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  • 1.
    Andersson, Torbjörn
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Pucar, Predrag
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Estimation of Residence Time in Continuous Flow Systems with Dynamics1995In: Journal of Process Control, ISSN 0959-1524, E-ISSN 1873-2771, Vol. 5, no 1, p. 9-17Article in journal (Refereed)
    Abstract [en]

    A method for estimation of residence time in continuous flow systems with varying dynamics is presented. By resampling, i.e., choosing time instants different from the given sampling instants, and interpolation between measured data points, we obtain a continuous flow system with constant residence time expressed in the new resampled time vector. We assume the flow patterns in the systems are invariant. The new data set is then used for identification of parameters in a chosen model structure. From the identified model, the residence time is readily calculated and a procedure for that is briefly described. The presented method is readily extended to enable use in recursive identification. In that case, however, as an improvement of tracking ability of an ordinary recursive routine. Keywords : System identification, residence time estimation, time-varying systems, variable flow and/or volume, continuous flow systems, recursive identification.

  • 2.
    Andersson, Torbjörn
    et al.
    Linköping University, Department of Medical and Health Sciences, Radiology. Linköping University, Faculty of Health Sciences.
    Pucar, Predrag
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Estimation of Residence Time in Continuous Flow Systems with Varying Flow and Volume1993Report (Other academic)
    Abstract [en]

    A method for estimation of residence time in continuous flow vessels with variable flow and volume is presented. By resampling, i.e., choosing time instants different from the given sampling instants, and interpolation of measured data points, we obtain a continuous flow system with constant residence time expressed in the new resampled time vector, assuming the flow patterns in the vessels and tanks are invariant. The new data set is then used for identification of parameters in a chosen model structure. From the identified model the residence time is easily calculated and a procedure for that is briefly described. The presented method is easily extended to enable use in recursive identification but then as an improvement of tracking ability of an ordinary recursive routine.

  • 3.
    Andersson, Torbjörn
    et al.
    Linköping University, Department of Medical and Health Sciences, Radiology. Linköping University, Faculty of Health Sciences.
    Pucar, Predrag
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Identifying Models using Piecewise Linear Approximation of Input Signals1992Report (Other academic)
    Abstract [en]

    Very often in system identification problems it is assumed that the input signal is piecewise constant but in many practical cases this is not the fact. In such cases when the input signal is continuous it shows that a piecewise linear approximation of the input signal leads to a better model. In this report it is shown how to handle system identification problems using state space descriptions and the assumption of piecewise linear input signals with MathWork's system identification software.

  • 4.
    Andersson, Torbjörn
    et al.
    Linköping University, Department of Medical and Health Sciences, Radiology. Linköping University, Faculty of Health Sciences.
    Pucar, Predrag
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Isaksson, Alf
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Projekt operatörsverktyg, delprojekt 4: Modeller för massatransport och beräkning av uppehållstid i fiberlinjen. Slutrapport1992Report (Other academic)
  • 5.
    Andersson, Torbjörn
    et al.
    Linköping University, Department of Medical and Health Sciences, Radiology. Linköping University, Faculty of Health Sciences.
    Pucar, Predrag
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Ljung, Lennart
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Identification Aspects of Inter-Sampling Behavior1994Report (Other academic)
    Abstract [en]

    In this contribution aspects of inter-sample input signal behavior are examined. The starting point is that parametric identication always is performed on basis of discrete-time data. This is valid for identication of discrete-time models as well as continuous-time models. The usual assumptions on the input signal are; i) it is band-limited, ii) it is piecewise constant or iii) it is piecewise linear. One point made in this paper is that if a discrete-time model is used, the best possible (in the model structure) adjustment to data is made. This is independent of the assumption on the input signal. However, a transformation of the obtained discrete model to a continuous one is not possible without additional assumptions on the input signal. The other point made is that the frequency functions of the discrete models very well coincides with the frequency functions of the discretized continuous time models and the continuous time transfer function fitted in the frequency domain.

