1 Department of Radiology, Institute of Health Sciences, Gyeongsang National University School of Medicine, Jinju, 90 Chilam-dong, Jinju, Gyeongsang-nam-do 660-702, Korea.
2 Department of Radiology, Gyeongsang National University Changwon Hospital, Changwon, Korea.
AJR Am J Roentgenol. 2018 Apr;210(4):734-741. doi: 10.2214/AJR.17.18537. Epub 2018 Feb 15.
The objective of our study was to evaluate the quality of virtual monoenergetic imaging (VMI) from dual-layer detector spectral CT and the effect of virtual monoenergetic images obtained at low energies on the detection of pulmonary embolism (PE) in patients with a suboptimally enhanced pulmonary artery on chest CT.
Of 1552 consecutive chest CT examinations performed with dual-layer detector spectral CT using a routine protocol with a tube voltage of 120 kVp, 79 examinations with suboptimal enhancement of the pulmonary artery (i.e., mean attenuation of pulmonary artery ≤ 180 HU) were included. The mean attenuation of the pulmonary artery, noise, contrast-to-noise ratio (CNR), and signal-to-noise ratio (SNR) of virtual monoenergetic images obtained at 40-200 keV were compared with those of the conventional 120-kVp images. The virtual monoenergetic images with the best CNR were compared with the 120-kVp images with regard to subjective image quality and diagnostic accuracy for detecting PE.
Sufficient attenuation of the pulmonary artery (> 180 HU) was obtained using VMI for 78 of the 79 examinations. The noise levels of the virtual monoenergetic images were gradually increased with decreasing energy level (i.e., kiloelectron volt setting). The CNR and SNR of virtual monoenergetic images at 40-65 keV were significantly higher (both, p < 0.001) than the CNR and SNR of the 120-kVp images. The CNR was the highest at 40 keV for all cases. Diagnostic accuracy for detecting PE was significantly higher for 40-keV images (reader 1: AUC = 0.992, p = 0.033; reader 2: AUC = 0.986, p = 0.043) than for 120-kVp images (reader 1, AUC = 0.911; reader 2, AUC = 0.933). The subjective quality was not different between these two images.
In chest CT examinations in which the pulmonary artery is suboptimally enhanced, obtaining virtual monoenergetic images at a low energy setting using dual-layer detector spectral CT allows sufficient attenuation of the pulmonary artery to be achieved while preserving image quality and increasing diagnostic performance for detecting PE.
本研究旨在评估双层探测器能谱 CT 虚拟单能量成像（VMI）的质量，并研究低keV 能谱 VMI 图像对胸部 CT 肺动脉增强不理想患者中肺动脉栓塞（PE）的检出效果。
对采用常规 120kVp 管电压方案行双层探测器能谱 CT 检查的 1552 例连续病例进行研究，其中 79 例肺动脉增强不理想（即平均肺动脉 CT 值≤180HU）。比较 40-200keV 能谱 VMI 与常规 120kVp 图像的肺动脉平均 CT 值、噪声、对比噪声比（CNR）和信噪比（SNR）。比较最佳 CNR 的 VMI 图像与 120kVp 图像在诊断 PE 方面的主观图像质量和诊断准确性。
79 例中有 78 例 VMI 获得了足够的肺动脉衰减（>180HU）。随着能量水平（即 keV 设置）的降低，VMI 的噪声水平逐渐升高。40-65keV 的 VMI 的 CNR 和 SNR 均明显高于（均为 p<0.001）120kVp 图像的 CNR 和 SNR。所有病例的 CNR 均以 40keV 时最高。PE 的诊断准确性在 40keV 图像时明显更高（阅片者 1：AUC=0.992，p=0.033；阅片者 2：AUC=0.986，p=0.043），而在 120kVp 图像时更低（阅片者 1，AUC=0.911；阅片者 2，AUC=0.933）。两种图像的主观质量无差异。
在肺动脉增强不理想的胸部 CT 检查中，使用双层探测器能谱 CT 采用低keV 能谱设置获取 VMI 图像可在保持图像质量的同时实现足够的肺动脉衰减，提高对 PE 的诊断性能。
