Department of Radiology, UC Davis, Sacramento, CA, USA.
Department of Radiology, UC Davis, Sacramento, CA, USA; Section of Nuclear Medicine, University Department of Radiological Sciences and Hematology, Università Cattolica del Sacro Cuore, Rome, Italy.
Semin Nucl Med. 2022 May;52(3):330-339. doi: 10.1053/j.semnuclmed.2022.01.002. Epub 2022 Mar 7.
Total-body PET has come a long way from its first conception to today, with both total-body and long axial field of view (> 1m) scanners now being commercially available world-wide. The conspicuous signal collection efficiency gain, coupled with high spatial resolution, allows for higher sensitivity and improved lesion detection, enhancing several clinical applications not readily available on current conventional PET/CT scanners. This technology can provide (a) reduction in acquisition times with preservation of diagnostic quality images, benefitting specific clinical situations (i.e. pediatric patients) and the use of several existing radiotracers that present transient uptake over time and where small differences in acquisition time can greatly impact interpretation of images; (b) reduction in administered activity with minimal impact on image noise, thus reducing effective dose to the patient, improving staff safety, and helping with logistical concerns for short-lived radionuclides or long-lived radionuclides with poor dosimetry profiles that have had limited use on conventional PET scanners until now; (c) delayed scanning, that has shown to increase the detection of even small and previously occult malignant lesions by improved clearance in regions of significant background activity and by reduced visibility of coexisting inflammatory processes; (d) improvement in image quality, as a consequence of higher spatial resolution and sensitivity of total-body scanners, implying better appreciation of small structures and clinical implications with downstream prognostic consequences for patients; (e) simultaneous total-body dynamic imaging, that allows the measurement of full spatiotemporal distribution of radiotracers, kinetic modeling, and creation of multiparametric images, providing physiologic and biologically relevant data of the entire body at the same time. On the other hand, the higher physical and clinical sensitivity of total-body scanners bring along some limitations and challenges. The strong impact on clinical sensitivity potentially increases the number of false positive findings if the radiologist does not recalibrate interpretation considering the new technique. Delayed scanning causes logistical issues and introduces new interpretation questions for radiologists. Data storage capacity, longer processing and reconstruction time issues are other limitations, but they may be overcome in the near future by advancements in reconstruction algorithms and computing hardware.
全身 PET 技术从最初的构想发展至今，目前全球范围内已可获得全身和长轴向视野（>1 米）的扫描仪。显著的信号采集效率提高，加上高空间分辨率，可实现更高的灵敏度和改善病灶检测，增强了当前常规 PET/CT 扫描仪无法实现的几种临床应用。该技术可提供：(a) 保持诊断质量图像的同时缩短采集时间，有利于特定临床情况（如儿科患者）和使用几种随时间推移出现短暂摄取的现有放射性示踪剂，而采集时间的微小差异会极大地影响图像的解读；(b) 减少给药剂量而对图像噪声影响最小，从而降低患者的有效剂量，提高工作人员的安全性，并有助于解决半衰期较短的放射性核素或半衰期长但剂量学特征不佳的放射性核素的后勤问题，这些放射性核素直到现在在常规 PET 扫描仪上的应用都很有限；(c) 延迟扫描，通过改善背景活动区域的清除效果和减少共存炎症过程的可见性，提高了对即使是小的且先前隐匿的恶性病灶的检测；(d) 图像质量的改善，这是全身扫描仪更高的空间分辨率和灵敏度的结果，意味着可以更好地观察小结构，并对患者的下游预后产生临床影响；(e) 全身动态成像的同步进行，可测量放射性示踪剂的完整时空分布、进行动力学建模和创建多参数图像，同时提供全身的生理和生物学相关数据。另一方面，全身扫描仪的更高物理和临床灵敏度带来了一些限制和挑战。如果放射科医生不根据新技术重新校准解释，那么强烈的临床灵敏度影响可能会增加假阳性发现的数量。延迟扫描会导致后勤问题，并给放射科医生带来新的解释问题。数据存储容量、更长的处理和重建时间问题也是其他限制因素，但在不久的将来，通过重建算法和计算硬件的进步可能会克服这些问题。
