表观弥散系数值在直肠癌术前分期中的应用

The Value of Diffusion-weighted Magnetic Resonance Imaging in the Staging of Preoperative Primary Rectal Cancer

目的:探讨磁共振弥散加权成像(DWI)的定量指标表观弥散系数(ADC)在直肠癌术前分期中的应用价值。方法:回顾性分析经手术病理证实的直肠腺癌患者34例(突破固有肌层19例为B组,未突破15例为A组),均于术前约一周内行磁共振检查,扫描序列包括T2WI和DWI(b=0,1000s/mm2)。两名医生分析图像,统计分析T2WI区分两组病灶的特异度、敏感度、阴性预测值及阳性预测值。DWI图像上测量并分析两组病灶ADC值是否具有差异,通过ROC分析得出最佳诊断阈值及敏感度和特异度。计算组内相关系数衡量两名医生的测量一致性。采用ROC方法比较ADC与T2WI在病灶是否突破固有肌层诊断方面的差异。结果:T2WI图像上诊断为未突破6例,突破28例,特异度、敏感度、阴性预测值及阳性预测值为40%、100%、100%、67.7%。A组ADC值(1.102±0.173)×10-3mm2/s明显高于B组的(0.880±0.008)×10-3mm2/s(t=4.588,P<0.05),ROC曲线分析获得最佳诊断阈值为0.923×10-3mm2/s,曲线下面积为0.902,敏感度及特异度为84.2%,86.7%。采用配对ROC方法比较ADC值与T2WI区分两组的准确性具有统计学意义(Z=2.025,P<0.05)。结论:与常规T2WI相比,ADC值的应用可提高判断术前直肠癌病灶是否突破固有肌层的特异度。

Purpose： To explore the performance of apparent diffusion coefficient（ADC） value in the T staging of preoperative primary rectal cancer. Methods：MR examination including T2-weighted imaging（T2WI）and diffusion-weighted magnetic resonance imaging（DWI）of 34 surgically resected rectal adenocarcinomas in 33 patients was retrospectively analyzed. Pathological examinations revealed 15 T1-T2（Group A） and 19 T3-T4（Group B） rectal adenocarcinomas. Two experienced radiologists reviewed the images and classified T staging of each tumor on T2-weighted imaging by mutual agreement. The diagnostic sensitivity, specificity, positive predictive value（PPV） and negative predictive value（NPV） of T2 WI for T staging were evaluated based on pathological results. Two experienced radiologists drew regions of interest（ROI） on the DWI images and ADC map to calculate mean ADC value of each tumor, and inter-observer agreement between the two radiologists was calculated. Receiver operating characteristic（ROC） analysis was used to analyze and compare the difference of ADC value and T2 WI in differentiating T1-2 group and T 3-4 group. Results： On T2 WI, the specificity, sensitivity, PPV and NPV was 40%, 100%, 100% and 67.7%, respectively. The mean ADC value of Group A was（1.102±0.173）×10-3mm2/s, which was higher than that in Group B whose mean ADC value was（0.880±0.008）×10-3mm2/s（P〈0.05）, and the inter-observer agreement was perfect, the intra-class correlation coefficient（ICC） was 0.853. The ADC value threshold for differentiating Group A from Group B was 0.923×10-3mm2/s. When the ADC value threshold was used for the diagnosis, the area under curve（AUC） of was 0.902, and the sensitivity was 84.2% and specificity was 86.7%. The difference in T staging between T2 WI and ADC value was with statistical significant（P〈0.05）. Conclusion： ADC value can be used to improve the specificity in judging whether the muscularis propria layer was invasted by the lesion.