A new technique to systematically minimize misregistration introduced errors in cardiac perfusion studies with attenuation correction

In cardiac perfusion studies (both PET and SPECT) with CT-based attenuation correction, intensive efforts have been made to minimize the emission/transmission misregistration in order to minimize the errors introduced by the misregistration in the attenuation corrected images. In this work, we propose a new technique to systematically minimize the errors introduced by the misregistration. In general, the emission/transmission misregistration is a combination of two types of misregistration: (A) the myocardial wall is moved toward the mediastinum or diaphragm, the attenuation coefficient of which is approximately the same as that of the myocardium; and (B) the myocardial wall is moved into the lungs, the attenuation coefficient of which is significantly lower than that of the myocardium. In the proposed technique, after the emission/transmission registration and prior to the reconstruction with attenuation correction (AC), we first segment the heart in the emission image; then set the voxels of the transmission image corresponding to the segmented heart the attenuation coefficient of soft tissue. This technique is expected to have negligible effect on the accuracy of AC when type (A) misregistration exists, but systematically reduce the errors introduced by type (B) misregistration. A series of SPECT studies with attenuation correction were simulated to evaluate this technique using the mathematical MCAT phantom. Results showed that perfusion errors were significantly reduced for type (B) misregistration but not for type (A) misregistration of magnitude of 1.2 cm. In conclusion, we developed a new technique that systematically minimized the errors introduced by emission/transmission misregistration for cardiac perfusion studies with attenuation correction.