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. For the positron emission tomography (PET), we newly designed a four-layer depth of interaction (DOI) detector, which is constructed of all the same crystal elements. In this DOI detector, appropriate insertion of the reflector controls 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 (2-D) 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 x 16 crystal array using [Gd.sub.2]Si[O.sub.5] crystals with Ce concentration of 0.5 mol %. Each crystal is in dimensions of 1.42 mm x 1.42 mm x 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 x 52.0 mm. We obtained sufficient positioning performance for this four-layer DOI detector on the 2-D position histogram. We concluded that it would be a promising device to realize a small animal PET scanner with high sensitivity and high resolution. Index Terms--Depth of interaction, positron emission tomography (PET), small animal study.