object pairs. A subsequent recognition task tested participants' memory performance. Unimodal analyses using voxel-based morphometry revealed that participants with better associative memory showed larger gray-matter volume in left anterior hippocampus. Results from the jICA revealed one component that comprised a covariance pattern between gray-matter volume in anterior and posterior MTL and encoding-related activity in IFG. Our findings suggest that gray matter within the MTL modulates distally distinct parts of the associative encoding circuit, and extend previous studies that demonstrated MTL-IFG functional connectivity during associative memory tasks.

  • 33. Berglund, Johan
    et al.
    Skorpil, Mikael
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Multi-scale graph-cut algorithm for efficient water-fat separation2017Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 78, nr 3, s. 941-949Artikel i tidskrift (Refereegranskat)
    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.

  • 34.
    Berthon, Beatrice
    et al.
    Wales Research and Diagnostic PET Imaging Centre, Cardiff University, Cardiff, UK.
    Häggström, Ida
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    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 universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    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 methods2015Ingår i: Physica medica (Testo stampato), ISSN 1120-1797, E-ISSN 1724-191X, Vol. 31, nr 8, s. 969-980Artikel i tidskrift (Refereegranskat)
    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.

  • 35.
    Boman, Kurt
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin. Research Unit, Department of Medicine, Skellefteå.
    Olofsson, Mona
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin. Research Unit, Department of Medicine, Skellefteå.
    Berggren, Peter
    Umeå universitet, Medicinska fakulteten, Institutionen för folkhälsa och klinisk medicin, Medicin. 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 Approach2014Ingår i: JACC Cardiovascular Imaging, ISSN 1936-878X, E-ISSN 1876-7591, Vol. 7, nr 8, s. 799-803Artikel i tidskrift (Refereegranskat)
    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. 

  • 36.
    Boraxbekk, Carl-Johan
    et al.
    Umeå universitet, Samhällsvetenskapliga fakulteten, Enheten för demografi och åldrandeforskning (CEDAR). Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI).
    Salami, Alireza
    Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Aging Research Center (ARC), Karolinska Institute, Stockholm, Sweden.
    Wåhlin, Anders
    Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Nyberg, Lars
    Umeå universitet, Medicinska fakulteten, Umeå centrum för funktionell hjärnavbildning (UFBI). Umeå universitet, Medicinska fakulteten, Institutionen för integrativ medicinsk biologi (IMB), Fysiologi. Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    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 approach2016Ingår i: NeuroImage, ISSN 1053-8119, E-ISSN 1095-9572, Vol. 131, s. 133-141Artikel i tidskrift (Refereegranskat)
    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.

  • 37.
    Boson, Jonas
    Umeå universitet, Medicinsk fakultet, Strålningsvetenskaper, Radiofysik.
    Improving accuracy of in situ gamma-ray spectrometry2008Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 38.
    Brandel, Jens
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Evaluation of 18F-fluorothymidine PET/MRI imaging in treated glioblastoma patients2018Självständigt arbete på grundnivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
  • 39. Brown, J
    et al.
    Jacobs, R
    Levring Jäghagen, Eva
    Umeå universitet, Medicinska fakulteten, Institutionen för odontologi, Tandläkarutbildning.
    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 Radiology2014Ingår i: Dento-Maxillo-Facial Radiology, ISSN 0250-832X, E-ISSN 1476-542X, Vol. 43, nr 1, artikel-id 20130291Artikel i tidskrift (Refereegranskat)
    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.

  • 40.
    Bryndahl, Fredrik
    Umeå universitet, Medicinska fakulteten, Institutionen för odontologi, Oral diagnostisk radiologi.
    Temporomandibular joint disk displacement and subsequent adverse mandibular growth: a radiographic, histologic and biomolecular experimental study2008Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 41.
    Bryndahl, Fredrik
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för odontologi, Oral diagnostisk radiologi.
    Warfvinge, G
    Eriksson, L
    Isberg, A
    Cartilage changes link retrognathic mandibular growth to TMJ disc displacement in a rabbit model2011Ingår i: International Journal of Oral and Maxillofacial Surgery, ISSN 0901-5027, E-ISSN 1399-0020, Vol. 40, nr 6, s. 621-627Artikel i tidskrift (Refereegranskat)
    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.

  • 42.
    Brynolfsson, Patrik
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Applications of statistical methods in quantitative magnetic resonance imaging2017Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    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.

  • 43.
    Brynolfsson, Patrik
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Axelsson, Jan
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Holmberg, August
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Jonsson, Joakim
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Goldhaber, David
    Jian, Yiqiang
    Illerstam, Fredrik
    Engström, Mathias
    Zackrisson, Björn
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Nyholm, Tufve
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Technical note: adapting a GE SIGNA PET/MR scanner for radiotherapy2018Ingår i: Medical physics (Lancaster), ISSN 0094-2405, Vol. 45, nr 8, s. 3546-3550Artikel i tidskrift (Refereegranskat)
    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.

