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3 May 2002 Convolution estimation of spill-down and scatter in dual isotope (99mTc/111In) SPECT
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Accurate attenuation correction in dual isotope single photon emission computed tomography (SPECT) requires spill-down and scatter correction. Convolution methods that allow such correction were investigated. Three energy windows were used: 1) a Compton scatter window placed below the Tc-99m photopeak window, 2) the Tc-99m photopeak, and 3) both In-111 photopeaks. Spill-down of In-111 into the Tc-99m window was measured using a small source of In-111 at depths of 5, 7, 9, and 11cm. From these data, the convolution kernel relating the In-111 image and the Tc-99m window spill-down image was computed for each depth. Using a small Tc-99m source at the same depths, the convolution kernels describing its spill-down into the Compton window were computed. A factor to scale the Tc-99m spill-down estimate by for obtaining the self-scatter estimate was determined from the total counts in the Tc-99m photopeak vs. the Compton scatter window when primary photons were blocked with a small lead disk. Depths of 5 and 9cm were optimal for spill-down and Tc-99m self-scatter correction, respectively. It was demonstrated that the spill-down and scatter correction increased effective attenuation coefficient towards its 'no-scatter' value and dramatically decreased the intensity of an In-111 source in Tc-99m projection images.
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Jian Feng, Bill C. Penney, and Xiaochuan Pan "Convolution estimation of spill-down and scatter in dual isotope (99mTc/111In) SPECT", Proc. SPIE 4682, Medical Imaging 2002: Physics of Medical Imaging, (3 May 2002);

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