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  • 1.
    Andersson, Karin M.
    et al.
    Department of Medical Physics, Faculty of Medicine and Health, Örebro University, Örebro, Sweden; Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Norrman, Eva
    Department of Medical Physics, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Geijer, Håkan
    Örebro University, School of Medical Sciences. Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Krauss, Wolfgang
    Örebro University, School of Medical Sciences. Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Cao, Yang
    Clinical Epidemiology and Biostatistics, School of Medical Sciences, Örebro University, Örebro, Sweden; Unit of Biostatistics, Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden.
    Jendeberg, Johan
    Örebro University, School of Medical Sciences. Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Geijer, Mats
    Department of Radiology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden; Department of Clinical Sciences, Lund University, Lund, Sweden.
    Lidén, Mats
    Örebro University, School of Medical Sciences. Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden .
    Visual grading evaluation of commercially available metal artefact reduction techniques in hip prosthesis computed tomography2016In: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 89, no 1063, article id 20150993Article in journal (Refereed)
    Abstract [en]

    Objectives: To evaluate metal artefact reduction (MAR) techniques from four computed tomography (CT) vendors in hip prosthesis imaging.

    Methods: Bilateral hip prosthesis phantom images, obtained by using MAR algorithms for single energy CT data or dual energy CT (DECT) data and by monoenergetic reconstructions of DECT data, were visually graded by five radiologists using ten image quality criteria. Comparisons between the MAR images and a reference image were performed for each scanner separately. Ordinal probit regression analysis was used.

    Results: The MAR algorithms in general improved the image quality based on the majority of the criteria (up to between 8/10 and 10/10) with a statistically improvement in overall image quality (P<0.001). However, degradation of image quality, such as new artefacts, was seen in some cases. A few monoenergetic reconstruction series improved the image quality (P<0.004) for one of the DECT scanners, but it was only improved for some of the criteria (up to 5/10). Monoenergetic reconstructions resulted in worse image quality for the majority of the criteria (up to 7/10) for the other DECT scanner.

    Conclusions: The MAR algorithms improved the image quality of the hip prosthesis CT images. However, since additional artefacts and degradation of image quality were seen in some cases, all algorithms should be carefully evaluated for every clinical situation. Monoenergetic reconstructions were in general concluded to be insufficient for reducing metal artifacts. Advances in knowledge: Qualitative evaluation of the usefulness of several MAR techniques from different vendors in CT imaging of hip prosthesis.

  • 2.
    Andersson, Karin M.
    et al.
    Örebro University, School of Medical Sciences.
    Norrman, Eva
    Örebro University, School of Medical Sciences. Örebro University Hospital.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Örebro University Hospital.
    Metal Artifacts in CT Imaging of Hip Prostheses: Evaluation of Metal Artifact Reduction Techniques Provided by Four Vendors2015Conference paper (Other academic)
    Abstract [en]

    PURPOSE: The aim of this study was to evaluate metal artifact reduction (MAR) techniques, provided by four vendors, in CT imaging of hip prostheses.

    METHOD AND MATERIALS: A water phantom containing hip prostheses mounted in calf bones was scanned with four CT scanners; Philips Ingenuity; Toshiba Aquilion ONE Vision edition; GE Discovery 750 HD and Siemens SOMATOM Definition Flash. An uncorrected (reference) image was obtained for every CT and compared with images acquired with the scanner specific MAR technique; either monoenergetic reconstruction of Dual Energy CT (DECT) data (GE and Siemens) or the use of a MAR algorithm software (Philips and Toshiba), or a combination of the two (GE). The MAR techniques were applied for varying tube voltage, kernel and reconstruction technique. The reference images were quantitatively compared to the MAR images by analyzing the noise and the CT number accuracy in region of interests (ROIs). Visual grading was performed by five radiologists based on ten image quality (IQ) criteria.

    RESULTS: The MAR algorithms implied a general noise reduction (by up to 77%) and improved IQ based on the majority of the visual grading criteria. The use of monoenergetic reconstructions of DECT data, without any MAR algorithm, did not decrease the noise in the ROIs to the same extent as the MAR algorithms (up to 41%) and did even increase the noise in one ROI. The visual grading evaluation showed that monoenergetic reconstructions in general degraded the IQ for one of the DECT scanners and improved the IQ for only a few of the criteria for the other DECT scanner.

    CONCLUSION: The quantitative analysis and the visual grading evaluation showed that the IQ was generally improved when the MAR algorithms were used. However, additional artifacts and degradation of the IQ were noted in some MAR image regions. The use of monoenergetic reconstruction was concluded to not reduce metal artifacts to the same extent as the MAR algorithms and to even degrade the IQ in several image regions.

    CLINICAL RELEVANCE/APPLICATION: This study points out advantages and potential risks of using MAR techniques in CT imaging of hip prostheses and will be useful for clinics when optimizing CT scan protocols and purchasing new CT systems.

  • 3.
    Andersson, Karin M.
    et al.
    Örebro University, School of Medical Sciences.
    Nowik, P.
    Department of Medical Physics, Karolinska University Hospital, Stockholm, Sweden.
    Persliden, Jan
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Medical Physics, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Thunberg, Per
    Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Norrman, Eva
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Medical Physics, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Metal artefact reduction in CT imaging of hip prostheses-an evaluation of commercial techniques provided by four vendors2015In: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 88, no 1052, article id 20140473Article in journal (Refereed)
    Abstract [en]

    Objective: The aim of this study was to evaluate commercial metal artefact reduction (MAR) techniques in X-ray CT imaging of hip prostheses.

    Methods: Monoenergetic reconstructions of dual-energy CT (DECT) data and several different MAR algorithms, combined with single-energy CT or DECT, were evaluated by imaging a bilateral hip prosthesis phantom. The MAR images were compared with uncorrected images based on CT number accuracy and noise in different regions of interest.

    Results: The three MAR algorithms studied implied a general noise reduction (up to 67%, 74% and 77%) and an improvement in CT number accuracy, both in regions close to the prostheses and between the two prostheses. The application of monoenergetic reconstruction, without any MAR algorithm, did not decrease the noise in the regions close to the prostheses to the same extent as did the MAR algorithms and even increased the noise in the region between the prostheses.

    Conclusion: The MAR algorithms evaluated generally improved CT number accuracy and substantially reduced the noise in the hip prostheses phantom images, both close to the prostheses and between the two prostheses. The study showed that the monoenergetic reconstructions evaluated did not sufficiently reduce the severe metal artefact caused by large orthopaedic implants.

    Advances in knowledge: This study evaluates several commercially available MAR techniques in CT imaging of large orthopaedic implants.

  • 4.
    Andersson, Karin M.
    et al.
    Örebro University, School of Medical Sciences. Department of Medical Physics, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Vallhagen Dahlgren, C.
    The Skandion clinic, Uppsala, Sweden.
    Reizenstein, J.
    Department of Oncology, Örebro University Hospital, Örebro, Sweden; , Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Ahnesjö, A.
    Medical Radiation Sciences, Department of Immunology-Genetics and Pathology, Uppsala University, Uppsala, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Department of Medical Physics , Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Impact of Metal Artifacts on Proton Therapy Treatment Planning Accuracy2017In: 56th Annual Meeting of the Particle Therapy Cooperative Group (PTCOG) 8-13 May 2017: Proceedings, The Particle Therapy Cooperative Group , 2017, Vol. 4, p. 68-68, article id 1Conference paper (Other academic)
    Abstract [en]

    Purpose: To evaluate for proton therapy treatment planning the feasibility of two commercial metal artifact reduction (MAR) algorithms in CT-imaging.

    Materials and Methods: A head phantom with removable dental fillings and a body phantom with a removable hip prosthesis were scanned to evaluate O-MAR (Philips) and iMAR (Siemens). Reference images (scans without metal) were acquired and subtracted from the uncorrected (no MAR) and MAR-images. CT number-differences were mapped to differences in stopping power ratios to water. In addition, proton treatment plans for a parotid, tonsil and prostate-target were optimized based on uncorrected and MAR images and recalculated on reference images. Beams were arranged to not traverse metal, enabling evaluation of metal artifact impact on target coverage.

    Results: MAR algorithms reduced the most extreme dental filling artifacts, but residual artifacts still remained. iMAR reduced hip prosthesis artifacts to large extent, while considerable artifacts still were present with O-MAR. For parotid and tonsil-plans, D98%to PTV was nearly intact in the reference recalculations for both uncorrected and MAR-based plans, with maximum-difference,0.3%. For uncorrected prostate plans, D98%decreased more than 4% in the reference recalculation. For the iMAR prostate plan, D98%was almost identical in the reference recalculation (97.5% versus 97.4%). A slight D98%-decrease was seen in the reference for the O-MAR based plan (96.8% versus 97.5%).

    Conclusion: Hip prosthesis artifacts reduced target coverage accuracy, but it was substantially improved with MAR algorithms. Dental filling artifacts were moderately reduced with MAR, but did not substantially affect target coverage

  • 5.
    Andersson, Karin M.
    et al.
    Örebro University, School of Medical Sciences.
    Vallhagen Dahlgren, Christina
    The Skandion Clinic, Uppsala, Sweden.
    Reizenstein, Johan
    Department of Oncology, Faculty of Medicine and Health, Örebro University, Sweden.
    Cao, Yang
    Örebro University, School of Medical Sciences. Örebro University Hospital. Unit of Biostatistics, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Ahnesjö, Anders
    Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences.
    CT image metal artifacts in proton radiotherapy treatment planning: evaluation of two commercial correction algorithmsManuscript (preprint) (Other academic)
  • 6.
    Andersson, Karin M.
    et al.
    Örebro University, School of Health Sciences. The Skandion Clinic, Uppsala, Sweden.
    Vallhagen Dahlgren, Christina
    The Skandion Clinic, Uppsala, Sweden.
    Reizenstein, Johan
    Department of Oncology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Cao, Yang
    Örebro University, School of Medical Sciences. Örebro University Hospital. Unit of Biostatistics, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
    Ahnesjö, Anders
    Medical Radiation Sciences, Department of Immunology, Genetics and Pathology, Uppsala University, Uppsala, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Department of Medical Physics.
    Evaluation of two commercial CT metal artifact reduction algorithms for use in proton radiotherapy treatment planning in the head and neck area2018In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 45, no 10, p. 4329-4344Article in journal (Refereed)
    Abstract [en]

    PURPOSE: To evaluate two commercial CT metal artifact reduction (MAR) algorithms for use in proton treatment planning in the head and neck (H&N) area.

