Universiti Sains Malaysia, School of Health Sciences, Malaysia.
Institut Kanser Negara, Nuclear Medicine Department, Ministry of Health Malaysia, Malaysia.
Med J Malaysia. 2021 Sep;76(5):637-642.
F-FDG imaging of overweight and obese patients is often challenging due to higher scattering and attenuation. Degradation of positron emission tomography (PET) image quality as the body weight increases is best overcome by using the quadratic dose protocol. Previously the implementation of this protocol on a Bismuth Germanium Oxide (BGO) scintillation crystal-based PET/CT system at Institut Kanser Negara (IKN), Malaysia practices using the linear dose protocol (T=2.5 minutes). Hence, this study aims to optimize the T of the quadratic dose protocol for F-FDG PET/CT.
This study was conducted based on the guideline published by the European Association of Nuclear Medicine (EANM) version 2.0 FDG-PET/CT and conducted in two phases. Firstly, 100 whole-body scan FFDG PET/CT images were selected for the average coefficient of variation (COV) analysis in the liver region. Second, a NEMA 2012/IEC2008 phantom was used to obtain the relationship between the COV and the scanning time. Finally, the images acquired using the two T were quantitatively compared using contrast recovery coefficient (Q), signal to noise ratio (SNR), and visibility (V). Independent t-test between each image quality parameter performed with p-value <0.05 considered significant.
The average COV of the liver was 17.7%. Currently, this value was clinically accepted to produce appropriate image quality at IKN. Interpolation at COV=17.7% gave a T value of 2.9 minutes. Comparisons show that the two T yielded equivalent PET/CT image quality (p-value of Q=0.774, SNR=0.780 and V=0.915).
The optimal T defined in this study was 2.9 minutes, 27.6% shorter than the Tmin previously defined based on COV=15%. Despite the higher average COV, the shorter T beneficial in the lower total F-FDG activity administered, reduce the internal dose to the patient while producing equivalent image quality.
由于散射和衰减较高，超重和肥胖患者的 F-FDG 成像常常具有挑战性。通过使用二次剂量方案，可以最大程度地克服随着体重增加而导致的正电子发射断层扫描（PET）图像质量下降的问题。先前，在马来西亚国家癌症研究所（IKN）的基于铋锗氧化物（BGO）闪烁晶体的 PET/CT 系统上实施该方案时，使用的是线性剂量方案（T=2.5 分钟）。因此，本研究旨在针对 F-FDG PET/CT 优化二次剂量方案的 T 值。
本研究基于欧洲核医学协会（EANM）第 2.0 版 FDG-PET/CT 发布的指南进行，并分两个阶段进行。首先，选择 100 例全身扫描 F-FDG PET/CT 图像进行肝区平均变异系数（COV）分析。其次，使用 NEMA 2012/IEC2008 体模获取 COV 与扫描时间之间的关系。最后，使用两种 T 值获取的图像进行定量比较，使用对比恢复系数（Q）、信噪比（SNR）和可视性（V）进行比较。当 p 值<0.05 时，进行每个图像质量参数的独立 t 检验，认为具有统计学意义。
肝的平均 COV 为 17.7%。目前，该值在 IKN 被临床接受，可产生适当的图像质量。COV=17.7%时的插值给出了 T 值为 2.9 分钟。比较表明，两种 T 值产生了等效的 PET/CT 图像质量（Q 的 p 值=0.774，SNR=0.780 和 V=0.915）。
本研究中定义的最佳 T 值为 2.9 分钟，比先前基于 COV=15%定义的 Tmin 短 27.6%。尽管平均 COV 较高，但较短的 T 值有利于减少患者接受的总 F-FDG 活性，降低患者的内部剂量，同时产生等效的图像质量。
