Combined PET and CT detector and method for using same

Not Applicable A combined positron emission tomography (PET) and computed tomography (CT) detector mounted on a single support on the same gantry of a combined PET and CT scanner. The common detector includes an array of scintillator crystals or pixels with each pixel mated to a photodetector. The photodetector is connected to discrete event circuitry, which provides discrete event information to the combined PET and CT scanner. Also, the photodetector is connected to integrating circuitry, which provides integrated count rate information to the CT scanner when the discrete event information is not adequate. By using a common detector, the registration of the PET image with the CT image is improved, less components are mounted on the gantry, the overall size of the gantry is reduced, resulting in a shorter tunnel and less rotating mass, and CT performance is enhanced by providing means for selecting the energy level of the x-rays to be detected.