    METHODS: An anthropomorphic head phantom with removable metallic implants (dental fillings or neck implant) was CT-scanned to evaluate the O-MAR (Philips) and the iMAR (Siemens) algorithms. Reference images were acquired without any metallic implants in place. Water equivalent thickness (WET) was calculated for different path directions and compared between image sets. Images were also evaluated for use in proton treatment planning for parotid, tonsil, tongue base, and neck node targets. The beams were arranged so as to not traverse any metal prior to the target, enabling evaluation of the impact on dose calculation accuracy from artifacts surrounding the metal volume. Plans were compared based on γ analysis (1 mm distance-to-agreement/1% difference in local dose) and dose volume histogram metrics for targets and organs at risk (OARs). Visual grading evaluation of 30 dental implant patient MAR images was performed by three radiation oncologists.

    RESULTS: In the dental fillings images, ΔWET along a low-density streak was reduced from -17.0 to -4.3 mm with O-MAR and from -16.1 mm to -2.3 mm with iMAR, while for other directions the deviations were increased or approximately unchanged when the MAR algorithms were used. For the neck implant images, ΔWET was generally reduced with MAR but residual deviations remained (of up to -2.3 mm with O-MAR and of up to -1.5 mm with iMAR). The γ analysis comparing proton dose distributions for uncorrected/MAR plans and corresponding reference plans showed passing rates >98% of the voxels for all phantom plans. However, substantial dose differences were seen in areas of most severe artifacts (γ passing rates of down to 89% for some cases). MAR reduced the deviations in some cases, but not for all plans. For a single patient case dosimetrically evaluated, minor dose differences were seen between the uncorrected and MAR plans (γ passing rate approximately 97%). The visual grading of patient images showed that MAR significantly improved image quality (P < 0.001).

    CONCLUSIONS: O-MAR and iMAR significantly improved image quality in terms of anatomical visualization for target and OAR delineation in dental implant patient images. WET calculations along several directions, all outside the metallic regions, showed that both uncorrected and MAR images contained metal artifacts which could potentially lead to unacceptable errors in proton treatment planning. ΔWET was reduced by MAR in some areas, while increased or unchanged deviations were seen for other path directions. The proton treatment plans created for the phantom images showed overall acceptable dose distributions differences when compared to the reference cases, both for the uncorrected and MAR images. However, substantial dose distribution differences in the areas of most severe artifacts were seen for some plans, which were reduced by MAR in some cases but not all. In conclusion, MAR could be beneficial to use for proton treatment planning; however, case-by-case evaluations of the metal artifact-degraded images are always recommended.

  • 7.
    Broxvall, Mathias
    et al.
    Örebro University, School of Science and Technology. Centre of Biomedical Engineering Research (MTFC), Örebro University Hospital, Örebro, Sweden.
    Emilsson, Kent
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Medical Physics and Centre of Biomedical Engineering Research (MTFC), Örebro University Hospital, Örebro, Sweden.
    Fast GPU based adaptive filtering of 4D echocardiography2012In: IEEE Transactions on Medical Imaging, ISSN 0278-0062, E-ISSN 1558-254X, Vol. 31, no 6, p. 1165-1172, article id 6099625Article in journal (Refereed)
    Abstract [en]

    Time resolved three-dimensional (3D) echocardiography generates four-dimensional (3D+time) data sets that bring new possibilities in clinical practice. Image quality of four-dimensional (4D) echocardiography is however regarded as poorer compared to conventional echocardiography where time-resolved 2D imaging is used. Advanced image processing filtering methods can be used to achieve image improvements but to the cost of heavy data processing. The recent development of graphics processing unit (GPUs) enables highly parallel general purpose computations, that considerably reduces the computational time of advanced image filtering methods. In this study multidimensional adaptive filtering of 4D echocardiography was performed using GPUs. Filtering was done using multiple kernels implemented in OpenCL (open computing language) working on multiple subsets of the data. Our results show a substantial speed increase of up to 74 times, resulting in a total filtering time less than 30 s on a common desktop. This implies that advanced adaptive image processing can be accomplished in conjunction with a clinical examination. Since the presented GPU processor method scales linearly with the number of processing elements, we expect it to continue scaling with the expected future increases in number of processing elements. This should be contrasted with the increases in data set sizes in the near future following the further improvements in ultrasound probes and measuring devices. It is concluded that GPUs facilitate the use of demanding adaptive image filtering techniques that in turn enhance 4D echocardiographic data sets. The presented general methodology of implementing parallelism using GPUs is also applicable for other medical modalities that generate multidimensional data.

  • 8.
    Dimitriou, Praxitelis
    et al.
    Department of Radiology, Örebro University Hospital , Örebro, Sweden.
    Kähäri, Anders
    Department of Clinical Physiology, Örebro University Hospital , Örebro, Sweden.
    Emilsson, Kent
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Clinical Physiology, Örebro University Hospital , Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden .
    Cardiovascular magnetic resonance imaging and transthoracic echocardiography in the assessment of stenotic aortic valve area: a comparative study2012In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 53, no 9, p. 995-1003Article in journal (Refereed)
    Abstract [en]

    Background: Magnetic resonance (MR) imaging and echocardiography both allow assessment of aortic valve stenosis. In MR the aortic valve area (AvA) is measured using planimetry while in transthoracic echocardiography (TTE) AvA is usually calculated by applying the continuity equation.

    Purpose: To compare the measured stenotic aortic valve areas using five different MR-acquisition alternatives with the corresponding area values calculated by TTE.

    Material and Methods: The aortic valve was imaged in 14 patients, with diagnosed aortic valve stenosis, using balanced steady state free precession (bSSFP) gradient echo (GE) and phase contrast imaging (PC). Three adjacent slices were planned to encompass the aortic valve and the aortic valve area was measured using planimetry. The two sets of complex valued images generated by the PC sequence formed three kinds of images that could be used for aortic valve area measurements: the magnitude image (PC/Mag), the modulus (PCA/M), and phase difference (PCA/P) between the two complex images, respectively. The valve area from TTE was calculated using the continuity equation. A cut-off of <1.0 cm(2) was used as a criteria for severe stenosis.

    Results: The mean area differences between the different MR acquisitions and TTE method were -0.05 ± 0.37 cm(2) (GE), -0.18 ± 0.46 cm(2) (bSSFP), 0.27 ± 0.43 cm(2) (PC/Mag), 0.15 ± 0.32 cm(2) (PCA/P), and 0.26 ± 0.27 cm(2) (PCA/M). The valve area was significantly overestimated using PCA/M that, in turn, implied a significant underestimation of the aortic valve stenosis severity compared to the assessments using TTE.

    Conclusion: The smallest area valve difference between TTE and an MR-acquisition alternative is obtained with gradient echo images. The use of PCA/M leads to significant differences in planimetry measurements of the aortic valve orifice and the gradation of the stenosis severity compared to TTE.

  • 9.
    Emilsson, Kent
    et al.
    Department of Clinical Physiology Karlskoga Hospital, Karlskoga, Sweden; Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Kähäri, Anders
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Bodin, Lennart
    Unit of Statistics Clinical Research Centre, Örebro University Hospital, Örebro, Sweden.
    Thunberg, Per
    Department of Biomedical Engineering Örebro University Hospital, Sweden.
    Comparison between angiographic right coronary artery motion and echocardiographic tricuspid annulus motion2004In: Scandinavian Cardiovascular Journal, ISSN 1401-7431, E-ISSN 1651-2006, Vol. 38, no 2, p. 85-92Article in journal (Refereed)
    Abstract [en]

    OBJECTIVE: To compare echocardiographic M-mode measurements of tricuspid annulus motion (TAM) with angiographic M-mode measurements of right coronary artery motion (RAM).

    DESIGN: Twenty-four patients were included and examined by echocardiography before the angiographic examination. The amplitudes and the velocities of TAM and the atrial contribution to the total amplitude of TAM were measured. The obtained values were compared with angiographic M-mode measurements of RAM at a proximal and a distal site of the second segment of the right coronary artery.

    RESULTS: There was no significant difference between several of the echocardiographic M-mode measurements of TAM and the angiographic M-mode measurements of RAM. However, the agreement was rather poor for some variables.

    CONCLUSION: Different parameters obtained from echocardiographic TAM are not interchangeable with values from angiographic RAM. If measurements of RAM are to be used in the assessment of right ventricular (RV) function further studies are needed to examine the correlation and agreement between RAM and different methods of measuring RV function, i.e. radionuclide angiography or magnetic resonance imaging.

