Sartoretti Thomas, Landsmann Anna, Nakhostin Dominik, Eberhard Matthias, Roeren Christian, Mergen Victor, Higashigaito Kai, Raupach Rainer, Alkadhi Hatem, Euler André
From the Institute of Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Raemistrasse 100, CH-8091 Zurich, Switzerland (T.S., A.L., D.N., M.E., C.R., V.M., K.H., H.A., A.E.); Department of Radiology and Nuclear Medicine, Maastricht University Medical Center, Maastricht University, Maastricht, the Netherlands (T.S.); and Siemens Healthcare, Forchheim, Germany (R.R.).
Radiology. 2022 May;303(2):339-348. doi: 10.1148/radiol.211931. Epub 2022 Feb 1.
Background An iterative reconstruction (IR) algorithm was introduced for clinical photon-counting detector (PCD) CT. Purpose To investigate the image quality and the optimal strength level of a quantum IR algorithm (QIR; Siemens Healthcare) for virtual monoenergetic images and polychromatic images (T3D) in a phantom and in patients undergoing portal venous abdominal PCD CT. Materials and Methods In this retrospective study, noise power spectrum (NPS) was measured in a water-filled phantom. Consecutive oncologic patients who underwent portal venous abdominal PCD CT between March and April 2021 were included. Virtual monoenergetic images at 60 keV and T3D were reconstructed without QIR (QIR-off; reference standard) and with QIR at four levels (QIR 1-4; index tests). Global noise index, contrast-to-noise ratio (CNR), and voxel-wise CT attenuation differences were measured. Noise and texture, artifacts, diagnostic confidence, and overall quality were assessed qualitatively. Conspicuity of hypodense liver lesions was rated by four readers. Parametric (analyses of variance, paired tests) and nonparametric tests (Friedman, post hoc Wilcoxon signed-rank tests) were used to compare quantitative and qualitative image quality among reconstructions. Results In the phantom, NPS showed unchanged noise texture across reconstructions with maximum spatial frequency differences of 0.01 per millimeter. Fifty patients (mean age, 59 years ± 16 [standard deviation]; 31 women) were included. Global noise index was reduced from QIR-off to QIR-4 by 45% for 60 keV and by 44% for T3D (both, < .001). CNR of the liver improved from QIR-off to QIR-4 by 74% for 60 keV and by 69% for T3D (both, < .001). No evidence of difference was found in mean attenuation of fat and liver ( = .79-.84) and on a voxel-wise basis among reconstructions. Qualitatively, QIR-4 outperformed all reconstructions in every category for 60 keV and T3D ( value range, <.001 to .01). All four readers rated QIR-4 superior to other strengths for lesion conspicuity ( value range, <.001 to .04). Conclusion In portal venous abdominal photon-counting detector CT, an iterative reconstruction algorithm (QIR; Siemens Healthcare) at high strength levels improved image quality by reducing noise and improving contrast-to-noise ratio and lesion conspicuity without compromising image texture or CT attenuation values. © RSNA, 2022 See also the editorial by Sinitsyn in this issue.
一种迭代重建（IR）算法被引入用于临床光子计数探测器（PCD）CT。目的：研究量子迭代重建算法（QIR；西门子医疗）在体模以及接受门静脉腹部PCD CT检查的患者中对虚拟单能图像和多色图像（T3D）的图像质量及最佳强度水平。材料与方法：在这项回顾性研究中，在充满水的体模中测量噪声功率谱（NPS）。纳入2021年3月至4月间接受门静脉腹部PCD CT检查的连续肿瘤患者。在不使用QIR（QIR关闭；参考标准）以及使用四个强度水平的QIR（QIR 1 - 4；指标测试）的情况下重建60 keV的虚拟单能图像和T3D。测量全局噪声指数、对比噪声比（CNR）以及体素层面的CT衰减差异。对噪声和纹理、伪影、诊断置信度以及整体质量进行定性评估。由四位阅片者对低密度肝病灶的可察觉性进行评分。使用参数检验（方差分析、配对检验）和非参数检验（弗里德曼检验、事后威尔科克森符号秩检验）来比较不同重建方法之间的定量和定性图像质量。结果：在体模中，NPS显示不同重建方法的噪声纹理不变，最大空间频率差异为每毫米0.01。纳入50例患者（平均年龄59岁±16[标准差]；31例女性）。对于60 keV图像，全局噪声指数从QIR关闭到QIR - 4降低了45%，对于T3D降低了44%（两者，P <.001）。肝脏的CNR从QIR关闭到QIR - 4，对于60 keV提高了74%，对于T3D提高了69%（两者，P <.001）。在脂肪和肝脏的平均衰减方面（P =.79 -.84）以及在不同重建方法的体素层面上未发现差异证据。定性地说，对于60 keV和T3D，QIR - 4在每个类别中均优于所有其他重建方法（P值范围，<.001至.01）。所有四位阅片者均将QIR - 4在病灶可察觉性方面评为优于其他强度（P值范围，<.001至.04）。结论：在门静脉腹部光子计数探测器CT中，高强度水平的迭代重建算法（QIR；西门子医疗）通过降低噪声、提高对比噪声比和病灶可察觉性来改善图像质量，而不影响图像纹理或CT衰减值。©RSNA，2022 另见本期中Sinitsyn的社论。