  • 44.
    Brynolfsson, Patrik
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Nilsson, David
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Torheim, Turid
    Asklund, Thomas
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Onkologi.
    Thellenberg Karlsson, Camilla
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Onkologi.
    Trygg, Johan
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Kemiska institutionen.
    Nyholm, Tufve
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Radiofysik.
    Garpebring, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Haralick texture features from apparent diffusion coefficient (ADC) MRI images depend on imaging and pre-processing parameters2017Ingår i: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 7, artikel-id 4041Artikel i tidskrift (Refereegranskat)
    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.

  • 45.
    Brynolfsson, Patrik
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Yu, Jun
    Umeå universitet, Teknisk-naturvetenskapliga fakulteten, Institutionen för matematik och matematisk statistik.
    Wirestam, Ronnie
    Lund University.
    Karlsson, Mikael
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Garpebring, Anders
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper. 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 modeling2015Ingår i: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 74, nr 4, s. 1156-1164Artikel i tidskrift (Refereegranskat)
    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.

  • 46.
    Brändström, Helge
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Anestesiologi och intensivvård.
    Sundelin, Anna
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Anestesiologi och intensivvård.
    Hoseason, Daniela
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Anestesiologi och intensivvård.
    Sundström, Nina
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper.
    Birgander, Richard
    Umeå universitet, Medicinska fakulteten, Institutionen för strålningsvetenskaper, Diagnostisk radiologi.
    Johansson, Göran
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Anestesiologi och intensivvård.
    Winsö, Ola
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Anestesiologi och intensivvård.
    Koskinen, Lars-Owe
    Umeå universitet, Medicinska fakulteten, Institutionen för farmakologi och klinisk neurovetenskap, Klinisk neurovetenskap.
    Haney, Michael
    Umeå universitet, Medicinska fakulteten, Institutionen för kirurgisk och perioperativ vetenskap, Anestesiologi och intensivvård.
    Risk for intracranial pressure increase related to enclosed air in post-craniotomy patients during air ambulance transport: a retrospective cohort study with simulation2017Ingår i: Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine, ISSN 1757-7241, E-ISSN 1757-7241, Vol. 25, artikel-id 50Artikel i tidskrift (Refereegranskat)
    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.

  • 47.
    Byenfeldt, Marie
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    Ultraljuds-baserad shear wave elastografi- En kvantitativ studie av faktorer som kan påverka tillförlitligheten i mätresultatet vid gradering av leverfibros2016Självständigt arbete på avancerad nivå (magisterexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Syftet: Syftet med studien var att undersöka olika faktorer som kan påverka tillförlitligheten av mätresultat med ultraljuds-baserad shear wave elastografi metoden, vid gradering av leverfibros hos patienter med kronisk leversjukdom.

     

    Bakgrund: Vid kroniska leversjukdomar kan leverfibros utvecklas och i värsta fall även leda till levercancer.  Idag finns kostnadskrävande antiviralbehandling och  bland de non-invasiva metoderna som utvecklats för att gradera leverfibros finns ultraljuds-baserad share wave elastografi. Den här nya metoden infördes 2014 på vid ultraljudssektionen, röntgenavdelningen på Östersunds Sjukhus, och när mätresultatet och den kliniska bedömningen inte överensstämmer, skapas ett problemområde.

    Design: Studien har utförts som en deskriptiv kvantiativ studie med retrospektiv design på magisternivå inom huvudämnet radiografi vid Umeå universitet.

    Metod: Mätresultat från 132 individer, som undersökts med ultraljudsmaskin Philips iU22 och ElastPQ shear wave elastografi program, har analyserats. Mätresultaten har delats in efter kvartilsavståndet varmed en studiegrupp och en kontrollgrupp bildats. Logistisk regressionsanalys har använts för att undersöka olika faktorers samband till grupperna.

    Resultat: Följande variabler visade signifikant samband med mindre tillförlitligt mätresultat: ålder, aktuell sjukdoms duration, steatos, antiviral-och/eller kardiovaskulär medicinering, ASAT och ALAT samt uppmätt avstånd mellan probeyta och leverkapsel. Vid bivariat regressionsanalys erhölls följande signifikanta fynd: ålder (p=0,002), aktuell sjukdoms duration (p=0,039), steatos (p=0,001), antiviral- och/eller kardiovaskulärmedicinering (p=0,045), ASAT (p=0,001), ALAT (p=0,038) samt uppmätt avstånd mellan probe yta och leverkapsel (p=0,000). Vid multivariat regressionsanalys kvarstod följande signifikanta fynd: antiviral- och/eller kardiovaskulärmedicinering (p=0,049) samt ökat avstånd mellan probeyta och leverkapsel (p=0,003).