  • 10.
    Emilsson, Kent
    et al.
    Department of Clinical Physiology Karlskoga Hospital, Karlskoga, Sweden; Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Kähäri, Anders
    Department of Radiology, Örebro University Hospital, Sweden.
    Bodin, Lennart
    Unit of Statistics Clinical Research Centre, Örebro University Hospital, ÖrebroSweden.
    Thunberg, Per
    Department of Biomedical Engineering Örebro University Hospital, Sweden.
    Outer contour and radial changes of the cardiac left ventricle: a magnetic resonance imaging study.2007In: Clinical Research in Cardiology, ISSN 1861-0684, E-ISSN 1861-0692, Vol. 96, no 5, p. 272-278Article in journal (Refereed)
    Abstract [en]

    Earlier studies have shown a +/-5% end-systolic decrease in the volume encompassed by the pericardial sack, manifesting as a radial diminution of the pericardial/epicardial contour of the left ventricle (LV). The aim of this study was to measure this radial displacement at different segmental levels of the LV and try to find out were it is as greatest and to calculate regional myocardial volume changes as a reference in healthy subjects. Eleven healthy subjects were examined by magnetic resonance imaging. Images were acquired using an ECG-triggered balanced fast field echo pulse sequence. The epicardial borders of the LV wall were delineated in end-diastole (ED) and end-systole (ES). Regional changes of the LV wall were analysed at three different levels (base, mid and apex) by dividing the myocardium into segments. The volumes obtained as the differences between the outer volume of the left ventricle at ED and ES at different slice levels were found to be greatest at the base of the heart and lowest at apex. The relative inward motion, that is the motion in short-axis direction of the epicardial border of the myocardium from ED to ES towards the centre of the LV, was greatest at the base and lowest at the mid level, something that has to be taken into account when measuring the LV during clinical exams. There was a significant difference in the relative inward motion between the segments at apex (p < 0.0001), mid (p = 0.036) and at base level (p < 0.0001).

  • 11.
    Funk, Eva
    et al.
    Örebro University, School of Health Sciences.
    Anderzen-Carlsson, Agneta
    Örebro University, School of Health Sciences. Örebro University Hospital.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Örebro University Hospital.
    Patient participation in MRI: patient experiences and image quality addressing breath-hold acquisitions2016In: ECR 2016 Book of Abstracts: B. Scientific Sessions and Clinical Trials in Radiology, Springer, 2016, p. S379-S379Conference paper (Other academic)
    Abstract [en]

    Purpose: To investigate two different breath-hold techniques, in terms of patient experience and image quality, and describe patients' experiences of magnetic resonance imaging.

    Methods and Materials: Thirty patients referred for an MRI of the liver conducted two separate breath-hold acquisitions in a randomised order, radiographer-directed and patient-initiated. Semi-structured interviews were held and analysed, and images were reviewed according to image quality.

    Results: The patients' general experiences of the MRI were that they felt a loss of control, and almost half of the patients seemed to prefer the self-initiated breath-hold. About 20 % of the patients preferred to hand over the responsibility to the radiographer, and for some the technique did not matter.The patients empathized in general the importance of achieving the best image quality. There were no significant differences identified between the two breath-hold techniques, in regards to image quality.

    Conclusion: The results show that self-initiated breath-hold acquisitions can be seen as a new alternative worth considering in clinical MRI since it is appreciated by the patients and give similar image quality compared to conventional breath-hold acquisitions. It also offers a possibility to achieve some control over the situation.

  • 12.
    Funk, Eva
    et al.
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden.
    Anderzén-Carlsson, Agneta
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Örebro University Hospital.
    Ingverud, Per
    Department of Diagnostic Radiology, Örebro University Hospital, Örebro, Sweden.
    Leander, Anna
    Department of Diagnostic Radiology, Örebro University Hospital, Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Örebro University Hospital.
    Patient-initiated breath-holds in MRI: an alternative for reducing respiratory artifacts and improving image quality2015In: Clinical imaging, ISSN 0899-7071, E-ISSN 1873-4499, Vol. 39, no 4, p. 619-622Article in journal (Refereed)
    Abstract [en]

    Purpose: To investigate MRI image quality using two different breath-hold techniques.

    Materials and methods: Thirty patients remitted for MRI, 2D-dual gradient echo acquisition of the liver conducted two separate breath-hold acquisitions in randomized order, operator-instructed and patient-initiated. The images were reviewed by two radiologists.

    Results: There were no significant differences in image quality between the two breath-hold techniques either in overall image quality or respiratory motion artifacts. This assessment was equal and concordant for both radiologists.

    Conclusion: In terms of image quality, the patient self-initiated breath-hold was shown to be an equal alternative to conventional breath-hold imaging.

  • 13.
    Funk, Eva
    et al.
    Örebro University, School of Health Sciences.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Örebro University Hospital.
    Anderzen-Carlsson, Agneta
    Örebro University, School of Health Sciences. Örebro University Hospital.
    Instructed or patient-initiated breath holds: what do the patients prefer?2013Conference paper (Other academic)
  • 14.
    Funk, Eva
    et al.
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden.
    Thunberg, Per
    Örebro University Hospital. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Anderzen-Carlsson, Agneta
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Örebro University Hospital. Centre for Health Care Sciences, Örebro University Hospital, Örebro, Sweden.
    Patients' experiences in magnetic resonance imaging (MRI) and their experiences of breath holding techniques2014In: Journal of Advanced Nursing, ISSN 0309-2402, E-ISSN 1365-2648, Vol. 70, no 8, p. 1880-1890Article in journal (Refereed)
    Abstract [en]

    Aims: To describe patients' experiences of magnetic resonance examination of the liver and their experiences of two breath-hold techniques.

    Background: Traditionally, patients are instructed by the radiographer to hold their breath during the examination. Alternatively, the patient can initiate the breath hold and start the image acquisition. Studies have revealed that magnetic resonance examinations can be experienced as challenging.

    Design: Descriptive qualitative.

    Methods: Semi-structured interviews were conducted with 28 patients and analysed using qualitative content analysis. The data collection was carried out from autumn 2010 to spring 2011.

    Results: The patients' main experience was that they felt loss of control. This was described in terms of feeling trapped, being lost in time and lost as a result of uncertainty. They had many questions in their mind that they did not ask. Although their statements often revealed no clear preference regarding the techniques, almost half of the patients seemed to prefer self-initiated breath hold, as it was easier and less stressful. Those who preferred the radiographer-directed technique felt more confident leaving the responsibility to the radiographer. In general, the patients understood the importance of achieving the best quality images possible.

    Conclusion: Magnetic resonance examination can be experienced as being in loss of control. Nevertheless, not all patients wished to actively participate in magnetic resonance examination. Some preferred to hand over the responsibility to the radiographer. These results can form a base for radiographers' reflections of how to individualize and optimize the nursing care of patients undergoing magnetic resonance examinations.

  • 15.
    Hellstrandh Jorstig, Stina
    et al.
    Örebro University, School of Medical Sciences.
    Waldenborg, Micael
    Örebro University, School of Health Sciences. Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Lidén, Mats
    Örebro University, School of Medical Sciences. Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Wodecki, Maciej
    Department of Clinical Physiology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Determination of Right Ventricular Volume by Combining Echocardiographic Distance Measurements2016In: Echocardiography, ISSN 0742-2822, E-ISSN 1540-8175, Vol. 33, no 6, p. 844-853Article in journal (Refereed)
    Abstract [en]

    Background: The position of the right ventricle (RV), often partly behind the sternum, implies difficulties to image the RV free wall using transthoracic echocardiography (TTE) and consequently limits the possibilities of stroke volume calculations. The aim of this study was to evaluate whether the volume of the right ventricle (RV) can be determined by combining TTE distance measurements that do not need the RV free wall to be fully visualized.

    Methods: The RV volume was approximated by an ellipsoid composed of three distances. Distance measurements, modeled RV stroke volumes (RVSV), and RV ejection fraction (RVEF) were compared to reference values obtained from cardiac magnetic resonance (CMR) imaging for 12 healthy volunteers.

    Results: Inter-modality comparisons showed that distance measurements were significantly underestimated in TTE compared to CMR. The modeled RV volumes using TTE distance measurements were underestimated compared to reference CMR volumes. There was, however, for TTE an agreement between modeled RVSV and left ventricular stroke volumes determined by biplane Simpson's rule. Similar agreement was shown between modeled RVSV based on CMR distance measurements and the CMR reference. Regarding RVEF, further studies including patients with a wider range of RVEF are needed to evaluate the method.

    Conclusion: In conclusion, the ellipsoid model of the RV provides good estimates of RVSVs, but volumes based on distance measurements from different modalities cannot be used interchangeably.

  • 16.
    Jorstig, Stina
    et al.
    Örebro University, School of Medical Sciences. Örebro University Hospital.
    Emilsson, Kent
    Department of Clinical Physiology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Waldenborg, Micael
    Örebro University, School of Health Sciences. Örebro University Hospital. Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Lidén, Mats
    Örebro University, School of Medical Sciences. Örebro University Hospital. Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Wodecki, M.
    Department of Clinical Physiology, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Örebro University Hospital. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Distance and area measurement of the right atrium and ventricle by echocardiography and cardiac magnetic resonance imaging: do we measure the same thing?2016Conference paper (Other academic)
    Abstract [en]

    Purpose: It has previously been shown that stroke volumes measured by transthoracic echocardiography (TTE) are underestimated, compared to cardiac magnetic resonance (CMR) imaging. The purpose of this study was to evaluate differences in distance and area measurements of the right atrium (RA) and the right ventricle (RV) by TTE and CMR.

    Methods: TTE examinations and CMR examinations were subsequently performed in 12 healthy volunteers. Three distances (RAL - right atrial length, RVIT3 - right ventricular inflow tract, RVLAX - right ventricular long axis) and one area (RVA - right ventricular area) were measured in TTE and CMR. Stroke volumes were also calculated using conventional methods available on each modality. Both intramodality and intermodality comparisons were performed based on measurements from three observers. One of the observers performed measurements in both TTE and CMR.

    Results: Intermodality comparisons showed that all distance and area measurements were significantly smaller using TTE (Table 1). Two of the measurements, RVIT3 and RVA, differed at about 50%. Calculated stroke volumes showed, consistent with previous results, that the TTE stroke volumes are substantially underestimated compared to CMR volumes. Intramodality variations of distance and area measurements were considerably smaller (Table 1).

