A radiation detector assembly is provided that includes a plurality of multi-detector arms (e.g., between 2 and 5), and plural detector head units disposed in each multi-detector arm. Each of the multi-detector arms defines a cavity therein. At least two detector head units are disposed within the cavity of each multi-detector arm. Each detector head unit includes an absorption member and associated processing circuitry, with the processing circuitry configured to generate electronic signals responsive to radiation received by the absorption member. Each detector head unit is configured to pivot along a sweep direction.