A STUDY OF X-RAY LUMINESCENCE AND SPECTRAL COMPATIBILITY OF EUROPIUM-ACTIVATED YTTRIUM-VANADATE (YVO4-EU) SCREENS FOR MEDICAL IMAGING APPLICATIONS

The X-ray luminescence efficiency of laboratory-prepared YVO4:Eu scree ns and their spectral compatibility to common optical detectors were s tudied under medical fluoroscopy conditions. YVO4:Eu screens were prep ared by sedimentation and with different coating thickness. Luminescen ce efficiency of the YVO4:Eu screens was measured at Various X-ray tub e voltages (50-250 k Vp) and for screens of different coating thicknes ses (20-180 mg/cm(2)). Spectral response was also measured and spectra l matching factors between the YVO4:Eu screens and some common optical detectors (photocathodes, photodiodes, photographic emulsion) were ca lculated. Experimental results on efficiency were fitted by formulas o f the theoretical model developed by Hamaker and Ludwig in order to de termine phosphor intrinsic X-ray-to-light conversion efficiency and in trinsic optical characteristics, such as coefficients related to light scattering and absorption. Although the luminescence efficiency of YV O4: Eu screens was found to be relatively low (3-11 mu W s/mR m(2)), t he matching factor of YVO4:Eu screens with some red sensitive optical detectors was excellent, of the order of 0.96. High spectral compatibi lity may indicate that YVO4: Eu scintillators could be used in medical image detectors.