Crosstalk and scatter correction in simultaneous dual isotope SPECT imaging using four energy windows method

One of the limitations of the simultaneous dual isotope SPECT with Tc-99m and I-123 is the crosstalk of the photons from one radionuclide to the other radionuclide's photopeak, which is serious since the difference between the photopeak of Tc-99m and I-123 is small (140 keV, 159 keV). We designed a method for correcting this crosstalk effect using four energy windows, by which we could reduce the effect of scatter as well as crosstalk. We also validated our method by comparing the corrected images to the single-isotope image acquired with phantom study. After defining the energy windows for each isotope, crosstalk fractions from the photopeak of one isotope to the photopeak/scatter windows of the other isotope were determined. Using these fractions, the effect of scatter and crosstalk was compensated. Relative errors were estimated between the single and the crosstalk/scatter corrected dual isotope images. Measured crosstalk fractions did not change regardless of the activity of each isotope. Contamination of activity was reduced as a result of crosstalk correction (CC), and image contrast was improved by scatter correction (SC). Relative errors decreased further after SC on CC images. Using four energy windows method, we could obtain a more accurate result in simultaneous dual isotope SPECT.