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Biomedical subjects

R Chandrasekhar

Publications and source records attributed to R Chandrasekhar.

6 recordsLinked to original sources
PubMed2006

Elastographic image quality vs. tissue motion in vivo.

Elastography is a noninvasive method of imaging tissue elasticity using standard ultrasound equipment. In conventional elastography, axial strain elastograms are generated by cross-correlating pre- and postcompression digitized radio frequency (RF) echo frames acquired from the tissue before and after a small uniaxial compression, respectively. The time elapsed between the pre- and the postcompression frames is referred to as the interframe interval. For in vivo elastography, the interframe interval is critical because uncontrolled physiologic motion such as heartbeat, muscle motion, respiration and blood flow introduce interframe decorrelation that reduces the quality of elastograms. To obtain a measure of this decorrelation, in vivo experimental data (from human livers and thyroids) at various interframe intervals were obtained from 20 healthy subjects. To further examine the effect of the different interframe intervals on the elastographic image quality, the experimental data were also used in combination with elastographic simulation data. The deterioration of elastographic image quality was objectively evaluated by computing the area under the strain filter (SF) at a given resolution. The experimental results of this study demonstrate a statistical exponential behavior of the temporal decay of the echo signal cross-correlation amplitudes from the in vivo tissues due to uncontrollable motion. The results also indicate that the dynamic range and height of the SF are reduced at increased interframe intervals, suggesting that good objective image quality may be achieved provided only that a high frame rate is maintained in elastographic applications.

Acoustics↗
PubMed2004

Water contamination in urban south India: household storage practices and their implications for water safety and enteric infections.

Water contamination, at source and during household storage, is a major cause of enterically transmitted infections in developing countries. This study assessed contamination of the municipal water in a south Indian town, which obtains its water intermittently from a surface lake and by pumping subsurface water from a dry river bed, and monitored microbial contamination during household storage. All samples of the 'treated' municipal water were contaminated when freshly pumped, and on household storage, 25/37 (67%) showed increased contamination during storage periods from 1 to 9 days. Household storage in brass, but not in containers of other materials significantly decreased contamination of water (p = 0.04). This was confirmed in the laboratory by testing water seeded with 10(3) to 10(5) Escherichia coli per 100 ml stored in containers of different materials (p < 0.01). Despite the requirements for provision of safe drinking water in municipal areas, in practice the water supplied in Vellore is contaminated and current household storage practices increase the level of contamination in at least two-thirds of households. The implementation of locally appropriate point-of-use disinfection and safe household storage practices in developing countries is an urgent need to ensure a safe, reliable year-round supply in areas where clean water is not available.

Adult↗
PubMed1997

A simple method for automatically locating the nipple on mammograms.

This paper outlines a simple, fast, and accurate method for automatically locating the nipple on digitized mammograms that have been segmented to reveal the skin-air interface. If the average gradient of the intensity is computed in the direction normal to the interface and directed inside the breast, it is found that there is a sudden and distinct change in this parameter close to the nipple. A nipple in profile is located between two successive maxima of this parameter; otherwise, it is near the global maximum. Specifically, the nipple is located midway between a successive maximum and minimum of the derivative of the average intensity gradient; these being local turning points for a nipple in profile and global otherwise. The method has been tested on 24 images, including both oblique and cranio-caudal views, from two digital mammogram databases. For 23 of the images (96%), the rms error was less than 1 mm at image resolutions of 400 microns and 420 microns per pixel. Because of its simplicity, and because it is based both on the observed behavior of mammographic tissue intensities and on geometry, this method has the potential to become a generic method for locating the nipple on mammograms.

Algorithms↗
PubMed1988

Alterations in rat brain polyphosphoinositide metabolism due to acute ethanol administration.

The effects of acute ethanol administration on the polyphosphoinositide metabolism of rat brain cerebral cortex were examined. Intracerebral injections of [gamma-32P]ATP proved to be an effective in vivo method to prelabel brain phospholipids, especially the polyphosphoinositides. High acute doses of ethanol (8 or 6 g/kg b.wt.) administered by gavage significantly inhibited the breakdown of polyphosphoinositides as judged by an elevation in the concentration as well as the labeling of these compounds. Concomitantly, there was a significant reduction in the level of diacylglycerols. Low acute doses of ethanol (2 g/kg b.wt.) did not seem to have any effects on the basal levels or labeling of these compounds. The changes in polyphosphoinositide labeling due to ethanol intoxication were reverted to near control values when animals regained their righting reflex (approximately 4 hr). These studies demonstrate that, under normal conditions, polyphosphoinositides and diacylglycerols are maintained in a dynamic equilibrium and that acute doses of ethanol can suppress the signal transduction process and disturb this equilibrium.

Adenosine Triphosphate↗
PubMed1987

Effects of chronic ethanol administration on rat brain phospholipid metabolism.

Alterations in brain phospholipid metabolism were observed after chronic ethanol administration for 16 days to developing rats. Animals were injected intraperitoneally with 32Pi 16 h prior to killing. Overall uptake of 32Pi by brain did not differ between the control and ethanol-treated groups, which were killed 2 h and 24 h after the last ethanol feeding. Except for an increase in the labeling of myelin after ethanol treatment, the amount of radioactivity recovered in the synaptosomal-mitochondrial and plasma membrane fractions of control and ethanol-treated groups was not different. Relative to the radioactivity of phosphatidylcholines, which indicated no change, there were increases (20-44%) in labeling of ethanolamine plasmalogens, phosphatidic acids, and phosphatidylinositols in cortical synaptosomes from the 2-h ethanol-treated group. In the plasma membrane fractions, however, increases (9-14%) in labeling of phosphatidylserines and phosphatidylinositols were observed in both 2- and 24-h ethanol-treated groups. In both membrane fractions, there was an obvious increase (44-86%) in labeling of polyphosphoinositides at 24 h after withdrawal from ethanol. Results thus indicate an adaptive increase in the biosynthesis of ethanolamine plasmalogen and brain acidic phospholipids due to chronic ethanol administration. Furthermore, the increase in labeling of polyphosphoinositides in the 24-h withdrawal group may reflect the hypoactivity associated with ethanol withdrawal.

Animals↗