[en] In this study, the conditions of patients to which cerebral revascularization through anastomosis of internal and external carotid arteries is applicable were investigated. In the first part, classification of the degree of cerebrovascular disease was attempted using positron emission tomography (PET) and in the second, cerebral blood circulation was evaluated using cerebral SPECT to consider in respect of advisability of the revascularization surgery. Since cerebral ischemia tends to be induced by enhancement of cerebral oxygen uptake, cerebral revascularization was thought to be restricted to the patients with cerebrovascular disease in stage 2. So, cerebral blood flow, cerebral blood volume and cerebral oxygen metabolism were compared among the patients in stage 1 and stage 2, and the normal control. The blood flow was decreased with the severity of disease and lowest in the patients of stage 2. There were significant differences in the oxygen metabolism and blood volume between the patient stage 1 and the control. The cerebral blood flow in patient in stage 2 was decreased to a level below the self-control range, leading to an increase in the cerebral oxygen uptake. Therefore, it was concluded that the severity of cerebrovascular disease could be estimated with cerebrocirculation index and vasodilation ability determined by cerebral SPECT. Patients of which cerebral blood flow is decreased by more than 28.0% can be regarded as the patient in stage 2. When cerebral blood volume determined by IMP-ARG method and PET method and was compared, underestimation was 34.5% for plane phantom and 11% for cranial pseudo phantom. Further classification would be made on the basis of vascular response under the conditions of Diamox loading and it was concluded that cases of which decrease in cerebral blood flow is 10% or less were applicable to cerebral revascularization. (M.N.)