Yang Yongfeng, Wu Yibao, Qi Jinyi, St James Sara, Du Huini, Dokhale Purushottam A, Shah Kanai S, Farrell Richard, Cherry Simon R
Department of Biomedical Engineering, University of California-Davis, Davis, California 95616, USA.
J Nucl Med. 2008 Jul;49(7):1132-40. doi: 10.2967/jnumed.107.049791. Epub 2008 Jun 13.
Detectors with depth-encoding allow a PET scanner to simultaneously achieve high sensitivity and high spatial resolution.
A prototype PET scanner, consisting of depth-encoding detectors constructed by dual-ended readout of lutetium oxyorthosilicate (LSO) arrays with 2 position-sensitive avalanche photodiodes (PSAPDs), was developed. The scanner comprised 2 detector plates, each with 4 detector modules, and the LSO arrays consisted of 7 x 7 elements, with a crystal size of 0.9225 x 0.9225 x 20 mm and a pitch of 1.0 mm. The active area of the PSAPDs was 8 x 8 mm. The performance of individual detector modules was characterized. A line-source phantom and a hot-rod phantom were imaged on the prototype scanner in 2 different scanner configurations. The images were reconstructed using 20, 10, 5, 2, and 1 depth-of-interaction (DOI) bins to demonstrate the effects of DOI resolution on reconstructed image resolution and visual image quality.
The flood histograms measured from the sum of both PSAPD signals were only weakly depth-dependent, and excellent crystal identification was obtained at all depths. The flood histograms improved as the detector temperature decreased. DOI resolution and energy resolution improved significantly as the temperature decreased from 20 degrees C to 10 degrees C but improved only slightly with a subsequent temperature decrease to 0 degrees C. A full width at half maximum (FWHM) DOI resolution of 2 mm and an FWHM energy resolution of 15% were obtained at a temperature of 10 degrees C. Phantom studies showed that DOI measurements significantly improved the reconstructed image resolution. In the first scanner configuration (parallel detector planes), the image resolution at the center of the field of view was 0.9-mm FWHM with 20 DOI bins and 1.6-mm FWHM with 1 DOI bin. In the second scanner configuration (detector planes at a 40 degrees angle), the image resolution at the center of the field of view was 1.0-mm FWHM with 20 DOI bins and was not measurable when using only 1 bin.
PET scanners based on this detector design offer the prospect of high and uniform spatial resolution (crystal size, approximately 1 mm; DOI resolution, approximately 2 mm), high sensitivity (20-mm-thick detectors), and compact size (DOI encoding permits detectors to be tightly packed around the subject and minimizes number of detectors needed).
具有深度编码的探测器可使正电子发射断层扫描（PET）扫描仪同时实现高灵敏度和高空间分辨率。
开发了一种原型PET扫描仪，它由深度编码探测器组成，该探测器通过用2个位置灵敏雪崩光电二极管（PSAPD）对正硅酸镥（LSO）阵列进行双端读出而构建。该扫描仪包括2个探测器板，每个探测器板有4个探测器模块，LSO阵列由7×7个元件组成，晶体尺寸为0.9225×0.9225×20毫米，间距为1.0毫米。PSAPD的有效面积为8×8毫米。对单个探测器模块的性能进行了表征。在2种不同的扫描仪配置下，在原型扫描仪上对线源体模和热棒体模进行成像。使用20、10、5、2和1个相互作用深度（DOI）区间重建图像，以证明DOI分辨率对重建图像分辨率和视觉图像质量的影响。
从两个PSAPD信号之和测得的泛洪直方图仅与深度有微弱相关性，并且在所有深度都能获得出色的晶体识别。随着探测器温度降低，泛洪直方图得到改善。当温度从20℃降至10℃时，DOI分辨率和能量分辨率显著提高，但随后温度降至0℃时仅略有改善。在10℃的温度下，获得了半高宽（FWHM）为2毫米的DOI分辨率和15%的FWHM能量分辨率。体模研究表明，DOI测量显著提高了重建图像分辨率。在第一种扫描仪配置（平行探测器平面）中，视野中心的图像分辨率在使用20个DOI区间时为0.9毫米FWHM，在使用1个区间时为1.6毫米FWHM。在第二种扫描仪配置（探测器平面成40度角）中，视野中心的图像分辨率在使用20个DOI区间时为1.0毫米FWHM，而仅使用1个区间时无法测量。
基于这种探测器设计的PET扫描仪具有实现高且均匀的空间分辨率（晶体尺寸约为1毫米；DOI分辨率约为2毫米）、高灵敏度（20毫米厚的探测器）以及紧凑尺寸（DOI编码允许探测器围绕受试者紧密排列并使所需探测器数量最小化）的前景。
