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

限制PET系统固有空间分辨率的主要因素是探测器中晶体元素的大小。为了提高灵敏度和实现高空间分辨率，必须使用先进的相互作用深度(DOI)探测器，并将它们布置在靠近对象的位置。DOI探测器通过减轻由视场中外围区域的闪烁体厚度引起的视差误差来帮助保持高空间分辨率。作为一种高灵敏度和高空间分辨率的脑PET扫描仪的最佳几何形状，我们提出并研制了头盔下巴PET，它使用54个4层DOI探测器，由尺寸为2.8×2.8×7.5 mm~3的GSOZ闪烁体晶体阵列组成。头盔下巴PET中使用的所有探测器都具有相同的空间分辨率。在这项研究中，我们对头盔PET的一种新的附加探测器布置进行了可行性模拟，将下巴探测器替换为分段晶体立方体，该立方体在各个方向都具有高空间分辨率，可以放置在口腔内。晶体立方体(我们称之为插口检测器)具有20×20×20个尺寸为1×1×1 mm~3的Lyso晶体片段。因此，扫描仪由头盔和口腔嵌入物检测器的组合形成，并被称为头盔-口腔嵌入物PET。结果表明，头盔插口正电子发射计算机断层扫描的灵敏度与头盔正电子发射计算机断层扫描的灵敏度相当，而半球中心附近的空间分辨率比头盔正电子正电子发射计算机断层扫描的高。

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.