An anatomical model in conjunction with experimentally determined absorption data provides a framework to simulate signals as obtained from the noninvasive Xenon-133 cerebral blood flow technique. The contribution of individual tissue compartments to the total signal as well as the effect on the computed results were investigated under normal conditions. The introduction of physiological abnormalities into the model allowed the determination of sensitivity of the technique with respect to size, position, and perfusion level of the lesion. In addition, effects of cross-talk between hemispheres and signal overlap of adjacent detectors were quantified. It was found that the change of externally measured blood flow is proportional to the decrement/increment of flow in the lesion. Contrary to earlier reports, the effects of cross-talk and signal overlap were not found to be serious limitations in identifying lesions.

Animals↗

PubMedDate not supplied

Regional cerebral blood flow in stroke: hemispheric effects of cognitive activity.

Regional cerebral blood flow (rCBF) was measured with the xenon-133 inhalation technique in 15 patients with unilateral cerebral infarction and 12 matched controls. Measurements were performed during a standard resting baseline condition and during the performance of standardized verbal analogies and spatial line orientation tasks. Resting and activated CBF were lower in patients than in controls, and there were differences in the hemispheric pattern of activated CBF. Control subjects replicated earlier findings of asymmetric increase in CBF for the cognitive tasks, whereas patients showed abnormalities in lateralized CBF changes consistent with side of infarction. These findings underscore the utility of cognitive challenges in the study of rCBF in stroke. This can lead to an experimental paradigm in clinical studies of the relation between behavioral deficits and regional brain dysfunction and may also improve the utility of CBF measurements in clinical settings.

Cerebrovascular Circulation↗

PubMedDate not supplied

Regional cerebral blood flow estimated by 133-xenon inhalation.

A method is described for estimating the clearance rate and fractional blood flow of the fast (gray matter) compartment of the brain from the first ten minutes of 122 XE clearance curves, following a one-minute inhalation. Computer-simulated data were used to test the adequacy of the two-compartmental model employed, and to evaluate the stability of the parameters in the presence of random noise. A comparison was made between this approach and the previously reported three-compartmental analysis. Regional cerbral blood flow data were obtained on 48 young control subjects and 20 elderly demented patients. Hemispheral, regional, and test-retest variations were determined, as well as differences between the groups.

Adult↗

PubMedDate not supplied

Spectrum subtraction technique for minimizing extracranial influence on cerebral blood flow measurements by 133xenon inhalation.

Estimates of regional cerebral blood flow (rCBF) by the 133Xe inhalation method are influenced by isotope contamination from slow clearing extracerebral tissues. Subtraction of x-ray (31 kev) from gamma-ray counts (81 kev) has been suggested as a means of yielding clearance curves that are relatively free of such contamination. In the present study, rCBF measurements based on the total 133Xe spectrum (x-ray plus gamma) were compared with those derived from the subtracted spectrum (x-ray minus gamma) in 20 young controls, using a two-compartmental analysis of the clearance curves. In comparison with addition, the subtraction data gave substantially higher estimates of blood flow for the slow (second) compartment. This, along with a shift in the relative weights of the two compartments, indicated a decreased contribution of slow tissue components, consistent with a reduction in extracerebral contamination. Blood flow values obtained by subtraction were in good agreement with those reported for the intracarotid injection method. A limitation of the subtraction technique, however, is the relatively high dose of isotope required for adequate signal-to-noise ratios.

Adult↗

PubMedDate not supplied

Automatic end-tidal gas sampling system for non-invasive rCBF measurements.

Non-invasive measurements of regional cerebral blood flow (133Xe inhalation or IV injection) require knowledge of the arterial 133Xe concentrations, which is usually estimated from the end-tidal expiration. An automated sampling system is described for measurement of end-tidal 133Xe concentration that can be used in both spontaneously breathing and mechanically ventilated patients. A comparison is made between the automatic sampling system and manual measurements performed on a continuous gas sample.

Blood Gas Analysis↗