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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
上期回顾： 单源瞬切能谱CT的单能量图像在低能量段（50keV或52 keV）可以提高腹部实质性脏器的小病灶检出，高能量段（110keV-140keV）可以减少金属伪影，消除肾囊肿的假强化现象。
本期内容： CT双能量成像中的CT值和辐射剂量
CT双能量成像中的CT值 Hounsfield units on dual-energy CT
多个体模和临床研究发现，CT双能量成像的CT值与多种因素有关：不同的双能成像方法、图像采集的期相和测量部位在扫描野中的位置，因此需要进一步研究。 In phantom studies and in evaluation of many body regions, the fidelity of virtual unenhanced attenuation values is a subject of continued investigation and may depend upon the scanner technology, the dynamic phase of images being evaluated, and the location in the bore of the tissue being evaluated. Sahni在双源双能量减影平台上进行了100例CTU，发现肝脏、肾实质、主动脉的虚拟平扫图像的CT值和真实平扫图像的CT值之间存在统计学差异。这种差异在脾脏和脂肪组织、以及不同期相的图像中并不存在[13]。 Sahni et al. [13] found a statistically significant difference in values of liver, renal parenchyma, and aorta, but no difference in spleen and fat values using a dsDECT system in 100 consecutive patients undergoing CT urograms with dual-energy technique. The same authors found that the contrast material phase did not affect the HU values on the virtual unenhanced images. 在另外一个双源双能量减影的体模和临床研究中，研究者对比了动脉期、静脉期的虚拟平扫图像和真实平扫图像的CT值差异，发现这种CT值差异存在于腹部各个器官中，其中主动脉、脾脏和脂肪的差异最明显[11]。另外一个研究使用了加了锌片滤过装置的双源成像平台，发现这种CT值的差异现象也存在于门脉期中[14]。 Yet in a phantom and patient study of dsDECT acquired in arterial and venous phases compared to conventional unenhanced CT, significant differences in HU of the abdominal organs were found and were the greatest in the aorta, spleen, and fat; the differences were below 15 HU in 95.5% of measurements [11]. The greater differences between the virtual and true unenhanced HU in the spleen and fat compared to other abdominal organs have been noted on portal phase dsDECT with the use of a tin-filter on dsDECT [14]. Matsuda在单源瞬切能谱平台上利用椭圆形体模研究CT值的稳定性，发现65keV单能量图像的CT值稳定性最好，和体模的形状无关[9]；然而传统CT的CT值在椭圆形体模的中心和边缘部位存在明显的统计学差异。其他研究者发现单源瞬切能谱平台的CT值和碘含量之间存在很好的相关性[10]。 On a phantom study using a rsDECT scanner, Matsuda et al. [9] found that attenuation measurements in HU on mono-energetic 65 keV images provided consistent values regardless of phantom shape, whereas conventional MDCT produced a statistically significant difference in HU measured in the center and periphery of an elliptical phantom. Other authors found higher-fitting coefficients for CT attenuation values and Iodine concentration using single-source rapid-switching imaging compared to conventional polychromatic beam CT [10]. CT双能量成像中的辐射剂量 Radiation Dose on dual-energy CT 在笔者所在的单位，单源瞬切能谱CT已经常规应用于肝脏和胰腺病人的多期相扫描：应用传统方法进行平扫、应用单源瞬切能谱进行肝动脉晚期或胰腺实质期扫描、应用传统方法进行门脉期扫描。 At our institution, rsDECT of the abdomen is typically employed for patients with suspected hepatic or pancreatic disease, and is part of a multiphasic examination consisting of: conventional unenhanced images obtained using SECT, late hepatic arterial or pancreatic parenchymal phase images obtained with rsDECT, and portal venous and equilibrium phase (if applicable) using standard polychromatic beam CT. Sarver在2012年美国腹部影像学年会上发表研究，阐述了应用上述多期相的扫描方法，患者接受的辐射剂量要低于同等扫描范围的传统扫描。 With this multiphasic method, patients scanned at our institution have lower radiation exposures as measured by DLP compared to similar anatomic coverage abdominal scans being obtained on other units in our department (Sarver et al. (2012) presented to the Society of Abdominal Radiology, unpublished data). 如果应用虚拟平扫代替传统平扫，多期相腹部扫描的辐射剂量可以降低30% - 50% [12, 16–18]。 If a multiphasic abdominal scanning technique is required, dose reduction achievable by omitting the conventional unenhanced scan was approximately 30%–50% [12, 16–18]. 《连载4》引用的参考文献： 9. Matsuda I, Akahane M, Sato J, et al. (2012) Precision of the measurement of CT numbers: comparison of dual-energy CT spectral imaging with fast kVp switching and conventional CT with phantoms. Jpn J Radiol 30:34–39 10. Wang L, Liu B, Wu X, et al. (2012) Correlation between CT attenuation value and iodine concentration in vitro: discrepancy between gemstone spectral imaging on single-source dual-energy CT and traditional polychromatic X-ray imaging. J Med Imaging Radiat Oncol 56:379–383 11. Toepker M, Moritz T, Krauss B, et al. (2012) Virtual non-contrast in second-generation, dual-energy computed tomography: reliabil- ity of attenuation values. Eur Radiol 81:e398–e405 12. deCecco C, Buffa V, Fedeli S, et al. (2010) Dual energy CT (DECT) of the liver: conventional versus virtual unenhanced images. Eur Radiol 20:2870–2875 13. Sahni VA, Shinagare AB, Silverman SG (2013) Virtual unenhanced CT images acquired from dual-energy CT urography: accuracy of attenuation values and variation with contrast material phase. Clin Radiol 68(3):264–271 14. Kaufmann S, Sauter A, Spira D, et al. (2013) Tin-filter enhanced dual-energy-CT: image quality and accuracy of CT numbers in virtual noncontrast imaging. Acad Radiol 20(5):596–603 15. Zatz LM, Alvarez RE (1977) An inaccuracy in computed tomog- raphy: the energy dependence of CT values. Radiology 124:91–97 16. Graser A, Becker CR, Staehler M, et al. (2010) Single-phase dual- energy CT allows for characterization of renal masses as benign or malignant. Investig Radiol 45(7):399–405 17. Mileto A, Mazziotti S, Gaeta M, et al. (2012) Pancreatic dual- source dual-energy CT: is it time to discard unenhanced imaging? Clin Radiol 67:334–339 18. Ascenti G, Mileto A, Gaeta M, et al. (2013) Single-phase dual- energy CT urography in the evaluation of haematuria. Clin Radiol 68(2):e87–e94 19. Silva AC, Morse BG, Hara AK, et al. (2011) Dual-energy (spectral) CT: applications in abdominal imaging. RadioGraphics 31:1031– 1046 下期预告： CT双能量成像在肾脏的应用。
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