Quantification of technetium-99m hexamethylpropylene amine oxime brain uptake in routine clinical practice using calibrated point sources as an external standard: phantom and human studies

Quantitative methods for calculation of regional cerebral blood flow with technetium-99m hexamethyl-propylene amine oxime (99mTc-HMPAO) have been proposed. These methods are very labour intensive and therefore are not useful in routine clinical practice. We describe a simple alternative method, using calibrated point sources as a scaling factor, whereby the tomographic slices are displayed as regional 99mTc-HMPAO brain uptake per cm3 brain tissue in percent of the injected lipophilic dose. The method was validated on Jaszczak and Hoffman phantoms using a three-detector system with HR parallel and HR fan-beam collimators. Under the optimal conditions described in this paper, the measured to real activity ratio was 1.00 (SD=0.06). The reproducibility of the cerebellar uptake in a group of ten normal volunteers and five patients was studied. Intra-individually a mean deviation of 12.6% was observed for the total group. For those patients with a heart rate difference of less than 5 units between the two studies, a mean deviation of 7.2% was obtained. Quantitative 99mTc-HMPAO brain uptake images can be useful for longitudinal studies, especially for follow-up, activation and pharmacological studies. (orig.)