扩散加权成像b值大小对肝脏良恶性病变的鉴别诊断价值

目的探讨不同b值情况下扩散加权成像ADC值对肝脏良恶性病变的鉴别诊断价值。方法 76例肝占位性病变、11例肝硬化病人行CT及MRI平扫加增强,DWI扫描,选取3种b值（300,500,700s/mm2）各扫描1次,测量正常肝脏及肝硬化肝脏的ADC值。同时测量病灶及相同层面的肝右叶无病灶肝实质ADC值,比较正常肝脏及肝硬化肝脏在3种b值时ADC值有无显著性差异,良恶性病变的ADC值及病灶与周围肝组织ADC值比值有无显著性差异。正常对照组30例,CT或MRI检查肝脏未见异常改变,肝功能化验各项指标均正常,CT和MR、DWI扫描方法同上。应用2个独立样本的Wilcoxon秩和检验进行统计学分析,比较良、恶性病变的ADC值是否有显著性差异。结果 76例肝脏占位性病变,恶性肿瘤25例,其中肝细胞肝癌13例,转移瘤10例,胆管细胞癌2例;良性病变51例,其中海绵状血管瘤23例,肝囊肿18例,肝脓肿7例,局灶性结节增生（FNH）3例。3种b值下正常肝脏的ADC值无显著性差异;正常肝脏与肝硬化的ADC值比较无显著性差异;恶性肿瘤ADC值明显低于良性病变,统计学上有显著差异（P〈0.05）,b=300时,以1.6×10-3mm2/s为阈值,鉴别良恶性病变的敏感性、特异性和准确性分别为71.4%、80.6%和76.9%;b=500时,以1.65×10-3mm2/s为阈值,分别为95.0%、78.1%和73.1%;b=700时,以1.41×10-3mm2/s为阈值,分别为90%、77.5%和77.5%;恶性、良性病变病灶ADC/肝脏ADC比值比较具有显著性差异,P〈0.05;以病灶与肝脏ADC的比值小于1.0为阈值,b=300时,诊断恶性病变的敏感性、特异性和准确性分别为60.0%、81.8%和73.6%;b=500时,分别为65.0%、86.1%和78.6%;b=700时,分别为75.0%、94.9%和88.1%。肝脓肿的ADC值变化较大,波动范围0.98～2.61×10-3mm2/s。结论肝脏恶性肿瘤的ADC值显著低于良性病变,恶性病灶与周围肝实质ADC值比值低于良性病变比值,取b=500,以ADC值1.65×10-3mm2/s为阈值,敏感性和特异性较高。但良恶性病变的ADC值仍有部分重叠,肝脓肿的ADC值变化差异较大,需结合常规MRI检查及临床症状和实验室检查。

B value selection of diffusion-weighted MR imaging in differentiating malignant and benign liver lesions

Objective：To evaluate the diagnostic value of diffusion-weighted imaging（DWI） in differentiating malignant and benign liver lesions by using different b values.Materials and Methods：Seventy-six consecutive patients with liver mass and eleven patients with liver cirrhosis were recruited and underwent CT and MR scans.DWI was performed on a 1.5 T MR scanner in all patients using three b values（300,500,700 s/mm2）.Thirty normal patients were recruited as control group.Apparent diffusion coefficient（ADC） values of the mass were calculated on the workstation and compared between malignant and benign lesions using two independent sample Wilcoxon rank sum test.Results：25 cases were diagnosed as malignant tumors including 13 cases of hepatocellular carcinoma,10 cases of metastasis,2 cases of cholangiocellular carcinoma;Fifty-one patients were diagnosed as benign lesions including 23 cases of cavernous hemangioma,18 cases of cyst,7 cases of abscesses,3 cases of focal nodular hyperplasia.The ADC values and the ratio of ADC of lesion/liver parenchyma of malignant lesions were significantly lower than those of benign lesions（p0.05）.The sensitivity,specificity and accuracy were 71.4%,80.6% and 76.9%,95.0%,78.1% and 73.1%,90.0%,77.5% and 77.5% respectively when b=300,500 and 700 by using a threshold ADC of less than 1.60,1.65,1.41×10-3 mm2/s respectively.The sensitivity,specificity and accuracy were 60.0%,81.8% and 73.6%,65.0%,86.1% and 78.6%,75.0%,94.9% and 88.1% respectively by using a threshold ADC ratio of lesion/liver less than 1.0.Liver abscesses had various ADC values ranging from 0.98 to 2.61×10-3 mm2/s.Conclusion：The ADC values and the ratios of ADC of lesion/liver parenchyma of malignant lesions were significantly lower than those of benign lesions.The differentiating diagnostic value is more effective when b=500 is used.But the ADC values were overlapping between the malignant and benign liver lesions.Liver abscesses had various ADC values and should be diagnosed by combining with clinical and laboratory examinations.