不同扫描方案对胸部CT成像质量和辐射剂量影响的对照研究

A controlled study on the impacts of different scanning protocols on image quality and radiation dose in chest CT

目的探讨不同扫描方案在胸部CT成像中对影像质量和辐射剂量的影响。方法临床研究:采用随机抽取的模式回顾性分析2023年6月至7月之间行胸部CT检查的患者65例,采用管电压120 kV,同时开启自动管电流调制及Z轴剂量调制技术。入组病例分为高分辨力组(34例)和常规组(31例),扫描方案设置均与模体研究相同。高分辨力组与常规组分别以层厚/间隔1 mm/1 mm及2 mm/1 mm重建横断面肺窗和纵隔窗薄层图像。模体研究:采用管电压120 kV、管电流150 mAs对Catphan500模体进行两种方案的扫描,其中,高分辨力扫描方案采用肺结节(Lung Nodule)扫描模式,螺距1.5,探测器组合16×0.75 mm,常规扫描方案采用体部(Body)扫描模式,螺距0.813,探测器组合16×1.5 mm。对两种扫描方案所得模体图像进行高对比分辨力客观评价。两组均重组5 mm/5 mm冠状面肺窗及横断面纵隔窗图像。将所得图像导入Radimetrics系统,比较两组间的体型特异性剂量估算值(SSDE)、体表敏感器官剂量及扫描时间的差异。在横断面纵隔窗固定解剖部位测量并计算对比度噪声比(CNR)、信噪比(SNR)及品质因数(FOM)。由两名高年资诊断医师对肺窗图像质量进行主观评价。结果模体研究结果表明,高分辨力扫描模式所得图像在XY平面内的空间分辨力比常规扫描模式提高约5%;在Z轴方向上的空间分辨力提高接近20%。临床研究的结果表明,常规组患者的甲状腺剂量、女性患者的乳腺剂量显著高于高分辨力组(t=2.8、2.3,P<0.05)。常规组患者的右侧斜方肌SNR、CNR、FOM值显著高于高分辨力组(t=4.1、5.8,z=4.4,P<0.001)。高分辨力组患者的胸主动脉SNR、CNR、FOM值显著高于常规组(t=3.4、4.4,z=3.4,P<0.001)。高分辨力组临床病例在肺窗横断面、冠状面上影像质量稳定性均有所提升,主观评分均在4分以上,平均分与常规组差异无统计学意义。结论行胸部CT检查时,观察重点为肺野内细节及纵隔时,宜采用高分辨力扫描方案;观察重点为体表软组织时,宜采用常规扫描方案。

Objective To explore and compare the impacts of different scanning protocols on image quality and radiation dose in chest computed tomography(CT)scans.Methods A retrospective analysis was conducted for the data of 65 randomly selected patients who underwent chest CT scans using a tube voltage of 120 kV,the automatic modulation technique for tube current,and z-axis radiation dose modulation at the Emergency Department of our hospital from June to July 2023.The enrolled cases were divided into two groups:the high-resolution group(n=34)and the conventional group(n=31),with the settings for scanning protocols identical to those for phantom scans.For patients in both groups,thin-layer images of the cross-sections in the lung and mediastinal windows were reconstructed using thickness/intervals of 1mm/1mm and 2mm/1mm,respectively.Meanwhile,high-resolution and conventional CT scans were conducted using a Catphan500 phantom under a tube voltage of 120 kV and a tube current of 150 mAs.Of both scanning protocols,the high-resolution CT scan utilized the lung nodule-orientated scanning mode,pitch of 1.5,and a detector combination providing a collimation of 16×0.75 mm.In contrast,the conventional CT scan was performed using the body-orientated scanning mode,pitch of 0.813,and a detector combination providing a collimation of 16×1.5 mm.Then,the high-contrast resolutions of the phantom images obtained using the two scanning protocols were objectively evaluated.Both coronal chest images in the lung window and cross-sectional images in the mediastinal window were reconstructed with a thickness/interval of 5mm/5mm for both groups.Then,the obtained images were imported into the Radimetrics system to compare the body size-specific dose estimation(SSDE),doses to sensitive organs on the body surface,and scanning time of both groups.For the cross-sectional images in the mediastinal window,the contrast-noise-ratio(CNR),signal-to-noise ratio(SNR),and figure-of-merit(FOM)were measured and calculated at the fixed anatomical parts.For the cross-sectional images in the lung window,their quality was subjectively evaluated by two senior diagnostic radiologists.Results The result of phantom scans indicated that high-resolution CT scans yielded images with an approximately 5%increase in the spatial resolution in the xy-plane and a nearly 20%increase in the spatial resolution along the z-axis compared to conventional CT scans.The result of clinical data demonstrated that the conventional group exhibited significantly higher doses to the thyroid and the female breast(t=2.8,2.3,P<0.05),along with notably elevated SNR,CNR,and FOM values of the right trapezius,compared to the high-resolution group(t=4.1,5.8,z=4.4,P<0.001).However,the high-resolution group manifested significantly higher SNR,CNR,and FOM values of the thoracic aorta compared to the conventional group(t=3.4,4.4,z=3.4,P<0.001).In addition,the cross-sectional and coronal images in the lung window of the clinical cases in the high-resolution group exhibited more stable quality,with subjective scores exceeding 4 and the average scores of both groups not statistically significantly different.Conclusions For chest CT examination,high-resolution CT scans are more suitable for observations focusing on the details of the lungs and mediastinum,while conventional CT is more suitable for those centering on soft tissues on the body surface.