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ABSTRACT: Improving the resolution in magnetic resonance imaging comes at the cost of either lower signal-to-noise ratio, longer acquisition time or both. This study investigates whether so-called super-resolution reconstruction methods can increase the resolution in the slice selection direction and, as such, are a viable alternative to direct high-resolution acquisition in terms of the signal-to-noise ratio and acquisition time trade-offs. The performance of six super-resolution reconstruction methods and direct high-resolution acquisitions was compared with respect to these trade-offs. The methods are based on iterative back-projection, algebraic reconstruction, and regularized least squares. The algorithms were applied to low-resolution data sets within which the images were rotated relative to each other. Quantitative experiments involved a computational phantom and a physical phantom containing structures of known dimensions. To visually validate the quantitative evaluations, qualitative experiments were performed, in which images of three different subjects (a phantom, an ex vivo rat knee, and a postmortem mouse) were acquired with different magnetic resonance imaging scanners. The results show that super-resolution reconstruction can indeed improve the resolution, signal-to-noise ratio and acquisition time trade-offs compared with direct high-resolution acquisition. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.
Magnetic Resonance in Medicine 01/2012; · 2.96 Impact Factor
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ABSTRACT: Tagged magnetic resonance imaging (tMRI) is a well-known noninvasive method for studying regional heart dynamics. It offers great potential for quantitative analysis of a variety of kine(ma)tic parameters, but its clinical use has so far been limited, in part due to the lack of robustness and accuracy of existing tag tracking algorithms in dealing with low (and intrinsically time-varying) image quality. In this paper, we evaluate the performance of four frequently used concepts found in the literature (optical flow, harmonic phase (HARP) magnetic resonance imaging, active contour fitting, and non-rigid image registration) for cardiac motion analysis in 2D tMRI image sequences, using both synthetic image data (with ground truth) and real data from preclinical (small animal) and clinical (human) studies. In addition we propose a new probabilistic method for tag tracking that serves as a complementary step to existing methods. The new method is based on a Bayesian estimation framework, implemented by means of reversible jump Markov chain Monte Carlo (MCMC) methods, and combines information about the heart dynamics, the imaging process, and tag appearance. The experimental results demonstrate that the new method improves the performance of even the best of the four previous methods. Yielding higher consistency, accuracy, and intrinsic tag reliability assessment, the proposed method allows for improved analysis of cardiac motion.
Medical image analysis 09/2011; 16(1):301-24. · 3.09 Impact Factor
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Journal of Cardiovascular Magnetic Resonance. 01/2011;
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ABSTRACT: Through labelling of cells with magnetic contrast agents it is possible to follow the fate of transplanted cells in vivo with magnetic resonance imaging (MRI) as has been demonstrated in animal studies as well as in a clinical setting. A large variety of labelling strategies are available that allow for prolonged and sensitive detection of the labelled cells with MRI. The various protocols each harbour specific advantages and disadvantages. In choosing a particular labelling strategy it is also important to ascertain that the labelling procedure does not negatively influence cell functionality, for which a large variety of assays are available. In order to overcome the challenges still faced in fully exploiting the benefits of in vivo cell tracking by MRI a good understanding and standardisation of the procedures and assays used will be crucial.
European Radiology 09/2009; 20(2):255-74. · 3.22 Impact Factor
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Eric Farrell, Piotr Wielopolski,
Predrag Pavljasevic,
Sandra van Tiel,
Holger Jahr,
Jan Verhaar,
Harrie Weinans,
Gabriel Krestin,
Fergal J O'Brien,
Gerjo van Osch,
Monique Bernsen
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ABSTRACT: Successful cell therapy will depend on the ability to monitor transplanted cells. With cell labeling, it is important to demonstrate efficient long term labeling without deleterious effects on cell phenotype and differentiation capacity. We demonstrate long term (7 weeks) retention of superparamagnetic iron oxide particles (SPIO) by mesenchymal stem cells (MSCs) in vivo, detectable by MRI. In vitro, multilineage differentiation (osteogenic, chondrogenic and adipogenic) was demonstrated by histological evaluation and molecular analysis in SPIO labeled and unlabeled cells. Gene expression levels were comaparable to unlabeled controls in adipogenic and chondrogenic conditions however not in the osteogenic condition. MSCs seeded into a scaffold for 21 days and implanted subcutaneously into nude mice for 4 weeks, showed profoundly altered phenotypes in SPIO labeled samples compared to implanted unlabeled control scaffolds, indicating chondrogenic differentiation. This study demonstrates long term MSC traceability using SPIO and MRI, uninhibited multilineage MSC differentiation following SPIO labeling, though with subtle but significant phenotypical alterations.
