An imaging system accounting for cascade gammas, said imaging system comprising: a PET scanner including detectors for detecting gamma rays emitted from a target volume of a subject, the detected gamma rays including cascade gammas emitted from a radionuclide within the target volume; at least one processor (58, 60) programmed to: receive event data describing the detected gamma rays simulate cascade and annihilation gamma emissions from the target volume and coincidence detection of the imaging system using a Monte Carlo simulation technique to generate a cascade dataset comprised of annihilation coincidence events and cascade coincidence events to determine a relationship between the annihilation coincidence events and the cascade coincidence events in the cascade dataset, wherein a decay property of the radionuclide is used to estimate the cascade gammas contribution to the event data; simulate scatter of annihilation gammas in the target volume to generate a scatter dataset comprised of primary coincidence events and scattered coincidence events to determine a relationship between the primary coincidence events and the scattered coincidence events in the scatter dataset; and reconstruct the event data into an image representation of the target volume with correction of cascade coincidence using the relationship between the annihilation coincidence events and the cascade coincidence events in the cascade data set, and with scatter correction using the relationship between the primary coincidence events and the scattered coincidence events. a PET scanner including detectors for detecting gamma rays emitted from a target volume of a subject, the detected gamma rays including cascade gammas emitted from a radionuclide within the target volume; at least one processor (58, 60) programmed to: receive event data describing the detected gamma rays simulate cascade and annihilation gamma emissions from the target volume and coincidence detection of the imaging system using a Monte Carlo simulation technique to generate a cascade dataset comprised of annihilation coincidence events and cascade coincidence events to determine a relationship between the annihilation coincidence events and the cascade coincidence events in the cascade dataset, wherein a decay property of the radionuclide is used to estimate the cascade gammas contribution to the event data; simulate scatter of annihilation gammas in the target volume to generate a scatter dataset comprised of primary coincidence events and scattered coincidence events to determine a relationship between the primary coincidence events and the scattered coincidence events in the scatter dataset; and reconstruct the event data into an image representation of the target volume with correction of cascade coincidence using the relationship between the annihilation coincidence events and the cascade coincidence events in the cascade data set, and with scatter correction using the relationship between the primary coincidence events and the scattered coincidence events. receive event data describing the detected gamma rays simulate cascade and annihilation gamma emissions from the target volume and coincidence detection of the imaging system using a Monte Carlo simulation technique to generate a cascade dataset comprised of annihilation coincidence events and cascade coincidence events to determine a relationship between the annihilation coincidence events and the cascade coincidence events in the cascade dataset, wherein a decay property of the radionuclide is used to estimate the cascade gammas contribution to the event data; simulate scatter of annihilation gammas in the target volume to generate a scatter dataset comprised of primary coincidence events and scattered coincidence events to determine a relationship between the primary coincidence events and the scattered coincidence events in the scatter dataset; and reconstruct the event data into an image representation of the target volume with correction of cascade coincidence using the relationship between the annihilation coincidence events and the cascade coincidence events in the cascade data set, and with scatter correction using the relationship between the primary coincidence events and the scattered coincidence events.