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Biomedical subjects

D A Roberts

Publications and source records attributed to D A Roberts.

41 records · Page 3Linked to original sources
PubMedDate not supplied

Magnetic resonance imaging of the brain: blood partition coefficient for water: application to spin-tagging measurement of perfusion.

We describe the use of relative proton density imaging to obtain spatially resolved measurements of the brain:blood partition coefficient for water. Values of relative proton density and apparent-T1 were calculated by performing a multidimensional nonlinear least squares fit of progressive saturation image data. Correction for magnetic field inhomogeneity was included. The partition coefficient was calculated by dividing the relative proton density of brain by the relative proton density of blood water. Results obtained from healthy volunteers demonstrate significant spatial variation in the partition coefficient in brain. Direct measurement of this parameter eliminates a source of error in the calculation of regional perfusion using arterial spin-tagging techniques.

Blood-Brain Barrier↗
PubMedDate not supplied

Analysis of vessel absorption profiles in retinal oximetry.

The optical densities of vessel absorption features in small bandwidth fundus photographs have been used by many people for finding the oxygenation of the blood in retinal vessels. The purpose of this article is to show that the information found in this way can be made more accurate, and more information can be found by considering the details of the absorption profile (intensity as a function of distance across the vessel). The "wings" of the profile are primarily determined by the line-spread function of the video camera or film. A four-parameter curve fitting procedure using the line-spread function and an "ideal" vessel profile can be used to eliminate the effects both of the line-spread function and of any central reflection (vessel reflex) that may be present, yielding estimates of the vessel diameter and central absorption. The conclusions concerning the reflection are supported by studies of reflections from capillary tubes and wires in a model eye.

Biophysical Phenomena↗