Biochemical and Biophysical Research Communications 06/2008; 369(4):1076-81. · 2.48 Impact Factor
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Timo Baks,
Robert-Jan van Geuns,
Elena Biagini, Piotr Wielopolski,
Nico R Mollet,
Filippo Cademartiri,
Willem J van der Giessen,
Gabriel P Krestin,
Patrick W Serruys,
Dirk J Duncker,
Pim J de Feyter
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ABSTRACT: The effects of reperfusion on early and late infarct size and left ventricular wall characteristics were studied by performing cine-magnetic resonance imaging, first-pass perfusion, and delayed enhancement imaging in 22 patients at five days and five months after successful primary angioplasty for first acute myocardial infarction. Infarct size, end-diastolic wall thickness, and segmental wall thickening were quantified, and the extent of microvascular obstruction (MO) was evaluated qualitatively. Infarct size decreased by 31%. Segments without MO had early increased wall thickness and late partially normalized wall thickening. Segments with MO showed late wall thinning and no functional recovery at five months.
We aimed to study the effects of early successful primary angioplasty for ST-segment elevation acute myocardial infarction (AMI) on early and late infarct size and left ventricular (LV) wall characteristics.
Early reperfusion treatment for AMI preserves LV function, but the effects on early and late infarct size, end-diastolic wall thickness (EDWT), and segmental wall thickening (SWT) are not well known.
In 22 patients with successful primary angioplasty for first AMI, cine-magnetic resonance imaging (MRI), first-pass perfusion, and delayed-enhancement imaging was performed at five days and five months. The extent of microvascular obstruction (MO) was evaluated on perfusion images. Infarct shrinkage was defined as the difference between the volume of delayed-enhancement at five days and five months. The EDWT and SWT were quantified on cine-MRI.
Infarct shrinkage occurred to the same extent in small and large infarctions [r = 0.92; p < 0.001], with a mean decrease of 31% (35 +/- 21 g to 24 +/- 17 g). Dysfunctional segments without MO had an increased EDWT at five days compared with remote myocardium (9.2 +/- 1.7 mm vs. 8.4 +/- 1.7 mm; p < 0.001). At five months, EDWT in these segments became comparable to the thickness of remote myocardium (7.8 +/- 1.6 mm vs. 7.6 +/- 1.4 mm; p = 0.60), and SWT improved (21 +/- 15% to 40 +/- 24%; p < 0.001) but remained impaired (40 +/- 24% vs. 71 +/- 29%; p < 0.001). Segments with MO demonstrated wall thinning at five months (6.4 +/- 1.3 mm vs. 7.6 +/- 1.4 mm; p = 0.006) and no significant recovery in SWT (12 +/- 14% to 17 +/- 20%; p = 0.15).
Infarct size decreased by 31%. Segments without MO had early increased wall thickness and late partial functional recovery. Segments with MO showed late wall thinning and no functional recovery at five months.
Journal of the American College of Cardiology 01/2006; 47(1):40-4. · 14.16 Impact Factor
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Timo Baks,
Robert-Jan van Geuns,
Elena Biagini, Piotr Wielopolski,
Nico R Mollet,
Filippo Cademartiri,
Eric Boersma,
Willem J van der Giessen,
Gabriel P Krestin,
Dirk J Duncker,
Patrick W Serruys,
Pim J de Feyter
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ABSTRACT: To study recovery of segmental wall thickening (SWT), ejection fraction (EF), and end-systolic volume (ESV) after acute myocardial infarction (AMI) in patients who underwent primary stenting with drug-eluting stents. Additionally, to evaluate the predictive value of magnetic resonance imaging (MRI)-based myocardial perfusion and delayed enhancement (DE) imaging.
