Detector Block Based on Pseudo-Slabs With DOI and TOF Capabilities for a Dedicated Brain PET Scanner

Most clinical PET scanners are based on pixelated detectors without DOI information, which is crucial to achieve a homogeneous spatial resolution in the entire field of view. Semi-monolithic (slab) crystals have shown the potential to combine timing capabilities of pixelated crystals and the 3D positioning accuracy of monolithic scintillators, including DOI information. An alternative design, inspired on such geometry, is the so-called pseudo-slabs. They consist on pixelated arrays that are optically coupled in one direction, but isolated in the transversal, confining the scintillation light to fewer photosensors. This improves energy and timing capabilities, while retrieving DOI information. We have studied the performance of a LYSO array of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$16 \times 16$</tex> pixels of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$1.5 \times 1.5 \times 20 ~\text{mm}^{3}$</tex> each. One pseudo-slab is formed by <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$2 \times 16$</tex> pixels, wrapped with ESR, except for the face that is coupled to the photosensor. The lateral faces of each pixel were unpolished, while the top and bottom ones are polished. An ESR film is used to separate the two pseudo-slabs that are in the same photosensor row. The proposed detector was studied in terms of energy, spatial and timing resolutions. Two methods were used to determine the impact position, as well as DOI methodologies based on either an analytical approach or a NN. A mean DOI resolution of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$5.2 \pm 1.2 ~\text{mm}$</tex> and 4.3 mm were obtained with the analytical method and NN, respectively. An average energy resolution of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$13.4 \pm 1.4 \%$</tex> was obtained, together with a coincidence time resolution of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$368 \pm 55$</tex> ps.