  • 6.
    Geijer, Håkan
    et al.
    Department of Radiology, Örebro Medical Centre Hospital, Örebro, Sweden.
    Verdonck, Bert
    Philips Medical Systems, Best, The Netherlands.
    Beckman, Karl-Wilhelm
    Department of Medical Physics, Örebro Medical Centre Hospital, Örebro, Sweden.
    Andersson, Torbjörn
    Department of Radiology, Örebro Medical Centre Hospital, Örebro, Sweden.
    Persliden, Jan
    Department of Medical Physics, Örebro Medical Centre Hospital, Örebro, Sweden.
    Digital Radiography of Scoliosis with a Scanning Method: Radiation Dose Optimization2003In: European Radiology, ISSN 0938-7994, E-ISSN 1432-1084, Vol. 13, no 3, p. 543-551Article in journal (Refereed)
    Abstract [en]

    The aim of this study was optimization of the radiation dose–image quality relationship for a digital scanning method of scoliosis radiography. The examination is performed as a digital multi-image translation scan that is reconstructed to a single image in a workstation. Entrance dose was recorded with thermoluminescent dosimeters placed dorsally on an Alderson phantom. At the same time, kerma area product (KAP) values were recorded. A Monte Carlo calculation of effective dose was also made. Image quality was evaluated with a contrast-detail phantom and Visual Grading. The radiation dose was reduced by lowering the image intensifier entrance dose request, adjusting pulse frequency and scan speed, and by raising tube voltage. The calculated effective dose was reduced from 0.15 to 0.05 mSv with reduction of KAP from 1.07 to 0.25 Gy cm2 and entrance dose from 0.90 to 0.21 mGy. The image quality was reduced with the Image Quality Figure going from 52 to 62 and a corresponding reduction in image quality as assessed with Visual Grading. The optimization resulted in a dose reduction to 31% of the original effective dose with an acceptable reduction in image quality considering the intended use of the images for angle measurements.

  • 7.
    Jansson, Margareta
    et al.
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Geijer, Håkan
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Andersson, Torbjörn
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Bowel preparation for excretory urography is not necessary: a randomized trial2007In: British Journal of Radiology, ISSN 0007-1285, E-ISSN 1748-880X, Vol. 80, no 956, p. 617-624Article in journal (Refereed)
    Abstract [en]

    Despite the fact that computed tomography is becoming more commonly used to investigate the genitourinary tract, intravenous urography still plays an important role in uroradiology. The aim of this study was to compare bowel purgation and two other preparation methods — dietary restrictions and no preparations at all — in an attempt to find the optimal procedure for uniform practice. 210 consecutive patients were randomised to three preparation groups with 70 in each group. Group 1 received standard bowel purgation, Group 2 was instructed to fast, while Group 3 had no preparation at all. Irrespective of preparation, all patients underwent the same examination procedure. The examining radiographer and evaluating radiologists were unaware of the type of preparation given. Image quality was assessed according to European Commission criteria for excretory urography. The effectiveness of bowel purgation and the amount of residual gas were scored separately. There was no statistically significant difference in the proportions with fulfilled criteria between preparation Groups 1 and 2 and Groups 1 and 3. A criterion was regarded as fulfilled only when all three observers agreed. Assessment of the amount of residual faeces proved the effectiveness of our standard bowel purgation. The results of our study show equality of the evaluated preparation methods and cannot justify further use of bowel purgation before excretory urography.

  • 8.
    Kähäri, Anders
    et al.
    Linköping University, Department of Medicine and Care, Radiology. Linköping University, Faculty of Health Sciences.
    Andersson, Torbjörn
    Linköping University, Department of Medicine and Care, Radiology. Linköping University, Faculty of Health Sciences.
    Danielewicz, Mikael
    Örebro.
    Emilsson, Kent
    Örebro.
    Wandt, Birger
    Göteborg.
    Circumflexrörelsen: en ny angiografisk metod för bedömning av vänsterkammarfunktionen2002In: Svenska Läkaresällskapets Handlingar,2002, 2002, p. 228-228Conference paper (Refereed)
  • 9.
    Kähäri, Anders
    et al.
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Emilsson, Kent
    Department of Clinical Physiology, Örebro University Hospital, Örebro, Sweden.
    Danielewicz, Mikael
    Department of Cardiology, Örebro University Hospital, Örebro, Sweden.
    Andersson, Torbjörn
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Wandt, Birger
    Department of Clinical Physiology, Sahlgrenska University Hospital, Gothenburg, Sweden.
    Circumflex artery motion: a new angiographic method for assessment of left ventricular function2003In: Scandinavian Cardiovascular Journal, ISSN 1401-7431, E-ISSN 1651-2006, Vol. 37, no 2, p. 80-86Article in journal (Refereed)
    Abstract [en]

