A NEW DUAL-ISOTOPE CONVOLUTION CROSS-TALK CORRECTION METHOD - A TL-201 TC-99M SPECT CARDIAC PHANTOM STUDY

Simultaneous dual-isotope SPECT imaging provides a clear advantage in situations where two concurrent metabolic, anatomic, or background mea surements are desired. It obviates the need for two separate imaging s essions, reduces patient motion problems, and provides exact image reg istration between images. However, a potential limitation of dual-isot ope SPECT imaging is contribution of scattered and primary photons fro m one radionuclide into the second radionuclide's photopeak energy win dow, referred to here as cross-talk. Cross-talk in both photopeak ener gy windows can significantly degrade image quality, resolution, and qu antitation to an unacceptable level. Simple cross-talk correction meth od used in dual-radionuclide in vitro counting, even applied on a pixe l-by-pixel basis, does not account for the differences in spatial dist ribution of the photopeak and cross-talk photons. Here a new convoluti on cross-talk correction method is presented. The convolution fitters are derived from point response functions (PRFs) for Tc-99m and Tl-201 point sources. Three separate acquisitions were performed, each with two 20% wide energy windows, one centered at 140 keV and another at 70 keV. The first acquisition was done with Tc-99m solution only, the se cond with Tl-201 solution only, and the third with a mixture of Tc-99m and Tl-201. The nonuniform RH-2 thorax-heart phantom was used to test a new correction technique. The main difficulty and limitation of the convolution correction approach is caused by the variation in PRF as a function of depth. Thus, average PRF should be used in the creation of an approximative filter. The results of this study show that simple cross-talk correction provides Tl-201 images of poor quality. However , the proposed method, based on convolution technique, improves the qu ality of the simultaneous Tl-201/Tc-99m SPECT imaging.