Edward L. Wills

Regional Cerebral Blood Flow by 133Xenon Inhalation

Repeated measurements of regional cerebral blood flow (rCBF) were made by the short (ten minutes) 133Xenon inhalation technique and bicompartmental analysis in 11 patients with cerebrovascular disorders, mainly acute cerebral infarction. rCBF was measured 3 to 11 times during one to two weeks. The blood flow of the fast compartment (f1) was calculated as well as the relative weight of this compartment (w1, assumed to correspond to gray matter). In addition a new flow index, the Initial Slope Index (ISI) modified for the inhalation technique, was used. This index of predominantly gray matter flow was calculated from a one-minute epoch of the early part of the clearance curve corrected for recirculation. In three of the patients the f1 and ISI varied in parallel and the w1 showed generally only minor variations from one measurement to the other. However, in the other eight patients fluctuation of the w1 and f1 values were seen which often showed no meaningful relation to the clinical course. The observed w1 changes indicated that some tissues (slowly perfused gray matter and/or rapidly perfused white extracerebral tissues) fluctuate between the fast and the slow compartment. In such cases the f1 values obtained cannot be used for comparison between measurements, since they represent flow rates of varying tissues and do not always represent a true gray matter blood flow. In these patients the ISI, which is independent of such weight changes, showed moderate and clinically likely variations.

133Xenon inhalation method. Analysis of reproducibility: some of its physiological implications.

Regional cerebral blood flow (rCBF) was simultaneously measured at seven locations in each hemisphere by the Obrist 133Xenon inhalation method. In each of 35 healthy right-handed subjects two rest measurements were performed on consecutive days. The data analysis comprises the two-compartmentally derived parameters for flow (f1), relative tissue weight (w1), and fractional flow (FF1) 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% (f1), 7.2% (w1), and 2.9% (FF1) 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% (f1), 7.7% (w1), and 1.9% (FF1) respectively; that of the hemispheric means of ISI, f1, and FF1 was found to be distinctly larger, whereas that of w1 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% (f1), 1.6% (w1), and 1.1% (FF1) 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 regions superimposed on the hemispheric mean level.

Focal right temporo-occipital blood flow changes associated with judgment of line orientation

Focal cerebral blood flow changes for judgment of line orientation were determined using the 133Xe inhalation technique with 18 normal right-handed male subjects. Measurements were made during three conditions in the same session: a line orientation task, a sensorimotor control task, and normal rest. Blood flow changes attributable to the judgment of line orientation were found for the measure f1 at a detector centered over the right temporo-occipital region. For the measure IS this activation was significant in the temporo-occipital region in both hemispheres but significantly greater in the right hemisphere. For f1 the change in blood flow and for IS the percent change in blood flow in the right temporo-occipital region attributable to judgment of line orientation decreased as performance on the line orientation task improved.

Focal changes in cerebral blood flow produced by a test of right-left discrimination☆

A sensorimotor control activation task was used to isolate the focal cerebral blood flow changes resulting from the visual and cognitive processing of a right-left discrimination task. Eleven normal right-handed males participated. The sensorimotor control task produced significant bilateral increases in flow in most cortical channels. Significant bilateral parieto-occipital activation was found for the right-left discrimination task over and above the flow changes produced by the sensorimotor control task. The left occipital flow increase resulting from the right-left discrimination task was found to be negatively related to task performance. An inverse relationship was also found between WAIS Performance IQ and the blood flow change in the left parietal channel. These results suggest areas for further testing concerning potential individual differences in cognitive processing during the performance of a right-left discrimination task.

Extraterrestrial Mössbauer spectrometry

We describe a combined backscatter Mössbauer spectrometer and X-ray fluorescence analyzer (BaMS/XRF) instrument suitable for planetary missions to the surfaces of Mars (MESUR Program), the Moon, asteroids, or other solid solar-system objects. The BaMS/XRF instrument is designed to be capable of concurrent analysis of a sample for its elemental abundances (XRF) and for the mineralogy of its iron-bearing phases (BaMS) without any sample preparation.

133Xenon inhalation method: significance of indicator maldistribution for distinguishing brain areas with impaired perfusion. An index for total flow.

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.

Measurement of activated rCBF by the 133Xe inhalation technique: a comparison of total versus partial curve analysis.

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 133Xe 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 133Xe 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.

Relevance of sensorimotor task components to the interpretation of task related blood flow changes

This study demonstrated the importance of documenting rCBF changes produced by the sensorimotor components of a cognitive task when making inferences regarding brain-behavior relations. Subjects were ten young, non-smoking adult, right-handed, normal male volunteers. They were administered two tasks having identical cognitive and similar sensory components but different response modalities (oral vs manual). The two tasks produced highly divergent rCBF landscapes. In conjunction with the results from a previous rCBF activation study, these data were used to illustrate the necessity of including sensorimotor control tasks in cognitive activation studies designed to elucidate brain-behavior relations.

The Use of STA-MCA Bypass in the Evaluation of rCBF

Objective means of evaluating patients who have undergone surgical procedures designed to augment collateral blood supply to the brain are necessary if these patients are to be assessed by means other than ongoing clinical examination and repeated angiography. We have studied seven consecutive patients selected for superficial temporal artery-middle cerebral artery (STA-MCA) bypass by clinical and angiographic criteria using 133xenon clearance as assessed by the inhalation technique.

Comparison of external lung monitoring with end-tidal air detection using the 133xenon inhalation method.

When the 133Xe inhalation method is employed for measuring regional cerebral blood flow, the arterial 133Xe 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 133Xe, suggested that the counts detected by an external lung probe could provide an alternative estimate for arterial blood concentration once the noise produced by 133Xe 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 133Xe 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.