The effects of center of rotation errors on SPECT imaging

In SPECT imaging, center of rotation (COR) errors lead to the misalignment of the projection data and can potentially degrade the quality of the reconstructed images. In this work, we study the effects of COR errors on the quality and clinical applications of SPECT images using point source, cardiac phantom, and patient studies. COR errors are simulated in both axial and transaxial directions in the projection data. The reconstructed images are evaluated in terms of point source resolution, image uniformity and lesion-to-background contrast (LBC) in cardiac phantom images, and clinical applications for patient images. It is shown that point source resolution degrades as COR errors increase. Using LEHR collimators. the full-width at half-maximum (FWHM) increases by less than 25% when the COR error increases from 0 to 0.96 cm. COR error of 0.64 cm or larger introduces visible but insignificant nonuniformity to the images of a uniform cardiac phantom. Increase of COR errors from 0 to 0.96 cm can decrease the LBC in the images of an abnormal cardiac phantom by as much as 20%, depending on the direction of COR errors and defect size. For the patient studies with COR errors up to 0.96 cm, images have the same diagnostic/prognostic values as those without COR errors. As a conclusion, for the limit number (n=4) of patient studies, COR errors of up to 0.96 cm are not likely to change the clinical applications of cardiac SPECT images.