Quantitative local cerebral blood flow measurements with technetium-99m HM-PAO: evaluation using multiple radionuclide digital quantitative autoradiography.

We investigated d,1 [99mTc]hexamethylpropyleneamine oxime complex (HM-PAO) as a tracer for quantitative measurement of local cerebral blood flow (LCBF) in a series of awake male rats. LCBF measurements with HM-PAO were compared to those of two other tracers, [14C] iodoantipyrine (IAP) and [201Tl]diethyldithiocarbamate (DDC), using quantitative double and triple tracer digital autoradiography. LCBF values with HM-PAO averaged 64% those of IAP and were generally linearly related. Detailed analysis suggested that the underestimation of LCBF by HM-PAO was related to blood constituent binding and/or rapid conversion to a noncerebrophilic compound, as well as noninstantaneous cerebral trapping, rather than to diffusion limitation.