Geometry calibration of a dual headed SPECT system, with rocking motion correction, for small animal imaging

A method for simultaneous geometry calibration of a dual detector SPECT system for small animal imaging is presented. For multi-headed SPECT systems, it is desirable that all detectors are calibrated with respect to a common spatial coordinate system, so that projection data from both detectors can be used to reconstruct the common object in the same image space. We adapted Beque´s geometry calibration procedure. We show that the procedure can be applied to a dual-headed imaging system by optimizing the combined objective function. Initially, the measured and predicted paths of calibration point sources had significant systematic differences which were dominant in the axial direction. The problem was caused by flexing of the gantry support due to the heavy weight of the detectors. While various correction models of different complexity and assumptions could be applied, we found that the errors were corrected well by including an angle-dependent sinusoidal function to the z-coordinate, which is in the axial direction