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Wigström, Lars
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Publications (10 of 65) Show all publications
Maier, A., Wigström, L., Hofmann, H. G., Hornegger, J., Zhu, L., Strobel, N. & Fahrig, R. (2011). Three-dimensional anisotropic adaptive filtering of projection data for noise reduction in cone beam CT. Medical physics (Lancaster), 38(11), 5896-5909
Open this publication in new window or tab >>Three-dimensional anisotropic adaptive filtering of projection data for noise reduction in cone beam CT
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2011 (English)In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 38, no 11, p. 5896-5909Article in journal (Refereed) Published
Abstract [en]

Purpose: The combination of quickly rotating C-arm gantry with digital flat panel has enabled the acquisition of three-dimensional data (3D) in the interventional suite. However, image quality is still somewhat limited since the hardware has not been optimized for CT imaging. Adaptive anisotropic filtering has the ability to improve image quality by reducing the noise level and therewith the radiation dose without introducing noticeable blurring. By applying the filtering prior to 3D reconstruction, noise-induced streak artifacts are reduced as compared to processing in the image domain. Methods: 3D anisotropic adaptive filtering was used to process an ensemble of 2D x-ray views acquired along a circular trajectory around an object. After arranging the input data into a 3D space (2D projections + angle), the orientation of structures was estimated using a set of differently oriented filters. The resulting tensor representation of local orientation was utilized to control the anisotropic filtering. Low-pass filtering is applied only along structures to maintain high spatial frequency components perpendicular to these. The evaluation of the proposed algorithm includes numerical simulations, phantom experiments, and in-vivo data which were acquired using an AXIOM Artis dTA C-arm system (Siemens AG, Healthcare Sector, Forchheim, Germany). Spatial resolution and noise levels were compared with and without adaptive filtering. A human observer study was carried out to evaluate low-contrast detectability. Results: The adaptive anisotropic filtering algorithm was found to significantly improve low-contrast detectability by reducing the noise level by half (reduction of the standard deviation in certain areas from 74 to 30 HU). Virtually no degradation of high contrast spatial resolution was observed in the modulation transfer function (MTF) analysis. Although the algorithm is computationally intensive, hardware acceleration using Nvidias CUDA Interface provided an 8.9-fold speed-up of the processing (from 1336 to 150 s). Conclusions: Adaptive anisotropic filtering has the potential to substantially improve image quality and/or reduce the radiation dose required for obtaining 3D image data using cone beam CT.

Place, publisher, year, edition, pages
American Association of Physicists in Medicine, 2011
Keywords
C-arm computed tomography (CT); low dose; noise; artifacts; image enhancement; hardware acceleration; GPU
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-73594 (URN)10.1118/1.3633901 (DOI)000296534000010 ()
Available from: 2012-01-09 Created: 2012-01-09 Last updated: 2017-12-08
Kvitting, J., Sigfridsson, A., Wigström, L., Bolger, A. & Karlsson, M. (2010). Analysis of human myocardial dynamics using virtual markers based on magnetic resonance imaging. Clinical Physiology and Functional Imaging, 30(1), 23-29
Open this publication in new window or tab >>Analysis of human myocardial dynamics using virtual markers based on magnetic resonance imaging
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2010 (English)In: Clinical Physiology and Functional Imaging, ISSN 1475-0961, E-ISSN 1475-097X, Vol. 30, no 1, p. 23-29Article in journal (Refereed) Published
Abstract [en]

Background: Myocardial dynamics are three-dimensional (3D) and time-varying. Cineradiography of surgically implanted makers in animals or patients is accurate for assessing these events, but this invasive method potentially alters myocardial motion. The aim of the study was to quantify myocardial motion using magnetic resonance imaging (MRI) and hence to provide a non-invasive approach to characterize 3D myocardial dynamics.

Methods: Myocardial motion was quantified in ten normal volunteers by tracking the Lagrangian motion of individual points (i.e. virtual markers), based on time-resolved 3D phase-contrast MRI data and Fourier tracking. Nine points in the myocardium were tracked over the entire cardiac cycle, allowing a wire frame model to be generated and systolic and diastolic events identified.

