头部体模扫描试验对成人头颅CT低剂量扫描的优化初探

目的：通过对头部体模扫描试验,探讨成人头颅CT低剂量扫描参数。方法：以层厚10 mm,扫描时间为1 s,通过改变mA值,以10 mA为间隔,20-300 mA间29个不同mA条件对头部体模进行轴向扫描,对容积CT剂量指数（CTDIvol）、噪声（SD）和对比-噪声比（CNR）进行客观评价分析与统计学处理,对图像低密度分辨力进行主观评价。结果：①CTDIvol随mAs增大而增大,呈线线关系;与300 mAs的CTDIvol（42 mGy）比较,80-150 mAs的CTDIvol（11-21 mGy）下降73%-50%。②SD值随mAs升高而降低;SD值随mAs变化曲线可分为SD改变非常显著段（20-50 mAs）、显著段（50-80 mAs）、缓坡段（90-150 mAs）和平缓段（160-300 mAs）。③CNR随mAs改变与SD值改变相反。④SD值与CNR统计学处理：20 mAs与30 mAs、30 mAs与50 mAs5、0 mAs与80 mAs、80 mAs与150 mAs、150 mAs与300 mAs的各SD值及CNR有统计学差异（P〈0.05）;160-300 mAs的各SD值与CNR无统计学差异（P〉0.05）。⑤图像LCR主观评价：20-50 mAs,分辨低密度圆柱体困难;50-80 mAs,主观图像质量明显下降,图像对诊断有影响;90-150 mAs主观图像质量有一定改变;160-300 mAs主观图像质量改变不明显。结论：80-150 mAs为低对比要求较高的成人颅脑低剂量平扫可用区间,为临床降低扫描剂量提供了依据。临床患者检查,可以用100 mAs进行平扫,CT剂量指数明显降低。

Optimization of parameters for low-dose nonenhanced adult head CT scanning:a head phantom study

Objective：To develop optimized acquisition parameters for low-dose CT of the adult head.Methods：A head phantom was scanned with the following parameters：slice thickness,10mm;scanning time,1s,tube current,20-300mA at each 10mA interval.The CT dose volume index（CTDIvol）,the imaging noise（SD,standard deviation of CT number） and contrast-to noise-ratio（CNR） were measured and analyzed statistically.The low contrast resolution（LCR） was assessed subjectively.Results：①The CTDIvol was linearly increased according to the rise of tube current.The CTDIvol values were 42mGy at 300mAs,21mGy at 150mA,11mGy at 80mA.②The SD value was reduced by increasing tube current.The SD-mAs curve was extremely steep downward in segment 20-50mAs,steep downward in segment 50-80mAs,transitional in segment 90-150mAs,and flat in segment 160-300mAs.③CNR was increased according to the rise of mAs.④CNR was significantly（P0.05） increased with the descent of SD value of 20-30mAs,30-50mAs,50-80mAs,80-150mAs,and 150-300mAs,however,CNR was not significantly increased（P0.05） with the descent of SD value of w 160-300mA.⑤In terms of subjective assessment of LCR,it was difficult to differentiate the low density cylinders at 20-50mAs.Subjective image quality was obviously decreased and the diagnosis of head diseases could be significantly influenced between 50 and 80mAs.Subjective image quality was decreased to a certain degree between 90 and 150mAs,while degradation of subjective image quality wasn＇t found at 160-300mAs.Conclusion：80-150mAs is optimized acquisition parameter for low-dose unenhanced CT scan of the adult head,providing diagnostic quality with reasonable radiation dose for the patients in clinical practice.The CTDIvol can be remarkably reduced with 100mAs in clinical examination.