A morphological grading of spinal stenosis: a radiological study on LSS and LBP patients : P173

Introduction: Clinical symptoms and degree of spinal stenosis based on cross sectional dural sac area correlate only weakly in lumbar spinal stenosis (LSS) patients. We conceived a four grade classification system (A, B, C & D) based on the morphology of the dural sac and its contents as seen on T2 axial MRI images. The categories take into account the rootlet/CSF ratio. We applied this grading to three patient groups: LSS scheduled for surgery; LSS following conservative treatment and patients with low back pain (LBP) without leg pain. Materials/Methods: A total of 346 T2 axial MRI images taken from LSS and LBP patients were included in this retroperspective study. 37 patients had decompressive surgery (132 MRI images), 31 conservative treatment (116 MRI images) and 27 patients had unspecific LBP (98 MRI images). Dural sac cross-sectional surface area and morphological grading of the canal were measured digitally both at disc and pedicle level. Intra- and inter-observer reliability were assessed (weighted Cohen's kappa statistics) from 50 MRI images taken from the surgery group. Results: At the most severe disc level, grade A (mild stenosis) was found in 3% of MRI images of the surgical group as opposed to 51% in the conservatively treated group and 85% in the LBP group. Grade B occurred in 8% of the surgical, 20% of the conservative and was negligible in LBP group (below 1%). Grade C and D (severe stenosis) was found in 89% of the surgical group, as opposed to 30% in conservative group and 11% in LBP group. The grades of all groups were comparable at the pedicle levels, exhibiting in 94% a grade A with a maximum at the A1 grade. Pedicle and disc level cross-sectional area were smallest in the surgery group and smaller in the conservative group as compared to the LBP group at the levels L2, L3 and L4. According to cross-sectional area measurements patients from the surgery group seems to have smaller vertebral canal although this was not related to smaller stature. Validation of grading: Average intra-and inter observer kappas were 0.76 and 0.69 respectively, for physicians working in the study originating institution. Combining all observers the kappa values were 0.57 +/- 0.19. and 0.44 +/- 0.19 respectively. Dural sac cross-sectional area measurements showed no statistically significant differences between observers. Conclusion: Since no specific measurement tools are needed the grading suits everyday clinical practice and favours communication of degree of stenosis between practising physicians. In our institution Grade A stenosis was less likely to require surgical treatment. This grading can therefore be an aid in surgical patient selection in teaching units.

Representing diffusion MRI in 5D for segmentation of white matter tracts with a level set method.

We present a method for segmenting white matter tracts from high angular resolution diffusion MR. images by representing the data in a 5 dimensional space of position and orientation. Whereas crossing fiber tracts cannot be separated in 3D position space, they clearly disentangle in 5D position-orientation space. The segmentation is done using a 5D level set method applied to hyper-surfaces evolving in 5D position-orientation space. In this paper we present a methodology for constructing the position-orientation space. We then show how to implement the standard level set method in such a non-Euclidean high dimensional space. The level set theory is basically defined for N-dimensions but there are several practical implementation details to consider, such as mean curvature. Finally, we will show results from a synthetic model and a few preliminary results on real data of a human brain acquired by high angular resolution diffusion MRI.

Perfusion measurement in brain gliomas with intravoxel incoherent motion MRI.