Results: Radius of curvature of the left ventricular (LV) wall was calculated from the virtual markers; the ratio between the anterior–posterior (AP) and septal–lateral (SL) walls in the LV shows an oval shape of the apical short axis plane at end systole (ES) and more circular at end diastole (ED). The AP/SL ratio for the basal plane shows an oval shape at ES and ED. We found that the rotation of the basal plane in ES was less compared to the apical plane [−2·0 ± 2·2 versus 4·1 ± 2·6 degrees (P<0·005)]. The apical plane rotated counter clock wise as viewed from the apex.

Conclusion: This new non-invasive tool, despite current limitations in temporal and spatial resolution, may provide a comprehensive set of virtual myocardial markers throughout the entire LV without the confounding effects introduced by surgical implantation.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-50587 (URN)10.1111/j.1475-097X.2009.00900.x (DOI)
Available from: 2009-10-13 Created: 2009-10-13 Last updated: 2017-12-12
Escobar Kvitting, J.-P., Dyverfeldt, P., Sigfridsson, A., Franzen, S., Wigström, L., Bolger, A. F. & Ebbers, T. (2010). In Vitro Assessment of Flow Patterns and Turbulence Intensity in Prosthetic Heart Valves Using Generalized Phase-Contrast MRI. JOURNAL OF MAGNETIC RESONANCE IMAGING, 31(5), 1075-1080
Open this publication in new window or tab >>In Vitro Assessment of Flow Patterns and Turbulence Intensity in Prosthetic Heart Valves Using Generalized Phase-Contrast MRI
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2010 (English)In: JOURNAL OF MAGNETIC RESONANCE IMAGING, ISSN 1053-1807, Vol. 31, no 5, p. 1075-1080Article in journal (Refereed) Published
Abstract [en]

Purpose: To assess in vitro the three-dimensional mean velocity field and the extent and degree of turbulence intensity (TI) in different prosthetic heart valves using a generalization of phase-contrast MRI (PC-MRI). Materials and Methods: Four 27-mm aortic valves (Bjork-Shiley Monostrut tilting-disc, St. Jude Medical Standard bileaflet, Medtronic Mosaic stented and Freestyle stentless porcine valve) were tested under steady inflow conditions in a Plexiglas phantom. Three-dimensional PC-MRI data were acquired to measure the mean velocity field and the turbulent kinetic energy (TKE), a direction-independent measure of TI. Results: Velocity and TI estimates could be obtained up and downstream of the valves, except where metallic structure in the valves caused signal void. Distinct differences in the location, extent, and peak values of velocity and TI were observed between the valves tested. The maximum values of TKE varied between the different valves: tilting disc, 100 J/m(3); bileaflet, 115 J/m(3); stented, 200 J/m(3); stentless, 145 J/m(3). Conclusion: The TI downstream from a prosthetic heart valve is dependent on the specific valve design. Generalized PC-MRI can be used to quantify velocity and TI downstream from prosthetic heart valves, which may allow assessment of these aspects of prosthetic valvular function in postoperative patients.

Place, publisher, year, edition, pages
John Wiley and Sons, Ltd, 2010
Keywords
turbulence intensity, prosthetic heart valves, phase-contrast magnetic resonance imaging
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-56524 (URN)10.1002/jmri.22163 (DOI)000277397100005 ()
Available from: 2010-05-21 Created: 2010-05-21 Last updated: 2013-09-03
Zachrisson, H., Engström, E., Engvall, J., Wigström, L., Smedby, Ö. & Persson, A. (2010). Soft tissue discrimination ex vivo by dual energy computed tomography. European Journal of Radiology, 75(2), E124-E128
Open this publication in new window or tab >>Soft tissue discrimination ex vivo by dual energy computed tomography
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2010 (English)In: European Journal of Radiology, ISSN 0720-048X, E-ISSN 1872-7727, Vol. 75, no 2, p. E124-E128Article in journal (Refereed) Published
Abstract [en]

