1. A method of nuclear medical imaging wherein gamma events are detected by gamma detectors of a scanner, said method comprising: simultaneously acquiring patient emission data and patient transmission data of gamma events detected by the gamma detectors, the patient emission data resulting from radioisotope in a patient, and the patient transmission data resulting from radiation from a transmission source external to the patient including radiation passing through the patient; using the patient transmission data for attenuation correction of the patient emission data; and using the attenuation corrected patient emission data for producing a tomographic image from the patient; wherein the method further includes correcting for spatially varying count rate effects on the attenuation correction.