Cerebral blood flow (CBF) and rate of oxygen metabolism (CMRO2) may be quantified using positron emission tomography (PET) with 15O-tracers, but the conventional three-step technique requires a relatively long study period, attributed to the need for separate acquisition for each of 15O2, H215O, and C 15O tracers, which makes the multiple measurements at different physiologic conditions difficult. In this study, we present a novel, faster technique that provides a pixel-by-pixel calculation of CBF and CMRO2 from a single PET acquisition with a sequential administration of 15O2 and H215O. Experiments were performed on six anesthetized monkeys to validate this technique. The global CBF, oxygen extraction fraction (OEF), and CMRO2 obtained by the present technique at rest were not significantly different from those obtained with three-step method. The global OEF (gOEF) also agreed with that determined by simultaneous arterio-sinus blood sampling (gOEFA-V) for a physiologically wide range when changing the arterial PaCO2 (gOEF = 1.03gOEFA-V -0.01, P<0.001). The regional values, as well as the image quality were identical between the present technique and three-step method for CBF, OEF, and CMRO2. In addition, a simulation study showed that error sensitivity of the present technique to delay or dispersion of the input function, and the error in the partition coefficient was equivalent to that observed for three-step method. Error sensitivity to cerebral blood volume (CBV) was also identical to that in the three-step and reasonably small, suggesting that a single CBV assessment is sufficient for repeated measures of CBF/CMRO2. These results show that this fast technique has an ability for accurate assessment of CBF/CMRO2 and also allows multiple assessment at different physiologic conditions.
- Dual tracer
- Rapid measurement