[Dual isotope SPECT with 99mTc and 123I using four-energy-window (FEW) method].

We devised "four-energy-window" (FEW) method which permits simultaneous acquisition for dual isotope single photon emission tomography (SPECT) studies using 99mTc and 123I of which photopeak is in close vicinity to each other. This acquisition method requires a total of four energy windows: two main windows for 99mTc (126-143 keV) and 123I (156-175 keV), respectively, and two 5% sub-windows which are set below the 99mTc window and above the 123I window, respectively. Two virtual windows (5%) are additionally set above the 99mTc and below the 123I window, respectively, to apply the triple-energy-window (TEW) method for the scatter correction. A phantom study demonstrated that photocounts from the two radionuclides could be completely separated from each other and that SPECT images obtained had preferable property for quantitative analysis. This method was applied to clinical, dual-radionuclide myocardial studies using 99mTc-MIBI and 123I-BMIPP, and was found to provide excellent images each tracer.