Leng Shuai, Shiung Maria, Duan Xinhui, Yu Lifeng, Zhang Yi, McCollough Cynthia H
From the Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905.
Radiology. 2015 Jul;276(1):184-90. doi: 10.1148/radiol.15142160. Epub 2015 Feb 25.
To develop software to automatically calculate size-specific dose estimates (SSDEs) and to assess the effect of variations in water-equivalent diameter (Dw) along the z-axis on SSDE for computed tomographic (CT) examinations of the torso.
In this institutional review board-approved, HIPAA-compliant, retrospective study, a software program was used to calculate Dw at each image position in 102 consecutive CT examinations of the combined chest, abdomen, and pelvis. SSDE was calculated by multiplying the size-dependent conversion factor and volume CT dose index (CTDIvol) at each image position. The variations in Dw along the z-axis were determined for six hypothetical scanning ranges: chest alone; abdomen alone; pelvis alone; chest and abdomen; abdomen and pelvis; and chest, abdomen, and pelvis. Mean SSDE was calculated in two ways: (a) from the SSDE at each position and (b) from the mean CTDIvol over each scan range and the conversion factor corresponding to Dw at the middle of the scan range. Linear regression analysis was performed to determine the correlation between SSDE values calculated in these two ways.
Across patients, for scan ranges 1-6, the mean of the difference between maximal and minimal Dw within a given patient was 5.2, 4.9, 2.5, 6.0, 5.6, and 6.5 cm, respectively. The mean SSDE values calculated by using the two methods were in close agreement, with root mean square differences of 0.9, 0.5, 0.5, 1.4, 1.0, and 1.1 mGy or 6%, 3%, 2%, 9%, 4%, and 6%, for the scan ranges of chest; abdomen; pelvis; chest and abdomen; abdomen and pelvis; and chest, abdomen, and pelvis, respectively.
Using the mean CTDIvol from the whole scan range and Dw from the image at the center of the scan range provided an easily obtained estimate of SSDE for the whole scan range that agreed well with values from an image-by-image approach, with a root mean square difference less than 1.4 mGy (9%).
开发一款软件，用于自动计算特定尺寸剂量估计值（SSDEs），并评估在体部计算机断层扫描（CT）检查中，水等效直径（Dw）沿z轴的变化对SSDE的影响。
在这项经机构审查委员会批准、符合健康保险流通与责任法案（HIPAA）的回顾性研究中，使用一个软件程序来计算102例连续的胸部、腹部和骨盆联合CT检查中每个图像位置的Dw。通过将每个图像位置的尺寸相关转换因子与容积CT剂量指数（CTDIvol）相乘来计算SSDE。针对六个假设的扫描范围确定Dw沿z轴的变化：仅胸部；仅腹部；仅骨盆；胸部和腹部；腹部和骨盆；胸部、腹部和骨盆。以两种方式计算平均SSDE：（a）根据每个位置的SSDE；（b）根据每个扫描范围内的平均CTDIvol以及与扫描范围中间位置的Dw相对应的转换因子。进行线性回归分析以确定这两种方式计算的SSDE值之间的相关性。
在所有患者中，对于扫描范围1 - 6，给定患者内最大Dw与最小Dw之间差异的平均值分别为5.2、4.9、2.5、6.0、5.6和6.5厘米。使用两种方法计算的平均SSDE值高度一致，对于胸部、腹部、骨盆、胸部和腹部、腹部和骨盆、胸部、腹部和骨盆的扫描范围，均方根差异分别为0.9、0.5、0.5、1.4、1.0和1.1 mGy，或分别为6%、3%、2%、9%、4%和6%。
使用整个扫描范围的平均CTDIvol以及扫描范围中心图像的Dw，可以轻松获得整个扫描范围的SSDE估计值，该值与逐图像方法得到的值高度一致，均方根差异小于1.4 mGy（9%）。
