64排螺旋CT腹部血管成像低剂量扫描的可行性研究

Feasibility study of low-dose scan in 64-slice spiral CT abdominal angiography

目的 探索腹部血管成像64排螺旋CT低剂量扫描的可行性和合理性.方法 采用120 kV、200～30 mAs之间每次降低10 mAs的条件进行模体测试图像采集,测量其CT值的标准差（SD）、高对比密度分辨率与低对比密度分辨率,分析三者与扫描所用mAs值的联系,找到3个mAs值进行临床病例分析.随机选取90例行腹部血管检查的患者平均分为3组,采用以上mAs值进行图像采集,进行平扫常规剂量SD值测量,并对增强低剂量扫描进行三维容积重建（VR）,再由3名CT诊断医师采用盲法评价进行VR图像质量评估,按优、中、差3个等级进行评定.3组平扫SD值与腹部血管成像VR图像进行质量相关性分析.结果 3组平扫SD值与腹部血管成像VR图像的质量相关性分析ROC曲线下面积分别为0.921、0.906、0.893.结论 腹部血管成像低剂量扫描切实可行,80 mAs可以较好地保证图像质量.在平扫SD值小于5.78时增强扫描可以采用60 mAs,而当平扫SD值大于11.8时增强扫描最好采用100 mAs或更高的mAs值.

Objective To explore the feasibility and reasonable of low-dose scan on abdominal angiography in 64-slice spiral helical CT. Methods Phantom test： at 120 KV and from 200 mAs to 30 mAs at an interval of 10 mAs in each image acquisition, it was measured standard deviation （SD） of CT number, high contrast resolution and low contrast resolution, and then analyzed the relationship between the three parameters and the mAs values. Three mAs values were chosen to undertake clinical analysis.Clinical analysis： 90 randomly selected objects with abdominal angiography were divided into three groups,scanning with above three mAs values.Measurement of the SD value at the plain scan images was performed and the enhanced low-dose scan images were used post-processing with three-dimensional volume reconstruction （VR）. The VR images were classified into three grades （excellent, moderate, bad） with the blind evaluation of three CT radiologists. The quality-correlation analysis was used between the standard deviation （SD） values of plain scan image and abdominal angiography VR image. Results According to the quality-correlation analysis between the standard deviation （SD） value of plain scan image and abdominal angiography VR image, the area under curve in receiver-operated characteristic （ROC） analysis was 0.921, 0.906 and 0.893 in each three group, respectively. Conclusions The low-dose scan of abdominal angiography is feasible. 80mAs can ensure better image quality. The enhanced scan probably can use 60mAs when the SD value is less than 5.78 in the plain scan; but when the SD value of plain scan is greater than 11.8, the enhanced scan is used best 100 mAs or higher.