Department of Nuclear Medicine, Zhongshan Hospital, Fudan University, 180 Fenglin Road, Shanghai, 200032, China.
Nuclear Medicine Institute of Fudan University, Shanghai, 200032, China.
Eur J Nucl Med Mol Imaging. 2021 Jul;48(8):2384-2394. doi: 10.1007/s00259-021-05357-5. Epub 2021 Apr 18.
The aim of the study was to determine a faster PET acquisition protocol for a total-body PET/CT scanner by assessing the image quality that is equivalent to a conventional digital PET/CT scanner from both a phantom and a clinical perspective.
A phantom study using a NEMA/IEC NU-2 body phantom was first performed in both a total-body PET/CT (uEXPLORER) and a routine digital PET/CT (uMI 780), with a hot sphere to background activity concentration ratio of 4:1. The contrast recovery coefficient (CRC), background variability (BV), and recovery coefficient (RC: RC and RC) were assessed in the uEXPLORER with different scanning durations and reconstruction protocols, which were compared to those acquired from the uMI 780 with clinical acquisition settings. The coefficient of variation (COV) of the uMI 780 with clinical settings was calculated and used as a threshold reference to determine the optimized scanning duration and reconstruction protocol for the uEXPLORER. The obtained protocol from the phantom study was subsequently tested and validated in 30 oncology patients. Images acquired from the uMI 780 with 2-3 min per bed position were referred as G780 and served as the reference for comparison. All PET raw data from the uEXPLORER were reconstructed using the data-cutting technique to simulate a 30-s, 45-s, or 60-s acquisition duration, respectively. The iterations were 2 and 3 for the uEXPLORER, referred as G30s_3i, G45s_2i, G45s_3i, G60s_2i, and G60s_3i, respectively. A 5-point Likert scale was used in the qualitative analysis to assess the image quality. The image quality was also evaluated by the liver COV, the lesion target-to-background ratio (TBR), and the lesion signal-to-noise ratio (SNR).
In the phantom study, CRC, BV, RC, and RC in the uEXPLORER with different scanning durations and reconstruction iterations were compared with those in the uMI 780 with clinical settings. A minor fluctuation was found among different scanning durations. COV of the uMI 780 with clinical settings was 11.6%, and a protocol with a 30-45-s scanning duration and 2 or 3 iterations for the uEXPLORER was found to provide an equivalent image quality as the uMI 780. An almost perfect agreement was shown with a kappa value of 0.875. The qualitative score of the G30s_3i in the uEXPLORER was inferior to the G780 reference (p = 0.001); however, the scores of other groups in the uEXPLORER with a 45-s and above acquisition time were higher than the G780 in the uMI 780. In quantitative analysis, the delay time between the two scans in the two orders was not significantly different. There was no significant difference of the liver COV between the G780 and G30s_3i (p = 0.162). A total of 33 lesions were analyzed in the clinical patient study. There was no significant difference in lesion TBR between the reference G780 and the G45s_2i obtained from the uEXPLORER (p = 0.072), while the latter showed a higher lesion SNR value compared to that in uMI 780 with clinical settings (p < 0.001).
This study showed that a fast PET protocol with a 30-45-s acquisition time in the total-body uEXPLORER PET/CT can provide an equivalent image quality as the conventional digital uMI 780 PET/CT with longer clinical acquisition settings.
本研究旨在通过评估等效于常规数字 PET/CT 扫描仪的图像质量，从体模和临床角度确定总身体 PET/CT 扫描仪的更快 PET 采集协议。
首先在总身体 PET/CT（uEXPLORER）和常规数字 PET/CT（uMI 780）中使用 NEMA/IEC NU-2 体模进行体模研究，其中热球与背景的活性浓度比为 4:1。在 uEXPLORER 中，使用不同的扫描时间和重建协议评估对比恢复系数（CRC）、背景变异性（BV）和恢复系数（RC：RC 和 RC），并将其与临床采集设置下从 uMI 780 获得的值进行比较。计算 uMI 780 的变异系数（COV），并将其用作确定 uEXPLORER 最佳扫描时间和重建协议的阈值参考。随后在 30 例肿瘤患者中测试和验证从体模研究中获得的协议。使用 2-3 分钟/床位位置的 uMI 780 采集的图像被称为 G780，并作为比较的参考。从 uEXPLORER 采集的所有 PET 原始数据均使用数据切割技术进行重建，以分别模拟 30 秒、45 秒或 60 秒的采集时间。uEXPLORER 的迭代次数为 2 和 3，分别称为 G30s_3i、G45s_2i、G45s_3i、G60s_2i 和 G60s_3i。使用 5 分制的定性分析来评估图像质量。还通过肝脏 COV、病变靶标与背景比（TBR）和病变信噪比（SNR）来评估图像质量。
在体模研究中，比较了 uEXPLORER 中不同扫描时间和重建迭代次数的 CRC、BV、RC 和 RC 与 uMI 780 临床设置中的值。不同扫描时间之间存在微小波动。uMI 780 临床设置的 COV 为 11.6%，发现 uEXPLORER 扫描时间为 30-45 秒，迭代次数为 2 或 3 的协议可提供与 uMI 780 相当的图像质量。一致性极好，kappa 值为 0.875。uEXPLORER 中 G30s_3i 的定性评分低于 G780 参考（p=0.001）；然而，uEXPLORER 中 45 秒以上采集时间的其他组的评分均高于 uMI 780 中的 G780。在定量分析中，两个扫描之间的延迟时间没有显著差异。G780 和 G30s_3i 之间的肝脏 COV 没有显著差异（p=0.162）。临床患者研究共分析了 33 个病灶。参考 G780 和从 uEXPLORER 获得的 G45s_2i 之间的病变 TBR 没有显著差异（p=0.072），而后者与具有临床设置的 uMI 780 相比，病变 SNR 值更高（p<0.001）。
本研究表明，总身体 uEXPLORER PET/CT 中 30-45 秒的快速 PET 协议可以提供等效于常规数字 uMI 780 PET/CT 的图像质量，具有更长的临床采集设置。
