SUMMARY An initial assessment of the differential sensitivity of total versus partial curve analysis in estimating task related focal changes in cortical blood flow measured by the 133 Xe inhalation technique was accomplished by comparing the patterns during the performance of two sensorimotor tasks by normal subjects. The validity of these patterns was evaluated by comparing them to the activation patterns expected from activation studies with the intra-arterial technique and the patterns expected from neuropsychological research literature. Subjects were 10 young adult nonsmoking healthy male volunteers. They were administered two tasks having identical sensory and cognitive components but different response requirements (oral versus manual). The regional activation patterns produced by the tasks varied with the method of curve analysis. The activation produced by the two tasks was very similar to that predicted from the research literature only for total curve analysis. To the extent that the predictions are correct, these data suggest that the 133 Xe inhalation technique is more sensitive to regional flow changes when flow parameters are estimated from the total head curve. The utility of the total head curve analysis will be strengthened if similar sensitivity is demonstrated in future studies assessing normal subjects and patients with neurological and psychiatric disorders.Stroke Xe in the mouth, sinuses and pharynx is one of the more serious of these methodological problems. Obrist et al 2 3 tried to reduce the influence of these artifacts by fitting a model to the subset of data collected after the concentration of xenon in end-expired air has fallen below 20 percent of its maximum value. However, their simulation studies showed that, in the absence of scattered radiation, estimates for K, (gray matter clearance) match the true value when model fitting is started near time zero and decline as the start fit time is increased. Thus, although the effects of scattered radiation are minimized, data corresponding to the inhalation phase (during which most of the relevant information on gray matter flow occurs) are discarded. Hazelrig et al. 4 have recently proposed a time domain correction method to adjust for the presence of these artifacts, thereby allowing utilization of the entire head curve in the estimation of the blood flow parameters.One of our long term goals is to determine whether analysis of the total head curve can improve the sensitivity of the l33 Xe inhalation technique in demonstrating focal activation of cortical flow relative to focal changes in flow estimated by the partial curve method. The purpose of this study was to make an initial assessFrom the
SUMMARY When the133 Xe inhalation method is employed for measuring regional cerebral blood flow, the arterial 133 Xe concentration is usually approximated by the end-tidal air concentration. However, this approximation may be invalid in the presence of certain lung pathologies or when the breathing pattern is irregular. Jaggi and Obrist, using an intravenous injection of Xe, suggested that the counts detected by an external lung probe could provide an alternative estimate for arterial blood concentration once the noise produced by Xe in superficial tissues is removed from the signal. A mathematical model, based on hypotheses similar to theirs is presented here together with a new computational procedure for removing the noise. Results from normal rest studies on ten healthy young males indicate that the approximations for arterial blood concentration obtained from end-tidal air and from corrected lung counts are not equivalent when l33 Xe is administered by inhalation. The concentration-time curves have different shapes, and these differences are reflected in blood flow values computed by head channel. However, there is no effect on comparisons between homologous regions of the left and right hemispheres.
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