Biomedical subjects

Ranjan Maitra

Publications and source records attributed to Ranjan Maitra.

4 recordsLinked to original sources

PubMed2006

Sex differences in the cerebral BOLD signal response to painful heat stimuli.

There are limited data addressing the question of sex differences in pain-related cerebral processing. This study examined whether pain-related blood oxygenation level-dependent (BOLD) signal change measured with functional magnetic resonance imaging (fMRI) demonstrated sex differences, under conditions of equivalent pain perception. Twenty-eight healthy volunteers (17 women, 11 men) were subject to a fMRI scan while noxious heat stimuli were applied to the dorsum of the left foot. Significant BOLD signal modulation was observed in several nociceptive processing regions of interest (ROIs) in all subjects. There were no sex differences in the spatial extent of BOLD signal change for any ROI, but the signal amplitude was lower for women in most ROIs and significantly so for the primary somatosensory cortex (S1), the midanterior cingulate cortex, and the dorsolateral prefrontal cortex (DLPFC). The BOLD signal response could be positive or negative, and frequently, both polarities were observed within a single ROI. In most ROIs, women show proportionately more voxels with negative signal change than men, and this difference was statistically significant for the S1 and the DLPFC. The time course of the negative signal change was very similar to that of the positive signal change, suggesting that the latter was not "driving" the former. The location of negative and positive clusters formed distinct patterns in several of the ROIs, and these patterns suggest something other than a local "steal" phenomenon as an explanation for the negative signal changes. Sex differences in baseline cerebral blood flow may contribute to the BOLD signal differences observed in this study.

Adult↗

PubMed2005

Reliability estimation of grouped functional imaging data using penalized maximum likelihood.

We analyzed grouped fMRI data and developed a reliability analysis for such data using the method of penalized maximum likelihood (ML). Specifically, this technique was applied to a somatosensory paradigm that used a mechanical probe to provide noxious stimuli to the foot, and a paradigm consisting of four levels of graded peripheral neuromuscular electrical stimulation (NMES). In each case, reliability maps of activation were generated. Receiver operating characteristic (ROC) curves were constructed in the case of the graded NMES paradigm for each level of stimulation, which revealed an increase in the specificity of activation with increasing stimulation levels. In addition, penalized ML was used to determine whether the grouped reliability maps obtained from one stimulus level were significantly different from those obtained at other levels. The results show a significant difference (P < 0.01) in the reliability of activation from one stimulation level to the next. These results are in agreement with those obtained using generalized linear modeling (GLM). While the reliability maps generated are not directly comparable, they are qualitatively similar to those obtained by controlling the expected false discovery rate (FDR). The proposed methodology can be used to objectively compare activation maps between groups, as well as to perform reliability assessments. Furthermore, this method potentially can be used to assess the longitudinal effect of treatment therapies within a group.

Analysis of Variance↗

PubMed2002

Test-retest reliability estimation of functional MRI data.

Functional magnetic resonance imaging (fMRI) data are commonly used to construct activation maps for the human brain. It is important to quantify the reliability of such maps. We have developed statistical models to provide precise estimates for reliability from several runs of the same paradigm over time. Specifically, our method extends the premise of maximum likelihood (ML) developed by Genovese et al. (Magn Reson Med 1997;38:497-507) by incorporating spatial context into the estimation process. Experiments indicate that our methodology provides more conservative estimates of true positives compared to those obtained by Genovese et al. The reliability estimates can be used to obtain voxel-specific reliability measures for activated as well as inactivated regions in future experiments. We derive statistical methodology to determine optimal thresholds for region- and context-specific activations. Empirical guidelines are also provided on the number of repeat scans to acquire in order to arrive at accurate reliability estimates. We report the results from experiments involving a motor paradigm performed on a single subject several times over a period of 2 months.

Brain↗

PubMedDate not supplied

Wrist circumference is related to patellar tendon thickness in healthy men and women.

The efficacy of dominant wrist circumference measurements to predict dominant lower extremity patellar tendon thickness at regions of interest for bone-patellar tendon-bone (BPTB) autograft harvest was studied among 24 healthy men and women. Dominant wrist circumference displayed good relationships with dominant lower extremity patellar tendon thickness as determined by two-dimensional diagnostic ultrasound. This initial screening method may assist surgeons as they consider graft selection for patients who may be at risk for developing or exacerbating preexisting patellofemoral joint or knee extensor mechanism conditions with BPTB autograft harvest.

Adult↗