    Conclusions: Our results show that RV distances and areas measured by TTE are smaller compared to CMR, probably due to differences in defining the endocardial borders. These differences subsequently result in smaller stroke volumes when using TTE. Caution should be taken when comparing distances, areas and volumes measured by TTE and CMR.

  • 17.
    Jorstig, Stina Hellstrand
    et al.
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Örebro University Hospital.
    Emilsson, Kent
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Lidén, Mats
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Örebro University Hospital. Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Thunberg, Per
    Örebro University Hospital. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    A study to determine the contribution to right ventricle stroke volume from pulmonary and tricuspid valve displacement volumes2015In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 35, no 4, p. 283-290Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Describing the systolic function of the right ventricle (RV) is a difficult task due to the complex shape and orientation of the RV. The purpose of this study was to investigate the extent to which the volumes encompassed by the pulmonary and tricuspid valve displacements contribute to the total right ventricle stroke volume (RVSV).

    METHODS: Twelve healthy volunteers were examined using cardiac magnetic resonance (CMR). Two series of time-resolved axially rotated MR images were acquired that encompassed the tricuspid valve and the pulmonary valve, respectively. The volume related to each valve movement, the tricuspid plane displacement (TPD) and the pulmonary plane displacement (PPD), was determined by delineation in diastole and systole. These volumes, RVSVTPD and RVSVPPD , were compared to the stroke volume to determine the contributions to the total stroke volume from the TPD and the PPD. The remaining volume of the total RVSV was referred to as RVSVOther . An initial in vitro study was carried out to validate the accuracy of volume measurements using axially rotated images.

    RESULTS: In vitro measurements indicated that the method for volumetric measurements using axially rotated images was a very accurate one, with a mean difference of 0·04 ± 0·10 ml. The in vivo measurements of RVSVTPD , RVSVPPD and RVSVOther were 45 ± 10%, 13 ± 2% and 42 ± 11%, respectively.

    CONCLUSIONS: Right ventricle stroke volume is determined by different individual volume changes as follows: RVSVTPD together with RVSVOther contributes to almost the entire RVSV in nearly equal proportions, while RVSVPPD contributes only a small amount and is approximately 30% of either RVSVTPD or RVSVOther.

  • 18.
    Jorstig, Stina Hellstrandh
    et al.
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden.
    Kähäri, Anders
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Emilsson, Kent
    Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Thunberg, Per
    Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Calculation of right ventricular stroke volume in short-axis MR images using the equation of the tricuspid plane2012In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 32, no 1, p. 5-11Article in journal (Refereed)
    Abstract [en]

    Short-axis (SA) magnetic resonance (MR) images are commonly planned parallel to the left atrioventricular valve. This orientation leads to oblique slices of the right ventricle (RV) with subsequent difficulties in separating the RV from the right atrium in the SA images. The insertion points of the tricuspid valve (TV) in the myocardium can be clearly identified in the right ventricle long axis (RVLA) and four-chamber (4CH) views. The purpose of this study was to develop a method that transfers the position of the tricuspid plane, as seen in the RVLA and 4CH views, to the SA images to facilitate the separation of the RV from the atrium. This methodology, termed Dissociating the Right Atrium from the Ventricle Volume (DRAW), was applied in 20 patients for calculations of right ventricular stroke volume (RVSV). The RVSV using DRAW (RVSVDRAW) was compared to left ventricular stroke volumes (LVSV) obtained from flow measurements in the ascending aorta. The RVSV was also determined using the conventional method (RVSVCONV) where the stack of images from the SA views are summarized, and a visual decision is made of the most basal slice to be included in the RV. The mean difference between RVSVDRAW and LVSV was 0.1 +/- 12.7 ml, while the mean difference between RVSVCONV and LVSV was 0.33 +/- 14.3 ml. Both the intra- and interobserver variability were small using the DRAW methodology, 0.6 +/- 3.5 and 1.7 +/- 2.7 ml, respectively. In conclusion, the DRAW method can be used to facilitate the separation of the RV and the atrium.

  • 19.
    Jorstig, Stina
    et al.
    Örebro University, School of Medical Sciences.
    Waldenborg, Micael
    School of Medical Sciences, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Lidén, Mats
    Örebro University, School of Medical Sciences.
    Thunberg, Per
    Örebro University, School of Medical Sciences.
    Right ventricular ejection fraction measurements using twodimensional echocardiographyManuscript (preprint) (Other academic)
  • 20.
    Jorstig, Stina
    et al.
    Örebro University, School of Medical Sciences. Örebro University Hospital. Faculty of Medicine and Health, Örebro University Biomedical Engineering, Örebro University Hospital, Örebro, Sweden.
    Waldenborg, Micael
    Örebro University Hospital. Örebro University, School of Medical Sciences. Faculty of Medicine and Health and Department of Clinical Physiology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Lidén, Mats
    Örebro University, School of Medical Sciences. Örebro University Hospital. Faculty of Medicine and Health and Department of Radiology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Örebro University Hospital. Faculty of Medicine and Health and Department of Medical Physics, Department of Medical Physics, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Right ventricular ejection fraction measurements using two-dimensional transthoracic echocardiography by applying an ellipsoid model2017In: Cardiovascular Ultrasound, ISSN 1476-7120, E-ISSN 1476-7120, Vol. 15, article id 4Article in journal (Refereed)
    Abstract [en]

    Background: There is today no established approach to estimate right ventricular ejection fraction (RVEF) using 2D transthoracic echocardiography (TTE). The aim of this study was to evaluate a new method for RVEF calculations using 2D TTE and compare the results with cardiac magnetic resonance (CMR) imaging and tricuspid annular plane systolic excursion (TAPSE).

    Methods: A total of 37 subjects, 25 retrospectively included patients and twelve healthy volunteers, were included to give a wide range of RVEF. The right ventricle (RV) was modeled as a part of an ellipsoid enabling calculation of the RV volume by combining three distance measurements. RVEF calculated according to the model, RVEFTTE, were compared with reference CMR-derived RVEF, RVEFCMR. Further, TAPSE was measured in the TTE images and the correlations were calculated between RVEFTTE, TAPSE and RVEFCMR.

    Results: The mean values were RVEFCMR = 43 +/- 12% (range 20-66%) and RVEFTTE = 50 +/- 9% (range 34-65%). There was a high correlation (r = 0.80, p < 0.001) between RVEFTTE and RVEFCMR. Bland-Altman analysis showed a mean difference between RVEFCMR and RVEFTTE of 6 percentage points (ppt) with limits of agreement from -11 to 23 ppt. The mean value for TAPSE was 19 +/- 5 mm and the correlation between TAPSE and RVEFCMR was moderate (r = 0.54, p < 0.001). The correlation between RVEFTTE and RVEFCMR was significantly higher (p < 0.05) than the correlation between TAPSE and RVEFCMR.

    Conclusions: The ellipsoid model shows promise for RVEF calculations using 2D TTE for a wide range of RVEF, providing RVEF estimates that were significantly better correlated to RVEF obtained from CMR compared to TAPSE.

  • 21.
    Karlsson, Leif
    et al.
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Örebro University Hospital. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Johansson, Bengt
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Örebro University Hospital. Department of Oncology, Örebro University Hospital, Örebro, Sweden.
    Persliden, Jan
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Örebro University Hospital. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    The impact of activating source dwell positions outside the CTV on the dose to treated normal tissue volumes in TRUS guided 3D conformal interstitial HDR brachytherapy of prostate cancer2014In: Journal of Contemporary Brachytherapy, ISSN 1689-832X, E-ISSN 2081-2841, Vol. 6, no 3, p. 282-288Article in journal (Refereed)
    Abstract [en]

    Purpose: Dose coverage is crucial for successful treatment in mono-brachytherapy. Since few and very high dose fractions are used, there is an important balance between dwell positioning outside the clinical target volume (CTV) and possible damage on adjacent normal tissue. The purpose of this study was to evaluate the possibility of having dwell positions close to the CTV surface, while maintaining an acceptable dose distribution, and to investigate the robustness in terms of known geometrical uncertainties of the implant.

    Material and methods: This study included 37 patients who had received brachytherapy for prostate cancer as a monotherapy with the following schedules: 2 x 14 Gy or 3 x 11 Gy, each fraction separated by two weeks. The source dwell positions were activated 5 mm outside CTV. New optimizations were simulated for dwell positions at 3, 2, 1, and 0 mm. Inverse and graphical optimization were applied according to the relative dose constraints: V-100 CTV >= 97%, D-max,D- urethra <= 110%, and D-10 rectal mucosa <= 65%. The V-100 normal tissue outside CTV was used to evaluate dose variations caused by different dwell positions. Prostate geometries and dose distributions for the different dwell positions outside the CTV were used to investigate the impact on the CTV dose distribution due to geometrical uncertainties.

    Results: Both V-100,V- CTV, and V-100,V- normal tissue decreased, 98.6% to 92.2%, and 17 cm(3) to 9.0 cm(3), for dwell activation from 5 rum to 0 mm. The evaluation of both simulated longitudinal geometrical uncertainties and different source dwell activations implied that V-100,V- CTV ranged from 98.6% to 86.3%.

    Conclusions: It is possible to reduce the V-100,V- normal tissue by decreasing the source dwell positions outside the CTV from 5 to 3 mm, while maintaining dose constraints. In combination with the estimated geometrical uncertainties, however, the source dwell positions need to be 5 mm from the surface in order to maintain a robust implant.

