Townsend David W, Carney Jonathan P J, Yap Jeffrey T, Hall Nathan C
Department of Medicine, University of Tennessee Medical Center, Knoxville, Tennessee 37920-6999, USA.
J Nucl Med. 2004 Jan;45 Suppl 1:4S-14S.
Accurate anatomic localization of functional abnormalities seen with PET is known to be problematic. Even though nonspecific tracers such as 18F-FDG visualize certain normal anatomic structures, the spatial resolution is generally inadequate for localization of pathology. Combining PET with a high-resolution anatomic imaging modality such as CT can resolve the localization issue, as long as the images from the two modalities are accurately coregistered. However, software-based registration techniques have difficulty accounting for differences in patient positioning and involuntary movement of internal organs, often necessitating labor-intensive nonlinear mapping that may not converge to a satisfactory result. Acquiring both CT and PET images in the same scanner obviates the need for software registration and routinely provides accurately aligned images of anatomy and function in a single scan.
A CT scanner positioned in tandem with a PET scanner and with a common patient couch and operating console has recently been explored as a solution to anatomic and functional image registration. Axial translation of the couch between the two modalities enables both CT and PET data to be acquired during a single imaging session. In addition, the CT images can be used to generate noiseless attenuation correction factors for the PET emission data. By minimizing patient movement between the CT and PET scans, and after accounting for the axial separation of the two modalities, accurately registered anatomic and functional images can be obtained. Since the introduction of the first PET/CT prototype a little over 5 years ago, several thousand cancer patients have been scanned on combined PET/CT devices. In the past 3 years, a number of commercial designs have become available featuring multidetector spiral CT scanners and high-performance PET devices. Initial experience has demonstrated an increased level of accuracy and confidence in the interpretation of the combined study compared with separate readings, particularly in the ability to distinguish pathology from normal physiologic uptake and to precisely localize abnormal foci.
Combined PET/CT scanners represent an important evolution in technology that is helping to bring molecular imaging to the forefront in cancer diagnosis, staging, and therapy monitoring.
已知正电子发射断层扫描（PET）所显示的功能异常的精确解剖定位存在问题。尽管诸如18F-氟代脱氧葡萄糖（18F-FDG）等非特异性示踪剂能使某些正常解剖结构显影，但空间分辨率通常不足以定位病变。将PET与高分辨率解剖成像模式（如CT）相结合可以解决定位问题，只要两种模式的图像能精确地配准。然而，基于软件的配准技术难以考虑患者体位差异和内部器官的不自主运动，这通常需要耗费大量人力的非线性映射，且可能无法得到满意的结果。在同一台扫描仪中获取CT和PET图像可避免软件配准的需求，并在单次扫描中常规提供解剖结构和功能精确对齐的图像。
最近探索了一种将CT扫描仪与PET扫描仪串联放置，并配备共同的患者检查床和操作控制台的方法，作为解剖和功能图像配准的解决方案。在两种模式之间轴向移动检查床可使CT和PET数据在单次成像过程中获取。此外，CT图像可用于为PET发射数据生成无噪声的衰减校正因子。通过尽量减少CT和PET扫描之间患者的移动，并考虑到两种模式的轴向间距，可获得精确配准的解剖和功能图像。自5年多前推出首个PET/CT原型机以来，已有数千名癌症患者接受了PET/CT联合设备的扫描。在过去3年中，出现了许多商业设计，其特点是多探测器螺旋CT扫描仪和高性能PET设备。初步经验表明，与单独阅读相比，联合检查结果解读的准确性和可信度有所提高，特别是在区分病变与正常生理性摄取以及精确定位异常病灶的能力方面。
PET/CT联合扫描仪代表了一项重要的技术进步，有助于将分子成像推向癌症诊断、分期和治疗监测的前沿。
