In Vivo Study of the Influence of CT Acquisition and Reconstruction Parameters on Chest CT Number
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摘要: 目的：探讨不同扫描参数及重建算法对在体胸部各组织CT值的影响。方法：在不同CT扫描条件下测量人体胸部的气管、血管、肺、椎体与肌肉的CT值。分别设定6组不同扫描参数及重建算法：S1层厚5 mm、50％多模型自适应迭代重建技术（ASIR-V）、低剂量；S2层厚5 mm、滤波反投影（FBP）、常规剂量；S3层厚1.25 mm、50％ASIR-V、低剂量；S4层厚1.25 mm、50％ ASIR-V、常规剂量；S5层厚1.25 mm、FBP、低剂量；S6层厚1.25 mm、FBP、常规剂量。扫描的辐射剂量采用两种噪声指数（NI）来进行控制，包括低剂量（NI=40）和常规剂量（NI=10）。采用t检验或秩和检验分析比较不同的两个组之间 CT值的差异。结果：扫描剂量仅对气管CT值的影响具有统计学意义，对其他组织CT值无影响；扫描层厚与重建算法对胸部各个组织CT值的影响均未见统计学差异。结论：人体胸部组织CT值受CT层厚、重建算法和CT剂量的影响小，具有良好的稳定性。Abstract: Objective: To explore the influence of different CT acquisition and reconstruction parameters on the CT number of the chest in vivo. Methods: The CT number of the trachea, blood vessels, lungs, vertebral bodies, and muscles of the human chest were measured under different CT scanning parameters. Six groups of different scanning parameters and reconstruction algorithms were set respectively: slice thickness 5 mm, 50% multi-model adaptive statistical iterative reconstruction Veo (ASIR-V) and low-dose for S1; slice thickness 5 mm, filtered back projection (FBP) and standard-dose for S2; slice thickness 1.25 mm, 50% ASIR-V and low-dose for S3; slice thickness 1.25 mm, 50% ASIR-V and standard-dose for S4; slice thickness 1.25 mm, FBP, low-dose for S5; slice thickness 1.25 mm, FBP, standard-dose for S6. The radiation dose of the scan was controlled using two noise indexes (NI), including low-dose (NI=40) and standard-dose (NI=10). Differences in CT number between two groups were compared using t-test or rank-sum test. Results: Significant differences of CT number of the trachea were detected between low-dose and standard-dose, but no significant differences of CT number of other tissues were detected between low-dose and standard-dose. No significant differences of CT number of chest tissues were detected between either 5 mm thickness and 1.25 mm thickness or 50% ASIR-V and FBP. Conclusion: The CT number of human chest tissues showed well stability which was scarcely influenced by slices thickness, reconstruction algorithm and scan dose.
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Key words:
- CT scan parameters /
- reconstruction algorithms /
- CT number /
- scan dose
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图 1 不同胸部组织在不同序列CT值分布
①气管 CT值在1-6序列中的分布，②血管 CT值在1-6序列中的分布，③肺 CT值在1-6序列中的分布，④椎体 CT值在1-6序列中的分布，⑤肌肉 CT值在1-6序列中的分布；通过对CT值两两比较，发现气管CT值在S5与S6两组的差异具有统计学意义，余各组织各序列相互比较均未见显著统计学差异。
Figure 1. Distribution of CT number measured in different sequences of each tissue
表 1 胸部CT扫描参数及重建方法
Table 1. Chest CT Scanning and reconstruction parameters
