QUANTIFICATION OF TC-99M HEXAMETHYLPROPYLENE AMINE OXIME BRAIN UPTAKEIN ROUTINE CLINICAL-PRACTICE USING CALIBRATED POINT SOURCES AS AN EXTERNAL STANDARD - PHANTOM AND HUMAN STUDIES

Quantitative methods for calculation of regional cerebral blood flow w ith technetium-99m hexamethyl-propylene amine oxime (Tc-99m-HMPAO) hav e been proposed. These methods are very labour intensive and therefore are not useful in routine clinical practice. We describe a simple alt ernative method, using calibrated point sources as a scaling factor, w hereby the tomographic slices are displayed as regional Tc-99m-HMPAO b rain uptake per cm3 brain tissue in 10(-6) 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 c erebellar uptake in a group of ten normal volunteers and five patients was studied. Intra-individually a mean deviation of 12.6% was observe d for the total group. For those persons with a heart rate difference of less than 5 units between the two studies, a mean deviation of 7.2% was obtained. Quantitative Tc-99m-HMPAO brain uptake images can be us eful for longitudinal studies, especially for follow-up, activation an d pharmacological studies.