Ultra-high-resolution depth-encoding small animal PET detectors: Using GAGG and LYSO crystal arrays.

PURPOSE

Small animal positron emission tomography (PET) scanners are widely used in current biomedical research. The study aimed to develop high-efficiency and ultra-high-resolution detectors that could be used to develop a small animal PET scanner with high sensitivity and spatial resolution approaching to its physical limit.

METHODS

Four crystal arrays were fabricated and measured in this study. Crystal arrays 1 and 2 consisted of 38 × 38 gadolinium aluminum gallium garnet (GAGG) and lutetium-yttrium oxyorthosilicate (LYSO) crystals of 0.4 × 0.4 × 20 mm size. Crystal array 3 consisted of 16 × 16 GAGG crystals of 0.3 × 0.3 × 20 mm size, and crystal array 4 consisted of 24 × 24 LYSO crystals 0.3 × 0.3 × 20 mm in size. The crystal arrays were dual-ended readouts using 8 × 8 silicon photomultiplier (SiPM) arrays of 2 × 2 mm pixel area. The SiPM array was readout using a signal multiplexing circuit to convert the 64 output signals into four position-encoding signals. The performances of the four detectors in terms of flood histogram, energy resolution, depth of interaction (DOI) resolution, and timing resolution were measured.

RESULTS

The GAGG detectors provided better flood histograms, ∼30% higher photopeak amplitude, ∼20% higher energy resolution, ∼12% worse DOI resolution, and ∼15% worse timing resolution compared with LYSO detectors of the same crystal size. These four detectors provided DOI resolutions of <2 mm, energy resolutions of <22%, and timing resolutions of <1.6 ns. All crystals of 0.4 × 0.4 × 20 mm and 0.3 × 0.3 × 20 mm could be clearly resolved if the crystal array was 1 mm smaller in the four sides than that in the SiPM array.

CONCLUSIONS

High DOI resolution PET detectors were developed using both GAGG and LYSO arrays with crystal sizes of 0.3 and 0.4 mm, respectively, and a length of 20 mm. The detectors can be used in the future to develop small animal PET scanners, especially dedicated mouse imaging PET scanners, which can simultaneously achieve high sensitivity and ultra-high spatial resolution.