An Analysis of the Arterial Input Curve for Technetium-99m-HMPAO: Quantification of rCBF Using Single-Photon Emission Computed Tomography

Arterial radioactivity content after the intravenous administra-tion of HMPAO in seven human subjects was analyzed. Arterial sampling of 99mTc-HMPAO was performed on each subject over a 25-min period postinjection. The lipophitic fraction of the tracer present in the blood was rapidly ex-tracted with octanol. An analysis of the time course of the extracted and nonextracted octanol fractions was performed in order to calculate the arterial input of the tracer available for brain extraction. HMPAO net regional brain clearances were then calculated and compared with rCBF values ob-tained in the same patients using 99~l'c-microspheres injected into the left ventricle of the heart. HMPAO brain clearances were 0.41 __ _ 0.01 and 0.27 + _ 0.01 ml/min/g for grey and white matter, respectively. Linear regression analysis was performed and the following result was obtained: Clearance (HMPAO) = 0.07 + 0.43 • rCBF with a high significance (p < 0.001). This equation can be used for the transformation of HMPAO clearances into rCBF values. Our study demonstrates that by using HMPAO and SPECT it is possible to obtain a quantitative stimate of rCBF in humans