Evaluation of SPECT Quantification of Radiopharmaceutical Distribution in Canine Myocardium

This study evaluates the quantitative accuracy of SPECT for in vivo distributions of 99mTc radiopharmaceuticals using fanbeam (FB) and parallel-beam (PB) collimators and compares uniform and nonuniform attenuation correction methods in terms of quantitative accuracy. SPECT quantification of canine myocardial radioactivity was performed followed by well counter measurements of extracted myocardial tissue samples. Transmission scans using a line source and an FB collimator were performed to generate nonuniform attenuation maps of the canine thorax. Emission scans with two energy windows were acquired. Images were reconstructed using a filtered backprojection algorithm, with a dual-window scatter subtraction combined with either no attenuation compensation or single iteration Chang attenuation compensation based on an uniform attenuation map (mu = 0.152 cm-1) or the nonuniform transmission map. The measured mean counts from the SPECT images were converted to radionuclide concentrations (MBq/g) using a standard source calibration and were compared with those obtained using the well counter. The experimental results demonstrate that, compared with well counter values, the in vivo distributions of 99mTc were most accurately determined in FB and PB SPECT reconstructions with nonuniform attenuation compensation, under-estimated without attenuation compensation and overestimated with uniform attenuation compensation.