A new compact high-resolution gamma-ray computed tomography measurement system (CompaCT) for determination of phase fraction distributions in multiphase flows, occurring in technical devices with dense housings and inlets, has been developed. The obtained measurement data can be used to understand fundamental physics behind flow processes and to validate multi-phase flow models. The CompaCT contains a¹³⁷Cs isotopic source and a thermally stabilized gamma-ray detector arc. Analogue and digital processing units are fully implemented within the detector. As examples, performance studies were accomplished in a steel rod bundle and a fixed bed reactor assembly.