  • 22.
    Karlsson, Leif
    et al.
    School of Health and Medical Sciences, Örebro University, Örebro, Sweden; Department of Medical Physics, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Örebro University Hospital. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    With, Anders
    Department of Medical Physics, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Mordhorst, Louise Bohr
    Örebro University, School of Medical Sciences. Department of Oncology, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Persliden, Jan
    Örebro University Hospital. School of Health and Medical Sciences, Örebro University, Örebro, Sweden; Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    3D image-based adapted high-dose-rate brachytherapy in cervical cancer with and without interstitial needles: measurement of applicator shift between imaging and dose delivery2017In: Journal of Contemporary Brachytherapy, ISSN 1689-832X, E-ISSN 2081-2841, Vol. 9, no 1, p. 52-58Article in journal (Refereed)
    Abstract [en]

    Purpose: Using 3D image-guided adaptive brachytherapy for cervical cancer treatment, it often means that patients are transported and moved during the treatment procedure. The purpose of this study was to determine the intra-fractional longitudinal applicator shift in relation to the high risk clinical target volume (HR-CTV) by comparing geometries at imaging and dose delivery for patients with and without needles.

    Material and methods: Measurements were performed in 33 patients (71 fractions), where 25 fractions were without and 46 were with interstitial needles. Gold markers were placed in the lower part of the cervix as a surrogate for HR-CTV, enabling distance measurements between HR-CTV and the ring applicator. Shifts of the applicator relative to the markers were determined using planning computed tomography (CT) images used for planning, and the radiographs obtained at dose delivery. Differences in the physical D-90 for HR-CTV due to applicator shifts were simulated individually in the treatment planning system to provide the relative dose variation.

    Results: The maximum distances of the applicator shifts, in relation to the markers, were 3.6 mm (caudal), and-2.5 mm (cranial). There was a significant displacement of-0.7 mm (SD = 0.9 mm) without needles, while with needles there was no significant shift. The relative dose variation showed a significant increase in D-90 HR-CTV of 1.6% (SD = 2.6%) when not using needles, and no significant dose variation was found when using needles.

    Conclusions: The results from this study showed that there was a small longitudinal displacement of the ring applicator and a significant difference in displacement between using interstitial needles or not.

  • 23.
    Krauss, Wolfgang
    et al.
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden.
    Gunnarsson, Martin
    Örebro University, School of Medicine, Örebro University, Sweden.
    Andersson, Torbjorn
    Örebro University, School of Medicine, Örebro University, Sweden.
    Thunberg, Per
    Department of Medical Physics, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Accuracy and reproducibility of a quantitative magnetic resonance imaging method for concurrent measurements of tissue relaxation times and proton density2015In: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 33, no 5, p. 584-591Article in journal (Refereed)
    Abstract [en]

    Purpose: To evaluate the accuracy and reproducibility of a quantitative magnetic resonance (qMR) imaging method (QRAPMASTER) for simultaneous measurements of T1 and T2 relaxation times, and proton density (PD).

    Materials and Methods: Measurements of T1, T2, and PD with qMR were performed using phantoms with different relaxation times and concentrations of heavy water. Healthy volunteers were examined with different head coils. Regional measurements were performed in normal-appearing white and gray matter from the healthy control subjects, and in multiple sclerosis (MS) patients.

    Results: In phantom measurements, QRAPMASTER slightly underestimated T1, and T2 variations between repeated measurements were modest. PD was generally overestimated. The overall relative difference was 1.2 5.3% (T1), 6.6 1.9% (12), and 0.7 5.1% (PD). In healthy volunteers, there were no statistically significant differences of T1, T2 or PD using different head coils. Values of T1, T2, and PD obtained in healthy controls and MS patients were within reference ranges. However, significant differences were found in normal-appearing gray and white matter.

    Conclusion: QRAPMASTER can be considered a sufficiently accurate and reproducible method for use in clinical practice. Neuropathology in normal-appearing brain tissue may be revealed using this MR method, with putative implications for quantification of tissue damage in neurological diseases. (C) 2015 Elsevier Inc. All rights reserved.

  • 24.
    Krauss, Wolfgang
    et al.
    Örebro University, School of Medical Sciences. Department of Radiology, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Gunnarsson, Martin
    Örebro University, School of Medical Sciences. Department of Neurology and Neurophysiology, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Nilsson, Margareta
    Centre for Medical Imaging and Physiology, Skåne University Hospital, Lund, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Department of Medical Physics, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Conventional and synthetic MRI in multiple sclerosis: a comparative study2018In: European Radiology, ISSN 0938-7994, E-ISSN 1432-1084, Vol. 28, no 4, p. 1692-1700Article in journal (Refereed)
    Abstract [en]

    OBJECTIVES: To compare the assessment of patients with multiple sclerosis (MS) using synthetic and conventional MRI.

    MATERIALS AND METHODS: Synthetic and conventional axial images were prospectively acquired for 52 patients with diagnosed MS. Quantitative MRI (qMRI) was used for measuring proton density and relaxation times (T1, T2) and then, based on these parameters, synthetic T1W, T2W and FLAIR images were calculated. Image stacks were reviewed blindly, independently and in random order by two radiologists. The number and location for all lesions were documented and categorised. A combined report of lesion load and presence of contrast-enhancing lesions was compiled for each patient. Agreement was evaluated using kappa statistic.

    RESULTS: There was no significant difference in lesion detection using synthetic and conventional MRI in any anatomical region or for any of the three image types. Inter- and intra-observer agreements were mainly higher (p < 0.05) using conventional images but there was no significant difference in any specific region or for any image type. There was no significant difference in the outcome of the combined reports.

    CONCLUSION: Synthetic MR images show potential to be used in the assessment of MS dissemination in space (DIS) despite a slightly lower inter- and intra-observer agreement compared to conventional MRI.

    KEY POINTS:

    • Synthetic MR images may potentially be useful in the assessment of MS.

    • Examination times may be shortened.

    • Inter- and intra-observer agreement is generally higher using conventional MRI.

  • 25.
    Kähäri, Anders
    et al.
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Thunberg, Per
    Department of Biomedical Engineering, Örebro University Hospital, Örebro, Sweden.
    Emilsson, Kent
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Clinical Physiology, Karlskoga Hospital, Karlskoga, Sweden.
    Geijer, Håkan
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Andersson, Torbjörn
    Wandt, Birger
    Assessment of left ventricular function from M-mode measurement of circumflex artery motion recorded by coronary angiography.2003In: Scandinavian Cardiovascular Journal, ISSN 1401-7431, E-ISSN 1651-2006, Vol. 37, no 5, p. 259-265Article in journal (Refereed)
    Abstract [en]

    OBJECTIVE: To evaluate the usefulness of M-mode measurement of circumflex artery motion (CAM) for assessment of left ventricular (LV) function.

    DESIGN: Seventy-two patients referred for coronary angiography and LV angiography were included. Ejection fraction (EF) was calculated from LV angiography and systolic and diastolic parameters of CAM were measured by M-mode from coronary angiography. Twenty-three patients, examined by echocardiography of mitral annulus motion (MAM) within 24 h before the angiographic examination, formed a subgroup for comparison between angiographic M-mode of CAM and echocardiographic M-mode of MAM.

    RESULTS: In addition to previous reported CAM amplitude and longitudinal fractional shortening (FSL) the maximal systolic velocity of CAM can be reliably recorded by M-mode. The diastolic indices, atrial contribution to the total amplitude and maximal early and late diastolic velocities, are also well monitored by M-mode of CAM in comparison with echocardiographic MAM.

    CONCLUSION: LV systolic and diastolic function can be assessed by M-mode of CAM.

  • 26.
    Lidén, Mats
    et al.
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Andersson, Torbjörn
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden.
    Broxvall, Mathias
    Örebro University, School of Science and Technology.
    Thunberg, Per
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Geijer, Håkan
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden.
    Urinary stone size estimation: a new segmentation algorithm-based CT method2012In: European Radiology, ISSN 0938-7994, E-ISSN 1432-1084, Vol. 22, no 4, p. 731-737Article in journal (Refereed)
    Abstract [en]

    The size estimation in CT images of an obstructing ureteral calculus is important for the clinical management of a patient presenting with renal colic. The objective of the present study was to develop a reader independent urinary calculus segmentation algorithm using well-known digital image processing steps and to validate the method against size estimations by several readers. Fifty clinical CT examinations demonstrating urinary calculi were included. Each calculus was measured independently by 11 readers. The mean value of their size estimations was used as validation data for each calculus. The segmentation algorithm consisted of interpolated zoom, binary thresholding and morphological operations. Ten examinations were used for algorithm optimisation and 40 for validation. Based on the optimisation results three segmentation method candidates were identified. Between the primary segmentation algorithm using cubic spline interpolation and the mean estimation by 11 readers, the bias was 0.0 mm, the standard deviation of the difference 0.26 mm and the Bland-Altman limits of agreement 0.0 +/- 0.5 mm. The validation showed good agreement between the suggested algorithm and the mean estimation by a large number of readers. The limit of agreement was narrower than the inter-reader limit of agreement previously reported for the same data. The size of kidney stones is usually estimated manually by the radiologist. An algorithm for computer-aided size estimation is introduced. The variability between readers can be reduced. A reduced variability can give better information for treatment decisions.

  • 27.
    Lidén, Mats
    et al.
    Örebro University, School of Medical Sciences.
    Jendeberg, Johan
    Örebro University, School of Medical Sciences.
    Längkvist, Martin
    Örebro University, School of Science and Technology.
    Loutfi, Amy
    Örebro University, School of Science and Technology.
    Thunberg, Per
    Örebro University, School of Medical Sciences.
    Discrimination between distal ureteral stones and pelvic phleboliths in CT using a deep neural network: more than local features needed2018Conference paper (Refereed)
    Abstract [en]

    Purpose: To develop a deep learning method for assisting radiologists in the discrimination between distal ureteral stones and pelvic phleboliths in thin slice CT images, and to evaluate whether this differentiation is possible using only local features.