序列号 层厚/mm 重建算法 辐射剂量 S1 5.00 50％ ASIR-V 低剂量 S2 5.00 FBP 常规剂量 S3 1.25 50％ ASIR-V 低剂量 S4 1.25 50％ ASIR-V 常规剂量 S5 1.25 FBP 低剂量 S6 1.25 FBP 常规剂量 
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表 2 两名研究者测量CT值一致性检验
Table 2. Interobserver variability test of CT number measured by two doctors
项目 ICC 95％ CI F P S1-气管CT值 0.90 0.83～0.94 19.05 <0.001 S2-气管CT值 0.75 0.59～0.85 6.85 <0.001 S3-气管CT值 0.95 0.91～0.97 39.26 <0.001 S4-气管CT值 0.93 0.87～0.96 25.72 <0.001 S5-气管CT值 0.68 0.49～0.80 5.19 <0.001 S6-气管CT值 0.64 0.44～0.78 4.58 <0.001 S1-血管CT值 0.96 0.93～0.97 23.42 <0.001 S2-血管CT值 0.85 0.74～0.92 6.78 <0.001 S3-血管CT值 0.83 0.71～0.91 6.03 <0.001 S4-血管CT值 0.89 0.80～0.94 8.95 <0.001 S5-血管CT值 0.85 0.73～0.91 6.46 <0.001 S6-血管CT值 0.84 0.71～0.91 6.14 <0.001 S1-肺CT值 0.73 0.52～0.84 3.61 <0.001 S2-肺CT值 0.91 0.84～0.95 11.13 <0.001 S3-肺CT值 0.92 0.86～0.96 12.65 <0.001 S4-肺CT值 0.81 0.66～0.89 5.16 <0.001 S5-肺CT值 0.91 0.84～0.95 10.75 <0.001 S6-肺CT值 0.93 0.88～0.96 118.26 <0.001 S1-椎体CT值 0.99 0.96～0.99 118.26 <0.001 S2-椎体CT值 0.98 0.97～0.99 55.34 <0.001 S3-椎体CT值 0.90 0.83～0.95 10.75 <0.001 S4-椎体CT值 0.90 0.81～0.94 9.26 <0.001 S5-椎体CT值 0.93 0.88～0.96 15.17 <0.001 S6-椎体CT值 0.88 0.78～0.93 8.03 <0.001 S1-肌肉CT值 0.84 0.72～0.91 6.23 <0.001 S2-肌肉CT值 0.87 0.77～0.93 7.77 <0.001 S3-肌肉CT值 0.75 0.56～0.86 3.99 <0.001 S4-肌肉CT值 0.88 0.79～0.93 8.47 <0.001 S5-肌肉CT值 0.80 0.64～0.88 4.90 <0.001 S6-肌肉CT值 0.88 0.79～0.93 8.37 <0.001
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表 3 各部位不同序列测量CT值的分布情况
Table 3. Distribution of CT number measured in different sequences of each tissue
序列 气管 血管 肺 椎体 肌肉 S1 -985.15±7.11 45.58±5.00 -887.22（-897.64～-865.48） 168.44（140.10～215.58） 53.57±5.85 S2 -983.95±7.11 41.94（44.98～49.66） -887.48（-902.30～-866.45） 166.67（138.18～214.14） 53.40（49.62～57.46） S3 -984.57±7.03 44.84±4.80 -884.84±27.11 177.88±50.97 53.83±6.09 S4 -985.93±6.49 45.58±5.41 -893.63（-908.19～-872.49） 178.76±51.34 138.60（165.74～221.41） S5 -981.90±6.81 45.11±4.78 -884.07±28.33 162.20（129.89～213.69） 53.58±6.57 S6 -984.89±6.54 45.52±6.01 -884.09±30.24 179.34±52.86 54.14（49.78～57.23）
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表 4 胸部各组织不同序列CT值比较
Table 4. Comparison of different sequence CT values of chest tissues
组织 S1 vs S3 S2 vs S6 S3 vs S4 S5 vs S6 S3 vs S5 S4 vs S6 z/t P z/t P z/t P z/t P z/t P z/t P 气管 -0.41 0.68 0.69 0.49 1.00 0.32 2.23 0.03 -1.93 0.06 -0.80 0.43 血管 0.75 0.46 -0.72 0.47 -0.98 0.33 -0.38 0.70 -0.28 0.78 0.29 0.78 肺 -0.64 0.52 -0.43 0.66 -0.61 0.54 0.00 >0.99 -0.14 0.89 -0.44 0.66 椎体 0.05 0.96 -0.06 0.95 -0.09 0.93 -0.38 0.70 -0.26 0.79 -0.06 0.96 肌肉 -0.21 0.83 -0.29 0.77 -0.18 0.86 -0.38 0.71 0.19 0.85 -0.11 0.91
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