Objective To investigate the value of the diffusion-weighted imaging(DWI) and apparent diffusion coefifcient(ADC) values in differential diagnosis of cervical lymph node lesions by applying a rage of b values,and try to ifnd an optimal b value of DWI at 3.0T MRI for cervical lymph nodes.Methods Conventional MR imaging was performed in 46 patients with histologically proven by using GE 3.0T scanner.28 cases of malignant(20 cases were metastatic nodes,8 cases were lymphoma),18 cases were benign lymph nodes(12 cases were inflammatory swelling,6 cases were tuberculosis).The lesion detectability of T1WI,T2WI and DWI.ADC values were measured in the lymph node lesions.The b-value of DWI was 0,20,50,100,200,400,600,1,000,1,200,1,400s/mm2 respectively.The SNR,ADC and the discrepancion between the b-value of ADC values of nodes were measured and compared at different b values.We analyzed the correlation between the b-value and ADC or SNR of each image,to determine an optimal b value.The optimal ADC threshold was determined by means of receiver operating characteristic(ROC)curve to differentiate between the malignant and benign lymph nodes.Results 1.When b≤1,000s/mm2,the SNR of DWI increased as the b-value increased,showing an inverse correlation.When b was 1,000s/mm2,the SNR of DWI reached its summit.When b>1,000s/mm2,the SNR of DWI decreased.2.The mean ADC value of the malignant lymph nodes was (0.83±0.19)×10-3mm2/s,the mean ADC value of the benign lymph nodes was (1.57±0.27)×10-3mm2/s.3.The ADC values of benign and malignant lymph nodes decreased as the b-value increased.The maximum difference in ADC between benign and malignant lymph nodes was observed when the b value was 1,000s/mm2.Conclusions For good image quality and valid differentiation between malignant and benign lymph nodes,the optimized b value of DWI at 3.0T for cervical lymph nodes was 1,000s/mm2.%目的探讨多b值弥散加权成像（diffusion-weighted imaging，DWI）及表观弥散系数（apparent diffusion coefifcient，ADC）值对颈部淋巴结病变的鉴别诊断价值，并探讨3.0T MR颈部淋巴结DWI合理的b值取值。方法对46例单侧或双侧颈部淋巴结肿大患者行MRI常规检查及DWI检查，b值分别采用0、20、50、100、200、400、600、1,000、1,200、1,400s/mm2。其中28例为恶性淋巴结（20例为转移性淋巴结，8例为淋巴瘤），18例为良性淋巴结（炎性反应性增生淋巴结12例，结核性淋巴结6例），全部病例均经手术及病理证实。测量并比较不同b值下，良、恶性淋巴结的平均ADC值和图像SNR的变化规律，以确定合适b值；在同一b值下分别比较良、恶性淋巴结的ADC值差异；应用ROC曲线，比较不同b值下ADC值对良、恶性淋巴结的鉴别诊断效能，并确定最佳阈值。结果1.b值≤1,000s/mm2时，DWI的SNR随b值的增加逐渐升高；当b值=1,000s/mm2时，DWI的SNR达到最高峰；当b值＞1,000s/mm2，SNR逐渐下降。2.恶性淋巴结的平均ADC值为（0.83±0.19）×10-3mm2/s，良性淋巴结平均ADC值为（1.57±0.27）×10-3mm2/s，恶性淋巴结平均ADC值明显小于良性淋巴结，两者之间有统计学意义。转移性淋巴结与淋巴瘤，反应增生性淋巴结与结核性淋巴结的平均ADC值之间差异无统计学意义。3.良、恶性淋巴结的ADC值随着b值的增加而下降，当b值取1,000s/mm2，良、恶性淋巴结之间的差异最大（0.65×10-3mm2/s）。结论取b值为1,000s/mm2，既能取得良好的图像质量，又能有效地鉴别淋巴结的良、恶性，是3.0T MR淋巴结最合理的b值取值。
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