Comparison of microsphere and xenon-133 clearance method in measuring skeletal muscle and cerebral blood flow

Abstract

In this study, we compared the Xenon-133 (133Xe) clearance method with the microsphere method in measurement of skeletal muscle and cerebral blood flow (CBF). Over a wide range of flows (1-47 ml/min x 100 g), we compared these two methods with direct measurements of venous outflow in the gracilis muscle. Regression equations relating the 133Xe (stochastic method) and microsphere measurements of flow to venous outflow were Y = 0.92X - 0.93 (r = 0.81) and Y = 1.01X - 0.42 (r = 0.94), respectively. Thus both 133Xe clearance and microspheres accurately measured flow in an isolated organ with a simple bloody supply. When CBF was measured with 133Xe, extracerebral contamination and scattered radiation were minimized by ligation of the external carotid artery, removal of the soft tissue of the head, injection of the 133Xe into the internal carotid artery, and use of lead shielding and a collimated detector. In the dog (n = 10), CBF (range, 12-200 ml/min x 100 g) measured with 133Xe was substantially less than that measured with microspheres. In baboons (n = 18), when mean CBF < 120 ml/min x 100 g, there was a good relationship between values obtained with 133Xe (stochastic method) and microspheres. The regression equation relating those two measurements was Y = 0.62X + 16.9 (r = 0.83). At flow rates > 120 ml/min x 100 g, values obtained for mean CBF with 133Xe (stochastic method) and microspheres differed widely. We also compared fast and slow clearance curves obtained with 133Xe (compartmental analysis) with grey and white matter flows measured with microspheres. The two techniques yielded results which differed widely. Although the 133Xe clearance method (stochastic analysis) and microspheres provide similar values for mean CBF in baboons under some experimental conditions, values obtained with the two techniques differ importantly under several conditions.