From the Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Raemistrasse 100, CH-8091 Zurich, Switzerland (V.M., L.J., T.S., S.B., K.H., K.M., H.A., A.E.); and Institute of Radiation Physics (IRA), Lausanne University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland (D.R., P.M.).
Radiology. 2022 Oct;305(1):107-115. doi: 10.1148/radiol.213260. Epub 2022 Jun 7.
Background Accurate CT attenuation and diagnostic quality of virtual noncontrast (VNC) images acquired with photon-counting detector (PCD) CT are needed to replace true noncontrast (TNC) scans. Purpose To assess the attenuation errors and image quality of VNC images from abdominal PCD CT compared with TNC images. Materials and Methods In this retrospective study, consecutive adult patients who underwent a triphasic examination with PCD CT from July 2021 to October 2021 were included. VNC images were reconstructed from arterial and portal venous phase CT. The absolute attenuation error of VNC compared with TNC images was measured in multiple structures by two readers. Then, two readers blinded to image reconstruction assessed the overall image quality, image noise, noise texture, and delineation of small structures using five-point discrete visual scales (5 = excellent, 1 = nondiagnostic). Overall image quality greater than or equal to 3 was deemed diagnostic. In a phantom, noise texture, spatial resolution, and detectability index were assessed. A detectability index greater than or equal to 5 indicated high diagnostic accuracy. Interreader agreement was evaluated using the Krippendorff α coefficient. The paired test and Friedman test were applied to compare objective and subjective results. Results Overall, 100 patients (mean age, 72 years ± 10 [SD]; 81 men) were included. In patients, VNC image attenuation values were consistent between readers (α = .60), with errors less than 5 HU in 76% and less than 10 HU in 95% of measurements. There was no evidence of a difference in error of VNC images from arterial or portal venous phase CT (3.3 HU vs 3.5 HU, = .16). Subjective image quality was rated lower in VNC images for all categories (all, < .001). Diagnostic quality of VNC images was reached in 99% and 100% of patients for readers 1 and 2, respectively. In the phantom, VNC images exhibited 33% higher noise, blotchier noise texture, similar spatial resolution, and inferior but overall good image quality (detectability index >20) compared with TNC images. Conclusion Abdominal virtual noncontrast images from the arterial and portal venous phase of photon-counting detector CT yielded accurate CT attenuation and good image quality compared with true noncontrast images. © RSNA, 2022 See also the editorial by Sosna in this issue.
背景 为了替代真实非对比（TNC）扫描，需要具有光子计数探测器（PCD）CT 的准确 CT 衰减和虚拟非对比（VNC）图像的诊断质量。
目的 评估腹部 PCD CT 的 VNC 图像与 TNC 图像相比的衰减误差和图像质量。
材料与方法 本回顾性研究纳入了 2021 年 7 月至 2021 年 10 月期间接受 PCD CT 三期检查的连续成年患者。VNC 图像是从动脉期和门静脉期 CT 重建的。两位读者分别测量了 VNC 图像与 TNC 图像之间的绝对衰减误差。然后，两位读者在不知道图像重建的情况下，使用五分制离散视觉量表（5=极好，1=无法诊断）评估整体图像质量、图像噪声、噪声纹理和小结构的勾画。整体图像质量大于或等于 3 被认为是有诊断价值的。在体模中，评估了噪声纹理、空间分辨率和可探测性指数。可探测性指数大于或等于 5 表明具有较高的诊断准确性。读者间的一致性采用克里普夫α系数进行评估。采用配对 t 检验和 Friedman 检验比较客观和主观结果。
结果 共有 100 例患者（平均年龄，72 岁±10[标准差]；81 例男性）纳入本研究。在患者中，VNC 图像的衰减值在两位读者之间具有一致性（α=.60），76%的测量值误差小于 5 HU，95%的测量值误差小于 10 HU。动脉期和门静脉期 CT 的 VNC 图像误差无差异（3.3 HU 比 3.5 HU， =.16）。在所有类别中，VNC 图像的主观图像质量评分均较低（均，<.001）。对于读者 1 和 2，VNC 图像在 99%和 100%的患者中达到诊断质量。在体模中，与 TNC 图像相比，VNC 图像的噪声高 33%，噪声纹理更斑驳，空间分辨率相似，但整体图像质量较差（可探测性指数>20）。
结论 与 TNC 图像相比，来自 PCD CT 动脉期和门静脉期的腹部虚拟非对比图像具有准确的 CT 衰减和良好的图像质量。
