64层螺旋CT低剂量扫描检测肺小结节敏感性的实验研究

目的 探讨64层螺旋CT胸部低剂量扫描对大小、密度不同肺小结节的检测敏感性及最优扫描参数. 方法 制作3组不同密度(软组织密度、较低密度、磨玻璃密度)、直径13～2.5 mm的人工肺结节,置于组织等效胸部模型中,使用Philips Brilliance 64层CT机以常规剂量(管电压120 kV,管电流250 mAs)和低剂量(管电压120 kV,管电流50、30 mAs和21 mAs)分别扫描.测量、记录剂量指标(CTDIw和DLP)、模型各部位CT值、CT值标准差,评估各组结节的可见度. 结果 64层螺旋CT采用低剂量扫描(21～50 mAs)的辐射剂量为常规剂量(250 mAs)的8%～20%.不同扫描剂量条件下模型各部位CT值差异无统计学意义(P>0.05);而CT值标准差差异有统计学意义(P<0.001)且随电流降低而增加.各组结节中仅2.5 mm和4 mm磨玻璃密度(-600 HU左右)结节在管电流21 mAs扫描时出现不可见情况. 结论 64层螺旋CT实验条件下30 mAs低剂量扫描最小直径2.5 mm磨玻璃密度结节,是最优扫描参数.

Experimental Study of Sensitivity in Pulmonary Nodules Detection with Low-dose 64-slice Spiral CT

Objective To evaluate the sensitivity and optimized scanning parameter of 64-slice spiral CT in detection of pulmonary nodules with different size and density. Methods Three groups of prosthesis nodules with diameter of 2.5～13 mm and different density (soft-tissue, low density, and ground glass opacity,GGO)were taken into the chest phantom equivalent to human tissue,then scanned with Philips Brilliance 64 scanner in standard dose(tube voltage:120 kV, tube current: 250 mAs)and low-dose(tube voltage:120 kV, tube current: 50, 30,and 21mAs) respectively. The radiation dose(CTDIw and DLP) of the scans, Hounsfield unit(HU) and standard deviation(SD) of CT values in different regions of the phantom, and visibility of the nodules was assessed and recorded.Results The radiation dose of 64-slices spiral CT scanning in low-dose(tube current 21～51 mAs) decreased to 8%～20% of which scanning in standard-dose(250 mAs). There was no statistical difference between the CT values in different regions of the phantom (P>0.05), while the SD of CT values was of statistical significantce (P<0.001) and SD increased with the increment of the density under different scanning parameters. None of the nodules besides of GGO nodules with 2.5 mm and 4 mm in size scanned at 21 mAs was invisible. Conclusion GGO nodules of 2.5 mm in diameter can be detected with 64-slice spiral CT using 30 mAs at experimental study, which might be the optimized dose for detecting pulmonary nodules.