基于不同体质量指数CT尿路成像辐射剂量控制

Radiation dose control for CT urography based on different body mass index

目的探讨不同体质量指数患者CT尿路成像扫描参数优化及辐射剂量控制措施。方法按常规参数(3种体型均120 kV,CARE Dose4D)、低kV[体质量指数(BMI)≤22.9:80 kV、22.9<BMI<30∶100 kV、BMI≥30∶120 kV,CARE Dose4D]、低mAs(120 kV,3种体型均在CARE Dose4D基础上mAs降低40%)3种扫描方式前瞻性收集CT尿路成像检查133例,测量各组图像噪声、信噪比(SNR)及对比噪声比(CNR)作为图像质量客观评价指标,主观评价由两名具有5年以上工作经验医师采用双盲法进行5分制评价。记录各组患者CT剂量报告中的容积CT剂量指数(CTDIvol)、剂量长度乘积(DLP),计算有效剂量(E)。结果80、100 kV扫描患者的有效剂量下降了77.7%、38.3%,差异有统计学意义(Z=-3.330、-5.595,P<0.05);80 kV扫描与常规扫描之间肾皮质的噪声、SNR、CNR及输尿管噪声差异有统计学意义(Z=-3.705^-2.392,P<0.05),但输尿管的SNR、CNR及肾盂的噪声、SNR、CNR差异无统计学意义(P>0.05),100 kV扫描与常规扫描之间肾皮质的噪声、SNR差异有统计学意义(Z=-5.096、-3.566,P<0.05),但肾皮质的CNR及肾盂、输尿管的噪声、SNR、CNR差异无统计学意义(P>0.05)。3种体型低mAs扫描的有效剂量较常规扫描分别下降了38.3%、32.0%、34.7%,差异有统计学意义(Z=-5.086、-5.912、-2.842,P<0.05),22.9<BMI<30组输尿管的CNR较常规扫描差异有统计学意义(Z=-2.587,P<0.05),其余肾皮质、肾盂、输尿管的噪声、SNR、CNR差异均无统计学意义(P>0.05);图像主观评价评分均>3分。结论针对不同体质量指数患者所采用的低kV、低mAs扫描方案可以有效降低患者的辐射剂量,并能达到临床诊断要求。

Objective To explore the optimization of CT urography imaging parameters and the control measures of radiation dose to patients with different body mass index.Methods A total of 133 patients who were required to undergo CT urography were prospectively selected in terms of three different types of CT urography scan;firstly,conventional parameter scan(120 kV,CARE Dose4D);secondly,low kV scan(BMI≤22.9∶80 kV,22.9<BMI<30∶100 kV,BMI≥30∶120 kV,CARE Dose4D)and thirdly,low mAs scan(120 kV,40%reduction in mAs on CARE Dose4D).Noise,signal-to-noise ratio(SNR)and contrast-to-noise ratio(CNR)of all images were measured as objective evaluation indicators of image quality.The subjective evaluation of the images was performed by two radiologists who had been working for more than five years using a double-blind method and a 5-score system evaluation.The effective dose values(CTDIvol,DLP,E)in each group were measured.Results Patients′effective dose was decreased by 77.7%in 80 kV group and 38.3%in 100 kV group,with a statistical difference between the two groups(Z=-3.330,-5.559,P<0.05).There was a statistically significant difference in renal cortex noise,SNR,CNR and ureteral noise between the 80 kV scan and the routine scan(Z=-3.705-2.392,P<0.05),but no significant difference in ureteral SNR,CNR and renal pelvis noise,SNR,CNR(P>0.05).There was a statistically significant difference in renal cortex noise and SNR between the 100 kV scan group and the routine scan group(Z=-5.096,-3.566,P<0.05),but no statistical difference in renal cortex CNR,renal pelvis and ureteral noise,SNR,CNR(Z=-5.086,-5.912,-2.842,P>0.05).The effective dose from low mAs scan in the three types of patients was decreased by 38.3%,32.0%,and 34.7%,respectively,with a statistical difference between them(P<0.05).There was no significant difference in noise,SNR,and CNR between renal cortex,renal pelvis and ureter(P>0.05)besides ureteral CNR in the 22.9<BMI<30 group(Z=-2.587,P<0.05).The subjective evaluation scores of all images were greater than 3 points.Conclusions In this study,the scan method for low kV and low mAs used for patients with different body mass index can effectively reduce the radiation dose to patients and meet the requirements of clinical diagnosis.