    Methods and materials: A limited field-of-view image data bank was retrospectively created, consisting of 5x5x5 cm selections from 1 mm thick unenhanced CT images centered around 218 pelvis phleboliths and 267 distal ureteral stones in 336 patients. 50 stones and 50 phleboliths formed a validation cohort and the remainder a training cohort. Ground truth was established by a radiologist using the complete CT examination during inclusion.The limited field-of-view CT stacks were independently reviewed and classified as containing a distal ureteral stone or a phlebolith by seven radiologists. Each cropped stack consisted of 50 slices (5x5 cm field-of-view) and was displayed in a standard PACS reading environment. A convolutional neural network using three perpendicular images (2.5D-CNN) from the limited field-of-view CT stacks was trained for classification.

    Results: The 2.5D-CNN obtained 89% accuracy (95% confidence interval 81%-94%) for the classification in the unseen validation cohort while the accuracy of radiologists reviewing the same cohort was 86% (range 76%-91%). There was no statistically significant difference between 2.5D-CNN and radiologists.

    Conclusion: The 2.5D-CNN achieved radiologist level classification accuracy between distal ureteral stones and pelvic phleboliths when only using the local features. The mean accuracy of 86% for radiologists using limited field-of-view indicates that distant anatomical information that helps identifying the ureter’s course is needed.

  • 28.
    Lidén, Mats
    et al.
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden.
    Thunberg, Per
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Kliniskt forskningscentrum (KFC), Univeritetssjukhuset, Örebro, Sverige.
    Broxvall, Mathias
    Örebro University, School of Science and Technology.
    Geijer, Håkan
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden.
    Two- and three-dimensional CT measurements of urinary calculi length and width: a comparative studyManuscript (preprint) (Other academic)
    Abstract [en]

    The standard imaging procedure for a patient presenting with renal colic is unenhanced CT. The CT measured size has a close correlation to the estimated prognosis for spontaneous passage of a ureteral calculus. Size estimations of urinary calculi in CT images are still based on 2d-reformats. In the present study we developed and validated a calculus oriented 3dmethod for measurements of length and width of urinary calculi and compared those with corresponding 2d measurements in axial and coronal reformats.

    Methods: Fifty unenhanced CT examinations demonstrating urinary calculi were included. A 3d-symmetric segmentation algorithm was validated against reader size estimations. The calculus-oriented size from the segmentation was then compared to the size in axial and coronal reformats.

    Results: The validation showed 0.1±0.7 mm agreement against reference measure. There was a 0.4 mm median bias for 3d-estimated calculus length compared to 2d (p<0.001), but no significant bias for 3d-width compared to 2d.

    Conclusion: The size of the urinary calculus becomes underestimated if its orientation is not aligned to the axial or coronal image plane. Future studies aiming to correlate calculus size with patient outcome should use a calculus oriented size estimation.

  • 29.
    Lidén, Mats
    et al.
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Örebro University Hospital. Department of Radiology, Örebro University Hospital, Örebro, Sweden; Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden.
    Thunberg, Per
    Örebro University Hospital. Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. School of Health and Medical Sciences, Örebro University, Örebro, Sweden; Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Broxvall, Mathias
    Modeling and Simulation Research Center, Örebro University, Örebro, Sweden.
    Geijer, Håkan
    Örebro University, School of Health and Medical Sciences, Örebro University, Sweden. Örebro University Hospital. Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Two- and three-dimensional CT measurements of urinary calculi length and width: a comparative study2015In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 56, no 4, p. 487-492Article in journal (Refereed)
    Abstract [en]

    Background: The standard imaging procedure for a patient presenting with renal colic is unenhanced computed tomography (CT). The CT measured size has a close correlation to the estimated prognosis for spontaneous passage of a ureteral calculus. Size estimations of urinary calculi in CT images are still based on two-dimensional (2D) reformats.

    Purpose: To develop and validate a calculus oriented three-dimensional (3D) method for measuring the length and width of urinary calculi and to compare the calculus oriented measurements of the length and width with corresponding 2D measurements obtained in axial and coronal reformats.

    Material and Methods: Fifty unenhanced CT examinations demonstrating urinary calculi were included. A 3D symmetric segmentation algorithm was validated against reader size estimations. The calculus oriented size from the segmentation was then compared to the estimated size in axial and coronal 2D reformats.

    Results: The validation showed 0.1 +/- 0.7mm agreement against reference measure. There was a 0.4mm median bias for 3D estimated calculus length compared to 2D (P < 0.001), but no significant bias for 3D width compared to 2D.

    Conclusion: The length of a calculus in axial and coronal reformats becomes underestimated compared to 3D if its orientation is not aligned to the image planes. Future studies aiming to correlate calculus size with patient outcome should use a calculus oriented size estimation.

  • 30.
    Lidén, Mats
    et al.
    Örebro University, School of Medical Sciences.
    Wodecki, Maciej
    Department of Clinical Physiology, Faculty of Medicine and Health, Örebro University, Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Department of Medical Physics.
    Rask, Peter
    Örebro University Hospital. Örebro University, School of Medical Sciences.
    Impact of Heart Rate on Flow Measurements in Aortic Regurgitation2017In: Journal of Heart Valve Disease, ISSN 0966-8519, E-ISSN 2053-2644, Vol. 26, no 5, p. 502-508, article id 4562Article in journal (Refereed)
    Abstract [en]

    BACKGROUND: Flow measurements using cardiac magnetic resonance imaging (CMRI) enable quantification of the stroke volume, regurgitant volume (RV) and regurgitant fraction (RF) in patients with aortic regurgitation (AR). These variables are used to assess the severity of the valve disease and for the timing of surgery. The aim of the study was to investigate the impact of an increased heart rate on measurement of the RV and RF in patients with AR.

    METHODS: Among 13 patients with known moderate or severe AR, regurgitant flow measurements, using phase-contrast cine magnetic resonance imaging, were obtained in the ascending aorta. Flow measurements were obtained at rest and at increased heart rates after intravenous administration of atropine.

    RESULTS: The mean heart rate was 61 beats per min at rest and 91 beats per min after atropine administration. The RV and RF were 52 ml and 35% at rest, respectively, and 34 ml (p <0.001) and 30% (p = 0.065) at increased heart rate, respectively.

    CONCLUSIONS: An increased heart rate leads to a decreased RV. The RF is more stable and may therefore be preferable for severity grading in AR.

  • 31.
    Längkvist, Martin
    et al.
    Örebro University, School of Science and Technology.
    Jendeberg, Johan
    Örebro University, School of Medical Sciences. Department of Radiology, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Department of Medical Physics, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Loutfi, Amy
    Örebro University, School of Science and Technology.
    Lidén, Mats
    Örebro University, School of Medical Sciences. Department of Radiology, Faculty of Health and Medical Sciences, Örebro University, Örebro, Sweden.
    Computer aided detection of ureteral stones in thin slice computed tomography volumes using Convolutional Neural Networks2018In: Computers in Biology and Medicine, ISSN 0010-4825, E-ISSN 1879-0534, Vol. 97, p. 153-160Article in journal (Refereed)
    Abstract [en]

    Computed tomography (CT) is the method of choice for diagnosing ureteral stones - kidney stones that obstruct the ureter. The purpose of this study is to develop a computer aided detection (CAD) algorithm for identifying a ureteral stone in thin slice CT volumes. The challenge in CAD for urinary stones lies in the similarity in shape and intensity of stones with non-stone structures and how to efficiently deal with large high-resolution CT volumes. We address these challenges by using a Convolutional Neural Network (CNN) that works directly on the high resolution CT volumes. The method is evaluated on a large data base of 465 clinically acquired high-resolution CT volumes of the urinary tract with labeling of ureteral stones performed by a radiologist. The best model using 2.5D input data and anatomical information achieved a sensitivity of 100% and an average of 2.68 false-positives per patient on a test set of 88 scans.

  • 32. Rudner, M.
    et al.
    Dahlström, Ö.
    Skagerstrand, Åsa
    Örebro University, School of Health Sciences.
    Alvinzi, L.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Örebro University Hospital.
    Sörqvist, P.
    Rönnberg, J.
    Lyxell, B.
    Möller, Claes
    Örebro University, School of Health Sciences.
    Does working memory training improve speech recognition in noise?2016Conference paper (Other academic)
    Abstract [en]

    Listening to speech in noise is often reported to be effortful, especially for individuals with hearing impairment, and many studies have shown that the ability to recognize speech in noise is positively associated with working memory capacity. We reasoned that if working memory capacity could be increased by training this might improve the ability to recognize speech in noise and modulate the neural activation associated with it. Adults with normal (NH) and impaired hearing (HI) were randomized to five weeks of CogMed QM training followed by five weeks of no training, or vice versa, according to a crossover design. Auditory and cognitive abilities were tested on four occasions: pre-training, T1; after 5 weeks, T2; after 10 weeks, T3 and after a further six months, T4. During fMRI scanning at T1, T2 and T3, the participants listened to stereotyped matrix type sentences in pink noise and competing talker noise at individually adapted 50% and 90% intelligibility levels as well as in quiet. Behavioural results show that although HI had worse auditory abilities than NH, there was no significant difference in cognitive ability, with the exception of phonological processing, which tended to be slower (cf Classon et al. 2013). Performance on most of cognitive tasks improved across sessions, although this could not be specifically attributed to training. We found no consistent pattern of correlations between working memory and the ability to understand speech in noise either before or after training. fMRI results did not reveal any significant effect of training and furthermore there was no significant effect of hearing status. However, there was a significant between group difference in activation of the left temporal gyrus (-44 -23 10) for the contrast speech in pink noise (across intelligibility levels) vs clear speech. There was also an interaction (p < .001 uncorrected) between group and testing occasion in the right superior frontal gyrus (7 58 16) for the contrast speech in noise (across types and levels) vs clear speech. Further, activation in left superior temporal gyrus (-56 -20 -2) correlated more strongly with intelligibility in NH compared HI participants.

