SELECTION OF COLLIMATOR FOR RCBF STUDIES AND EVALUATION OF TRIPLE-HEADED SPET USING NOISE-RESOLUTION PLOTS

We investigated the effect of collimator selection on image quality in regional cerebral blood flow (rCBF) studies of the brain performed wi th Tc-99(m)-HMPAO. A triple-headed SPET system (GE/CGR Neurocam) was u sed, together with three sets of parallel-hole collimators - general-p urpose (GP), high-resolution (HR) and ultra-high-resolution (UHR). Two image quality parameters were used to describe the image quality, nam ely, noise and resolution. Noise was measured in experimental and Mont e-Carlo simulated SPET studies of a cylinder phantom of uniform activi ty as the pixel root mean square error (RMS) and as the coefficient of variation (CV) of quantitative rCBF values. Resolution was measured a s full-width at half-maximum in experimental SPET studies of a line-so urce. Plots of noise versus resolution for the different collimators w ere obtained by varying the cut-off frequency of the Hanning filter ap plied in the reconstruction of transaxial slices. From these noise-res olution plots, we were able to determine which collimator gave the bes t resolution for a specific noise level. A lowest reasonable noise lev el may be established by comparison with the inter-observer CV of the quantification method.