- Cerebral Blood Flow (CBF): 500 MBq of [15O]H2O is injected intravenously. At injection a three minute PET image acquisition of the brain is started together with arterial blood sampling (also three minutes) with an automated blood radioactivity sampler that draws 7 ml blood per minute. The PET acquisition is done on a Siemens High Resolution Research Tomograph (HRRT) in list mode.