Quantification of two radionuclides in simultaneous /sup 123/I//sup 99m/Tc SPECT with artificial neural networks

This study was carried out to reconstruct quantitative images in simultaneous /sup 123/I//sup 99m/Tc SPECT. In the /sup 123/I //sup 99m/Tc SPECT study the image reconstructed with the counts of primary photons emitted from the isotope with low photo-peak energy (/sup 99m/Tc) is distorted by Compton scattered photons originating in the isotope with high photo-peak energy (/sup 123/I). To quantify each radioisotope in the simultaneous data acquisition, we have proposed a method with an artificial neural network, in which ten energy windows were used. But the method is not commercially available except for a specially designed gamma camera system. In this paper we proposed a new method, which uses only three energy windows. The performance of our method was investigated with Monte Carlo simulations, experiments with a brain phantom and a cardiac phantom, and clinical studies. The results showed that despite the fact that this method used only three windows its performance was comparable to that obtained with our previously reported method with ten windows. Our proposed method could separate /sup 99m/Tc and /sup 123/I with an error of only about 5%. The results will help make feasible clinical use with dual-isotope SPECT.