Cerebral Oxygen Metabolism of Rats using Injectable 15O-Oxygen with a Steady-State Method

To develop a less-stressful and simple method for measurement of the cerebral metabolic rate of oxygen (CMRO(2)) in small animals, the steady-state method was applied to injectable (15)O(2)-PET ((15)O(2)-positron emission tomography) using hemoglobin-containing vesicles ((15)O(2)-HbV). Ten normal rats and 10 with middle cerebral arterial occlusion (MCAO) were studied using a small animal PET scanner. A series of (15)O-PET scans with C(15)O-labeled HbV, H(2)(15)O, and (15)O(2)-HbV were performed with 10 to 15 minutes intervals to measure cerebral blood volume (CBV), cerebral blood flow (CBF), and CMRO(2). Positron emission tomography scans were started with a tracer injection using a multiprogramming syringe pump, which provides a slowly increasing injection volume to achieve steady-state radioactivity for H(2)(15)O and (15)O(2)-HbV scans. The radioactivity concentration of (15)O rapidly achieved equilibrium in the blood and whole brain at about 2 minutes after H(2)(15)O and (15)O(2)-HbV administration, which was stable during the scans. The whole brain mean values of CBF, CBV, and CMRO(2) were 54.3±2.0 mL per 100 g per minute, 4.9±0.4 mL/100 g, and 2.8±0.2 μmoL per g per minute (6.2±0.4 mL per 100 g per minute) in the normal rats, respectively. In the MCAO model rats, all hemodynamic parameters of the infarction area on the occlusion side significantly decreased. The steady-state method with (15)O-labeled HbV is simple and useful to analyze hemodynamic changes in studies with model animals.