SUMMARY Regional cerebral blood flow (rCBF) was simultaneously measured at seven locations in each hemisphere by the Obrist '"xenon inhalation method. In each of 35 healthy righthanded subjects two rest measurements were performed on consecutive days. The data analysis comprises the two-compartmentally derived parameters for flow (f,), relative tissue weight (w,), and fractional flow (FF,) respectively of the first compartment, and in addition the initial slope index (ISI). At each detector location the coefficient of variation (C.V.) of the change from first to second measurement was on average 10.4% (ISI), 14.2% (f,), 7.2% (w,), and 2.9% (FF,) respectively. However, when each regional measurement was expressed as a percentage of its hemispheric mean, the C.V. of the intermeasurement change was on average 4.4% (ISI), 7.0% (f,), 7.7% (w,), and 1.9% (FF,) respectively; that of the hemispheric means of ISI, f,, and FF, was found to be distinctly larger, whereas that of w, was about equal in size. The interhemispheric coefficient of variation for the change of the hemispheric means from first to second measurement was only 2.3% (ISI), 4.4% (f,), 1.6% (w,), and 1.1% (FF,) respectively.The findings suggest that (1) the variability of rCBF from subject -to subject and in consecutive measurements in the same subject is to a substantial degree of physiological origin, and that (2) there are two determinants of rCBF which may operate independently: a determinant of the hemispheric mean level, probably a single determinant for both hemispheres, and a set of determinants for each separate region superimposed on the hemispheric mean level.

rCBF was measured by 133Xenon inhalation at rest and during pCO2 manipulation in 19 patients prior to and at various times after STA-MCA bypass surgery. The resting flow increased gradually postoperatively, seemingly more due to progressive clinical recovery from the original neurologic disability than due to the surgical intervention. CO2 reactivity increased in some patients, more in those who preoperatively had the poorest reactivity. The negative relationship between preoperative reactivity and postoperative change in reactivity was highly significant. These observations are consistent with the interpretation that the surgery did not significantly affect the resting flow level but did augment the collateral reserve in those cases in which it had been most severely impaired by the arterial lesion.

This paper introduces a new index for the assessment of regional cerebral blood flow. The index is proportional to total flow, and is obtained from the ratio of regional count rate to arterial indicator input to a region. This index is a more sensitive indicator of impaired perfusion than the traditional flow rate indices which express flow per unit mass of tissue per minute. It accounts for brain tissue partly or totally deprived of its blood supply. Examples of clinical application are reported. A good correlation with the findings of computer-assisted tomography has been found.

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SUMMARY Ultrasonic scanning of the upper abdomen is a valuable method in diagnosing malignant pancreatic tumours. A series of 12 patients is presented. The method also provides information about the size of the gallbladder and the condition of the liver parenchyma.