Cesium iodide doped with thallium, CsI: Tl, is a high efficiency scintillator yielding high resolution images. It has been used in several diagnostic equipment, especially in fluoroscopy, in single photon emission computed tomography (SPECT) and in x-ray computed tomography (CT) systems. Lutetium-yttrium based scintillators, such as LYSO: Ce, are high effective atomic number, non-hygroscopic, fast emitting materials, promising candidates for use in positron emission (PET) imagers. The present study investigates the light emission characteristics of LYSO: Ce and CsI: Tl single crystal scintillators under UV and x-ray medical imaging conditions. To this aim parameters related to the luminescence emission spectrum and emission efficiency were studied using experimental methods. Various x-ray tube voltages currently employed in x-ray imaging techniques were used. In addition the emission spectrum under UV and x-ray excitation was used to determine the spectral compatibility to optical photon detectors incorporated in medical imaging systems. LYSO: Ce was found of equally high efficiency, however LYSO: Ce may be considered more suitable for computerized tomographic applications due to its very fast temporal response.