The luminescence of LuYSiO5:Ce (LYSO:Ce) and Gd2SiO5:Ce (GSO:Ce) crystals was studied for use in tomographic medical X-ray imaging. Both crystals were compared to CsI:Tl scintillator, used in X-ray and gamma-ray imaging. LYSO:Ce and GSO:Ce are high density (7.1 g/cm3 and 6.71 g/cm3 respectively), high atomic number (71 for Lu and 64 for Gd), non-hydroscopic, and short decay time (40 ns and 60 ns respectively) scintillators. CsI:Tl is a slightly hygroscopic, high light yield (≥104 photons/MeV) scintillator but of relatively slow decay time (>200 ns). Evaluation was performed by determining: 1) the absolute luminescence efficiency (emitted light flux over incident X-ray exposure) in X-ray energies employed in general X-ray imaging (40-140 kV) and in mammographic X-ray imaging (22-49 kV), 2) the light emission spectrum, determined at various X-ray energies (22-140 kV), and 3) the spectral compatibility to optical photon detectors incorporated in medical imaging systems. The light emission performance of the three scintillation materials studied, were found adequately high for X-ray imaging. LYSO:Ce and GSO:Ce were found most efficient (between 8 and 12μW×m-2) in the range from 40 to 60 kV. LYSO:Ce and GSO:Ce were found adequately most compatible with the S-20 photocathode (0.902 and 0.903 respectively against 0.763 of CsI:Tl) and adequately compatible to a-Si photodiode (0.705 and 0.737 respectively against 0.851 of CsI:Tl).