Biomedical subjects

F Calamante

Publications and source records attributed to F Calamante.

22 records · Page 2Linked to original sources

PubMed1999

Reperfusion in a gerbil model of forebrain ischemia using serial magnetic resonance FAIR perfusion imaging.

BACKGROUND AND PURPOSE: Existing methods for the quantitative measurement of the changing cerebral blood flow (CBF) during reperfusion suffer from poor spatial or temporal resolution. The aim of this study was to implement a recently developed MRI technique for quantitative perfusion imaging in a gerbil model of reperfusion. Flow-sensitive alternating inversion recovery (FAIR) is a noninvasive procedure that uses blood water as an endogenous tracer. METHODS: Bilateral forebrain ischemia of 4 minutes' duration was induced in gerbils (n=8). A modified version of FAIR with improved time efficiency was used to provide CBF maps with a time resolution of 2.8 minutes after recirculation had been initiated. Quantitative diffusion imaging was also performed at intervals during the reperfusion period. RESULTS: On initiating recirculation after the transient period of ischemia, the FAIR measurements demonstrated either a symmetrical, bilateral pattern of flow impairment (n=4) or an immediate side-to-side difference that became apparent with respect to the cerebral hemispheres in the imaged slice (n=4). The flow in each hemisphere displayed a pattern of recovery close to the preocclusion level or, alternatively, returned to a lower level before displaying a delayed hypoperfusion and a subsequent slow recovery. The diffusion measurements during this latter response suggested the development of cell swelling during the reperfusion phase in the striatum. CONCLUSIONS: The CBF during the reperfusion period was monitored with a high time resolution, noninvasive method. This study demonstrates the utility of MRI techniques in following blood flow changes and their pathophysiological consequences.

Animals↗

PubMed1999

Quantitative MR diffusion mapping and cyclosporine-induced neurotoxicity.

Apparent diffusion coefficient maps of two patients with cyclosporine-induced neurotoxicity showed areas of increased diffusion that corresponded to the characteristic regions of signal change on routine T2-weighted sequences. The majority of lesions subsequently resolved without residual T2 or diffusion signal alteration. These findings suggest that, in our patients, the neurotoxic effects of cyclosporine resulted in a partially reversible extravasation of fluid into the cerebral interstitium and were not associated with acute ischemia.

Anemia, Sickle Cell↗

PubMed1997

Effects of diffusion anisotropy on lesion delineation in a rat model of cerebral ischemia.

The effects of white and gray matter diffusion anisotropy on ischemic lesion delineation have been studied in the rat model of middle cerebral artery occlusion. Apparent diffusion coefficient (ADC) maps obtained by conventional pulsed gradient spin echo diffusion-weighted imaging (PGSE-DWI) were compared with maps of the trace of the diffusion tensor in both normal and occluded animals. Diffusion tensor trace maps were derived from the average of the ADC maps from three separate experiments with diffusion weighting along three orthogonal axes, and also from a single-scan method. A marked degree of diffusion anisotropy was observed in both cortical gray matter and white matter from ADC maps of the control animals. In the occluded animals, the systematic effects of anisotropy on ADC and lesion area influenced the delineation of the ischemic territory in the PGSE-DWI ADC maps. However, the two trace methods eliminated these effects and gave consistent ischemic lesion depiction, despite the use of differing diffusion times in the two measurements.

Animals↗

PubMed1996

A model for quantification of perfusion in pulsed labelling techniques.

A model for quantification of perfusion in pulsed labelling techniques is described, based on solving the modified Bloch equation including the effects of flow. The model is designed to fit experimental data acquired in two separate measurements (inversion and control, or selective and non-selective inversions) for different inversion times using a biexponential. Although the signal contrast is 50% less than the continuous labelling technique, it seems more appropriate for human studies because of its lower power deposition, shorter transit time and the use of an interleaved acquisition. The importance is shown of including in the model the difference in relaxation time between blood and tissue. Neglecting this difference can lead to an overestimation of flow, which can be as big as 100% in white matter and 20% in grey matter.

Cerebrovascular Circulation↗