    These results suggest that even when cognitive abilities are matched and intelligibility is individually adjusted, there are differences relating to hearing impairment in the neural mechanisms supporting speech in noise processing. The pattern of results suggests hearing-related differences in bottom-up processing mechanisms across time and hearing-related differences in top-down mechanisms that change over time. However, we found no evidence that working memory training improves speech recognition in noise.

    References:Classon, E., Rudner, M. & Rönnberg, J. (2013). Working memory compensates for hearing relatedphonological processing deficit. Journal of Communication Disorders, 46, 17-29.doi:10.1016/j.jcomdis.2012.10.001CogMed QM, developed by CogMed Cognitive Medical Systems AB, Stockholm, Sweden, 2006

  • 33.
    Skagerstrand, Åsa
    et al.
    Örebro University, School of Health Sciences. Linnaeus Centre HEAD, Linköping University, Linköping, Sweden; Audiological Research Center, Örebro University Hospital, Örebro, Sweden.
    Lyxell, Björn
    Linnaeus Centre HEAD, Linköping University, Linköping, Sweden.
    Thunberg, Per
    Örebro University, School of Medical Sciences. Örebro University Hospital. Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Sörqvist, Patrik
    Linnaeus Centre HEAD, Linköping University, Linköping, Sweden; EDepartment of Building, Energy and Environmental Engineering, University of Gävle, Gävle, Sweden.
    Lundin, Margareta
    Audiological Research Center, Örebro University Hospital, Örebro, Sweden; Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Johnsrude, Ingrid
    Linnaeus Centre HEAD, Linköping University, Linköping, Sweden; School of Communication Sciences and Disorders, University of Western Ontario, London, Canada.
    Rudner, Mary
    Linnaeus Centre HEAD, Linköping University, Linköping, Sweden.
    Rönnberg, Jerker
    Linnaeus Centre HEAD, Linköping University, Linköping, Sweden.
    Möller, Claes
    Örebro University, School of Health Sciences. Linnaeus Centre HEAD, Linköping University, Linköping, Sweden; Audiological Research Center, Örebro University Hospital, Örebro, Sweden.
    Cognitive training and effects on speech-in noise performance in normal hearing and hearing impaired individuals2015In: CHSCOM2015: Abstract book, 2015, p. 127-127Conference paper (Other academic)
    Abstract [en]

    Cognitive training might have potential to improve speech understanding under adverse listening conditions. Here, we have examined the effects of a 5-week computer-based cognitive training program on speech-in-noise-performance, in normal hearing (NH) participants and in participants with mild-to-moderate sensorineural hearing loss (HI).

    Two groups, matched on gender and age (45-65 years), of 20 participants each (HI and NH respectively) are recruited. Participants perform four test-sessions; inclusion (t0), five weeks (t1), ten weeks (t2) and six months (t3). Training is performed either between t0 and t1, or between t1 and t2 (using a cross-over design), using the computer-based Cogmed training program, approximately 30-40 minutes per day, five days per week, during five weeks. At each session participants are tested in three different ways: (a) cognitive testing (KIPS, SICSPAN, TRT); (b) auditory performance (pure tone-audiometry (air- and bone-conduction) and speech audiometry (HINT, Swedish SPIN-test (SNR +4dB))); (c) cortical activation (MR sessions where participants performed a speech-in-noise task using Hagerman-sentences with steady-state speech-spectrum noise (SSN) and with two competing talkers). MR imaging is performed on a Philips Achieva 1.5 Tesla scanner using a sparse imaging technique in which stimuli are presented during the silent period between successive scans. Participants listen to auditory stimuli under eight different conditions: clear speech, SSN or two competing talkers (each at 90%, 50% and 0% intelligibility), and silent rest. Pre- and post-training, hearing disability is assessed by the Speech-Spatial-Qualities-Questionnaire.

    The study is on-going and behavioral results as well as results from fMRI will be presented.

  • 34.
    Thunberg, Per
    et al.
    Department of Biomedical Engineering, Örebro University Hospital, Örebro, Sweden.
    Emilsson, Kent
    Örebro University, School of Health and Medical Sciences. Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Rask, Peter
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Kähäri, Anders
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Estimation of ejection fraction and stroke volume using single- and biplane magnetic resonance imaging of the left cardiac ventricle2008In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 49, no 9, p. 1016-1023Article in journal (Other academic)
    Abstract [en]

    Background: In cardiac magnetic resonance imaging (MRI), left ventricular stroke volume (SV) and ejection fractions (EF) are occasionally calculated using single-plane and biplane ellipsoid models. In previous studies, the calculated SV and EF using single- and biplane ellipsoid models have been compared to reference values calculated from short-axis (SA) images. In these studies, however, it has been emphasized that through-plane motion of the basal SA images represents an important source of error, which may result in incorrect reference values.

    Purpose: To compare the calculated SV and EF using single-plane and biplane ellipsoid models with SV and EF calculated from SA images in which compensation was made for through-plane motion.

    Material and Methods: A group of 20 patients who underwent MRI examination were included in the study. SV and EF were calculated using the stack of SA images (which had been compensated for through-plane motion) and compared to the SV and EF calculated according to the single- and biplane ellipsoid models.

    Results: The mean difference between the single-plane model and the reference was -0.3±6.5 for EF and 7.2±17.1 ml for SV. Corresponding comparison between the biplane method and the reference resulted in a mean difference of 0.3±6.1 for EF and 11.8±14.9 ml for SV.

    Conclusion: The results from this study show that left ventricular EF can be adequately estimated using the single- and biplane ellipsoid models, while SV tends to be overestimated using both geometrical models

  • 35.
    Thunberg, Per
    et al.
    Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Emilsson, Kent
    Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Rask, Peter
    Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Kähäri, Anders
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Flow and peak velocity measurements in patients with aortic valve stenosis using phase contrast MR accelerated with k-t BLAST2012In: European Journal of Radiology, ISSN 0720-048X, E-ISSN 1872-7727, Vol. 81, no 9, p. 2203-2207Article in journal (Refereed)
    Abstract [en]

    Objective: To investigate the accuracy of velocity measurements in patients with aortic valve stenosis using phase contrast (PC) imaging accelerated with SENSE (Sensitivity Encoding) and k-t BLAST (Broad-use Linear Acquisition Speed-up Technique).

    Methods: Accelerated quantitative breath hold PC measurements, using SENSE and k-t BLAST, were performed in twelve patients whose aortic valve stenosis had been initially diagnosed using echocardiography. Stroke volume (SV) and peak velocity measurements were performed on each subject in three adjacent slices using both accelerating methods.

    Results: The peak velocities measured with PC MRI using SENSE were -8.0±9.5% lower (p<0.01) compared to the peak velocities measured with k-t BLAST and the correlation was r=0.83. The stroke volumes when using SENSE were slightly higher 0.4±17.1 ml compared to the SV obtained using k-t BLAST but the difference was not significant (p>0.05).

    Conclusions In this study higher peak velocities were measured in patients with aortic stenosis when combining k-t BLAST with PC MRI compared to PC MRI using SENSE. A probable explanation of this difference is the higher temporal resolution achieved in the k-t BLAST measurement. There was, however, no significant difference between calculated SV based on PC MRI using SENSE and k-t BLAST, respectively.

  • 36.
    Thunberg, Per
    et al.
    Örebro University, School of Health and Medical Sciences. Department of Biomedical Engineering.
    Emilsson, Kent
    Örebro University, School of Health and Medical Sciences. Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Rask, Peter
    Department of Clinical Physiology,, Örebro University Hospital, Örebro, Sweden.
    Kähäri, Anders
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Separating the left cardiac ventricle from the atrium in short axis MR images using the equation of the atrioventricular plane2008In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 28, no 4, p. 222-228Article in journal (Refereed)
    Abstract [en]

    Short axis (SA) images obtained from cardiac magnetic resonance imaging are used to advantage in the calculation of important clinical parameters such as the ejection fraction and stroke volume (SV). A prerequisite for these calculations is the separation of the left ventricle and the left atrium. When only using the information seen in the SA images this separation can be a source of error due to the through-plane motion of the basal part of the left ventricle. In this study a method is proposed where the separation of the left ventricle and the atrium is performed by identifying the intersections of the atrioventricular plane in the SA images. The equation of the atrioventricular plane was determined in both systole and diastole using long axis and four chamber image views. Stroke volumes were measured in 20 patients using SA images where the endocardium had been delineated. The SV obtained using the new method was compared with quantitative flow measurements and the conventional technique for calculation of SV from SA images, respectively. The agreement of SV was, according to Bland-Altman analysis, 2.0 ml (95% CI -12.0 to 15.9 ml) in comparison with the flow measurements and 2.2 ml (95% CI -9.2 to 13.6 ml) compared to the conventional method. Inter- and intra-observer variability, when using the new proposed method, was small. This study shows that the identification of the left atrioventricular plane in SA images can be used in the separation of the left atrium and ventricle.

  • 37.
    Thunberg, Per
    et al.
    Department of Biomedical Engineering, Örebro University Hospital, Örebro, Sweden; Department of Biomedical Engineering, Linköping University, Linköping, Sweden; 3Department of Medicine and Care, Division of Clinical Physiology, Linköping University, Linköping, Sweden.
    Karlsson, Matts
    Department of Biomedical Engineering, Linköping University, Linköping, Sweden.
    Wigström, Lars
    2Department of Biomedical Engineering, Linköping University, Linköping, Sweden; 3Department of Medicine and Care, Division of Clinical Physiology, Linköping University, Linköping, Sweden.
    Accuracy and reproducibility in phase contrast imaging using SENSE2003In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 50, no 5, p. 1061-0168Article in journal (Refereed)
    Abstract [en]

    The purpose of this study was to evaluate the accuracy and reproducibility of phase contrast imaging using the sensitivity encoding (SENSE) method at different reduction factors. Analytical expressions were derived that state how reproducibility is influenced for velocity and flow measurements. Computer simulations, and in vitro and in vivo studies were performed in order to validate these expressions and to assess how accuracy is affected when different reduction factors are applied. It was shown that reproducibility depends on the reduction and geometry factors. Since the geometry factor varies spatially, so does the reproducibility for phase contrast imaging. In areas with high geometry factors, the standard deviation (SD) may become so large that aliasing occurs. The accuracy of phase contrast imaging is not influenced directly when SENSE is used, but may be indirectly influenced due to high SDs of the measured phase that may subsequently cause aliasing. The current results show that it is possible to achieve accurate flow measurements even at high reduction factors. By taking the geometry factor into account, it may be possible to find areas where phase contrast imaging is accurate even at high reduction factors.

