Correlation between 99mTc-bicisate and regional CBF measured with iodo-[14C]antipyrine in a primate focal ischemia model.

The need for an agent to quantitatively measure regional cerebral blood flow in humans using single photon emission computed tomography has led to the development of a new 99mTc-labeled agent: bicisate (ethyl cysteinate dimer). We have utilized an acute stroke model in the baboon to examine the ability of this agent to quantitatively measure regional cerebral blood flow in ischemic tissue. One hour after occlusion of either the left anterior cerebral or the middle cerebral artery, 99mTc-bicisate was administered intravenously, followed 20 min later by the measurement of local cerebral blood flow using iodo-[14C]antipyrine. With use of double-label autoradiography, the distribution of 99mTc-bicisate was correlated with the local cerebral blood flow images. A cerebral blood flow parameter was calculated from the 99mTc-bicisate tissue distribution and the arterial blood tracer concentration using an indicator fractionation model. For cerebral blood flows above approximately 40-50 ml 100 g-1 min-1, 99mTc-bicisate underestimates cerebral blood flow by as much as 20%, while for blood flows below approximately 15 ml 100 g-1 min-1, blood flow is overestimated by the 99mTc-bicisate distribution by an average of 3-4 ml 100 g-1 min-1. This apparent hyperfixation at very low blood flows may be related to a higher extraction of this tracer by ischemic tissue.