One of the preferred embodiments includes: (a) creating a summed 3D nuclear medicine imaging data by summing a plurality of 3D nuclear medicine imaging data pixel by pixel, wherein each of the plurality of 3D nuclear medicine imaging data is associated with a different phase of a cardiac cycle (b) determining pixels corresponding to myocardial regions in the summed 3D nuclear medicine imaging data (c) defining a plurality of tracing directions based on the summed 3D nuclear medicine imaging data, and determining a reference myocardial center base point, a reference inner myocardial wall base point and a reference outer myocardial wall base point for each of the tracing directions (d) determining a phase-specific myocardial center base point for each of the tracing directions for each of the phases based on the corresponding 3D nuclear medicine imaging data and (e) seeking a difference between the reference myocardial center base point and the phase-specific myocardial center base point, and determining a phase-specific inner myocardial wall base point and a phase-specific outer myocardial wall base point by shifting the reference inner myocardial wall base point and the reference outer myocardial wall base point respectively based on the determined difference, for each of the tracing directions for each of the phases.
