Calibrating gain of scintillator detector

Methods and devices for calibrating a gain of a scintillator detector are disclosed, where a scintillation crystal of the scintillator detector includes two or more energy regions. In an example, the scintillation crystal of the scintillator detector is adopted as a radiation source for calibrating. Electric signals outputted from a rear end of the scintillator detector are collected, and actual counts of the electric signals from each of at least two energy regions of the scintillation crystal at a specified position are obtained, respectively. Then, a gain of the scintillator detector may be adjusted according to the obtained actual counts of the electric signals from the at least two energy regions.