Performance evaluation of a whole-body prototype PET scanner with four-layer DOI detectors
Performance evaluation of a whole-body prototype PET scanner with four-layer DOI detectors
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DOI：
10.1088/1361-6560/ab18b2
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发表时间：
2019-05-01
影响因子：
3.5
通讯作者：
Yamaya, Taiga
中科院分区：
文献类型：
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作者：
Akamatsu, Go;Tashima, Hideaki;Yamaya, Taiga
探测器晶体厚度引起的视差误差降低了扫描仪视场外围区域的空间分辨率。为了解决这一问题，相互作用深度（DOI）测量是提高整个视场空间分辨率及其均匀性的一种很有前途的解决方案。尽管DOI探测器已用于小环形直径的专用系统，如人脑、乳房和小动物，但DOI探测器用于大口径全身PET系统尚未得到证实。我们已经开发了一个四层DOI检测器，并且在我们之前的开发中已经证明了它作为大脑专用系统的潜力。在目前的工作中，我们通过开发世界上第一个全身原型，研究了四层DOI探测器在大孔径PET系统中的使用。我们按照NEMA NU 2标准对其性能特性进行了评估。此外，利用NEMA NU 4图像质量模型评估纳入DOI信息的影响。采用滤波后反投影法（FBP）重建点源图像，获得平均空间分辨率为5.2 +/- 0.7 mm。对于FBP图像，四层DOI信息在20cm偏移位置将径向空间分辨率提高了48%。在7.4 kBq ml（-1）时，峰值噪声等效计数率（NECR）为22.9 kcps，散射分数为44%。系统灵敏度为5.9 kcps MBq（-1）。对于NEMA NU 2图像质量幻影，10毫米球体清晰可见，没有任何伪影。对于NEMA NU 4图像质量模体，我们在0,10和20 cm偏移位置测量了模体。结果发现，虽然在没有DOI的图像上无法识别直径为2mm的热柱，但在四层DOI的图像上可以看到直径为2mm的热柱。5个热棒（1-5 mm）在0、10和20 cm偏移位置的回收率系数平均提高了0.3%、4.4%和26.3% （1 mm直径的棒在20 cm偏移位置除外）。尽管在扫描仪投入临床使用之前还需要解决一些实际问题（如增加端护罩），但我们发现，四层DOI技术在视场上提供了更高、更均匀的空间分辨率，并改善了位于外周视场的小摄取区域的对比度，这可以提高对淋巴结转移等小和远端病变的可检测性，特别是在肥胖患者中。
Parallax error caused by the detector crystal thickness degrades spatial resolution at the peripheral regions of the field-of-view (FOV) of a scanner. To resolve this issue, depth-of-interaction (DOI) measurement is a promising solution to improve the spatial resolution and its uniformity over the entire FOV. Even though DOI detectors have been used in dedicated systems with a small ring diameter such as for the human brain, breast and small animals, the use of DOI detectors for a large bore whole-body PET system has not been demonstrated yet. We have developed a four-layered DOI detector, and its potential for a brain dedicated system has been proven in our previous development. In the present work, we investigated the use of the four-layer DOI detector for a large bore PET system by developing the world's first whole-body prototype. We evaluated its performance characteristics in accordance with the NEMA NU 2 standard. Furthermore, the impact of incorporating DOI information was evaluated with the NEMA NU 4 image quality phantom. Point source images were reconstructed with a filtered back projection (FBP), and an average spatial resolution of 5.2 +/- 0.7 mm was obtained. For the FBP image, the four-layer DOI information improved the radial spatial resolution by 48% at the 20 cm offset position. The peak noise-equivalent count rate (NECR) was 22.9 kcps at 7.4 kBq ml(-1) and the scatter fraction was 44%. The system sensitivity was 5.9 kcps MBq(-1). For the NEMA NU 2 image quality phantom, the 10 mm sphere was clearly visualized without any artifacts. For the NEMA NU 4 image quality phantom, we measured the phantom at 0, 10 and 20 cm offset positions. As a result, we found the image with four-layer DOI could visualize the 2 mm-diameter hot cylinder although it could not be recognized on the image without DOI. The average improvements in the recovery coefficients for the five hot rods (1-5 mm) were 0.3%, 4.4% and 26.3% at the 0, 10 and 20 cm offset positions, respectively (except for the 1 mm-diameter rod at the 20 cm offset position). Although several practical issues (such as adding end-shields) remain to be addressed before the scanner is ready for clinical use, we showed that the four-layer DOI technology provided higher and more uniform spatial resolution over the FOV and improved contrast for small uptake regions located at the peripheral FOV, which could improve detectability of small and distal lesions such as nodal metastases, especially in obese patients.