Validation of quantitative brain dopamine D2 receptor imaging with a conventional single-head SPET camera

Abstract

Phantom measurements were performed with a conventional single-head single-photon emission tomography (SPET) camera in order to validate the relevance of the basal ganglia/frontal cortex iodine-123 iodobenzamide (IBZM) uptake ratios measured in patients. Inside a cylindrical phantom (diameter 22 cm), two cylinders with a diameter of 3.3 cm were inserted. The activity concentrations of the cylinders ranged from 6.0 to 22.6 kBq/ml and the cylinder/background activity ratios varied from 1.4 to 3.8. From reconstructed SPET images the cylinder/ background activity ratios were calculated using three different regions of interest (ROIs). A linear relationship between the measured activity ratio and the true activity ratio was obtained. In patient studies, basal ganglia/frontal cortex IBZM uptake ratios determined from the reconstructed slices using attenuation correction prior to reconstruction were 1.30±0.03 in idiopathic Parkinson's disease (n=9), 1.33±0.09 in infantile and juvenile neuronal ceroid lipofuscinosis (n=7) and 1.34±0.05 in narcolepsy (n=8). Patients with Huntington's disease had significantly lower ratios (1.09±0.04, n=5). The corrected basal ganglia/frontal cortex ratios, determined using linear regression, were about 80% higher. The use of dual-window scatter correction increased the measured ratios by about 10%. Although comprehensive correction methods can further improve the resolution in SPET images, the resolution of the SPET system used by us (1.52 cm) will determine what is achievable in basal ganglia D2 receptor imaging.