Lyso

LYSO, or lutetium–yttrium oxyorthosilicate, is a cerium-doped inorganic scintillator widely used in medical imaging and radiation detection. The crystal formula is Lu2(1−x)YxSiO5:Ce, where cerium doping provides the luminescent centers. LYSO is non-hygroscopic, chemically stable, and transparent to its own emission, enabling efficient light collection when coupled to photodetectors.

Physical and scintillation properties include a density of about 7.1 g/cm3, an effective atomic number around 65, and a radiation length near 1.14 cm. The Moliere radius is approximately 2 cm. It produces roughly 32,000–40,000 photons per MeV, with an emission peak in the blue region near 420 nm, well matched to common silicon photodetectors. The scintillation decay time is fast, typically about 40 nanoseconds, supporting high-rate timing and, in some configurations, time-of-flight PET performance. The refractive index is around 1.8–1.82 at the emission wavelength.

Applications include being a dominant scintillator for PET detectors, including PET/CT and PET/MRI systems, due to its high light yield, fast timing, and good energy resolution. It is also used in various radiation-detection and calorimetric applications.

Considerations include that natural lutetium contains Lu-176, which is radioactive; LYSO thus exhibits a small intrinsic background. This is usually managed by energy-window settings in PET but may be relevant for ultra-sensitive measurements. LYSO competes with LSO and offers similar performance with slightly higher light yield and tunable properties through Lu/Y substitution.