儿童颅脑外伤CT扫描参数的优化设置

The Optimization of CT Parameters Settings of Children with Head Injury

目的研究儿童头颅外伤患者CT扫描参数的设置。在不影响影像诊断的前提下,尽可能降低辐射剂量。方法用不同的CT扫描参数对随机分组的小儿进行扫描,有3个变量电压分为120、140kV;毫安状态分为normal、low;层厚分为7、10mm。分别组合成8组不同的扫描参数组。记录各组的辐射计量(权重CT剂量学指数,CTDIW);用CT值的标准差和诊断阳性率作为图像质量的主客观标准进行分析。结果①在自动mA状态下,140KV比120KV剂量平均降低22.7%;降低毫安状态从normal到low可使剂量降低18.1%;选择较大层厚10mm比7mm辐射剂量平均降低19.7%;若同时同向改变参数,辐射剂量最大可减少近50%。②各组之间图像质量的CT值标准差(CTsd)和CT诊断阳性率的差异无显著性意义。结论用高KV、低毫安状态(low)、较大层厚均可以降低辐射剂量,且图像质量对诊断没有影响。因此对于外伤患者建议用140KV、自动mAs的低毫安状态(low)和10mm层厚为最佳扫描方式。

Objective： Investigating CT parameter settings of children with head injury in order to reduce radiation dose as low as possible under the permission of image quality. Methods： Using different parameter groups to scan the children with head injury, three variable parameters were applied： Voltage （120 or 140kV）;the mode of Ampere （normal or low） ; collimation （7 or 10mm）. These parameters could form eight groups of scanning settings;recording the doses of every group （CT dose index weighted, CTDIW）;analyzing the image quality （CT standard deviation,CTsd） and the positive rate of every group. Results：Under the same condition, the radiation dose produced by 140kV was 22.7% less than that produced by 120kV;to choose the status of tube current from the Normal to Low could decrease radiation dose by approximately 18.15;the radiation dose of 10mm collimation reduced 19.7% averagely than those of 7 mm;if higher voltage,smaller tube current and larger collimation are used simultaneously, the totally reduced radiation dose is about 50% without causing obvious damage of CT image quality. The standard deviation of CT value is of no statistical significance,and the positive diagnostic ratios of every parameter group are similar to each other. Conclusion：As to the children with head injury, using the higher KV and the lower status of tube current as well as larger collimation can lead to the lowest radiation dose,and the accuracy of CT diagnosis remains the same.