[en] We evaluated the usefulness of diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) value in characterizing breast tumors. One hundred and two female subjects (112 lesions, 86 malignant, 26 benign) with histopathologically proven breast tumors underwent 1.5 T magnetic resonance (MR) imaging including DWI. We classified tumors as benign tumors, noninvasive ductal carcinoma (NIDCs), and invasive ductal carcinoma (IDCs) and evaluated the distribution patterns of high signal on DWI for each group. We also calculated the ADC values of the breast tumors to investigate the difference in mean ADC values between benign and malignant tumors; among benign tumors, NIDCs, and IDCs; and among the histological types. P<0.05 was considered statistically significant. The distribution patterns of high signal on DWI were inhomogeneous in a number of benign tumors and IDCs, but spotty or nodular in NIDCs. The mean ADC value of benign tumors was 1.31±0.36 x 10^-3 mm²/s; of malignant tumors, 0.84±0.31 x 10^-3 mm²/s; of IDCs, 0.82±0.33 x 10^-3 mm²/s; and of NIDCs, 0.89±0.20 x 10^-3 mm²/s. There were significant differences between benign and malignant tumors and among benign tumors, NIDCs, and IDCs. The mean ADC value of papillotubular types was 0.86±0.30 x 10^-3 mm²/s; of scirrhous types, 0.71±0.20 x 10^-3 mm²/s; and of solid-tubular types, 0.76±0.21 x 10^-3 mm²/s; that of papillotubular types was significantly higher than that of scirrhous types. The distribution patterns of high signal on DWI and ADC values were useful for characterizing the breast tumors. (author)