Cerebral blood volume measured with inhaled C¹⁵O and positron emission tomography

Local cerebral blood volume (CBV) has been measured previously with inhaled ¹¹CO and positron emission tomography (PET). The model used assumes that equilibrium in tracer concentration has occurred between arterial and systemic venous blood before the PET measurement is made. To verify that this model may be used with the much shorter half-lived C¹⁵O, we have simultaneously measured arterial and venous blood radioactivity following C¹⁵O inhalation. Equilibrium occurred 95 ± 39 s after inhalation (n = 7). If the PET measurement is commenced prior to arteriovenous equilibrium, significant errors occur in calculated CBV. These data indicate that C¹⁵O may be used as a tracer for CBV measurement provided that emission data collection commences at ~120 s after inhalation. Strict quality control measures must be maintained to minimize the contamination of administered C¹⁵O with ¹⁵O-labeled CO₂.