Twenty-two patients underwent cine-MRI, first-pass perfusion, and DE imaging 5 days after successful placement of a drug-eluting stent in the infarct-related coronary artery. Regional myocardial perfusion and the transmural extent of DE were evaluated. A per patient perfusion score was calculated and consisted of a summation of all segmental scores. Myocardial infarct size was quantified by measuring the volume of DE. At 5 months after AMI, cine-MRI was performed and SWT, EF, and ESV were quantified. EF increased from 48+/-11 to 55+/-9% (P<0.01). SWT at 5 months was inversely related to baseline segmental DE scores (P<0.001) and segmental perfusion scores (P<0.001). EF and ESV at 5 months were related to acute infarct size (R(2)=0.65; P<0.001 and R(2)=0.78; P<0.001, respectively) and the calculated perfusion score (R(2)=0.23; P=0.02 and R(2)=0.14; P=0.09, respectively) at baseline.
Marked recovery of left ventricular function was observed in patients receiving a drug-eluting stent for AMI. DE imaging appears to be a better prognosticator than perfusion imaging.
European Heart Journal 06/2005; 26(11):1070-7. · 10.48 Impact Factor
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ABSTRACT: Intraluminal stent signal characterization by MRI is generally hampered by signal loss from the metallic stent material. This signal loss is related to magnetic susceptibility and RF shielding. Even when stent materials with low magnetic susceptibility are used, RF shielding can still be problematic. In this article we have shown that high flip angle imaging enables morphology assessment and tissue characterization in stents made of stainless steel 316L, NiTinol, and ABI-alloy.
Magnetic Resonance in Medicine 11/2003; 50(4):879-83. · 2.96 Impact Factor
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ABSTRACT: Diagnostic strategies for pulmonary embolism are complex and consist of non-invasive diagnostic tests done to avoid conventional pulmonary angiography as much as possible. We aimed to assess the diagnostic accuracy of magnetic resonance angiography (MRA) for the diagnosis of pulmonary embolism, using conventional pulmonary angiography as a reference method.
In a prospective study, we enrolled 141 patients with suspected pulmonary embolism and an abnormal perfusion scan. Patients underwent MRA before conventional pulmonary angiography. Two reviewers, masked with respect to the results of conventional pulmonary angiography, assessed MRA images independently. Statistical analyses used chi(2) and 95% CI.
MRA was contraindicated in 13 patients (9%), and images were not interpretable in eight (6%). MRA was done in two patients in whom conventional pulmonary angiography was contraindicated. Thus, MRA and conventional pulmonary angiography results were available in 118 patients (84%). Prevalence of pulmonary embolism was 30%. Images were read independently in 115 patients, and agreement obtained in 105 (91%), kappa=0.75. MRA identified 27 of 35 patients with proven pulmonary embolism (sensitivity 77%, 95% CI 61-90). Sensitivity of MRA for isolated subsegmental, segmental, and central or lobar pulmonary embolism was 40%, 84%, and 100%, respectively (p<0.01 for isolated subsegmental vs segmental or larger pulmonary embolism). However, subgroups contained small numbers. MRA identified pulmonary embolism in two patients with normal angiogram (98%, 92-100).
MRA is sensitive and specific for segmental or larger pulmonary embolism. Results are similar to those obtained with helical computed tomography, but MRA has safer contrast agents and does not involve ionising radiation. MRA could become part of the diagnostic strategy for pulmonary embolism.
The Lancet 05/2002; 359(9318):1643-7. · 38.28 Impact Factor
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ABSTRACT: Until recently, visualization of the coronary arteries was the sole domain of catheter-based x-ray angiography. In an effort to detect and assess coronary artery disease noninvasively, magnetic resonance imaging, electron beam computed tomography, and multislice spiral computed tomography have emerged as potential modalities. Besides visualization of the vessel lumen, these techniques may be capable of imaging and characterizing atherosclerotic plaques. None of these techniques are yet routinely used, but considering the pace of the technical advancements, clinically reliable noninvasive coronary angiography can be expected in the coming years.
Reviews in cardiovascular medicine 02/2002; 3(2):77-84. · 0.58 Impact Factor
