A method for dead time compensation for a gamma camera of a SPECT system, the compensation being a function of real-time detection of the radiation from a shielded and calibrated point source, the method comprising: detecting emissions with the gamma camera comprising a collimator, a detector and detector electronics, the emissions including the radiation from the shielded and calibrated point source connected at the gamma camera to emit radiation from a radioisotope in the shielded point source, and radioisotope emissions from a patient, the radioisotope emissions from the patient being from a same radioisotope as the radioisotope in the shielded point source; and correcting a system or detector sensitivity using a processor, wherein the correction is a function of first and second point source count rates, wherein the first count rate is a count rate from a blank scan which detects emissions from the point source without emissions from the patient, and a second count rate is a count rate from a patient scan, detecting emissions from the point source, wherein the second count rate is subject to dead time but the second count rate does not include the emissions from the patient, and wherein the emissions used for the first and second count rate are distinguished from the emissions from the patient based on the location of their detection on the gamma camera, and wherein the correction further includes the following steps carried out by the processor: calculating a ratio of the second count rate to the first count rate, and normalizing the sensitivity, by multiplying the sensitivity with the ratio, generating a reconstructed image based on the corrected sensitivity, wherein detecting the first and second count rates comprises detecting in a same region of interest of the point response function of the gamma camera for both the first and second count rates and/or wherein detecting the first and second count rates comprises detecting the first and second count rates in a same energy window. detecting emissions with the gamma camera comprising a collimator, a detector and detector electronics, the emissions including the radiation from the shielded and calibrated point source connected at the gamma camera to emit radiation from a radioisotope in the shielded point source, and radioisotope emissions from a patient, the radioisotope emissions from the patient being from a same radioisotope as the radioisotope in the shielded point source; and correcting a system or detector sensitivity using a processor, wherein the correction is a function of first and second point source count rates, wherein the first count rate is a count rate from a blank scan which detects emissions from the point source without emissions from the patient, and a second count rate is a count rate from a patient scan, detecting emissions from the point source, wherein the second count rate is subject to dead time but the second count rate does not include the emissions from the patient, and wherein the emissions used for the first and second count rate are distinguished from the emissions from the patient based on the location of their detection on the gamma camera, and wherein the correction further includes the following steps carried out by the processor: calculating a ratio of the second count rate to the first count rate, and normalizing the sensitivity, by multiplying the sensitivity with the ratio, generating a reconstructed image based on the corrected sensitivity, wherein detecting the first and second count rates comprises detecting in a same region of interest of the point response function of the gamma camera for both the first and second count rates and/or wherein detecting the first and second count rates comprises detecting the first and second count rates in a same energy window. the first count rate is a count rate from a blank scan which detects emissions from the point source without emissions from the patient, and a second count rate is a count rate from a patient scan, detecting emissions from the point source, wherein the second count rate is subject to dead time but the second count rate does not include the emissions from the patient, and wherein the emissions used for the first and second count rate are distinguished from the emissions from the patient based on the location of their detection on the gamma camera, and wherein the correction further includes the following steps carried out by the processor: calculating a ratio of the second count rate to the first count rate, and normalizing the sensitivity, by multiplying the sensitivity with the ratio, generating a reconstructed image based on the corrected sensitivity, wherein detecting the first and second count rates comprises detecting in a same region of interest of the point response function of the gamma camera for both the first and second count rates and/or wherein detecting the first and second count rates comprises detecting the first and second count rates in a same energy window. calculating a ratio of the second count rate to the first count rate, and normalizing the sensitivity, by multiplying the sensitivity with the ratio, generating a reconstructed image based on the corrected sensitivity, wherein detecting the first and second count rates comprises detecting in a same region of interest of the point response function of the gamma camera for both the first and second count rates and/or wherein detecting the first and second count rates comprises detecting the first and second count rates in a same energy window.