How to interpret differing cerebral blood flow patterns estimated with 99Tcm-HMPAO and 99Tcm-ECD SPET in a healthy population.

Two radiopharmaceuticals, 99Tcm-hexamethyl propylene amine oxime (99Tcm-HMPAO) and 99Tcm-ethyl cysteinate dimer (99Tcm-ECD), are currently used to determine cerebral blood flow. 99Tcm-ECD is, by virtue of its greater stability, superseding 99Tcm-HMPAO for routine examinations. Since the clinical assessment of 99Tcm-ECD images is usually based on experience with 99Tcm-HMPAO, we used both radiopharmaceuticals to compare regional cerebral blood flow in the same individuals. Eleven healthy subjects aged 67.1 +/- 6.3 years (mean +/- S.D.) underwent 99Tcm-ECD followed by 99Tcm-HMPAO single photon emission tomography. Cerebral blood flow was quantified in cortical and central regions of interest (basal ganglia, ventricles, white matter) in relation to cerebellar uptake. The intra-subject comparison of cerebral blood flow in the cortical areas revealed higher levels of perfusion in the posterior parietal, parieto-occipital and temporo-occipital areas using 99Tcm-ECD. In contrast to the cortical areas, cerebral blood flow in the central areas was greater using 99Tcm-HMPAO, especially in the centrum semiovale, basal ganglia, frontal white matter and frontal horns. This difference in cerebral blood flow when imaging healthy individuals with 99Tcm-ECD and 99Tcm-HMPAO should be taken into account in clinical practice when changing from one radiopharmaceutical to the other.