PURPOSE: Dual Energy Computed Tomography (DECT) may provide additional information about the chemical composition of tissues compared to examination with a single X-ray energy. The aim of this in vitro study was to test whether combining two energies may significantly improve the detection of soft tissue components commonly present in arterial plaques. METHODS: Tissue samples of myocardial and psoas muscle, venous and arterial thrombus as well as fat from different locations were scanned using a SOMATOM Definition Dual Source CT system (Siemens AG, Medical Solutions, Forchheim, Germany) with simultaneous tube voltages of 140 and 80kV. The attenuation (Hounsfield units, HU) at 80 and 140kV was measured in representative regions of interest, and the association between measured HU values and tissue types was tested with logistic regression. RESULTS: The combination of two energy levels (80 and 140kV) significantly improved (p<0.001) the ability to correctly classify venous thrombus vs arterial thrombus, myocardium or psoas; arterial thrombus vs myocardium or psoas; myocardium vs psoas; as well as the differentiation between fat tissue from various locations. Single energy alone was sufficient for distinguishing fat from other tissues. CONCLUSION: DECT offers significantly improved in vitro differentiation between soft tissues occurring in plaques. If this corresponds to better tissue discrimination in vivo needs to be clarified in future studies.

Place, publisher, year, edition, pages
Elsevier, 2010
Keywords
Dual-source computed tomography; Dual energy CT imaging; Soft tissue characterization; Plaque
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-57906 (URN)10.1016/j.ejrad.2010.02.001 (DOI)000281484400049 ()20219308 (PubMedID)
Available from: 2010-07-05 Created: 2010-07-05 Last updated: 2017-12-12
Engström, E., Persson, A., Berge, J., Engvall, J., Wigström, L. & Zachrisson, H. (2008). Dual-energy CT of ex-vivo tissue samples.. In: Cardiovaskulära vårmötet,2008.
Open this publication in new window or tab >>Dual-energy CT of ex-vivo tissue samples.
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2008 (English)In: Cardiovaskulära vårmötet,2008, 2008Conference paper, Published paper (Refereed)
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-44850 (URN)77850 (Local ID)77850 (Archive number)77850 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-10-21
Ebbers, T., Haraldsson, H., Dyverfeldt, P., Sigfridsson, A., Warntjes, M. J. & Wigström, L. (2008). Higher order weighted least-squares phase offset correction for improved accuracy in phase-contrast MRI. Paper presented at ISMRM.
Open this publication in new window or tab >>Higher order weighted least-squares phase offset correction for improved accuracy in phase-contrast MRI
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2008 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Phase-contrast magnetic resonance imaging has the ability to accurately measure blood flow and myocardial velocities in the human body. Unwanted spatially varying phase offsets are, however, always present and may deteriorate the measurements significantly. Some of these phase offsets can be estimated based on the pulse sequence (1), but effects caused by eddy currents are more difficult to predict. A linear fit of the phase values is often estimated from either a number of manually defined areas containing stationary tissue or by semi-automatic detection of stationary tissue using the

National Category
Biomedical Laboratory Science/Technology
Identifiers
urn:nbn:se:liu:diva-61147 (URN)
Conference
ISMRM
Available from: 2010-11-09 Created: 2010-11-04 Last updated: 2013-09-03Bibliographically approved
Haraldsson, H., Wigström, L., Lundberg, M., Bolger, A. F., Engvall, J., Ebbers, T. & Escobar Kvitting, J.-P. (2008). Improved estimation and visualization of two-dimensional myocardial strain rate using MR velocity mapping. Journal of Magnetic Resonance Imaging, 28(3), 604-611
Open this publication in new window or tab >>Improved estimation and visualization of two-dimensional myocardial strain rate using MR velocity mapping
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2008 (English)In: Journal of Magnetic Resonance Imaging, ISSN 1053-1807, E-ISSN 1522-2586, Vol. 28, no 3, p. 604-611Article in journal (Refereed) Published
Abstract [en]

