Quantitative measurement of cerebral blood flow and oxygen metabolism in small animals with 15O gas inhalation PET: A comparison between arterial blood sampling and image derived input function

Objectives Measurement of arterial input function is essential for quantitative estimation of cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) in 15O gas inhalation PET. However, repetitive arterial blood sampling (ABS) may disturb circulation dynamics in small animals. The purpose of this study was to evaluate the feasibility image derived input function (IDIF) instead of ABS.

Methods Seven rats (mean body weight 299.2 ± 18.6 g) were investigated by steady state inhalation method of 15O-CO2 and 15O-O2 under intramuscular anesthesia. ABS was performed to measure the radioactivity of whole blood and plasma during steady state. Volumes of interest were placed on the blood pool inside the left ventricle of 15O-CO2 and 15O-O2 images during steady state and used as IDIF. CBF, CMRO2, and oxygen extraction fraction (OEF) were compared between ABS and IDIF. Partial volume effect was estimated by NEMA-4 phantom. We assumed cardiac chamber diameter of rats to be 5mm. PVE corrected IDIF and non-corrected IDIF was compared.

Results Quantitative values calculated by the ABS were 39.2 ± 11.7 mL/100ml/min for CBF, 4.3 ± 0.7 mL/100ml/min for CMRO2 and 65.4 ± 13.1 % for OEF. The ratios of non PVE corrected IDIF were 361.4% for CBF, 112.0% for OEF, 412.1% for CMRO2. The ratios of PVE corrected IDIF were 74.7% for CBF, 110.3% for OEF, 81.4% for CMRO2.

Conclusions This study demonstrated the feasibility of the IDIF method when it is appropriately corrected for partial volume effect of radioactivity in cardiac chamber.