锥形束CT和多层螺旋CT对寰枢椎成像的辐射剂量和图像质量差异研究

Study on radiation dose and image quality differences between cone-beam CT and multi-slice spiral CT for atlantoaxial spine imaging

目的比较锥形束CT(CBCT)和多层螺旋CT(MSCT)应用于寰枢椎成像的检查剂量和成像质量的差异。方法使用普兰梅卡CBCT扫描仪的30种曝光条件和东芝320排MSCT的15种曝光条件对头颈部体模进行扫描。基于蒙特卡罗算法剂量评价软件PCXMC计算CBCT的有效剂量(E);以剂量长度乘积(DLP)乘以成人颈部特异性转换系数得到MSCT的E值。两独立样本的t检验或Wilcoxon秩和检验用于比较两种成像方式的辐射剂量和主、客观图像质量。采用双盲法对图像的边缘清晰度、对比度、软组织层次、伪影进行5分制主观评分,测量感兴趣区(ROI)的信号与噪声,计算对比信噪比(CNR)。结果 CBCT容积剂量指数、E值分别为2.9 mGy、27.61 μSv,均低于MSCT的8.8 mGy、433.16 μSv,差异有统计学意义(z=-3.05、-5.25,P<0.05);CBCT组的噪声和CNR分别为27.74 HU和3.69,MSCT组为7.84 HU和27.1,差异有统计学意义(z=-5.39、-5.42,P<0.05);CBCT组的总体图像质量、对比度、伪影评分分别为3.5、3.0、5分,均高于MSCT组2.0、2.0、4.0分,差异有统计学意义(z=-2.32、-2.46、-3.31,P<0.05)。结论寰枢椎CBCT和MSCT扫描均可获得满足诊断要求的图像质量,与MSCT相比,CBCT寰枢椎扫描有效地降低了辐射剂量,符合辐射防护最优化原则。

Objective To compare the differences in radiation dose and image quality between cone-beam CT(CBCT)and multi-slice spiral CT(MSCT)applied to atlantoaxial spine imaging.Methods Head and neck phantom was scanned at 30 exposure parameter combinations using Pramerica CBCT scanner and 15 parameter combinations using Toshiba 320-row MSCT.The effective dose(E)of CBCT was calculated based on the Monte Carlo dose estimation software PCXMC,the E value of MSCT was obtained by multiplying the dose length product(DLP)by the related factor.t-test for two independent samples or Wilcoxon rank sum test were used for comparison of radiation dose and subjective and objective image quality between two modalities.The subjective evaluation was a 5-point subjective scale using double-blind method for edge sharpness,contrast,soft tissue level,and artifacts of the images.The signal and noise in the region of interest(ROI)were measured and the contrast signal-to-noise ratio(CNR)was calculated.Results For radiation dose,the volumetric dose index and E values of 2.9 mGy and 27.61μSv for CBCT were lower than those of 8.8 mGy and 433.16μSv for MSCT,and the differences were statistically significant(z=-3.05,-5.25,P<0.05).For objective evaluation of image quality,the noise and CNR were 27.74 HU and 3.69 in CBCT group,7.84 HU and 27.1 in MSCT group.The difference between them were statistically significant(z=-5.39,-5.42,P<0.05).The overall image quality,contrast and artifact scores of the CBCT group were 3.5,3.0 and 5 were higher than those of the MSCT group at 2.0,2.0,and 4.0,respectively(z=-2.32,-2.46,-3.31,P<0.05).Conclusions Both atlantoaxial CBCT and MSCT scans provide image quality that meets diagnostic requirements.Compared to MSCT,CBCT atlantoaxial scans can effectively reduce radiation dose according to the principle of optimization of radiation protection.