Biomedical subjects

Vivek Singh

Publications and source records attributed to Vivek Singh.

5 recordsLinked to original sources

PubMed2006

Spatial patterns of cortical thinning in mild cognitive impairment and Alzheimer's disease.

Cortical thickness is a more reliable measure of atrophy than volume due to the low variability in the cytoarchitectural structure of the grey matter. However, this more desirable measure of disease-related alterations is not fully evaluated in early dementia. The study presented here is the first to report the spatial patterns of cortical thickness in the pre-clinical stages of Alzheimer's disease, namely mild cognitive impairment (MCI). Cortical thickness measurements for 34 healthy elderly, 62 MCI and 42 Alzheimer's disease subjects were made using fully automated magnetic resonance imaging-based analysis techniques in order to determine the pattern of cortical thinning as a function of disease progression. The thickness of the cortex decreased significantly when the healthy elderly brains were compared to those with MCI, mainly in the medial temporal lobe region and in some regions of the frontal and the parietal cortices. With the progression of disease from MCI to Alzheimer's disease, a general thinning of the entire cortex with significant extension into the lateral temporal lobe was found. In all cases, the results were more pronounced in the left hemisphere. In conclusion, we have shown that there is a specific pattern in the thinning of the cortical ribbon which is in agreement with the previous histological reports. These novel findings support the notion of increased isocortical involvement with the progression of disease.

Aged↗

PubMed2005

Automated 3-D extraction and evaluation of the inner and outer cortical surfaces using a Laplacian map and partial volume effect classification.

Accurate reconstruction of the inner and outer cortical surfaces of the human cerebrum is a critical objective for a wide variety of neuroimaging analysis purposes, including visualization, morphometry, and brain mapping. The Anatomic Segmentation using Proximity (ASP) algorithm, previously developed by our group, provides a topology-preserving cortical surface deformation method that has been extensively used for the aforementioned purposes. However, constraints in the algorithm to ensure topology preservation occasionally produce incorrect thickness measurements due to a restriction in the range of allowable distances between the gray and white matter surfaces. This problem is particularly prominent in pediatric brain images with tightly folded gyri. This paper presents a novel method for improving the conventional ASP algorithm by making use of partial volume information through probabilistic classification in order to allow for topology preservation across a less restricted range of cortical thickness values. The new algorithm also corrects the classification of the insular cortex by masking out subcortical tissues. For 70 pediatric brains, validation experiments for the modified algorithm, Constrained Laplacian ASP (CLASP), were performed by three methods: (i) volume matching between surface-masked gray matter (GM) and conventional tissue-classified GM, (ii) surface matching between simulated and CLASP-extracted surfaces, and (iii) repeatability of the surface reconstruction among 16 MRI scans of the same subject. In the volume-based evaluation, the volume enclosed by the CLASP WM and GM surfaces matched the classified GM volume 13% more accurately than using conventional ASP. In the surface-based evaluation, using synthesized thick cortex, the average difference between simulated and extracted surfaces was 4.6 +/- 1.4 mm for conventional ASP and 0.5 +/- 0.4 mm for CLASP. In a repeatability study, CLASP produced a 30% lower RMS error for the GM surface and a 8% lower RMS error for the WM surface compared with ASP.

Algorithms↗

PubMed2005

Anticonvulsants in bipolar disorder.

In recent years, a number of anticonvulsants have been more rigorously investigated for their potential mood-stabilizing properties. They are heterogeneous in their mechanisms of action and in their efficacy in the various mood states in bipolar illness (Table 3). At present, evidence from well-controlled studies supports the role of DIV and CBZ in the treatment of acute mania. DIV seems to have better efficacy than lithium in mixed mania or mania associated with depressive symptoms and is recommended as a first-line pharmacologic option in acutely manic or mixed manic patients. Neither CBZ nor DIV have robust evidence supporting their efficacy in the treatment of acute bipolar depression, although DIV clearly possesses beneficial effects on depressive symptomatology and prophylaxis against depressive episodes during long-term treatment. Results from a large study indicate that LAM has significant efficacy in bipolar depression without the associated risks of cycle acceleration or manic/hypomanic switches. LAM should be considered a primary option in patients with bipolar depression and in bipolar II patients with rapid cycling. DIV is recommended as a first-line option in bipolar I patients with rapid cycling. LAM has proven efficacy in the prophylaxis of bipolar I disorder and should be considered along with lithium or DIV as treatment of choice in the long-term management of bipolar disorder. For the other anticonvulsants, including CBZ and OXC, there is still inadequate evidence of efficacy as monotherapy in the long-term management of bipolar disorder. Even less data exist for other available AEDs, and consensus is growing that someAEDs (eg, GBP) have little or no specific effect in bipolar disorder. Despite the progress made in the past decade, a wider therapeutic armamentarium is critically needed, because a large proportion of bipolar patients do not respond to acute treatments during a manic or depressive episode and have frequent relapse and recurrences during long-term treatment. As additional AEDs become available, rigorously designed and large-scale studies examining AEDs as monotherapy and AEDs in combination therapies versus placebo must be undertaken to assess efficacy and safety more adequately to provide better guidance for the clinician faced with the management of this challenging mood disorder.

Anticonvulsants↗

PubMed2004

Ulnar stress reaction from crutch use following amputation for tibial osteosarcoma.

Stress fractures of the ulnar diaphysis occur most commonly in association with upper-limb dominated sports. Their occurrence in association with crutch use is rare. Following a review of the world literature we report the third such case in a patient using crutches following above knee amputation for recurrent tibial osteosarcoma. MRI was performed to rule out metastatic disease.

Adult↗

PubMedDate not supplied

Image segmentation for automatic particle identification in electron micrographs based on hidden Markov random field models and expectation maximization.

Three-dimensional reconstruction of large macromolecules like viruses at resolutions below 10 A requires a large set of projection images. Several automatic and semi-automatic particle detection algorithms have been developed along the years. Here we present a general technique designed to automatically identify the projection images of particles. The method is based on Markov random field modelling of the projected images and involves a pre-processing of electron micrographs followed by image segmentation and post-processing. The image is modelled as a coupling of two fields--a Markovian and a non-Markovian. The Markovian field represents the segmented image. The micrograph is the non-Markovian field. The image segmentation step involves an estimation of coupling parameters and the maximum á posteriori estimate of the realization of the Markovian field i.e, segmented image. Unlike most current methods, no bootstrapping with an initial selection of particles is required.

Algorithms↗