Reliability of regional cerebral blood flow activation to cognitive tasks in elderly normal subjects.

The assessment of cerebral blood flow (CBF) using noninvasive 133Xe techniques provides an indirect measurement of cortical metabolic activity. The utility of this method in longitudinal clinical studies depends on the stability and reproducibility of resting and activated flow measures. We evaluated CBF in a sample of 16 elderly normal subjects (aged 54-73 years) at rest and during task performance in two sessions separated by an average of 9 weeks. Resting global CBF was lower in the second session, a finding consistent with the known effects of habituation previously reported. Regionally specific activated CBF did not change with repeated measurements. The results provide evidence that the 133Xe technique is reliable and of potential utility in evaluating the effect of the natural course of brain disease, as well as the effects of therapeutic interventions on brain activity.