Objective To observe the differential diagnostic value on benign and malignant lung lesions by DWI with different b values. Methods Seventy-one patients with pulmonary lesions underwent conventional MRI and DWI. ADC values of the lesions were measured at b = 300 s/mm2, 500 s/mm2 and 800 s/mm2, respectively. All lesions were divided in malignant and benign lesions according pathological or clinical diagnosis. ADC of benign and malignant lesions at the same b value and different b value of malignant and benign lesions were compared. Threshold ADC values and area under the ROC curve with the various b values were ascertained and the sensitivity, specificity, accuracy, positive predictive value and negative predictive value were calculated. Results Fourty-seven lesions were malignant, 24 were benign. The mean ADC values of malignant lesions were statistically lower than that of benign lesions with various b values (all P<0. 05). There were different mean ADC values with various b values in malignant and benign lesions. The b values increased with the decreased of the mean ADC values (all P<0. 05). The area under the ROC of the ADC values with b=300, 500, 800 s/mm2 was 0. 79, 0. 84, 0. 83, respectively. Therefore the diagnostic efficiency was the highest when the b value was 500 s/mm2 and the threshold of ADC value was 1. 50 X 10-3 mm2/s. The sensitivity, specificity, accuracy, positive predictive value and negative predictive value in differential diagnosis of benign and malignant lung lesions was 91.49%, 75.00%, 85. 92%, 87. 76% and 81. 82%, respectively. Conclusion With various b values (300, 500 and 800 s/mm2), the mean ADC value can be used to distinguish benign and malignant pulmonary diseases. When the b value is 500 s/mm2, the diagnostic efficiency is the highest.%目的 评价不同b值下DWI鉴别肺部良、恶性病变的价值.方法 对71例肺部肿块或结节行常规MRI和DWI检查,分别测量b值为300、500、800 s/mm2时的病变表观扩散系数(ADC)值,比较同一b值下良、恶性病变及不同b值下良、恶性病变的ADC值的差异.根据ROC曲线确定各个b值下的ROC曲线下面积及诊断阈值,并计算各个阈值下的敏感度、特异度、准确率、阳性预测值、阴性预测值.结果 71例中,恶性病变47例,良性病变24例.不同b值下恶性病变的平均ADC值均明显小于良性病变,差异均有统计学意义(P均＜0.05).恶性、良性病变的平均ADC值在不同b值时各不相同,随着b值的增大而减小,差异均有统计学意义(P均＜0.05),b值取300、500、800 s/mm2时,曲线下面积分别为0.79、0.84、0.83;其中b=500 s/mm2时诊断效能最高,ADC阈值为1.50×10-3mm2/s,鉴别诊断肺部良、恶性病变的敏感度、特异度、准确率、阳性预测值、阴性预测值分别为91.49％、75.00％、85.92％、87.76％、81.82％.结论 b值取300、500、800 s/mm2,ADC值均有助于肺部良、恶病变的鉴别诊断,其中b值取500 s/mm2时诊断效能最高.
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