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Biomedical subjects

K Verghese

Publications and source records attributed to K Verghese.

4 recordsLinked to original sources
PubMed2000

Dexamethasone metabolism in dexamethasone suppression test suppressors and nonsuppressors.

BACKGROUND: Variable dexamethasone kinetics is a possible confound in the dexamethasone suppression test. Modifications to include dexamethasone plasma levels and specific dexamethasone "windows" have been proposed. Our study aims to validate our proposed dexamethasone windows in an independent sample of 121 subjects. METHODS: We performed dexamethasone suppression tests in 162 subjects with mixed psychiatric diagnoses. Dexamethasone levels and beta-phase half-life of dexamethasone were computed for suppressors and nonsuppressors. RESULTS: Dexamethasone levels were lower in nonsuppressors than in suppressors. Dexamethasone levels correlated inversely with cortisol levels in the total sample, but were nonsignificant or weakly associated in those samples restricted to the windows. The beta-phase half-life of dexamethasone was shorter in nonsuppressors. The dexamethasone windows were validated at 3:00 PM and 10:00 PM. We propose 4.0 ng/mL as a revised upper limit of the 8:00 AM dexamethasone window. CONCLUSIONS: The plasma dexamethasone level is confirmed as a confound in the dexamethasone suppression test through more rapid dexamethasone clearance in nonsuppressors. Application of dexamethasone windows will reduce this source of test variance.

Adrenal Cortex Function Tests↗
PubMed2000

Digital mammography image simulation using Monte Carlo.

Monte Carlo simulations of digital images of the contrast detail phantom and the ACR phantom are presented for two different x-ray digital mammography modalities: a synchrotron mammography system and a next-generation scanning slot clinical system. A combination of variance reduction methods made it possible to simulate accurate images using real pixel dimensions within reasonable computation times. The complete method of image simulation, including a simple detector response model, a simple noise model, and the incorporation of system effects (MTF), is presented. The simulated images of the phantoms show good agreement with images measured on the two systems.

Algorithms↗
PubMed1998

Measured molecular coherent scattering form factors of animal tissues, plastics and human breast tissue.

Photon scattering angular distributions from various animal tissues were measured at two energies of a monochromatic synchrotron x-ray beam. Two plastics and human breast tissue were also measured. From these two measurements, the molecular coherent scattering form factor of each material was extracted. A new data analysis technique that uses Monte Carlo based corrections for air scattering, incoherent scattering and multiple scattering was used. The form factors of the 16 materials are presented in tabular form, suitable for use in computer calculations.

Animals↗