Impact of the laser-processed X´tal cube detector with 1 mm isotropic resolution in PET imaging

The X´tal cube is our original PET detector, which is being developed to achieve isotropic 3D positioning detectability. The X´tal cube is based on a 3D segmented crystal block for which all surfaces are covered with photo-detectors. In the last year, instead of our initial approach of gluing segmented pieces of crystals, we successfully constructed a crystal block segmented by laser processing, and we developed the X´tal cube with the laser-processed 3D grids of 2 mm. In the present work, we developed the X´tal cube with 3D grids of 1 mm and a new one-pair prototype system which we used to simulate a ring-type scanner. The one-pair prototype system consisted of two X´tal cubes, two rotating stages, and a 192-channel data acquisition system. Each X´tal cube consisted of the L YSO cubic crystal block of (18 mm)3 in which the 3D grids of 1 mm pitch were fabricated by internal laser processing. The 4 × 4 arrays of multi pixel photon counters were optically coupled to each surface of the crystal block. The detector positions were automatically controlled to simulate a ring-type PET with a 14.6 cm diameter. Data were collected for all assumed detector positions and then a sinogram was obtained. The data were reconstructed using filtered backprojection. We successfully obtained uniform spatial resolution of 1.3 mm full width at half maximum (FWHM) averaged over the FOV. By applying deconvolution with the assumption that the source distribution can be represented as a Gaussian function with 1 mm FWHM, we estimated the averaged spatial resolution of the system as 0.86 mm. In conclusion, we confirmed the potential of the X´tal cube for uniform and high resolution imaging.