Alignment of transmission and emission scans of PET to correct for subject movement using a sinogram consistency criterion

Subject movement leads to misalignment between transmission and emission PET scans acquired at different times. This leads to inaccurate attenuation correction and causes errors in PET images. We propose a new method, which seeks to minimize the variance of the total counts of attenuation corrected emission sinogram among all projection angles. The underlying basis of the method is that if the transmission and emission scans are aligned, the total counts (after attenuation correction) at different projection angles should be equal (i.e., with zero variance). Therefore, by adjusting the spatial transformation parameters between the transmission and emission images to minimize such a variance as a cost function, the two scans would be aligned. The effectiveness of this method is demonstrated in two-dimensional situations with computer simulated data and with a physical phantom PET study.