Abstract： Objective To estimate the applications of ADC value and rADC value in the diagnosis of nodular lesions of breasts.Methods Fifty-two cases with 66 nodular lesions of breasts confirmed by histopathology underwent diffusion-weighted magnetic resonance imaging.Three b values (0,800 and 1000 s/mm2) were applied.The mean ADC values of the breast nodules,the ADC values of ipsilateral breast( rADC1 ) and ADC values of contralateral breast (rADC2 )were respectively measured.The independent-samples t-test and chi-square test were used for statistical analyses.Results Of the 52 patients,there were 18 patients with infiltrating ductal carcinoma and 34 patients with fibroadenoma.50 patients with 64 lesions were examined by DWI.( 1 ) at b = 800 s/mm2,the mean ADC values of malignant nodules [ ( 1.01 ±0.09) × 10-3 mm2/s],rADC800-1 (0.52 ±0.07)and rADC800-2 (0.51 ±0.06) were lower than that of the benign nodules [ ADC value = ( 1.54 ± 0.28 ) × 10 -3 mm2/s,t = 8.217,P ＜ 0.01 ; rADC800-1 =0.77 ±0.15,t =9.339,P＜0.01 ; rADC800-2 =0.76 ±0.14,t = 10.394,P ＜0.01 ].The one-side upper limits of 95％ medical reference value of mean values of infiltrating ductal carcinoma were adopted as the threshold point to distinguish the malignant from the benign.The threshold value of breast malignant nodule ADC,the rADC800-1 and rADC800-2 were respectively 1.05 × 10-3 mm2/s,0.55 and 0.53.The sensitivities of the three methods were 75.0％,65.0％ and 60.0％ ; the specificities were 100.0％,95.7％ and 97.8％ ;the positive predictive values were respectively 100.0％,86.7％ and 92.3％ ; the negative predictive values were 90.2％,86.3％ and 84.9％; the diagnosis accordance rates were respectively 92.4％,86.4％ and 86.4％.( 2 ) at b = 1000 s/mm2,the mean ADC values of malignant nodules [ ( 0.93 ± 0.08 ) ×10-3 mm2/s],rADC1000-1 (0.53 ±0.09) and rADC1000-2 (0.52 ±0.07) were also lower than that of the benign nodules[ ADC value= (1.45 ±0.28) ×10-3 mm2/s,t=11.844,P＜0.01; rADC1000-1 =0.75 ±0.16,t=5.820,P ＜ 0.01 ; rADC1000-2 = 0.74 ± 0.15,t = 8.082,P ＜ 0.01 ].The threshold value points breast malignant nodule ADC,the rADC1000-1 and rADC1000-2 were respectively 0.97 × 10-3 mm2/s,0.58,0.55.The sensitivities were all 70.0％ ; the specificities were respectively 100.0％,95.7％ and 93.5％ ;the positive predictive values were 100.0％,87.5％ and 82.4％ ; the negative predictive values were 88.5％,88.0％ and 87.8％ ; the diagnosis accordance rates were 90.9％,87.9％ and 86.5％ respectively.There were no significant differences in specificities and the diagnosis accordance rates ( x2 = 1.232,2.263 ; P =0.942,0.812 ).Conclusions ADC value and rADC value are both important parameters of MRI in differentiating benign and malignant breast diseases.The study indicated that ADC value ( at b =800 s/mm2) was the most valuable parameter.