Radiation detector developments in medical applications: inorganic scintillators in positron emission tomography.

In recent years, a number of new gamma-ray scintillators are commercially available. These scintillators are either derived from known scintillators, e.g. Lu1-xYxAlO3: Ce (LuYAP) from LuAlO3:Ce and Lu(2(1-x))Y2xSiO5:Ce (LYSO) from Lu2SiO5:Ce or are the result of new discoveries, e.g. LaCl3:Ce and LaBr3:Ce. The first two materials are primarily of interest because of the relatively high detection efficiency and fast response; LYSO has found application in time-of-flight (TOF) positron-emission tomography (TOF PET) and the LuYAP-LYSO combination is used in small-animal PET. The halide scintillators have an excellent energy resolution of approximately 3% at 662 keV and they have a relatively high light yield. LaBr3:Ce is being studied for application in TOF PET. At the same time, the search for and research on new scintillator materials are going on. For example, LuI3:Ce is a new material with a very high light yield (approximately 90,000 photons MeV(-1)). Other examples of new materials are (C6H13NH3)2PbI4 and (C3H7NH3)2PbBr4, organic-inorganic hybrid compounds, of which the former has a very fast sub-nanosecond response. The new scintillators show great promise for new developments in medical applications, in particular, for PET systems.