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

    DESIGN: Seventy-three consecutive patients referred for coronary angiography and LV angiography were included. Ejection fraction (EF) was calculated from LV angiography and CAM was measured from coronary angiography.

    RESULTS: The ratio between CAM and the end-diastolic length of the ventricle, which can be denominated long-axis fractional shortening (FS(L)), was found to be a better index of LV function than CAM per se. There was a significant linear correlation between EF and FS(L) (r = 0.81, SEE = 8.2, p < 0.001). When values of FS(L) > or =10% were selected to define a normal EF (> or =50%) there was a sensitivity of 95% and a specificity of 93%. Visual estimation of EF from CAM was not as good as the use of calculated FS(L) but may me useful as a fast screening method.

    CONCLUSION: LV systolic function can be assessed by studying CAM recorded by coronary angiography.

  • 10.
    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
    Department of Clinical Physiology, Karlskoga Hospital, Karlskoga, Sweden.
    Geijer, Håkan
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Andersson, Torbjörn
    Department of Radiology, Örebro University Hospital, Örebro, Sweden.
    Wandt, Birger
    Department of Clinical Physiology, Sahlgrenska University Hospital, Gothenburg, Sweden.
    Assessment of left ventricular function from M‐mode measurement of circumflex artery motion recorded by coronary angiography2003In: 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 (FS L ) 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.

  • 11.
    Ljung, Lennart
    et al.
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Glad, Torkel
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Andersson, Torbjörn
    Linköping University, Department of Electrical Engineering, Automatic Control. Linköping University, The Institute of Technology.
    Identifiability Implies Robust Identifiability1993Report (Other academic)
    Abstract [en]

    In identification from a deterministic point of view an algorithm is said to be robustly convergent if the true system is regained when the noise level tends to zero. In this paper we introduce a concept close to this performance measure: robust global identifiability. A model structure, i.e. a smoothly parametrized set of models, is said to be robustly globally identifiable if there exist an identification algorithm such that the true parameters are regained when the noise level tends to zero. We show that global identifiability implies robust global identifiability when the model structure in consideration is a characteristic set of differential polynomials.

  • 12.
    Lundin, Margareta
    et al.
    Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
    Lidén, M
    Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
    Magnusson, A,
    Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
    Abdulilah Mohammed, A.
    Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
    Geijer, Håkan
    Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
    Andersson, Torbjörn
    Linköping University, Department of Medical and Health Sciences, Radiology. Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Faculty of Health Sciences.
    Persson, Anders
    Linköping University, Department of Medical and Health Sciences, Radiology. Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Diagnostics, Department of Radiology in Linköping.
    Virtual non-contrast dual-energy CT compared to single-energy CT of the urinary tract: a prospective study2012In: Acta Radiologica, ISSN 0284-1851, E-ISSN 1600-0455, Vol. 53, no 6, p. 689-694Article in journal (Refereed)
    Abstract [en]

    Background: Dual-energy computed tomography (DECT) has been shown to be useful for subtracting bone or calcium in CT angiography and gives an opportunity to produce a virtual non-contrast-enhanced (VNC) image from a series where contrast agents have been given intravenously. High noise levels and low resolution have previously limited the diagnostic value of the VNC images created with the first generation of DECT. With the recent introduction of a second generation of DECT, there is a possibility of obtaining VNC images with better image quality at hopefully lower radiation dose compared to the previous generation.

    Purpose: The aim of this study is to compare the image quality of the single-energy series to a VNC series obtained with a two generations of DECT scanners. CT of the urinary tract was used as a model.

