Su Datong, Feng Lei, Jiang Yingjian, Wang Ying
Department of Radiology, Tianjin Medical University General Hospital, Tianjin 300052, China.
Department of Radiology, Tianjin Xiqing Hospital, Tianjin 300000, China.
Zhongguo Fei Ai Za Zhi. 2017 Aug 20;20(8):562-567. doi: 10.3779/j.issn.1009-3419.2017.08.11.
The computed tomography (CT) follow-up of indeterminate pulmonary nodules aiming to evaluate the change of the volume and CT value is the common strategy in clinic. The CT dose needs to considered on serious CT scans in addition to the measurement accuracy. The purpose of this study is to quantify the precision of pulmonary nodule volumetric measurement and CT value measurement with various tube currents and reconstruction algorithms in a phantom study with dual-energy CT.
A chest phantom containing 9 artificial spherical solid nodules with known diameter (D=2.5 mm, 5 mm, 10 mm) and density (-100 HU, 60 HU and 100 HU) was scanned using a 64-row detector CT canner at 120 Kilovolt & various currents (10 mA, 20 mA, 50 mA, 80 mA,100 mA, 150 mA and 350 mA). Raw data were reconstructed with filtered back projection and three levels of adaptive statistical iterative reconstruction algorithm (FBP, ASIR; 30%, 50% and 80%). Automatic volumetric measurements were performed using commercially available software. The relative volume error (RVE) and the absolute attenuation error (AAE) between the software measures and the reference-standard were calculated. Analyses of the variance were performed to evaluate the effect of reconstruction methods, different scan parameters, nodule size and attenuation on the RPE.
The software substantially overestimated the very small (D=2.5 mm) nodule's volume [mean RVE: (100.8%±28%)] and underestimated it attenuation [mean AAE: (-756±80) HU]. The mean RVEs of nodule with diameter as 5 mm and 10 mm were small [(-0.9%±1.1%) vs (0.9%±1.4%)], however, the mean AAEs [(-243±26) HU vs (-129±7) HU)] were large. The ANOVA analysis for repeated measurements showed that different tube current and reconstruction algorithm had no significant effect on the volumetric measurements for nodules with diameter of 5 mm and 10 mm (F=5.60, P=0.10 vs F=11.13, P=0.08), but significant effects on the measurement of CT value (F=34.79, P<0.001 vs F=156.14, P<0.001).
CONCLUSIONS: An infinitesimally small errors of volumetric measurement of 5 mm or 10 mm nodule could achieved with very low current and ASIR reconstruction, suggesting a possibility of remarkable radiation dose reductions, while it is not applicable for 5 mm nodule. The attenuation acquired through three dimensional software has large measurement error and can not applied in clinical currently. .
针对肺内不确定结节进行计算机断层扫描（CT）随访以评估其体积和CT值变化是临床常用策略。除测量准确性外，在频繁的CT扫描中还需考虑CT剂量。本研究目的是在双能CT模体研究中，量化不同管电流和重建算法下肺结节体积测量及CT值测量的精度。
使用64排探测器CT扫描仪，在120千伏及不同电流（10毫安、20毫安、50毫安、80毫安、100毫安、150毫安和350毫安）条件下，对包含9个已知直径（D = 2.5毫米、5毫米、10毫米）和密度（-100HU、60HU和100HU）的人工球形实性结节的胸部模体进行扫描。原始数据采用滤波反投影及三级自适应统计迭代重建算法（FBP、ASIR；30%、50%和80%）进行重建。使用商用软件进行自动体积测量。计算软件测量值与参考标准之间的相对体积误差（RVE）和绝对衰减误差（AAE）。进行方差分析以评估重建方法、不同扫描参数、结节大小和衰减对相对体积误差的影响。
软件对非常小（D = 2.5毫米）的结节体积显著高估[平均RVE：（100.8%±28%）]，对其衰减低估[平均AAE：（-756±80）HU]。直径为5毫米和10毫米结节的平均RVE较小[（-0.9%±1.1%）对（0.9%±1.4%）]，但平均AAE较大[（-243±26）HU对（-129±7）HU]。重复测量的方差分析表明，不同管电流和重建算法对直径5毫米和10毫米结节的体积测量无显著影响（F = 5.60，P = 0.10对F = 11.13，P = 0.08），但对CT值测量有显著影响（F = 34.79，P < 0.001对F = 156.14，P < 0.001）。
采用极低电流和ASIR重建可实现5毫米或10毫米结节体积测量的极小误差，提示有显著降低辐射剂量的可能性，但不适用于2.5毫米结节。通过三维软件获取的衰减测量误差较大，目前不能应用于临床。
