A method for localizing optical emission is disclosed. The method involves identifying a first readout channel of a first pixellated photodetector array based on an impact of a first photon on the first pixellated photodetector array. The first photon is emitted by a scintillator unit of a scintillator array and the first readout channel corresponds to a column of one or more pixels of the first pixellated photodetector array. The method also involves identifying a second readout channel of a second pixellated photodetector array based on an impact of a second photon on the second pixellated photodetector array. The second photon is emitted by the scintillator unit and the second readout channel corresponds to a row of one or more pixels of the second pixellated photodetector array. The method further involves identifying the scintillator unit based on the first readout channel and the second readout channel.