Cester D, Flohr T, Zanini B, Alkadhi H
Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Switzerland.
Diagnostic and Interventional Radiology, University Hospital Zurich, University of Zurich, Switzerland.
Radiography (Lond). 2025 Aug;31(5):103088. doi: 10.1016/j.radi.2025.103088. Epub 2025 Jul 11.
The purpose of this study was to describe the impact of the latest metal artefact reduction algorithm (MAR) on a photon-counting CT (PCCT) in a phantom study simulating metal hip prostheses.
Two phantoms were scanned on a clinical PCCT with different configurations of laterally placed metal inserts. Acquisitions were performed at 140 kVp and reconstructed as virtual monoenergetic images (VMI) at 60-190 keV in 10-keV steps using a standard abdominal kernel, with and without iterative MAR (iMAR). Artefacts were quantified with the Root Mean Square of the image Difference (RMSD). Image quality was assessed by means of noise properties (noise, NPS), frequency response (TTF) and detectability index (d') and compared with the reference (70 keV VMI, no implants).
increasing VMI energy did not always result in a reduction of artefacts measured by RMSD; the minimum values were always obtain with iMAR, which provided a further 32 % and 60 % best RMSD reduction with two steel and two titanium rods, respectively. Combining low-energy VMI and iMAR resulted in the closest NPS texture to the metal-free reference. The detectability of the high-contrast task with two steel rods decreased by 27-66 % with VMI alone compared to the reference, and by only 8.5 % with iMAR at 70 keV. The detectability with iMAR was never smaller than with VMI alone (within one standard deviation).
iMAR showed better and more consistent noise and artefact reductions compared to VMI technique alone for all configurations. In 10 cases out of 12 the best detectability was observed with a combination of iMAR and VMI at 60 or 70 keV.
iMAR should be activated in the presence of metal hip implants to effectively reduce metal artefacts, particularly in combination with low VMI energies.
本研究的目的是在模拟金属髋关节假体的体模研究中，描述最新的金属伪影减少算法（MAR）对光子计数CT（PCCT）的影响。
在临床PCCT上对两个体模进行扫描，体模带有横向放置的不同配置的金属插入物。扫描在140 kVp下进行，并使用标准腹部内核，在有和没有迭代MAR（iMAR）的情况下，以10 keV步长在60 - 190 keV重建为虚拟单能图像（VMI）。使用图像差异的均方根（RMSD）对伪影进行量化。通过噪声特性（噪声、NPS）、频率响应（TTF）和可检测性指数（d'）评估图像质量，并与参考图像（70 keV VMI，无植入物）进行比较。
增加VMI能量并不总是导致通过RMSD测量的伪影减少；最小值总是通过iMAR获得，对于两根钢棒和两根钛棒，iMAR分别进一步降低了32%和60%的最佳RMSD。低能量VMI和iMAR相结合产生的NPS纹理最接近无金属参考图像。与参考图像相比，仅使用VMI时，两根钢棒的高对比度任务的可检测性降低了27 - 66%，而在70 keV使用iMAR时仅降低了8.5%。iMAR的可检测性从未低于仅使用VMI时（在一个标准差内）。
与单独的VMI技术相比，对于所有配置，iMAR在减少噪声和伪影方面表现更好且更一致。在12个案例中的10个中，在60或70 keV下iMAR和VMI相结合时观察到最佳可检测性。
在存在金属髋关节植入物的情况下应激活iMAR，以有效减少金属伪影，特别是与低VMI能量相结合时。
