LYSO:Ce showed the light yield of 39,900 ph/MeV. This value is slightly higher than the value of 34,100 ph/MeV ,Despite a comparable light output, LYSO:Ce shows a better energy resolution compared with LSO:Ce. due to the energy spectra for 662 keV of The energy resolution of 8.2% obtained with LYSO:Ce is better than that of 10.6% obtained with LSO:Ce.It suggested looking at the nonproportionality of the light yield versus gamma ray energy