Investigation of spatial resolution improvement by use of mouth-insert detector in the helmet PET

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The dominant factor that limits the intrinsic spatial resolution of a PET system is the size of the crystal elements in the detector. To increase the sensitivity and achieve high spatial resolution, it is essential to use advanced depth-of-interaction (DOI) detectors and arrange them close to the subject. The DOI detectors help to maintain high spatial resolution by mitigating the parallax error caused by the thickness of the scintillator at the peripheral regions in the field-of-view. As an optimal geometry for a brain PET scanner with high sensitivity and high spatial resolution, we proposed and developed the helmet-chin PET using 54 4-layered DOI detectors consisting of 16×16×4 array of GSOZ scintillator crystals with dimensions of 2.8×2.8×7.5 mm3. All the detectors used in the helmet-chin PET had the same spatial resolution. In this study, we conducted a feasibility simulation of a new add-on detector arrangement for the helmet PET by replacing the chin detector with a segmented crystal cube, having high spatial resolution in all directions, which can be placed inside the mouth. The crystal cube (which we call the mouth-insert detector) has 20×20×20 LYSO crystal segments with dimensions of 1×1×1 mm3. Thus, the scanner is formed by the combination of the helmet and mouth-insert detectors, and is referred to as the helmet-mouth-insert PET. The results show that the sensitivity of the helmet-mouth-insert PET had a comparable sensitivity and an improved spatial resolution near the center of the hemisphere compared to those of the helmet chin PET.