宽体探测器CT低剂量扫描在婴幼儿先天性心脏病中的图像质量及辐射剂量研究

The investigation on image quality and radiation dose of low dose wider detector array CT scanning for young children with congenital heart disease

目的 探讨在应用自动管电流调制技术（ATCM）和自动管电压调制技术（CARE kV）行头颈部和胸部CT螺旋扫描时，不同扫描中心对辐射剂量的影响。方法 联合ATCM和CARE kV技术，对头颈部和胸部模体行CT螺旋扫描。头颈部模体选取眼球中心向上4 cm、眼球、眼球与外耳孔连线中点、外耳孔、外耳孔向下5 cm 5种不同的扫描中心（即不同检查床高度），胸部模体选取乳腺向上5 cm和4 cm、乳腺、腋前线、腋中线、腋后线6种不同的扫描中心。每种扫描中心时定位像扫描3次，然后1次螺旋扫描。头颈部模体在眼眶中心及第5颈椎（C5）椎体上缘层面选取感兴趣区（ROI），胸部模体在肺尖及气管分叉层面选取ROI，测量记录对比噪声比（CNR）。用热释光剂量计（TLD）测量每次扫描时眼晶状体和乳腺的器官剂量。记录每次扫描的容积CT剂量指数（CTDIvol）。结果 头颈部模体5种不同扫描中心时，眼晶状体累积辐射剂量最高在眼球与外耳孔连线中点为中心（8.851 mGy），CTDIvol最高在外耳孔向下5 cm为中心（15.850 mGy）。眼晶状体累积辐射剂量最低在外耳孔向下5 cm为中心（7.096 mGy），CTDIvol最低在眼球、眼球与外耳孔连线中点、外耳孔为中心（均为15.380 mGy）。胸部模体6种不同扫描中心时，乳腺累积辐射剂量最高在乳腺为中心（6.467 mGy），CTDIvol最高在腋前线为中心（4.120 mGy）。腋后线为中心上述值最低（分别为4.794和3.540 mGy）。头颈部模体眼眶中心层面、C5椎体上缘层面的CNR分别为87.22~108.88和136.13~175.57；胸部模体肺尖层面、气管分叉处层面的CNR分别为75.19~116.92和42.85~86.78。结论 CT扫描中心的选择对CT扫描部位的辐射剂量，特别是对射线敏感的组织和器官的辐射剂量有很大影响。

Objective To investigate the influence of different scanning centers on the radiation dose of head-neck and chest spiral scanning in CT with automatic tube current modulation（ATCM） and automatic tube voltage modulation（CARE kV）.Methods Combined with ATCM and CARE kV techniques, spiral CT scanning was performed on head-neck and chest phantoms. The head-neck phantom was scanned using 5 different scanning centers, with the levels of 4 cm above the eye, the eye, the midpoint of the eye and the outer ear hole, the external ear hole, 5 cm below the outer ear hole, respectively, according to different heights of check bed. The chest phantom was scanned using 6 different scanning centers with the levels of 5 cm above breast, 4 cm above breast, anterior axillary line,midaxillary line, posterior axillary line, respectively. At each scanning center they were scanned three times of scout and one spiral. ROIs were selected at the slices of orbital center and C5 upper edge level for head-neck phantom, and at the slices of the apical and tracheal bifurcation level for chest phantom. The values of contrast-to-noise ratios （CNRs） were measured and recorded. The organ dose of eye lens and mammary gland were measured with thermoluminescent dosimeters （TLD） for all of scans. The volume CT dose index （CTDIvol） of each scan was recorded.Results With 5 different scanning centers for the head-neck phantom, the maximum eye lens dose appeared at the level of midpoint of the eye and the outer ear hole（8.851 mGy）, while the maximum CTDIvol and minimum eye lens dose at the level of 5 cm below the outer ear hole（15.850 mGy and 7.096 mGy）. With 6 different scanning centers for the chest phantom, the maximum mammary gland dose emerged from the level of breast（6.467 mGy）, while the maximum CTDIvol from the level of the anterior axillary line（4.120 mGy）, the minimum gland dose and CTDIvol from the level of the posterior axillary line（4.794 mGy and 3.540 mGy）. In the head-neck phantom images, the CNR values at the level of orbital center and C5 upper edge were 87.22 to 108.88,136.13 to 175.57 respectively. In the chest phantom images,the CNR values at the level of the apical and tracheal bifurcation were 75.19 to 116.92,42.85 to 86.78 respectively.Conclusions The selection of CT scanning center has great influence on the radiation dose of CT scanning, especially for radiation sensitive tissues and organs.