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Biomedical subjects

S S Shukla

Publications and source records attributed to S S Shukla.

13 recordsLinked to original sources
PubMed1995

Regional analysis of D2 dopamine receptors in Parkinson's disease using SPECT and iodine-123-iodobenzamide.

UNLABELLED: The goal of this study was to examine the relationship between D2 dopamine receptor density and levodopa dosage, disease duration and dyskinesia in Parkinson's disease (PD). METHODS: Iodine-123-iodobenzamide SPECT scans were obtained from 14 PD patients and 12 age-matched controls using a three-headed camera in conjunction with MRI and a fiducial-based image registration system to define regions of interest. Basal ganglia/cerebellum counts/voxel ratios in dorsal and ventral head of caudate and anterior and posterior putamen were measured at 30, 60, 120 and 180 min postinjection. As in 11C-raclopride studies, ratios obtained at that time when they asymptomatically approach a maximum value (180 min) were accepted as the best measure of receptor density. RESULTS: Among PD patients, a trend towards an inverse correlation between regional basal ganglia/cerebellum ratios and levodopa dosage achieved significance in ventral caudate (F = 6.244, p = 0.037); similarly, an inverse correlation between these ratios and disease duration achieved significance in anterior putamen (F = 13.144, p = 0.007). Ratios were significantly lower in anterior putamen in patients with dyskinesia (t = 3.068, p = 0.042). CONCLUSION: In PD, the previously observed inverse correlation between levodopa dosage and D2-receptor density appears to be most prominent in the least dopamine-depleted region, ventral caudate. There may be a genuine effect of disease duration on receptor density in putamen and reduced receptor density in anterior putamen may be associated with dyskinesia.

Aged↗
PubMed1994

A technique to localize activation in the human brain with technetium-99m-HMPAO SPECT: a validation study using visual stimulation.

UNLABELLED: This study extends and validates a system for localizing brain activity changes based on fiducial markers, coregistration of SPECT and MRI structural images and atlas/MRI-assisted localization. METHODS: Ten normal subjects underwent 99mTc-HMPAO SPECT during a resting eyes-closed baseline measurement and during visual stimulation (8-Hz reversing checkerboard). SPECT scans were registered with MRI scans obtained from each individual using a fiducial-based system that minimized z-axis and rotational errors, and registration was further refined along the x- and y-axes by superimposing corresponding axial SPECT and MRI slices. Regions of interest (ROIs) were located on MRI slices with the aid of an atlas. Corresponding loci on SPECT slices were chosen and incrementally adjusted such that the center of a ROI was located precisely at the maximum of activity in the visual cortex or the cortical gray matter ribbon. RESULTS: Activity in the calcarine cortex increased by 44.39% during visual stimulation (p < 0.001). Adjustment of ROI location in accordance with local activity maxima yielded superior results to a method relying strictly on atlas/MRI localization. Premotor cortex activity declined by 16.91% on the right (p < 0.01) and 13.85% on the left (p > 0.05), whereas no changes occurred in the somatosensory cortex. CONCLUSION: Changes in visual cortical activity were most comparable to previous functional MRI studies but also congruent with PET and SPECT findings. Using the locus of peak activity to aid in defining cortical ROIs improves the signal-to-noise ratio by reducing noise related to inevitable minor registration errors.

Adolescent↗
PubMed1986

Trabecular bone mineral density measurement in vivo: use of the ratio of coherent to Compton-scattered photons in the calcaneus.

Trabecular bone mineral density (TBMD) was measured in vivo in the calcaneus by a new method that uses the ratio of coherent to Compton-scattered photons arising from irradiation of a small volume of trabecular bone by a gamma ray source with highly collimated geometry. TBMD values for healthy men (22-77 years) were in the range of 180-357 mg/ml, and values for healthy women (18-73 years) were in the range of 160-321 mg/ml. In contrast, values in a small group of paraplegics were in the range of 90-199 mg/ml.

Adult↗
PubMedDate not supplied

Method for registering brain SPECT and MR images.

We have developed a simple method for locating functional regions of interest on successive SPECT scans obtained at different times and for locating neuroanatomical regions defined with MR on functional images obtained with SPECT. Plastic molds are made for each external auditory meatus and the glabella. A pocket is then made in each mold in which either a 57Co disk (for SPECT) or an identical disk containing CuSO4 solution (for MRI) can be placed. Transaxial tomographic slices are reconstructed with the same slice thickness in the two modalities. The SPECT software rotates both SPECT and MRI reconstructed images so that the three 57Co markers lie in one SPECT reference plane and the three CuSO4 markers lie in one MRI reference plane. Corresponding SPECT and MR images may then be displayed simultaneously to locate chosen regions of interest. The technique was validated by taping test markers to the forehead of 12 subjects; the difference between the positions of the centers of the test markers on SPECT and MR scans was within 1 SPECT acquisition pixel size.

Brain↗
PubMedDate not supplied

Quantitative assessment of bone mineral by photon scattering: accuracy and precision considerations.

A method to determine the bone mineral density of the calcaneum has been reported earlier by our laboratory. In this method, the calcaneum is irradiated by a 60-keV photon beam from 241Am source and both the coherent and Compton scattered photons are detected by a high-purity Ge detector. The bone mineral density is determined by measuring the ratio of coherent-to-Compton scattered photons. The accuracy and the precision (in vitro) of the method are reported in this paper. The accuracy was determined to be 5%. This was obtained by comparing the bone mineral density values of cadaver calcanea measured directly by Archimedes' volume displacement method with the values measured by the scattering method. The precision was determined to be 3% by measuring the bone mineral density of a calibration phantom intermittently over a ten-month period by the scattering method.

Bone and Bones↗
PubMedDate not supplied

Quantitative assessment of bone mineral by photon scattering: calibration considerations.

The ratio of the coherent-to-Compton photons scattered from bone can be used to measure its mineral density. Conversion of this ratio (R) to bone mineral density (BMD) requires calibration using bone simulating phantoms. The widely used aqueous solution of K2HPO4 proved unsatisfactory for calibration purposes when using the coherent-to-Compton technique. These solutions differ markedly in their scatter spectra and composition from trabecular bone. In this study a new and more realistic series of phantoms is proposed which simulates well the trabecular bone of the calcaneum. These phantoms are made of bone ash suspended in white petrolatum in varying concentrations. A calibration curve has been established using these phantoms with a range of BMD values of 0 to 347 mg/cm3. The scatter spectra, and range of R values and BMD of these phantoms are in very good agreement with those of real trabecular bone. A measuring device has been built for the determination of the BMD of the calcaneum by using the established calibration curve.

Biophysical Phenomena↗
PubMedDate not supplied

A study of the homogeneity of the trabecular bone mineral density in the calcaneus.

In the past our laboratory has reported a method of measuring trabecular bone mineral density (TBMD) in the calcaneus in vivo by using the coherent-to-Compton scattering ratio. In the present work the distribution of TBMD in the calcaneus has been studied, and the reproducibility of this technique in vivo has been determined. It is found that although the TBMD may vary within the calcaneus, a region exists over which the variation in density is not large. This region coincides with the midportion of the heel and is the site chosen for the measurement of TBMD by the coherent-to-Compton scattering ratio technique. The reproducibility of this technique in vivo has been determined to be 3.4%.

Bone and Bones↗