A depth of interaction detector for PET with GSO crystals doped with different amount of Ce

A new method for a 4-stage depth of interaction (DOI) detector was proposed. The 4-stage DOI detector is constructed with two kinds of Gd₂SiO₅:Ce (GSO) crystals doped with different amount of Ce, 0.5 mol% and 1.5 mol%. The amount of Ce in GSO determines the scintillation decay time constant and it is 60 ns for the 0.5 mol% GSO and 35 ns for 1.5 mol% GSO. This difference led to introduce pulse shape discrimination, which would distinguish between two kinds event data from respective GSOs and sort them into two groups. By independently applying Anger-type position arithmetic to the data of each group, two 2-dimensional histograms are obtained. The crystal of interaction can be identified on these histograms in which only 0.5 mol% or 1.5 mol% GSO crystal elements are expressed. To evaluate this method, we constructed the 4-stage DOI detector by alternately stacking 1.5 mol% GSO crystal stages and 0.5 mol% stages. The result of ¹³⁷Cs gamma ray beam scanning measurement proved that the DOI detector had enough accuracy in crystal identification.