Scatter corrections for simultaneously acquired dual-isotope SPECT imaging using three windows

The authors investigated the feasibility of using a third energy window (EW) for rest ²⁰¹Tl/stress ^99mTc scatter corrections in order to obtain improved quantification and image quality compared with dual-isotope myocardial perfusion imaging using two photopeak energy windows (PEWs). Three low energy ultra-high resolution parallel beam collimators were mounted on a triple-camera SPECT system and used to obtain planar and SPECT images. To obtain the relationships between the intermediate EW (IEW) and dual-isotope scatter EWs (SEWs), five different EWs, including an IEW (103 keV±22%) between the dual-isotope PEWs, were used. Then, the scatter subtraction coefficients obtained from line source measurements with an anthropomorphic phantom were applied to the IEW´s scatter correction. The IEW was used for the scatter correction for both isotopes. The crosstalk into each PEW measured with a cardiac phantom was similar in air; however, in water ^99mTc to ²⁰¹Tl crosstalk was greater than twice of that in air. After attenuation and scatter compensation, the quantitative analysis and image quality were improved compared with dual-isotope imaging which used two PEWs, especially with ²⁰¹Tl scans acquired in the presence of background activity. These results demonstrate that the IEW may be used for dual-isotope scatter compensation, and three window acquisition provides improved myocardial SPECT imaging in an anthropomorphic phantom