Rapid quantitative measurement of CMRO₂ and CBF by dual administration of ¹⁵O-labeled oxygen and water during a single PET scan - A validation study and error analysis in anesthetized monkeys

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 (gOEF_A-V) for a physiologically wide range when changing the arterial PaCO₂ (gOEF = 1.03gOEF_A-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.