MAGNETIC RESONANCE IN MEDICINE 19, zyxwvut 2 17-220 zyxwvu ( 199 1 ) Functional Variations in Parenchymal Microvascular Systems within the Brain" JOSEPH FENSTERMACHER, HIROYUKI NAKATA,? ATSUSHI TAJIMA,$ AND DANIEL BERECZKI SHINN-ZONG LIN,~ TADAHIRO OTSUKA,~ VIRGIL ACUFF, LING WEI, zyx Department ofNeurologica1 Surgery, HSC, zyxwvuts T12-080, State University ofNew York, Stony Brook, New York 11 794-8122; ?Department of Neurosurgery, Osaka University Medical School, Osaka, Japan; $Department zyxwvutsr of Neurosurgery, Juntendo University, Urayasu Hospital, Urayasu, Japan; 9Department of Neurosurgery. National Defense Medical Center, Taipei, Taiwan; and YDepartment of Neurosurgery, Kumamoto University, Kumamoto, Japan Received February zyxwv 1, 199 1 Variations in microvascular system functions were observed among a number of brain areas. The rates of local blood flow varied 18-fold among areas and were extremely high in neuroendocrine structures. Marked differences in blood flow were also found within some brain structures. The volume of radiolabeled blood in perfused parenchymal micro- vessels ranged from 5 to 70 pl/g and correlated closely with local cerebral blood flow. The hematocrits within parenchymal microvessels were 45-7570 of the arterial hematocrit, which indicates that red cells more rapidly traverse brain microvessels than do plasma proteins. The mean transit times of blood through parenchymal microvessels were extremely short and ranged from 0.3 to 0.6 s. zyxwvu o I991 Academic Press, h c . INTRODUCTION Among areas within the central nervous system there are broad differences in func- tions such as local neuronal activity, afferent and efferent connections, neurotrans- mitters, endocrine role, and glucose utilization. In view of these interarea variations in neurophysiologicalactivities, local differences in capillary bed structures and function are also likely to exist. The purpose of this study was to test this possibility; accordingly, the volumes of circulating labeled red cells, albumin, and blood in parenchymal mi- crovessels; microvessel hematocrit; local cerebral blood flow; and mean transit time of blood passage were quantitated in a number of brain areas, including cortical gray matter, small hypothalamic nuclei, white matter, and several circumventricular organs (CVOs) . MET H 0 D zyxwv S Radiotracer studies. Male Sprague-Dawley rats weighing 280-350 g were lightly anesthetized with halothane. Intravenous and intraarterial catheters were inserted. * Presented at SMRM Workshop on Future Directions in MRI of Difision and Microcirculation,Bethesda, MD, June 7 and 8, 1990. 217 0740-3194/91 $3.00 Copyright 0 1991 by Academic Press, Inc. All rights of reproduction in any fom reserved.