MacKenzie Davidson Memorial Lecture given on May 19,1977

This is a summary of clinical findings made with a quantitative technique—the 133Xe intra-arterial injection method—which permits measurement of the blood flow in several circumscribed regions of the brain simultaneously. Since the blood flow through the nervous tissue is controlled by the neuronal activity and its oxidative metabolism, it follows that multi-regional flow measurements may be used to study the distribution of function, as well as functional variations in the brain (Ingvar and Lassen, 1975). Some technical points and limitations of the 133Xe method used for measurements of the regional cerebral blood flow (rCBF) will first have to be considered. Then, some of the main findings in normal brain will be summarized. Finally, it will be shown that multi-regional rCBF studies can be used to reveal abnormal brain functions in patients, even in those who in investigations with other diagnostic procedures appear to have a normal nervous system. Emphasis will be given to the fact that flow measurements picture functional states and functional changes, while conventional neuro-radiological methods, including computer-aided tomography, reveal morphological conditions in the brain. It appears likely the two approaches to the study of the brain will be used more and more in a complementary fashion, especially when both types can be implemented with atraumatic techniques. The principles of the intra-arterial xenon clearance technique, an isotope residue detection method, have been described elsewhere (Lassen and Ingvar, 1972).