III I I II I I II I II I Kinetic Behavior of Technetium-99m-HMPAO in the Human Brain and Quantification of Cerebral Blood Flow Using Dynamic SPECT

The kinetic behavior of 9~Tc-hexamethylpropyleneamine ox-ime (HMPAO) in the human brain was investigated in 11 patients with various brain diseases (176 regions), using dynamic SPECT and a four-compartment model with five parameters (KI: rate constant for the transport of HMPAO from blood to brain, K2: backdiffusion from brain to blood, K3: conversion to a hydrophilic form in the brain, K5: conver-sion to a nondiffusible form in the blood, and f,: fraction of radioactivity attributable to the vascular compartment). Al-though K1 correlated well with cerebral blood flow (CBF) measured by the 133Xe inhalation method (Xe-CBF) (r = 0.888), its value was underestimated by 28.9 % + 11.9%, indicating a low extraction fraction (E) for HMPAO. From E = K1/CBF, a regression equation of E = 0.857- 0.00335. Xe-CBF was obtained. Significant correlations were observed for K2 versus Xe-CBF (r = 0.679), for K3 versus Xe-CBF (r = 0.483), for K3/(K2 + K3) versus Xe-CBF (r---0.487), for K3/ K2 versus Xe-CBF (r =-0.501), and for K2 + K3 versus Xe-CBF (r = 0.655), but not for K1/K2 versus Xe-CBF (r = 0.005). Thus, this model was useful for elucidating the kinetic behav-ior of HMPAO in the human brain, and correction for E appears to be indispensable for accurate CBF quantification using HMPAO. J Nucl Med 1992; 33:135-143 Over the last decade, several brain imaging radiophar-maceuticals have been developed that permit routine cerebral blood flow (CBF) imaging by single-photon emis-sion computed tomography (SPECT). These include N-iso-propyl-p-[|23I]iodoamphetamine (IMP) (l), N,N,N'-tri-methyl-N'-[2 hydroxy-3 methyl-5-[|23I]iodobenzyl]- 1,3-propanediamine (HIPDM) (2), 2°tTl-demethyldithiocar-bamate (DDC) (3), 99mTc-hexamethylpropyleneamine ox