ISSN 1004-4140
CN 11-3017/P

基于头颅模体不同扫描模式与噪声指数对内耳CT图像质量和辐射剂量的影响研究

Impact of Different Scanning Modes and Noise Index on Inner Ear CT Image Quality and Radiation Dose

  • 摘要: 目的:探讨不同扫描模式与噪声指数对内耳CT检查的图像质量与辐射剂量的影响研究。方法:①使用64排螺旋CT对头部拟人模体进行扫描,采用逐层(Axial)扫描与螺旋(Helical)扫描2种扫描模式,每组扫描均采用逐渐增加的噪声指数(NI)值(3~6,共21个)。每个NI值的扫描的Helical模式按照两种模式重建图像获得常规Helical组和螺旋伪影矫正重建(IQE)组,可获得3组图像,共采集并重建出63组序列图像。扫描条件为Axial扫描模式转速1S;Helical扫描模式螺距0.531∶1,转速1S,其他扫描参数固定。②记录不同扫描条件下的CTDIvol、DLP并进行辐射剂量的分析。③图像质量比较分为客观和主观评价,分别对3组图像进行客观评价,计算感兴趣区(ROI)的信噪比(SNR)、对比度噪声比(CNR)影像质量因子(FOM)。采用双盲法分别对3组图像以5分制进行主观评价,评价轴位和多平面重组(MPR)的图像边缘对比度、图像层次、噪声、伪影情况,参考FOM值和图像质量获得最佳扫描NI值。结果:①Axial和Helical两种模式辐射剂量比较,两模式CTDIvol,DLP均随NI值增加而减少,CTDIvol差异无统计学意义(F=0.03,P>0.05),但DLP差异存在统计学意义(F=19.78;P<0.05)。②Axial和Helical常规模式与IQE模式下3组图像的软组织SNR、骨组织SNR、CNR、FOM差异存在统计学意义(F=27.92、20.14、15.71、1146.98P<0.05),参考FOM值和主观评价,以NI为4.7的Axial图像质量为最优。结论:64排CT当进行内耳CT扫描(扫描范围≤4 mm)时,采用相近的探测器宽度并采取逐层单次扫描不需要移床获得的薄层图像可进行MPR重组无断层伪影,考虑到辐射剂量和图像质量均优于常规螺旋扫描甚至是IQE扫描,内耳检查NI建议设为4.7作为质量参考水平,可获得较低辐射剂量下的满意的图像质量。

     

    Abstract: Objective: This study investigates the effects of different scanning modes and noise index (NI) on inner ear computed tomography (CT) image quality and radiation dose. Methods: (1) Head anthropomorphs phantoms were scanned using a 64-slice helical CT scanner. Both axial and helical scanning modes were employed, with each mode using progressively increasing NI values (3–6, totaling 21 values). In the helical mode, each NI value was used to reconstruct images in two modes: conventional helical reconstruction and helical reconstruction with spiral artifact correction (IQE). Three groups of images were obtained, each comprising 63 sequential images collected and reconstructed. Axial scanning was performed with a rotational speed of 1 second, a helical scanning pitch of 0.531:1, and a speed of 1 second, whereas the other scanning parameters remained constant. (2) Volume CT dose index (CTDIvol) and dose-length product (DLP) were recorded under different scanning conditions to analyze radiation dose. (3) Both objective and subjective image quality assessments were performed. Objective evaluations were conducted on three image groups, calculating the signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and figure of merit (FOM) for the region of interest (ROI). Subjective evaluations included assessments of image edge contrast, image intensity, axial noise and artifacts, and multiplanar reconstruction (MPR) quality; a double-blinded method with a 5-point scale was used. The optimal NI value was determined based on the FOM values and subjective image quality assessments. Results: (1) In both axial and helical scanning modes, CTDIvol and DLP decreased as NI values increased. No significant difference was observed in CTDIvol (F=0.03, P > 0.05), but a significant difference was noted in DLP (F=19.78, P < 0.05). (2) Statistically significant differences were observed in soft tissue SNR, as well as SNR, CNR, and FOM for bone tissue, between axial and helical conventional modes and IQE mode (F=27.92, 20.14, 15.71, 1146.98, respectively; P < 0.05), Axial imaging with an NI of 4.7 yielded optimal FOM and subjective evaluation scores. Conclusion: For inner ear CT scanning (range ≤4 mm) using a 64-row CT scanner, MPR reconstruction without fault artifacts can be achieved by obtaining thin-layer images through single-layer scanning without bed movement. Considering that the radiation dose and image quality are better than those of conventional spiral scans or even IQE scans, MPR reconstruction without fault artifacts can be performed using 64-row CT. The recommended NI setting for inner ear imaging is 4.7, as it provides satisfactory image quality while minimizing radiation exposure.

     

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