  • 38.
    Thunberg, Per
    et al.
    Department of Biomedical Engineering, Örebro University Hospital, Örebro, Sweden; Department of Biomedical Engineering, Linköping University, Linköping, Sweden; Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden.
    Karlsson, Matts
    Department of Biomedical Engineering, Linköping University, Linköping, Sweden; Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden.
    Wigström, Lars
    Center for Medical Image Science and Visualization (CMIV), Linköping University, Linköping, Sweden; Department of Medicine and Care, Division of Clinical Physiology, Linköping University, Linköping, Sweden.
    Comparison of different methods for combining phase-contrast images obtained with multiple coils2005In: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 23, no 7, p. 795-799Article in journal (Refereed)
    Abstract [en]

    The ability to determine coil sensitivities implies that a method optimized in terms of maximized signal-to-noise ratio (SNR) can be applied to the combination of multiple coil images. An optimization of SNR subsequently results in a minimized variance in quantitative velocity measurements using phase-contrast imaging. When coil sensitivities are unknown, the weighted mean method, utilizing the square of the signal magnitude as weights, is suitable for combination of multiple phase images. In this study, the optimized method using estimated coil sensitivities was compared to the weighted mean method both theoretically and experimentally. It is shown that absence of noise correlation between the different coil images implies no difference between the methods regarding the variance of the phase. In the practical situation, noise correlation does exist, implying an opportunity for further reduction of phase variance using the optimized method. In vitro and in vivo studies showed, however, no significant difference between the two methods studied.

  • 39.
    Thunberg, Per
    et al.
    Department of Medical Physics, Örebro University Hospital, Örebro, Sweden.
    Kähäri, Anders
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Visualization of through-plane blood flow measurements obtained from phase-contrast MRI2011In: Journal of digital imaging, ISSN 0897-1889, E-ISSN 1618-727X, Vol. 24, no 3, p. 470-477Article in journal (Refereed)
    Abstract [en]

    The purpose of this work was to develop a visualization method for concurrent observation of both velocity and magnitude data obtained from through-plane velocity measurements using phase-contrast magnetic resonance imaging. Magnitude and velocity images were combined using an opacity transfer function (OTF) where the opacity was a function of a velocity range defined by the velocity encoding (v (enc)) parameter. Measured velocities were color-coded according to a predefined color scale and then combined into one image with the gray-scale magnitude image according to the OTF. In the combined images, simultaneous information of velocity and anatomy was presented. The proposed visualization method facilitated the understanding of how the measured blood flow was related to the underlying anatomy. Results are shown where the method is used to visualize blood flow measurements in the ascending aorta and the aortic valve. Adjustments of the OTF render possible identification of the peak velocities and their localization. Forward and backward blood flow is easily shown when applying appropriate OTF and color-coding. An advantage when using the proposed method is the ability of developing standardized protocol settings since the velocity information is quantitative and not relative as is the case for data obtained from the magnitude images. The intended application of the visualization method is the analysis of common flow studies used in the diagnosis of different cardiovascular diseases.

  • 40.
    Thunberg, Per
    et al.
    Department of Biomedical Engineering, Örebro University Hospital, Örebro, Sweden; Department of Biomedical Engineering, Linköping University, Linköping, Sweden; Department of Medicine and Care, Division of Clinical Physiology, Linköping University, Linköping, Sweden.
    Wigström, Lars
    Department of Biomedical Engineering, Linköping University, Linköping, Sweden; Department of Medicine and Care, Division of Clinical Physiology, Linköping University, Linköping, Sweden.
    Ebbers, Tino
    Department of Medicine and Care, Division of Clinical Physiology, Linköping University, Linköping, Sweden.
    Karlsson, Matts
    Department of Biomedical Engineering, Linköping University, Linköping, Sweden.
    Correction for displacement artifacts in 3D phase contrast imaging2002In: Journal of Magnetic Resonance Imaging, ISSN 1053-1807, E-ISSN 1522-2586, Vol. 16, no 5, p. 591-597Article in journal (Refereed)
    Abstract [en]

    Purpose: To correct for displacement artifacts in 3D phase contrast imaging.

    Materials and Methods: A 3D phase contrast pulse sequence was modified so that displacements of velocity measurements were restricted to one direction. By applying a postprocessing method, displaced measurements could be traced back to their accurate positions. Flow studies were performed using a phantom that generated flow through a stenosis, directed oblique relative to the phase and frequency encoding directions. Velocity profiles and streamline visualization were used to compare displaced and corrected velocity data to a reference.

    Results: Velocity profiles obtained from the original measurement showed skewed profiles due to the displacement artifact, both at close proximity to the orifice as well as further downstream. After correction, concordance with the reference improved considerably.

    Conclusion: The displacement artifact, which restricts the accuracy of phase contrast measurements, can be corrected for using the proposed method. Correction of the phase contrast velocity data may improve the accuracy of subsequent flow analysis and visualization.

  • 41.
    Thunberg, Per
    et al.
    Department of Biomedical Engineering, Linköping University, Linköping, Sweden; Department of Medicine and Care, Division of Clinical Physiology, Linköping University, Linköping, Sweden.
    Wigström, Lars
    Department of Biomedical Engineering, Linköping University, Linköping, Sweden; Department of Medicine and Care, Division of Clinical Physiology, Linköping University, Linköping, Sweden.
    Wranne, Bengt
    Department of Medicine and Care, Division of Clinical Physiology, Linköping University, Linköping, Sweden.
    Engvall, Jan
    Department of Medicine and Care, Division of Clinical Physiology, Linköping University, Linköping, Sweden.
    Karlsson, Matts
    Department of Biomedical Engineering, Linköping University, Linköping, Sweden.
    Correction for acceleration-induced displacement artifacts in phase contrast imaging2000In: Magnetic Resonance in Medicine, ISSN 0740-3194, E-ISSN 1522-2594, Vol. 43, no 5, p. 734-738Article in journal (Refereed)
    Abstract [en]

    The acceleration-induced displacement artifact impairs the accuracy of MR velocity measurements. This study proposes a post processing method for correction of this artifact. Velocity measurements were performed in a flow phantom containing a constriction. Velocity curves were obtained from streamlines parallel to the frequency, phase, and slice directions, respectively. The acceleration-induced displacement artifact was most prominent when the frequency encoding direction was aligned with the flow direction. After correction, velocity assignment improved and a more accurate description of the flow was obtained. In vivo measurements were performed in the aorta in a patient with a repaired aortic coarctation. The correction method was applied to velocity data along a streamline parallel to the frequency encoding direction. The result after correction was a new location of the peak velocity and improved estimates of the velocity gradients.

  • 42.
    Thunberg, Per
    et al.
    Department of Biomedical Engineering, Örebro University Hospital, Örebro, Sweden.
    Zetterberg, Per
    Noise distribution in SENSE- and GRAPPA-reconstructed images: a computer simulation study2007In: Magnetic Resonance Imaging, ISSN 0730-725X, E-ISSN 1873-5894, Vol. 25, no 7, p. 1089-1094Article in journal (Refereed)
    Abstract [en]

    This work presents a descriptive study of noise distributions in images reconstructed according to the parallel imaging methods SENSE and GRAPPA. In the computer simulations, two different settings were used for describing an object. The first setting included a synthetic object and eight complex-valued coil sensitivities. In the second setting, a complex-valued in vitro object, composed of four individual coil images, was used. After adding noise and subsampling k-space for each coil image, reconstruction was performed according to SENSE, with and without regularization, and GRAPPA for different reduction factors. A set of images was created for three different reduction factors. Noise distributions were determined for each data set and compared with each other. The results of this study show that the noise distributions in SENSE- and GRAPPA-reconstructed images differ. The noise in images reconstructed according to GRAPPA has a more uniform spatial distribution compared with SENSE-reconstructed images, in which the noise varies regionally according to the geometry factor. The noise distribution in SENSE-reconstructed images using regularization showed a similar but lowered pattern of noise compared with images reconstructed according to SENSE without regularization.

  • 43.
    Trincavelli, Marco
    et al.
    Örebro University, School of Science and Technology.
    Coradeschi, Silvia
    Örebro University, School of Science and Technology.
    Loutfi, Amy
    Örebro University, School of Science and Technology.
    Söderquist, Bo
    Örebro University Hospital, Örebro, Sweden .
    Thunberg, Per
    Örebro University Hospital, Örebro, Sweden .
    Direct identification of bacteria in blood culture samples using an electronic nose2010In: IEEE Transactions on Biomedical Engineering, ISSN 0018-9294, E-ISSN 1558-2531, Vol. 57, no 12, p. 2884-2890Article in journal (Refereed)
    Abstract [en]

    In this paper, we introduce a method for identification of bacteria in human blood culture samples using an electronic nose. The method uses features, which capture the static (steady state) and dynamic (transient) properties of the signal from the gas sensor array and proposes a means to ensemble results from consecutive samples. The underlying mechanism for ensembling is based on an estimation of posterior probability, which is extracted from a support vector machine classifier. A large dataset representing ten different bacteria cultures has been used to validate the presented methods. The results detail the performance of the proposed algorithm and show that through ensembling decisions on consecutive samples, significant reliability in classification accuracy can be achieved.

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