Purpose: To estimate regional myocardial strain rate, with reduced sensitivity to noise and velocities outside the region of interest, and provide a visualization of the spatial variation of the obtained tensor field within the myocardium. Materials and Methods: Myocardial velocities were measured using two-dimensional phase contrast velocity mapping. Velocity gradients were estimated using normalized convolution and the calculated 2D strain rate tensor field was visualized using a glyph representation. Validation utilized a numerical phantom with known strain rate distribution. Strain rate glyph visualizations were created for normal myocardium in both systole and diastole and compared to a patient with an anteroseptal infarction. Results: In the phantom study the strain rate calculated with normalized convolution showed a very good agreement with the analytic solution, while traditional methods for gradient estimation were shown to be sensitive to both noise and surrounding velocity data. Normal myocardium showed a homogenous strain rate distribution, while a heterogeneous strain rate can be clearly seen in the patient data. Conclusion: The proposed approach for quantification and visualization of the regional myocardial strain rate can provide an objective measure of regional myocardial contraction and relaxation that may be valuable for the assessment of myocardial heart disease. © 2008 Wiley-Liss, Inc.

National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-43136 (URN)10.1002/jmri.21471 (DOI)000259106900007 ()71981 (Local ID)71981 (Archive number)71981 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
Al-Ahmad, A., Wigström, L., Sandner-Porkristl, D., Wang, P., Zei, P., Boese, J., . . . Fahrig, R. (2008). Time-resolved three-dimensional imaging of the left atrium and pulmonary veins in the interventional suite-A comparison between multisweep gated rotational three-dimensional reconstructed fluoroscopy and multislice computed tomography. Heart Rhythm, 5(4), 513-519
Open this publication in new window or tab >>Time-resolved three-dimensional imaging of the left atrium and pulmonary veins in the interventional suite-A comparison between multisweep gated rotational three-dimensional reconstructed fluoroscopy and multislice computed tomography
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2008 (English)In: Heart Rhythm, ISSN 1547-5271, Vol. 5, no 4, p. 513-519Article in journal (Refereed) Published
Abstract [en]

Background: Cardiac computed tomography (CT) is commonly used to visualize left atrial (LA) anatomy for ablation of atrial fibrillation. We have developed a new imaging technique that allows acquisition and visualization of three-dimensional (3D) cardiac images in the catheter lab. Objective: We sought to compare LA and pulmonary vein (PV) dimensions acquired using gated multisweep rotational fluoroscopy (C-arm CT) system and multislice computed tomography (MSCT) in an in vivo porcine model. Methods: A Siemens AXIOM Artis dTA C-arm system (Siemens AG, Medical Solutions) was modified to allow acquisition of four bidirectional sweeps during synchronized acquisition of the electrocardiogram signal to allow retrospective gating. C-arm CT image volumes were then reconstructed. Gated MSCT (SOMATOM Sensation 16 and 64, Siemens AG, Medical Solutions) and C-arm CT images were acquired in six animals. The two main PV diameters were measured in orthogonal axes. LA volumes were calculated. C-arm CT measurements were compared with the MSCT measurements. Results: The average PV diameters using the C-arm CT were 2.24 × 1.35 cm, versus 2.27 × 1.38 cm for CT. The average difference was 0.034 cm (1.9%) between the C-arm CT and standard CT. The average LA volume using MSCT was 49.1 ± 12.7 cm3, as compared with 51.0 ± 8.7 cm3 obtained by the C-arm CT. The average difference between the C-arm CT and the MSCT was 1.9 cm3 (3.7%). There were no significant differences in either the PV or LA measurements. Conclusions: Visualization of 3D cardiac anatomy during ablation procedures is possible and highly accurate. The 3D cardiac reconstructions acquired during ablation procedures will be valuable for procedural planning and guidance. © 2008 Heart Rhythm Society.

Keywords
3D imaging, C-arm CT, Computed tomography, Multisegment reconstruction, Pulmonary veins, Retrospective cardiac gating
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-46477 (URN)10.1016/j.hrthm.2007.12.027 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2011-01-10
Hope, T., Markl, M., Wigström, L., Alley, M., Miller, D. & Herfkens, R. (2007). Comparison of flow patterns in ascending aortic aneurysms and volunteers using four-dimensional magnetic resonance velocity mapping. Journal of Magnetic Resonance Imaging, 26(6), 1471-1479
Open this publication in new window or tab >>Comparison of flow patterns in ascending aortic aneurysms and volunteers using four-dimensional magnetic resonance velocity mapping
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2007 (English)In: Journal of Magnetic Resonance Imaging, ISSN 1053-1807, E-ISSN 1522-2586, Vol. 26, no 6, p. 1471-1479Article in journal (Refereed) Published
Abstract [en]

