Dual layer doI detector modules for a dedicated mouse brain PET/MRI

The outcome of preclinical imaging studies are enhanced by simultaneous, high-resolution anatomical and molecular data, which advanced PET/MRI systems provide. Nevertheless, mapping of neuroreceptors and accurate quantification of PET tracer distribution in mouse brains is not trivial. The restricted spatial resolution and sensitivity in commercial animal PET systems limits the image quality and the quantification accuracy. We are currently developing a PET/MRI system dedicated for mouse brain studies. The PET system will offer system dimensions of approx. 30 mm in diameter and an axial length of more than 38 mm. This work discusses two system geometries including their associated block detectors. Both configurations were based on a dual layer offset structure with small crystals sizes, in the order of 1  ×  1  ×  4/6 mm³, to provide discrete depth of interaction information. The detector for configuration 'A' was based on a 4  ×  4 silicon photomultiplier (SiPM) array attached to an optical diffusor, and a 12  ×  12 as well as a 9  ×  11 LSO crystal array, to achieve optimal system sensitivity. This configuration was evaluated by a double layer of 12  ×  12 crystals. Configuration 'B' was composed of three 2  ×  2 SiPM arrays equipped with a 1 mm diffusor to read out an LSO stack of 20  ×  6 and 19  ×  5 individual crystals. The average peak-to-valley ratio of the inner/outer layer was 3.5/3.6 for detector 'A', and 3.4/2.8 for detector 'B'. The average full width at half maximum (FWHM) energy resolution of the block detectors were 22.24%  ±  3.36% for 'A' and 30.67%  ±  5.37% for 'B'. The FWHM of the full block timing resolution of the inner/outer layer was 1.4 ns/1.2 ns for detector 'A' and 1.8 ns/1.4 ns for 'B'. The performance of the crystal position profile, the energy, and timing resolution indicate that configuration 'A' is more appropriate for a mouse brain PET/MRI system.