Abstract: According to one embodiment of the invention, a variable length correlation method is provided for compensating for body motions and heart creep in a sequence of image frames obtained by single-photon emission computed tomograph (SPECT) myocardial perfusion imaging. Abrupt body motions, gradual body motions, and heart upward creep are detected and corrected in the sequence of image frames, based on varying correlation lengths. A linear transformation is used to compensate for appearance changes of the heart under different acquisition angles so as to achieve high accuracy of motion detection and correction. The detecting and correcting step is applied in the two-dimensional image domain. The method also includes the steps of detecting and excluding high intensity, non-heart regions in a particular image frame so that non-heart motions such as bowel gas, spleen, and liver motions are excluded from being involved in the motion detection and correction procedure.