Quantitation of rat cerebral blood flow using ^99mTc-HMPAO

Introduction: Technetium-99m-hexamethylpropyleneamine oxime (^99mTc-HMPAO) is potentially useful for the assessment of cerebral blood flow (CBF) in small animals. In this paper, a procedure for quantitation of rat CBF using ^99mTc-HMPAO was determined. Methods: Biodistribution of ^99mTc-radioactivity in normal rats was determined after intravenous administration of ^99mTc-HMPAO. Acetazolamide treated rats were intravenously administered with the mixture of ^99mTc-HMPAO and N-isopropyl-[¹²⁵I]iodoamphetamine ([¹²⁵I]IMP), and arterial blood was then collected for 5 min. After blood sampling, the brain radioactivity concentration was measured with the auto-well γ counter. Results: The brain radioactivity concentration after intravenous administration of ^99mTc-HMPAO was steady from 14 s to 60 min post-injection. A double tracer experiment using ^99mTc-HMPAO and [¹²⁵I]IMP showed that 19 s was the average of the optimal integration interval of arterial blood ^99mTc-radioactivity concentration to obtain CBF values measured by ^99mTc-HMPAO identical to those determined by [¹²⁵I]IMP. The CBF value determined by ^99mTc-HMPAO, calculated by dividing the brain radioactivity concentration at 5 min post-injection by the integrated arterial blood radioactivity concentration until 19 s post-injection, was well correlated with CBF as determined by [¹²⁵I]IMP. Conclusion: These results suggest that the CBF quantitation procedure described in this paper could be useful for rat CBF assessment.