    Material and Methods: Thirty patients referred for evaluation of haematuria were examined with an older system (Somatom Definition) and another 30 patients with a new generation (Somatom Definition Flash). One single-energy series was obtained before and one dual-energy series after administration of intravenous contrast media. We created a VNC series from the contrast-enhanced images. Images were assessed concerning image quality with a visual grading scale evaluation of the VNC series with the single-energy series as gold standard.

    Results: The image quality of the VNC images was rated inferior to the single-energy variant for both scanners, OR range 11.5-67.3 for the Definition and OR 2.1-2.8 for the Definition Flash. Visual noise and overall quality were regarded as better with Flash than Definition.

    Conclusions: Image quality of VNC images obtained with the new generation of DECT is still slightly inferior compared to native images. However the difference is smaller with the new compared to the older system.

  • 13.
    Lundin, Margareta
    et al.
    Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
    Magnusson, A,
    Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
    Geijer, Håkan
    Department of Radiology, Örebro University Hospital, 701 85 Örebro, Sweden.
    Andersson, Torbjörn
    Linköping University, Department of Medical and Health Sciences, Radiology. Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Faculty of Health Sciences.
    Persson, Anders
    Linköping University, Department of Medical and Health Sciences, Radiology. Linköping University, Center for Medical Image Science and Visualization, CMIV. Linköping University, Faculty of Health Sciences. Östergötlands Läns Landsting, Centre for Diagnostics, Department of Radiology in Linköping.
    Accuracy of stone size measurement using dual-energy virtual non-contrast enhanced CT images: a phantom studyManuscript (preprint) (Other academic)
    Abstract [en]

    Background: Accurate estimation of calculus size is an important prediction factor for spontaneous passage. The method used for calculus-size estimation needs to be as precise as possible. Previous studies have shown that the image quality of virtual non-contrast (VNC) images obtained with the new generation of dual-energy CT (DECT) is still inferior compared to native images. However, the difference in assessed image quality compared to native series is smaler with the new than with the older system.

    Purpose: The aim of this study is to evaluate the accuracy of measurements of renal calculi in a VNC image series obtained with the new generation of dual-energy CT, compared to actual stone size and single-energy image series in a phantom study.

    Material and Methods: For the purpose of this study a ureter phantom was created. The phantom was scanned with DECT (Somatom Definition Flash) at three different radiation-dose settings with single and dual energy, first with water in the ureters then with i.v. contrast medium solution. At each energy level CDTI were set equal for single and dual-energy. VNC series were created. All image series were assessed for stone visibility and size.

    Results: All calculi were visible in single- and dual-energy images with water in phantom tubes. With the VNC calculi in the size range 1.42 – 2.02 mm were missed. Results of intraobserver variability in investigated dose levels shows very good agreement between assessments of stone size by both evaluators, with correlation coefficient (CC) variying from 0.97 (95% CI 0.91–0.99) to 1.0 (95% CI 0.99–1.0). Results of correlation tests between the mean of maximal stone size and maximal stone size measured with electronic callipers show good agreement, with a CC variability from 0.93 (95% CI 0.76-0.98) to 0.99 (95% CI 0.96-0.99), a limit of agreement of "1.65 to 1.38 and bias "0.14. With one of the observers, the results of correlation tests in assessments made by the same reader of stone-size in dual-energy and VNC image series for corresponding dose levels show lower ICC for the low dose level, 0.77 (CI 0.36–0.93), with limits of agreement of -2.23–0.57 and bias "0.33.

    Conclusions: This study shows that detection of small stones is not reliable despite better image quality with the new DECT and that small stones will be missed with VNC imaging. In larger stones, the inherent measurement error with CT is magnified with VNC imaging.

  • 14.
    Persliden, Jan
    et al.
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radio Physics.
    Beckman, Karl-Wilhelm
    Geijer, Håkan
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiology.
    Andersson, Torbjörn
    Linköping University, Faculty of Health Sciences. Linköping University, Department of Medicine and Care, Radiology.
    Dose-image optimisation in digital radiology with a direct digital detector: an example applied to pelvic examination2002In: European Radiology, ISSN 0938-7994, E-ISSN 1432-1084, Vol. 12, p. 1584-1588Article in journal (Refereed)
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CiteExportLink to result list
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