Purpose: To determine the difference in flow patterns between healthy volunteers and ascending aortic aneurysm patients using time-resolved three-dimensional (3D) phase contrast magnetic resonance velocity (4D-flow) profiling. Materials and Methods: 4D-flow was performed on 19 healthy volunteers and 13 patients with ascending aortic aneurysms. Vector fields placed on 2D planes were visually graded to analyze helical and retrograde flow patterns along the aortic arch. Quantitative analysis of the pulsatile flow was carried out on manually segmented planes. Results: In volunteers, flow progressed as follows: an initial jet of blood skewed toward the anterior right wall of the ascending aorta is reflected posterolaterally toward the inner curvature creating opposing helices, a right-handed helix along the left wall and a left-handed helix along the right wall, retrograde flow occurred in all volunteers along the inner curvature between the location of the two helices. In the aneurysm patients, the helices were larger, retrograde flow occurred earlier and lasted longer. The average velocity decreased between the ascending aorta and the transverse aorta in volunteers (47.9 mm/second decrease, P = 0.023), while in aneurysm patients the velocity increased (145 mm/second increase, P < 0.001). Conclusion: Dilation of the ascending aorta skews normal flow in the ascending aorta, changing retrograde and helical flow patterns. © 2007 Wiley-Liss, Inc.

Keywords
Ascending aortic aneurysms, Cardiac, Flow, Magnetic resonance imaging, Phase contrast
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:liu:diva-47678 (URN)10.1002/jmri.21082 (DOI)
Available from: 2009-10-11 Created: 2009-10-11 Last updated: 2017-12-13
Carlhäll, C., Kindberg, K., Wigström, L., Daughters, G. T., Millers, D. C., Karlsson, M. & Ingels Jr, N. B. (2007). Contribution of mitral annular dynamics to LV diastolic filling with alteration in preload and inotropic state. American Journal of Physiology. Heart and Circulatory Physiology, 293(3), G1473-H1479
Open this publication in new window or tab >>Contribution of mitral annular dynamics to LV diastolic filling with alteration in preload and inotropic state
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2007 (English)In: American Journal of Physiology. Heart and Circulatory Physiology, ISSN 0363-6135, E-ISSN 1522-1539, Vol. 293, no 3, p. G1473-H1479Article in journal (Refereed) Published
Abstract [en]

Mitral annular (MA) excursion during diastole encompasses a volume that is part of total left ventricular (LV) filling volume (LVFV). Altered excursion or area variation of the MA due to changes in preload or inotropic state could affect LV filling. We hypothesized that changes in LV preload and inotropic state would not alter the contribution of MA dynamics to LVFV. Six sheep underwent marker implantation in the LV wall and around the MA. After 7–10 days, biplane fluoroscopy was used to obtain three-dimensional marker dynamics from sedated, closed-chest animals during control conditions, inotropic augmentation with calcium (Ca), preload reduction with nitroprusside (N), and vena caval occlusion (VCO). The contribution of MA dynamics to total LVFV was assessed using volume estimates based on multiple tetrahedra defined by the three-dimensional marker positions. Neither the absolute nor the relative contribution of MA dynamics to LVFV changed with Ca or N, although MA area decreased (Ca, P < 0.01; and N, P < 0.05) and excursion increased (Ca, P < 0.01). During VCO, the absolute contribution of MA dynamics to LVFV decreased (P < 0.001), based on a reduction in both area (P < 0.001) and excursion (P < 0.01), but the relative contribution to LVFV increased from 18 ± 4 to 45 ± 13% (P < 0.001). Thus MA dynamics contribute substantially to LV diastolic filling. Although MA excursion and mean area change with moderate preload reduction and inotropic augmentation, the contribution of MA dynamics to total LVFV is constant with sizeable magnitude. With marked preload reduction (VCO), the contribution of MA dynamics to LVFV becomes even more important.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-41883 (URN)10.1152/ajpheart.00208.2007 (DOI)59289 (Local ID)59289 (Archive number)59289 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2017-12-13
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