Scatter and crosstalk correction in simultaneous 99mTc and 123I dual-isotope SPECT imaging using five energy windows method

2150 Objectives In simultaneous dual-isotope imaging, the down-scatter is unavoidable error even by using high energy resolution detectors, especially when the difference between the scanned radionuclide’s photopeak is small. To improve the accuracy of simultaneous 99mTc (141 keV) and 123I (159 keV) imaging, a scatter and crosstalk correction method was developed for our prototype CdTe semiconductor SPECT with high energy resolution (6.6% FWHM, at 140 keV). Methods Five different energy windows (Tc-lower, Tc-main, intermediate for Tc-upper and I-lower, I-main, and I-upper) and pre-measured sensitivity of each energy window for primary annihilation photons of 99mTc and 123I were used. The scatter in I-main was corrected by using Triple-energy window technique (TEW) for I-windows. Then, the crosstalk in Tc-windows were compensated by using scatter corrected I-main projection and the sensitivity relationships between I-main and each Tc-windows. Finally, the scatter in Tc-main was corrected by using TEW for Tc-windows. To evaluate the quantitative accuracy of the correction method, three phantom experiments were conducted with our prototype CdTe human brain SPECT. Results The determination coefficients between the activity and pixel value were 0.997 for 99mTc and 0.998 for 123I in image of a phantom which had five various mixtures of 99mTc and 123I and a cold segments. The pixel value ratio of 99mTc (111 MBq) image to mixture of 99mTc (111 MBq) and 123I (75 MBq) image was 0.99 in a same cylindrical phantom image. The images of 99mTc and 123I were clearly discriminated in characters shape phantom image. Conclusions A simple and fast, scatter and crosstalk correction method for semiconductor SPECT using five energy windows was developed. By using the developed correction method, our prototype human brain SPECT provides high quantitative dual-isotope imaging.