Study of Cerebral Vascular Reserve Using Pharmacological Testing With Acetazolamide: A Non-Inferiority Study of PET Method Compared to Conventional Reference Scintigraphy

Inclusion Criteria: * Chronic stenosing cerebral vascular pathology (stenosis \> 70% on Doppler examination or angiography). * Patient aged over 18 years. * Patient who has voluntarily agreed to participate in the study and has signed the written informed consent. * Patient affiliated with a social security system. Exclusion Criteria: * Patient with stenosis less than 70% on Doppler examination or angiography. * Patient with a contraindication to 18F-FDG PET examinations: severe claustrophobia, poorly controlled diabetes during 18F-FDG PET examinations (fasting capillary blood glucose ≥ 11 mmol/L). * Patient with a contraindication to scintigraphy. * Patient with an allergy to sulfonamides (Acetazolamide DIAMOX®). * Patient enrolled in another clinical study with a specified exclusion period. * Minor patient. * Patient unable to give informed consent. * Vulnerable individuals