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SUMMARY Distribution of cerebral blood flow was measured with an array of 200 ultra-pure germanium radiation detectors and 133-Xe by inhalation. The array "sees" the head as a composite of different subvolumes and enables measurement of the concentration history of tracer every 1-10 sec in each subvolume simultaneously. Subvolume mean flows, (f m ), and partition coefficients, X m , are derived by compartmental analysis of tissue concentration washout curves. Errors from "cross talk," scalp radiation, "look through," and assumed partition coefficients are eliminated. Average f m adjusted for 40 mm Hg P,\co2' n 14 cortical subvolumes (7 right, 7 left) of four normal 21-24 year old controls ranged from SO to 60 ml/100 cc tissue/min, and X m ranged from 0.97 to 1.14. Average f m and >.", in white matter was 24 ml/100 cc/ min and 1.42 -1.14 respectively. During CO 2 inhalation, right and left hemispheric f m increased 6.4% and 5.7%/mm Hg respectively, whereas white matter f m increased 2.2% and 3.4% mm Hg respectively. There was no systematic difference between front and back or dominant vs non-dominant sides. Three 73-84 year old controls had reduced f m and CO 2 reactivity in all subvolumes. >. m was in the same range as in younger controls. Two patients with intracranial cerebrovascular disease showed excellent localization of ischemic subvolumes. One patient with asymptomatic unilateral 98% stenosis of the internal carotid artery had a similar distribution of blood flow in both hemispheres. Stroke Vol 16, No 1, 1985 IN PREVIOUS PUBLICATIONS we described an instrument that enables measurement of the 3-D distribution of the cerebral blood flow in the entire brain simultaneously using gamma photon emitting radioisotopes.'2 The CEREFLO instrument consists of 200 high purity germanium (HPGe) radiation detectors located about the head in precisely determined orientation. The array "sees" the head as a composite structure of anatomic subvolumes and measures the concentration of tracer in each subvolume every 1-10 sec depending upon the count rate. Blood flow in each subvolume is computed from the concentration history (/LtCi/cc tissue) of 133-Xe. Some important attributes of the method are that "cross-talk" is not a source of error, that radiation from the scalp is not a source of error (the scalp is an actual subvolume in which tracer concentration is measured), that "look-through" is eliminated, that knowledge of partition coefficients is unnecessary (though they may be determined if desired), that radiation exposure is low, and that the entire head is studied simultaneously.In this report we present results to demonstrate the capability of the CEREFLO technique to measure the distribution of cerebral blood flow in healthy human subjects and in patients with cerebrovascular disease. The CEREFLO SystemThe heart of the CEREFLO system is the stationary array of 200 HPGe detectors located about the head in precisely determined orientation ( fig. 1) surveys the object within its confine, i.e. the head and brain, as if ...

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