An imaging system (102) includes a detector array (104) with a ring (106) with a first layer (110i) that detects gamma radiation and X-ray radiation and a second layer (110N) that detects only gamma radiation, wherein the first and second layers are concentric closed rings. A method includes detecting gamma radiation with a first layer of a dual layer detector in response to imaging in PET mode, detecting gamma radiation with a second layer of the dual layer detector in response to imaging in PET mode, and generating PET image data with the radiation detected with the first and second layers. The method further includes detecting X-ray radiation with the first layer in response to imaging in CT mode and generating CT image data the radiation detected with the first layer. The method further includes displaying the image data. The imaging system allows a single gantry for both PET/CT imaging.