BGO DOI-detector composed of three-dimensional crystal array for PET

We found that Bi₄Ge₃O₁₂ (BGO) scintillator can be a feasible alternative for a 4-layer depth of interaction (DOI) detector and was proved with a 12times12times4 array of BGO crystals in dimensions of 2.9 mmtimes2.9 mmtimes7.5 mm coupled to a 256 channel flat panel position sensitive photomultiplier tube. Appropriate reflector insertion in the array makes all crystal identification possible on one position histogram. Despite the large refractivity and small light output of BGO, the 4-layer BGO detector showed no significant variation in the full energy peaks and energy resolutions among crystal elements. When no optical grease was used in the construction of the BGO DOI-block and irradiated with gamma-rays from ¹³⁷Cs, 0.71 full energy peak of a top layer crystal relative to a bottom layer crystal and about 20 % energy resolutions for each layer crystal was achieved. The obtained two-dimensional position histogram from the irradiation was clear enough to allow identification of the crystals of interaction. Profiles of the histogram show peak-to-valley ratio of 1.9:1 for the top layer crystals and larger ratio for other layer crystals