ISSN 1004-4140
    CN 11-3017/P

    超高分辨力CT腕关节成像适宜曝光参数的选择

    Selection of appropriate exposure parameters for wrist joint imaging using ultra-high-resolution CT

      摘要
    • 摘要: 目的：探讨超高分辨力CT（U-HRCT）腕关节扫描中的适宜曝光参数。方法：以自制弹道明胶与成人手腕骨制成的腕关节模体作为被照体，应用U-HRCT及多层螺旋CT（MSCT）对模体进行曝光：U-HRCT管电压在60~100 kV范围内间隔5 kV变化，管电流在2~10 mA范围内间隔2 mA变化，固定曝光时间对模体进行扫描获取CT图像。MSCT在120 kV及自动管电流调制技术（ATCM）下，对腕关节模体进行常规CT扫描。用热释光剂量计(TLD)对上述两种扫描方案每次曝光时腕关节模体的辐射剂量（取两片测量的平均值）进行测量，并计算品质因数（FOM）。对不同条件下的信噪比（SNR）、对比噪声比(CNR)、背景噪声(SD)、剂量面积乘积（DAP）、入射面空气比释动能（Ka,e）、品质因数（FOM）进行分析，确定最佳的曝光参数。结果：曝光参数选择60 kV和2 mA时，CNR、SNR、DAP和（Ka,e）值最小（分别为3.5、5.4、23.68 mGy·cm2和0.40 mGy），曝光条件选择100 kV和10 mA时，CNR、SNR、DAP和（Ka,e）最大（分别为13.8、18.1、368.75 mGy·cm2和12.21 mGy）。60 kV和2 mA时SD最大为383.8，100 kV和10 mA时SD最小为64.7。FOM因子在70 kV和2 mA时最大为84.3。70 kV和2 mA组的（Ka,e）为0.73 mGy，MSCT的（Ka,e）为5.48 mGy，经计算U-HRCT的（Ka,e）比MSCT降低约86.68%。结论：管电压和管电流的选择对U-HRCT图像质量与辐射剂量影响较大，70 kV和2 mA既能满足临床诊断需求，又能降低受检者的辐射剂量，可作为U-HRCT的推荐扫描参数。

       

      Abstract: Objective To explore appropriate exposure parameters for wrist joint imaging using ultra-high-resolution CT (U-HRCT). Methods Wrist joint models prepared from self-made ballistic gelatin and adult wrist bones were used. U-HRCT and multi-slice spiral CT (MSCT) were applied to expose the models. The tube voltage of U-HRCT varied at 5-kV intervals in the range of 60–100 kV, and the tube current varied at 2 mA-intervals in the range of 2–10 mA. The CT images were obtained by scanning the mold at a fixed exposure time. MSCT was conducted with conventional CT scans of the wrist joint phantom at 120 kV and automatic tube current modulation technology (ATCM). The radiation dose of the wrist joint phantom at each exposure of the two scanning schemes was measured using a thermoluminescence dosimeter (TLD), and the average of the two measurements was used to calculated the quality factor (FOM). The signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), background noise (SD), dose-area product (DAP), incident plane air release energy (Ka,e), and quality factor (FOM) under different conditions were analyzed to determine the optimal exposure parameters. Results When the exposure parameters were selected as 60 kV and 2 mA, the lowest values for CNR, SNR, DAP, and specific release energy of Ka,e were 3.5, 5.4, 23.68 mGy·cm2, and 0.40 mGy, respectively. When the exposure conditions were selected as 100 kV and 10 mA, the highest values for CNR, SNR, DAP and Ka,e were 13.8, 18.1, 368.75 mGy·cm2, and 12.21 mGy, respectively. The maximum SD was 383.8 at 60 kV and 2 mA and the minimum was 64.7 at 100 kV and 10 mA. The maximum FOM factor was 84.3 at 70 kV and 2mA. The Ka,e of the 70 kV and 2 mA group was 0.73 mGy, while that of the MSCT group was 5.48 mGy. After the calculation, the Ka,e of U-HRCT was approximately 86.68% lower than that of MSCT. Conclusion The selection of tube voltage and current had a significant impact on the image quality and radiation dose of U-HRCT. The results suggest that the tube voltage of 70 kV and tube current of 2 mA can not only meet the clinical diagnostic requirements but also reduce the radiation dose of the examinee. Thus, these scanning parameters can be recommended for U-HRCT.

       

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