ISSN 1004-4140
    CN 11-3017/P

    单能量成像联合O-MAR技术在优化金属植入物患者口咽CT图像质量中的价值

    The Value of VMI Imaging Combined with O-MAR Technology in Optimizing Oropharyngeal CT Image Quality in Patients with Metal Implants

    • 摘要:
      目的 探讨联合使用不同keV虚拟单能量成像(VMI)和金属伪影抑制(O-MAR)技术在优化口腔金属植入物患者口咽部CT图像质量中的应用价值。
      方法 模体研究:以Philips IQon Spectral CT临床口咽部扫描方案为基准,对Catphan600模体CTP528模块进行扫描,分别开启和不开启O-MAR重建66 keV、80~160 keV(间隔20keV)单能量图像并测算调制传递函数(MTF)。临床研究:回顾性分析口咽部CT检查55例,其中含高密度伪影25例,低密度伪影30例,分别开启和不开启O-MAR重建常规影像(CI)、66 keV、80~160 keV的单能量图像。选择伪影最严重的层面为伪影层面,相邻不受伪影干扰的层面为参考层面,测算伪影层面兴趣区的伪影系数(AI),伪影层面与参考层面兴趣区的CT值偏差 \Delta A_v ,参考层面兴趣区的绝对对比度(AC)和对比噪声比(CNR)。采用Likert三分量表对图像进行伪影抑制能力、新生伪影情况及伪影抑制区组织可信度等3个维度进行主观评价。
      结果 模体研究:启用O-MAR对MTF值无影响,使用VMI较CI图像的MTF值有约3%小幅降低;O-MAR联合VMI(VMIMAR)使用时,高/低密度伪影的伪影系数和高密度伪影的CT值偏差随能量水平得升高而降低,平均值由CI图像的125.89/192.47和166.04 HU降低到160 keV时的27.61/18.30和10.36 HU。低密度伪影的CT值偏差在100keV时最小为平均−4.35 HU。单独使用VMI时,高/低密度伪影的伪影系数平均数分别在120/160 keV时最低为65.16/125.31,CT值偏差平均值在160 keV时最小为12.87/−46.11 HU。图像的AC/CNR均随能量等级的升高而降低。O-MAR联合VMI使用时,当能量水平达到120 keV后主观评分在3个维度上均达到3分。单独使用VMI时主观评分最高为2分。
      结论 使用VMI联合O-MAR技术可有效降低口腔金属植入物伪影对周围组织观察的影响,选择120 keV左右的VMIMAR图像可兼顾伪影抑制效果和图像对比度。

       

      Abstract: Objective: To explore the application value of the combined use of different keV virtual monoenergetic images (VMI) and metal artifact reduction (O-MAR) technologies to optimize the image quality of oropharyngeal computed tomography (CT) in patients with oral metal implants. Methods: Phantom study based on the clinical oropharyngeal scanning protocol for spectral CT; the CTP528 module of the Catphan600 phantom was scanned. Images at 66 keV and 80−160 keV (20 keV intervals) were reconstructed with and without the O-MAR, and the modulation transfer function (MTF) was measured. Clinical study: A retrospective analysis was conducted on 55 oropharyngeal CT examinations performed using Philips IQon Spectral CT, including 25 cases with high-density artifacts and 30 cases with low-density artifacts. Conventional images (CI), 66keV, and 80−160 keV (20 keV intervals) VMI were reconstructed with and without the O-MAR. The layer with the most severe artifacts was selected as the artifact layer, and the adjacent layer without artifact interference was selected as the reference layer. The artifact index (AI) of the region of interest (ROI) in the artifact layer, CT value deviation of the ROI between the artifact and reference layers, absolute contrast (AC), and contrast-to-noise ratio (CNR) of the ROI in the reference layer were measured. The images were subjectively evaluated in three dimensions using a three-point Likert scale: artifact removal ability, new artifact formation, and tissue credibility in the artifact removal area. Results: Phantom study: Enabling the O-MAR had no effect on MTF values. The MTF values of the VMI images were approximately 3% lower than those of the CI images. When the O-MAR and VMI (VMIMAR) were used together, the artifact coefficient of high/low-density artifacts and the CT value deviation of high-density artifacts decreased with increasing energy levels. The average values decreased from 125.89/192.47 and 166.04 HU in CI images to 27.61/18.30 and 10.36 HU at 160 keV. The CT value deviation of low-density artifacts was the smallest at 100 keV, with an average of −4.35 HU. When VMI was used alone, the average artifact coefficient of high/low-density artifacts was the lowest at 120/160 keV (65.16/125.31), and the average CT value deviation was the smallest at 160 (12.87/−46.11 HU. The AC/CNR ratio of the images decreased with increasing energy levels. When the O-MAR and VMI were used together, the subjective score reached 3 points in all three dimensions when the energy level reached 120 keV. When VMI was used alone, the highest subjective score was 2 points. Conclusion: The combined use of VMI and O-MAR can effectively reduce the impact of oral metal implant artifacts on the observation of surrounding tissues. Selecting VMIMAR images with a virtual energy level around 120 keV balances the artifact removal effect and image contrast.

       

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