Dual radioisotopes simultaneous SPECT of ^99mTc-tetrofosmin and ¹²³I-BMIPP using a semiconductor detector

The energy resolution of a cadmium-zinc-telluride (CZT) solid-state semiconductor detector is about 5%, and is superior to the resolution of the conventional Anger type detector which is 10%. Also, the window width of the high-energy part and of the low-energy part of a photo peak window can be changed separately. In this study, we used a semiconductor detector and examined the effects of changing energy window widths for ^99mTc and ¹²³I simultaneous SPECT. The energy "centerline" for ^99mTc was set at 140.5 keV and that for ¹²³I at 159.0 keV. For ^99mTc, the "low-energy-window width" was set to values that varied from 3% to 10% of 140.5 keV and the "high-energy-window width" were independently set to values that varied from 3% to 6% of 140.5 keV. For ¹²³I, the "low energy-window-width" varied from 3% to 6% of 159.0 keV and the high-energy-window width from 3% to 10% of 159 keV. In this study we imaged the cardiac phantom, using single or dual radionuclide, changing energy window width, and comparing SPECT counts as well as crosstalk ratio. The contamination to the ¹²³I window from ^99mTc (the crosstalk) was only 1% or less with cutoffs of 4% at lower part and 6% at upper part of 159KeV. On the other hand, the crosstalk from ¹²³I photons into the ^99mTc window mostly exceeded 20%. Therefore, in order to suppress the rate of contamination to 20% or less, ^99mTc window cutoffs were set at 3% in upper part and 7% at lower part of 140.5 KeV. The semiconductor detector improves separation accuracy of the acquisition inherently at dual radionuclide imaging. In, this phantom study we simulated dual radionuclide simultaneous SPECT by ^99mTc-tetrofosmin and ¹²³I-BMIPP. We suggest that dual radionuclide simultaneous SPECT of ⁹⁹mTc and ¹²³I using a CZT semiconductor detector is possible employing the recommended windows