An apparatus and method to map the body habitus, without the use of ionizing radiation, and to simultaneously track the position of an ionizing radiation imaging detector with respect to the body habitus map so that the radiotracer distribution of the patient can be fused with the body habitus map and thus provide an anatomical reference for the radiotracer distribution within the patient. A depth camera, capable of imaging a 3-dimensional surface, is attached to an ionizing radiation imaging detector where the relative position between the two is known.