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SUMMARY Using positron emission tomography, regional cerebral blood flow and oxygen utilisation were measured in the contralateral cortex of 14 patients with a variety of intracranial tumours. A comparison was made with cortical values derived from 14 normal controls. Compared with normal subjects, patients with brain tumours had a significant reduction in oxygen utilisation and blood flow in their contralateral cortex. Decompression resulting from craniotomy and biopsy, led to a partial reversal of this cerebral hypofunction.With the advent of positron emission tomography (PET) it has become possible to measure, quantitatively, regional cerebral blood flow and a variety of metabolic processes in man non-invasively. '-3 Most of the workers in the PET field who have studied the pathophysiology of intracerebral tumours have compared the values obtained for flow and metabolism in the tumour with that of contralateral "normal" brain.4 5 In some studies it was noted that intracerebral tumours were associated with a depression of oxygen metabolism and blood flow in the overlying ipsilateral cortex We have suspected for some time that an intracranial tumour may profoundly affect not only blood flow but oxygen utilisation in the contralateral supposedly normal brain. This study was undertaken to clarify the situation in man, using PET. The aim of the study was two-fold and both parts dealt with regional blood flow and oxygen utilisation in cortical tissue only. Firstly a comparison was made between the physiology of the contralateral cortex of brain tumour patients and that of normal controls. Patients on steroid therapy were excluded from the study as it has been shown that the administration of dexamethasone to patients with brain tumours is associated with a reduction in cortical blood flow and regional blood volume as measured by the oxygen-15 steady-state technique (Leenders et al, in preparation). Most of the published PET work dealing with regional blood flow and metabolism in cerebral tumour patients to date has included patients on steroid therapy. In the second part of this study the effect of cerebral decompression on

Summary:The kinetics of the regional cerebral uptake of ["C] 3-0-methyl-o-glucose (["C1MeG), a competitive in hibitor of o-glucose transport, have been studied in normal human subjects and patients with cerebral tu mours using positron emission tomography (PET), Con comitant measurement of regional cerebral blood volume and blood flow enabled corrections for the contribution of intravascular tracer signal in PET scans to be carried out and regional unidirectional cerebral ["C1MeG extrac tions to be determined, A three-compartment model con taining an arterial plasma and two cerebral compartments was required to produce satisfactory fits to experimental regional cerebral [ l lCJMeG uptake data. Under fasting, resting conditions, normal controls had mean unidirec tional whole-brain, cortical, and white matter ["C1MeG extractions of 14, 13, and 17%, respectively. Mean values of k, and k2, first-order rate constants describing forward and back transport, respectively, of tracer into the first cerebral compartment, were similar for ["C1 MeG and ['8F] 2-fluoro-2-deoxy-o-glucose ( , 8FDG), a second comStudies on intact dog and rat brain, and also on isolated cerebral rat brain capillaries, have shown that D-glucose transport across the blood-brain barrier (BBB) is a passive facilitated process (Crone, 1965; Betz et aI., 1973 Betz et aI., , 1979 Pard ridge and Oldendorf, 1975). 3-0-Methyl-D-glucose (MeG) and 2-deoxY-D-glucose (2-DG) have both been shown to