BACKGROUND AND PURPOSE: Intravoxel incoherent motion MRI has been proposed as an alternative method to measure brain perfusion. Our aim was to evaluate the utility of intravoxel incoherent motion perfusion parameters (the perfusion fraction, the pseudodiffusion coefficient, and the flow-related parameter) to differentiate high- and low-grade brain gliomas. MATERIALS AND METHODS: The intravoxel incoherent motion perfusion parameters were assessed in 21 brain gliomas (16 high-grade, 5 low-grade). Images were acquired by using a Stejskal-Tanner diffusion pulse sequence, with 16 values of b (0-900 s/mm(2)) in 3 orthogonal directions on 3T systems equipped with 32 multichannel receiver head coils. The intravoxel incoherent motion perfusion parameters were derived by fitting the intravoxel incoherent motion biexponential model. Regions of interest were drawn in regions of maximum intravoxel incoherent motion perfusion fraction and contralateral control regions. Statistical significance was assessed by using the Student t test. In addition, regions of interest were drawn around all whole tumors and were evaluated with the help of histograms. RESULTS: In the regions of maximum perfusion fraction, perfusion fraction was significantly higher in the high-grade group (0.127 ± 0.031) than in the low-grade group (0.084 ± 0.016, P < .001) and in the contralateral control region (0.061 ± 0.011, P < .001). No statistically significant difference was observed for the pseudodiffusion coefficient. The perfusion fraction correlated moderately with dynamic susceptibility contrast relative CBV (r = 0.59). The histograms of the perfusion fraction showed a "heavy-tailed" distribution for high-grade but not low-grade gliomas. CONCLUSIONS: The intravoxel incoherent motion perfusion fraction is helpful for differentiating high- from low-grade brain gliomas.

Micro-Structural Brain Alterations in Aviremic HIV+ Patients with Minor Neurocognitive Disorders: A Multi-Contrast Study at High Field.

OBJECTIVE: Mild neurocognitive disorders (MND) affect a subset of HIV+ patients under effective combination antiretroviral therapy (cART). In this study, we used an innovative multi-contrast magnetic resonance imaging (MRI) approach at high-field to assess the presence of micro-structural brain alterations in MND+ patients. METHODS: We enrolled 17 MND+ and 19 MND- patients with undetectable HIV-1 RNA and 19 healthy controls (HC). MRI acquisitions at 3T included: MP2RAGE for T1 relaxation times, Magnetization Transfer (MT), T2* and Susceptibility Weighted Imaging (SWI) to probe micro-structural integrity and iron deposition in the brain. Statistical analysis used permutation-based tests and correction for family-wise error rate. Multiple regression analysis was performed between MRI data and (i) neuropsychological results (ii) HIV infection characteristics. A linear discriminant analysis (LDA) based on MRI data was performed between MND+ and MND- patients and cross-validated with a leave-one-out test. RESULTS: Our data revealed loss of structural integrity and micro-oedema in MND+ compared to HC in the global white and cortical gray matter, as well as in the thalamus and basal ganglia. Multiple regression analysis showed a significant influence of sub-cortical nuclei alterations on the executive index of MND+ patients (p = 0.04 he and R(2) = 95.2). The LDA distinguished MND+ and MND- patients with a classification quality of 73% after cross-validation. CONCLUSION: Our study shows micro-structural brain tissue alterations in MND+ patients under effective therapy and suggests that multi-contrast MRI at high field is a powerful approach to discriminate between HIV+ patients on cART with and without mild neurocognitive deficits.

Usefulness of late enhancement MRI as diagnostic tool to differentiate myocardial infarction from myocarditis

Introduction: Residual pulmonary artery (PA) anomalies are a major concern after surgery for cono-truncal malformations. This study sought to assess residual PA anomalies using MRI/MRA. Methods: 43 MRI/MRA studies were performed in 37 patients after corrective surgery for cono-truncal malformations. MRI/MRA studies comprised spin-echo, cine, velocity-encoded and 3D Gadolinium-enhanced MRA sequences. Residual PA anomalies were searched in ail patients; angiographie data were available in 13 patients and a comparison with MRI/MRA was made. Results: 32/37 patients had postoperative anomalies of the pulmonary arterial tree. Left pulmonary artery stenosis was the most common finding (14/32), followed by stenosis at multiple sites (11/32). Isolated right pulmonary artery stenosis was rare (2/32). The median time interval between MRI/MRA and angiography in the 13 patients undergoing both types of studies was 54 days. The findings between the two examinations were identical regarding stenoses and collateral vessels. In 4 patients, the MRI/MRA study allowed to plan interventional catheterization with balloon dilatation and/or stenting of the obstructed arteries or co il-occlusion of systemic collaterals. Eleven patients had additional surgery based on MRI/MRA findings. Conclusions: Post-operative anomalies of the PA in cono-truncal malformations can reliably be detected with MRI/MRA. This technique allows planning of the intervention al or surgical procedure to correct the residual anomalies and may th us replace or precede catheterization during the follow-up of surgically corrected cono-truncal malformations.