    Slutsats: Vid gradering av leverns fibrosgrad med ultraljuds-baserad shear wave elastografi av lever kan vid stort avstånd mellan probeyta och leverkapsel, enligt studiens huvudfynd, innebära mindre tillförlitligt mätresultat. Patienterna kan därför med fördel läggas i vänster sidoläge vid mätning, för att minska avståndet mellan probeytan och leverkapseln. Det finns behov av vidare forskning för variabler som påverkar mätresultatens tillförlitlighet samt vilken kvalitetsindikator som ska användas vid leverelastografi med ARFI teknik.

  • 48.
    Byenfeldt, Marie
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    Elvin, Anders
    Fransson, Per
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    Influence of Probe Pressure on Ultrasound-Based Shear Wave Elastography of the Liver Using Comb-Push 2-D Technology2019Ingår i: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 45, nr 2, s. 411-428Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It has been postulated that in the liver, applying increased probe pressure during ultrasound-based shear wave elastography (SWE) might lead to a false increase in the SWE result. We aimed to determine the influence of increased intercostal probe pressure when performing SWE of the liver. We also investigated the number of measurements required to achieve technically successful and reliable SWE examinations. This prospective, clinical study included 112 patients and 2240 SWE measurements of the liver. We applied probe pressure intercostally, to reduce the skin-to-liver capsule distance (SCD), which could stabilize the SWE signal and thus increase the number of technically successful measurements. We performed 10 measurements with maximum probe pressure and 10 with normal pressure in each patient. Thus, two analysis groups were compared for differences. Compared with normal pressure, maximum probe pressure significantly reduced the SCD (p < 0.001) and significantly increased the number of technically successful measurements from 981 to 1098, respectively (p < 0.001). The SWE results with normal and maximum probe pressure were 5.96 kPa (interquartile range: 2.41) and 5.45 kPa (interquartile range: 1.96), respectively (p < 0.001). In obese patients, a large SCD poses a diagnostic challenge for ultrasound SWE. We found that maximum intercostal probe pressure could reduce the SCD and increase the number of technically successful measurements, without falsely increasing the SWE result. Only three measurements were required to achieve technically successful and reliable SWE examinations.

  • 49.
    Byenfeldt, Marie
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    Elvin, Anders
    Fransson, Per
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    On patient related factors and their impact on ultrasound-based shear wave elastography of the liver2018Ingår i: Ultrasound in Medicine and Biology, ISSN 0301-5629, E-ISSN 1879-291X, Vol. 44, nr 8, s. 1606-1615Artikel i tidskrift (Refereegranskat)
    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 ) 

  • 50.
    Bylund, Sara
    et al.
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    Sundén, Anna
    Umeå universitet, Medicinska fakulteten, Institutionen för omvårdnad.
    Magnetfältstyrkans betydelse för personer med multipel skleros eller kliniskt isolerat syndrom: en litteraturstudie2016Självständigt arbete på grundnivå (yrkesexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    Titel: Magnetfältstyrkans betydelse för personer med multipel skleros eller kliniskt isolerat syndrom - en litteraturstudie Bakgrund: Multipel skleros (MS) är en demyeliniserande autoimmun sjukdom i centrala nervsystemet som debuterar främst hos unga vuxna. MS diagnostiseras utifrån kliniska och radiologiska fynd enligt McDonaldkriterierna där inga krav ställs på vilken fältstyrka som bör användas. Magnetkameror med högre fältstyrkor blir dock vanligare. Syfte: Att undersöka om högre fältstyrka (Tesla, T) gav bättre detektion av lesioner vid magnetresonanstomografiundersökningar av personer med multipel skleros eller kliniskt isolerat syndrom. Metod: I denna litteraturstudie gjordes sökningarna i databaserna PubMed, Web of Science och Scopus mellan 8 och 11 mars 2016. Tio kvantitativa artiklar kvalitetsgranskades och analyserades för att slutligen sammanställas i resultatet. Resultat: Resultatet presenteras under fyra huvudrubriker och totalt tolv underrubriker. Huvudrubrikerna är skillnad mellan fältstyrkor, fältstyrkor och anatomiska regioner, fältstyrkor och pulssekvenser samt artefakter och bildkvalitet. Konklusion: 3T och 7T är bättre än 1,5T och att 7T ofta är bättre än 3T på att detektera lesioner. Dock måste andra aspekter tas i beaktning då det är många parametrar som spelar in vid en magnetresonanstomografiundersökning. Ytterligare studier gällande bland annat optimering av pulssekvenser samt patienters upplevelser av ultrahöga fältstyrkor rekommenderas. 

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