Biomedical subjects

D C Alsop

Publications and source records attributed to D C Alsop.

39 records · Page 3Linked to original sources

PubMed1994

MRI characterization of diffusion coefficients in a rat spinal cord injury model.

Apparent diffusion coefficients (ADC) were measured in a rat spinal cord weight-drop injury model. After sacrifice, the spinal cords were fixed in situ and excised for MR imaging and ADC measurement. Diffusion is anisotropic in normal gray and white matter. There were significant decreases in ADCs measured along the longitudinal axis of the injured cord and increases in ADCs measured transverse to the cord. Injured segments demonstrated reductions in diffusion anisotropy in the white matter. Diffusion was completely isotropic at the epicenter of the weight-drop injury. Significant decreases in longitudinal ADC and increases in transverse ADC were observed in portions of the cord which appeared normal on conventional spin-echo and calculated T2 images. Thus ADC measurement may complement routine imaging for evaluation of spinal cord injury.

Animals↗

PubMedDate not supplied

The efficiency of adiabatic inversion for perfusion imaging by arterial spin labeling.

Velocity-driven adiabatic inversion is an attractive method for labeling arterial blood spins for quantitative perfusion imaging. To quantify perfusion and to optimize experimental parameters, an accurate estimate of labeling efficiency is required. We present theoretical and numerical methods to calculate the labeling efficiency over a wide range of experimental and physiologic parameters. The results are compared to experimental measurements in vivo. Inversion efficiency was found to be higher than previously assumed and relatively insensitive to flow velocity and the amplitude of the RF irradiation used for inversion. Assuming laminar flow, labeling efficiencies of greater than 90% are easily obtainable over a broad range of flow velocities. For applications where RF power deposition is a limiting factor such as at high field strengths, labeling efficiency can be maintained by reducing the labeling gradient. These results further illustrate the capability of adiabatic inversion to effectively label flowing blood.

Adult↗

PubMedDate not supplied

The parahippocampus subserves topographical learning in man.

The hippocampus has been proposed as the site of neural representation of large-scale environmental space, based upon the identification of place cells (neurons with receptive fields for current position in the environment) within the rat hippocampus and the demonstration that hippocampal lesions impair place learning in the rat. The inability to identify place cells within the monkey hippocampus and the observation that unilateral hippocampal lesions do not selectively impair topographic behavior in humans suggest that alternate regions may subserve this function in man. To examine the contribution of the hippocampus and adjacent medial-temporal lobe structures to topographic learning in the human, a 'virtual' maze was used as a task environment during functional magnetic resonance imaging studies. During the learning and recall of topographic information, medial-temporal activity was confined to the para- hippocampal gyri. This activity accords well with the lesion site known to produce topographical disorientation in humans. Activity was also observed in cortical areas known to project to the parahippocampus and previously proposed to contribute to a network subserving spatially guided behavior.

Adult↗