Weighted Logratio Biplots, Correspondence Analysis and Spectral Maps

Starting with logratio biplots for compositional data, which are based on the principle of subcompositional coherence, and then adding weights, as in correspondence analysis, we rediscover Lewi's spectral map and many connections to analyses of two-way tables of non-negative data. Thanks to the weighting, the method also achieves the property of distributional equivalence

A Monte Carlo-Based Fiber Tracking Algorithm using Diffusion Tensor MRI

Diffusion tensor magnetic resonance imaging, which measures directional information of water diffusion in the brain, has emerged as a powerful tool for human brain studies. In this paper, we introduce a new Monte Carlo-based fiber tracking approach to estimate brain connectivity. One of the main characteristics of this approach is that all parameters of the algorithm are automatically determined at each point using the entropy of the eigenvalues of the diffusion tensor. Experimental results show the good performance of the proposed approach

Self-Navigation with Compressed Sensing for 2D Translational Motion Correction in Free-Breathing Coronary MRI: A Feasibility Study.

PURPOSE: Respiratory motion correction remains a challenge in coronary magnetic resonance imaging (MRI) and current techniques, such as navigator gating, suffer from sub-optimal scan efficiency and ease-of-use. To overcome these limitations, an image-based self-navigation technique is proposed that uses "sub-images" and compressed sensing (CS) to obtain translational motion correction in 2D. The method was preliminarily implemented as a 2D technique and tested for feasibility for targeted coronary imaging. METHODS: During a 2D segmented radial k-space data acquisition, heavily undersampled sub-images were reconstructed from the readouts collected during each cardiac cycle. These sub-images may then be used for respiratory self-navigation. Alternatively, a CS reconstruction may be used to create these sub-images, so as to partially compensate for the heavy undersampling. Both approaches were quantitatively assessed using simulations and in vivo studies, and the resulting self-navigation strategies were then compared to conventional navigator gating. RESULTS: Sub-images reconstructed using CS showed a lower artifact level than sub-images reconstructed without CS. As a result, the final image quality was significantly better when using CS-assisted self-navigation as opposed to the non-CS approach. Moreover, while both self-navigation techniques led to a 69% scan time reduction (as compared to navigator gating), there was no significant difference in image quality between the CS-assisted self-navigation technique and conventional navigator gating, despite the significant decrease in scan time. CONCLUSIONS: CS-assisted self-navigation using 2D translational motion correction demonstrated feasibility of producing coronary MRA data with image quality comparable to that obtained with conventional navigator gating, and does so without the use of additional acquisitions or motion modeling, while still allowing for 100% scan efficiency and an improved ease-of-use. In conclusion, compressed sensing may become a critical adjunct for 2D translational motion correction in free-breathing cardiac imaging with high spatial resolution. An expansion to modern 3D approaches is now warranted.

Segmentació de teixit i lesions en imatges de MRI de malalts d'esclerosi múltiple

Actualment, en l'àmbit mèdic, la ressonància magnètica, MRI Magnetic Resonance Imaging, és un dels sistemes més utilitzats per a la realització de diagnòstics i el seguiment de l'evolució de malalties com l'esclerosi múltiple (EM). No obstant, la gran quantitat d'informació que proporciona aquesta modalitat té com a conseqüència una tasca feixuga d'anàlisi i d'interpretació per part dels radiòlegs i neuròlegs. L'objectiu general d'aquest projecte és desenvolupar un sistema per ajudar als metges a segmentar les imatges de MRI del cervell. S'ha implementat amb MATLAB. Durant tot el procés s'han utilitzat dades sintètiques, de la base de dades simulada BrainWeb, i reals, proporcionades pels grup de metges col•laboradors amb el grup VICOROB.El projecte s'emmarca dins d'un projecte de recerca del grup de Visió per Computador i Robòtica de la Universitat de Girona