A four-layer depth of interaction detector block for small animal PET

We are now planning to develop a positron emission tomograph dedicated to small animals such as rats and mice which meets the demand for higher sensitivity. We propose a new depth of interaction (DOI) detector arrangement to obtain DOI information by using a four-layer detector with all the same crystal elements. In this DOI detector, we control the behavior of scintillation photons by inserting the reflectors between crystal elements so that the DOI information of four layers can be extracted from one two-dimensional (2D) position histogram made by Anger-type calculation. As a preliminary experiment, we measured crystal identification performance of the DOI detector which consists of four layers of a 16 × 16 crystal array using Gd₂SiO₅ crystals with Ce concentration of 0.5 mol %. Each crystal is 1.42 mm × 1.42 mm × 4.5 mm. A crystal block is optically coupled to a 256-channel flat panel position sensitive photomultiplier tube whose opening area is 52.0 mm × 52.0 mm. We obtained sufficient positioning performance for this four-layer DOI detector on the 2D position histogram. We concluded it would be a promising device to realize a small animal positron emission tomography scanner with high sensitivity and high resolution.