James Sara St, Yang Yongfeng, Wu Yibao, Farrell Richard, Dokhale Purushottam, Shah Kanai S, Cherry Simon R
Department of Biomedical Engineering, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA.
Phys Med Biol. 2009 Jul 21;54(14):4605-19. doi: 10.1088/0031-9155/54/14/015. Epub 2009 Jun 30.
Small animal PET scanners may be improved by increasing the sensitivity, improving the spatial resolution and improving the uniformity of the spatial resolution across the field of view. This may be achieved by using PET detectors based on crystal elements that are thin in the axial and transaxial directions and long in the radial direction, and by employing depth of interaction (DOI) encoding to minimize the parallax error. With DOI detectors, the diameter of the ring of the PET scanner may also be decreased. This minimizes the number of detectors required to achieve the same solid angle coverage as a scanner with a larger ring diameter and minimizes errors due to non-collinearity of the annihilation photons. In this study, we characterize prototype PET detectors that are finely pixelated with individual LSO crystal element sizes of 0.5 mm x 0.5 mm x 20 mm and 0.7 mm x 0.7 mm x 20 mm, read out at both ends by position sensitive avalanche photodiodes (PSAPDs). Both a specular reflector and a diffuse reflector were evaluated. The detectors were characterized based on the ability to clearly resolve the individual crystal elements, the DOI resolution and the energy resolution. Our results indicate that a scanner based on any of the four detector designs would offer improved spatial resolution and more uniform spatial resolution compared to present day small animal PET scanners. The greatest improvements to spatial resolution will be achieved when the detectors employing the 0.5 mm x 0.5 mm x 20 mm crystals are used. Monte Carlo simulations were performed to demonstrate that 2 mm DOI resolution is adequate to ensure uniform spatial resolution for a small animal PET scanner geometry using these detectors. The sensitivity of such a scanner was also simulated using Monte Carlo simulations and was shown to be greater than 10% for a four ring scanner with an inner diameter of 6 cm, employing 20 detectors per scanner ring.
小型动物正电子发射断层扫描（PET）扫描仪可通过提高灵敏度、改善空间分辨率以及提高视野范围内空间分辨率的均匀性来改进。这可以通过使用基于轴向和横向薄而径向长的晶体元件的PET探测器，并采用相互作用深度（DOI）编码来最小化视差误差来实现。使用DOI探测器时，PET扫描仪环的直径也可以减小。这将实现与具有较大环直径的扫描仪相同立体角覆盖所需的探测器数量最小化，并最小化由于湮灭光子的非共线性导致的误差。在本研究中，我们对原型PET探测器进行了表征，这些探测器采用尺寸为0.5 mm×0.5 mm×20 mm和0.7 mm×0.7 mm×20 mm的单个LSO晶体元件进行精细像素化，并由位置敏感雪崩光电二极管（PSAPD）在两端读出。对镜面反射器和漫反射器都进行了评估。基于清晰分辨各个晶体元件的能力、DOI分辨率和能量分辨率对探测器进行了表征。我们的结果表明，与当今的小型动物PET扫描仪相比，基于这四种探测器设计中任何一种的扫描仪都将提供更高的空间分辨率和更均匀的空间分辨率。当使用尺寸为0.5 mm×0.5 mm×20 mm晶体的探测器时，空间分辨率将得到最大程度的提高。进行了蒙特卡罗模拟，以证明2 mm的DOI分辨率足以确保使用这些探测器的小型动物PET扫描仪几何结构具有均匀的空间分辨率。还使用蒙特卡罗模拟对这种扫描仪的灵敏度进行了模拟，结果表明，对于内径为6 cm的四环扫描仪，每个扫描仪环采用20个探测器，其灵敏度大于10%。
