Center for Medical Imaging

United Kingdom

Center for Medical Imaging

United Kingdom

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Chan R.W.,Center for Medical Imaging | Von Deuster C.,ETH Zurich | Von Deuster C.,King's College London | Giese D.,King's College London | And 6 more authors.
Journal of Magnetic Resonance | Year: 2014

Diffusion tensor imaging (DTI) of moving organs is gaining increasing attention but robust performance requires sequence modifications and dedicated correction methods to account for system imperfections. In this study, eddy currents in the "unipolar" Stejskal-Tanner and the velocity-compensated "bipolar" spin-echo diffusion sequences were investigated and corrected for using a magnetic field monitoring approach in combination with higher-order image reconstruction. From the field-camera measurements, increased levels of second-order eddy currents were quantified in the unipolar sequence relative to the bipolar diffusion sequence while zeroth and linear orders were found to be similar between both sequences. Second-order image reconstruction based on field-monitoring data resulted in reduced spatial misalignment artifacts and residual displacements of less than 0.43 mm and 0.29 mm (in the unipolar and bipolar sequences, respectively) after second-order eddy-current correction. Results demonstrate the need for second-order correction in unipolar encoding schemes but also show that bipolar sequences benefit from second-order reconstruction to correct for incomplete intrinsic cancellation of eddy-currents. © 2014 Elsevier Inc. All rights reserved.

Menys A.,Center for Medical Imaging | Menys A.,University College London | Hamy V.,Center for Medical Imaging | Hamy V.,University College London | And 9 more authors.
Physics in Medicine and Biology | Year: 2014

At present, registration-based quantification of bowel motility from dynamic MRI is limited to breath-hold studies. Here we validate a dual-registration technique robust to respiratory motion for the assessment of small bowel and colonic motility. Small bowel datasets were acquired in breath-hold and free-breathing in 20 healthy individuals. A pre-processing step using an iterative registration of the low rank component of the data was applied to remove respiratory motion from the free breathing data. Motility was then quantified with an existing optic-flow (OF) based registration technique to form a dual-stage approach, termed Dual Registration of Abdominal Motion (DRAM). The benefit of respiratory motion correction was assessed by (1) assessing the fidelity of automatically propagated segmental regions of interest (ROIs) in the small bowel and colon and (2) comparing parametric motility maps to a breath-hold ground truth. DRAM demonstrated an improved ability to propagate ROIs through free-breathing small bowel and colonic motility data, with median error decreased by 90% and 55%, respectively. Comparison between global parametric maps showed high concordance between breath-hold data and free-breathing DRAM. Quantification of segmental and global motility in dynamic MR data is more accurate and robust to respiration when using the DRAM approach. © 2014 Institute of Physics and Engineering in Medicine.

Tremoulheac B.,University College London | Atkinson D.,Center for Medical Imaging | Arridge S.R.,University College London
Proceedings - International Symposium on Biomedical Imaging | Year: 2013

Higher spatial and temporal resolution of dynamic MR imaging can be achieved by sparse and sub-Nyquist sampling of (k-t)-space. However, direct inversion of this inverse problem can result in artefact in reconstructed images. In combination with a golden angle pseudo-radial acquisition, we propose in this paper to use prior information based on the rank to regularize the problem. The iterative scheme to reconstruct the dynamic imaging series is based on an accelerated proximal gradient algorithm designed for large-scale low-rank matrix completion. The method is tested on simulated and clinical datasets and, besides being simple, proves to be fast and efficient for high acceleration factors. © 2013 IEEE.

Menys A.,Center for Medical Imaging | Makanyanga J.,Center for Medical Imaging | Plumb A.,Center for Medical Imaging | Bhatnagar G.,Center for Medical Imaging | And 3 more authors.
Inflammatory Bowel Diseases | Year: 2016

Background: Inflammation-related enteric dysmotility has been postulated as a cause for abdominal symptoms in Crohn's disease (CD). We investigated the relationship between magnetic resonance imaging-quantified small bowel (SB) motility, inflammatory activity, and patient symptom burden. Methods: The Harvey-Bradshaw index (HBI) and fecal calprotectin were prospectively measured in 53 patients with CD (median age, 35; range, 18-78 years) the day before magnetic resonance enterography, which included a dynamic (cine), breath-hold motility sequence, repeated to encompass the whole SB volume. A validated registration-based motility quantitation technique produced motility maps, and regions of interest were drawn to include all morphologically normal SB (i.e., excluding diseased bowel). Global SB motility was correlated with calprotectin, HBI, and symptom components (well-being, pain, and diarrhea). Adjustment for age, sex, smoking, and surgical history was made using multivariate linear regression. Results: Median calprotectin was 336 (range, 0-1280). Median HBI, motility mean, and motility variance were 3 (range, 0-16), 0.33 (0.18-0.51), and 0.01 (0.0014-0.034), respectively. Motility variance was significantly negatively correlated with calprotectin (rho-0.33, P 0.015), total HBI (rho-0.45, P < 0.001), well-being (rho-0.4, P 0.003), pain (rho-0.27, P 0.05), and diarrhea (rho-0.4, P 0.0025). The associations remained highly significant after adjusting for covariates. There was no association between mean motility and calprotectin or HBI (P > 0.05). Conclusions: Reduced motility variance in morphologically normal SB is associated with patient symptoms and fecal calprotectin levels, supporting the hypothesis that inflammation-related enteric dysmotility may explain refractory abdominal symptoms in CD. © 2016 Crohn's & Colitis Foundation of America, Inc.

Dorrius M.D.,Center for Medical Imaging | Jansen-Van Der Weide M.C.,Center for Medical Imaging | Van Ooijen P.M.A.,Center for Medical Imaging | Pijnappel R.M.,Center for Medical Imaging | Oudkerk M.,Center for Medical Imaging
European Radiology | Year: 2011

Objectives To evaluate the additional value of computer-aided detection (CAD) in breast MRI by assessing radiologists' accuracy in discriminating benign from malignant breast lesions. Methods A literature search was performed with inclusion of relevant studies using a commercially available CAD system with automatic colour mapping. Two independent researchers assessed the quality of the studies. The accuracy of the radiologists' performance with and without CAD was presented as pooled sensitivity and specificity. Results Of 587 articles, 10 met the inclusion criteria, all of good methodological quality. Experienced radiologists reached comparable pooled sensitivity and specificity before and after using CAD (sensitivity: without CAD: 89%; 95% CI: 78-94%, with CAD: 89%; 95%CI: 81-94%) (specificity: without CAD: 86%; 95% CI: 79-91%, with CAD: 82%; 95% CI: 76-87%). For residents the pooled sensitivity increased from 72% (95% CI: 62-81%) without CAD to 89% (95% CI: 80-94%) with CAD, however, not significantly. Concerning specificity, the results were similar (without CAD: 79%; 95% CI: 69-86%, with CAD: 78%; 95% CI: 69-84%). Conclusions CAD in breast MRI has little influence on the sensitivity and specificity of experienced radiologists and therefore their interpretation remains essential. However, residents or inexperienced radiologists seem to benefit from CAD concerning breast MRI evaluation. © The Author(s) 2011.

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