Imaging performances of LaCl3:Ce scintillation crystals in SPECT

Over the last three years, there is a growing interest in the development of a new class of fast scintillators like LaCl₃:Ce and LaBr₃:Ce. The new scintillation crystals for the first time, have the main characteristic in producing a light photon number higher than NaI(Tl) at a wavelength suited for the photocathode. The most important characteristic of these crystals is represented from the scintillation light to be yield proportionality as a function of incident gamma ray energy. With the aim to investigate on their potential in single photon imaging three one inch square LaCl₃:Ce continuous scintillation crystals with 3 and 6 mm thickness were specifically designed for position measurements. They have been coupled to a flat panel PMT through a 3 mm thickness glass window. In order to highlight all the characteristics of the detection system the third one, 3 mm thick, was integral assembled with a one inch PSPMT Hamamatsu R5900-C8. Free and collimated point radioactive sources were used for energy resolution measurements as well for scanning crystals to investigate spatial resolution and position response. Energy resolution values were compared with ones obtained from a sample of LaBr₃:Ce with one inch diameter and one thickness designed for spectrometric measurements. LaCl₃:Ce with 3 mm thickness shown energy resolution values worse than expected (13% at 140 KeV) due to the sub-optimal size and configuration for light collection. On the contrary LaBr₃:Ce carried out 6% relative energy resolution at 140 keV. Intrinsic spatial resolution values of 1 mm and 1.3 mm were obtained from 3 mm thickness LaCl₃:Ce crystals in the two configurations investigated.