Department of Imaging Physics, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Med Phys. 2012 Feb;39(2):777-87. doi: 10.1118/1.3676688.
Positron emission tomography (PET) detectors that use a dual-ended-scintillator readout to measure depth-of-interaction (DOI) must have an accurate DOI function to provide the relationship between DOI and signal ratios to be used for detector calibration and recalibration. In a previous study, the authors used a novel and simple method to accurately and quickly measure DOI function by irradiating the detector with an external uniform flood source; however, as a practical concern, implementing external uniform flood sources in an assembled PET system is technically challenging and expensive. In the current study, therefore, the authors investigated whether the same method could be used to acquire DOI function from scintillator-generated (i.e., internal) radiation. The authors also developed a method for calibrating the energy scale necessary to select the events within the desired energy window.
The authors measured the DOI function of a PET detector with lutetium yttrium orthosilicate (LYSO) scintillators. Radiation events originating from the scintillators' internal Lu-176 beta decay were used to measure DOI functions which were then compared with those measured from both an external uniform flood source and an electronically collimated external point source. The authors conducted these studies with several scintillators of differing geometries (1.5 × 1.5 and 2.0 × 2.0 mm(2) cross-section area and 20, 30, and 40 mm length) and various surface finishes (mirror-finishing, saw-cut rough, and other finishes in between), and in a prototype array.
All measured results using internal and external radiation sources showed excellent agreement in DOI function measurement. The mean difference among DOI values for all scintillators measured from internal and external radiation sources was less than 1.0 mm for different scintillator geometries and various surface finishes.
The internal radioactivity of LYSO scintillators can be used to accurately measure DOI function in PET detectors, regardless of scintillator geometry or surface finish. Because an external radiation source is not needed, this method of DOI function measurement can be practically applied to individual PET detectors as well as assembled systems.
使用双端闪烁体读出技术来测量相互作用深度（DOI）的正电子发射断层扫描（PET）探测器必须具有精确的 DOI 功能，以提供 DOI 与信号比之间的关系，从而用于探测器的校准和重新校准。在之前的研究中，作者使用了一种新颖而简单的方法，通过用外部均匀的注水源照射探测器来准确快速地测量 DOI 函数；然而，作为一个实际的关注点，在组装的 PET 系统中实现外部均匀注水源在技术上具有挑战性且昂贵。因此，在当前的研究中，作者研究了是否可以使用相同的方法从闪烁体产生的（即内部）辐射中获取 DOI 函数。作者还开发了一种方法来校准选择所需能量窗口内事件所需的能量刻度。
作者使用硅酸镥（LYSO）闪烁体测量了 PET 探测器的 DOI 函数。利用闪烁体内部 Lu-176 贝塔衰变产生的辐射事件来测量 DOI 函数，然后将其与来自外部均匀注水源和电子准直外部点源的测量结果进行比较。作者使用不同几何形状（1.5×1.5 和 2.0×2.0 平方毫米的横截面积和 20、30 和 40 毫米的长度）和不同表面处理（镜面处理、锯切粗糙处理和其他处理）的多个闪烁体以及在原型阵列中进行了这些研究。
使用内部和外部辐射源进行的所有测量结果在 DOI 函数测量方面均显示出极好的一致性。对于不同的闪烁体几何形状和各种表面处理，从内部和外部辐射源测量的所有闪烁体的 DOI 值的平均差异小于 1.0 毫米。
LYSO 闪烁体的内部放射性可用于准确测量 PET 探测器中的 DOI 函数，无论闪烁体的几何形状或表面处理如何。由于不需要外部辐射源，因此 DOI 功能测量的这种方法可以实际应用于单个 PET 探测器以及组装系统。
