综述：CT双能量成像在腹部的应用（连载一）Dual-energy CT of the abdomen

作者：Desiree E. Morgan

作者单位：Department of Radiology, University of Alabama at Birmingham, JTN452 619 South 19th Street, Birmingham, AL 35249, USA

本文发表于：Abdominal Imaging (2014) 39:108–134

虽然CT双能量成像的概念起源于20世纪70年代，但直到2006年，CT双能量成像才逐渐应用于临床。最近几年，多种CT双能量技术也相继开发出来，使得CT双能量成像的临床应用更加成熟。本文将从技术角度探讨CT双能量成像的硬件平台，通过回顾最近的临床文献，为临床放射科医生提供CT双能量成像在腹部各器官的临床应用指南。

Although conceived of in the 1970s, practical use of dual- energy CT in the clinical setting did not come to fruition until 2006, and since that time an ever expanding exploration of the technology has been underway. This article will discuss technical aspects of the two commercially available CT scanners, review the recent literature, and provide an organ-based description of abdominal dual-energy CT applications for the practicing radiologist. 

在过去的6年间，CT双能量成像的应用和文献数量逐步增加。对于放射科医生来说，熟悉CT双能量成像的硬件技术，理解其能力和局限，有助于推动CT双能量成像在临床的应用。

Over the past 6 years the use of dual-energy CT has increased steadily and the number of publications dramatically. Familiarity with the technology and an understanding of the capabilities and challenges associated with the types of scanners presently available for clinical use may help radiologists to enhance their practice. 

一、CT双能量成像的硬件技术    Technology-scanners

在美国，有两种FDA审批通过可进行应用的（commercially available) CT双能量成像平台：双源双能量减影平台和能谱平台。

There are two types of commercially available dual-energy scanners presently available in the United States: Dual Source Dual-energy CT and Spectral CT. 

双源双能量减影平台（dsDECT，西门子，德国），应用2个球管（2个球管呈90度夹角）分别发射低能量（80 或 100 kVp) X线 和 高能量（140kVp）X线。这2组X线分别产生2组独立的Dicom图像，对这2组图像在“图像空间（Image Space)”进行不同权重的融合及减影。双源CT的2个球管有不同的扫描视野（FOV, Field of View）：1250px和825px。因此有效的双能扫描野只有825px，这限制了大体型病人的双能减影扫描，并要求技师对病人的摆位非常小心。 

The dual-source dual-energy CT scanner (dsDECT) (Definition FLASH Siemens Medical Solutions, Erlangen, Germany) has two approximately 90° offset tubes that generate separate low (80 or 100 kVp) and high (140 kVp) energy beams which produce two separate image data sets that are then combined to create blended images in ‘‘image space’’. These tubes have two different fields of view (FOV), the larger being 50 cm and the smaller tube initially being limited to 33-cm coverage. This smaller second tube FOV constraint limited applications in larger patients and required careful patient positioning on the part of CT technologists at sites that used dsDECT scanners.

能谱平台（rsDECT, 高低压瞬时切换CT，通用电气，美国），应用单球管进行高电压（140kVp）和低电压（80kVp)的瞬时切换，通过一个反应快速的探测器（译者注：宝石探测器），可以获得“同源、同时、同向” 的CT原始数据(single tube, simutaneous datasets)。这种方法的能谱扫描视野没有限制，达到1250px FOV。“同源、同时、同向”的CT原始数据，可以在原始数据空间（Projection space）产生“基物质图像”和“单能量图像”。和双源双能量减影平台不同，能谱平台并不产生80kVp和140kVp的图像。能谱平台产生的是单能量图像，能量范围是（40-140keV），其中70keV或78keV的图像用来进行常规PACS存储、诊断读片和胶片打印。在之后的章节里，我们将讨论如何根据不同的腹部脏器，利用不同的最佳keV单能量图像进行诊断。(知识点：kVp定义的是混合能量X线能量谱的最高能量，keV定义的是单一能量X线的X线光子能量。）

The rapid kilovoltage switching dual-energy CT scanner (rsDECT) (General Electric Healthcare, Waukesha, WI) uses a single rapidly switching tube to acquire near simultaneous 140 and 80 kVp datasets using a single fast response detector. This system acquires dual-energy image over the entire 50 cm FOV.  The data is used to generate material density images and simulated monoenergetic images in ‘‘projection space’’. Typically, 70 or 78 keV images are generated and used for diagnostic interpretation, and unlike dsDECT, separate 80 and 140 kVp images are not created. The simulated monoenergetic images are available over a range of energies from 40 to 140 keV; clinical utility of viewing the images at different energies will be explained in the organ specific sections to follow. (As opposed to kVp, which defines the upper limit X-ray energy for a poly- chromatic X-ray spectra, the keV specifies the proton energy for a monochromatic X-ray source.

还有两种CT双能量成像方法：三明治探测器CT和光子计数CT。因为这两种方法还不能进行临床应用，因此本文并没有对其进行阐述。

Other dual-energy CT approaches not discussed in this article include the use of a single-tube source with a dual-layer detector or photon counting detector, neither presently available for clinical use。 

在之后的章节里，本文将从临床图像和应用指南两个角度，提供给读者CT双能量成像在腹部成像应用中的最新进展。本文所引用的病例和描述主要来自于能谱CT在腹部的临床应用。

This article will provide the reader with an updated general review of abdominal dual-energy CT technology and applications, with case illustrations focusing on spectral or rapid-switching dual-energy methods.

下期预告：

什么是双能减影图像呢？能谱CT又会产生哪些特殊的临床图像呢？什么是基物质图像？什么是单能量图像？什么又是虚拟平扫图像呢？