Differentiation of various malignant breast cancer, eg, invasive ductal carcinoma (IDC) and ductal carcinoma in situ (DCIS), is essential for treatment and management of breast cancer. Moreover, quantitative evaluation of perfusion and diffusion information is useful for the diagnosis, monitoring, and treatment management of breast cancer [1, 2]. Intravoxel incoherent motion (IVIM) analysis with diffusion-weighted images can provide perfusion and diffusion information [3]. However, these overlap with each other, and theoretically there are three diffusion components, ie, perfusion-related diffusion, fast-free diffusion, and slow-restricted diffusion [4]. Therefore, to acquire more detailed information on perfusion and diffusion in breast cancer, we analyzed these three diffusion components using triexponential function. On a 3.0-T MRI, single-shot diffusion echo planar imaging with multiple b-values of 0 to 3000 s/mm² (15 points) was performed in 41 patients with IDC (mean age, 55.8 years; range, 31-85 years) and 7 patients with DCIS (mean age, 52.7 years; range, 41-69 years). The signal intensity at each b-value in the lesion was obtained. Then, we derived perfusion-related diffusion (D_p), fast free diffusion (D_f), and slow restricted diffusion coefficients (D_s) calculated from triexponential function by a two-step approach in which the literature value of the diffusion coefficient of free water at 37 degrees centigrade (3.0×10^-3 mm²/s) was assigned to D_f [5]. In addition, we derived perfusion-related diffusion (D^*) and slow restricted diffusion coefficients (D) using biexponential analysis to compare with triexponential analysis. We compared these parameters between the IDC and DCIS groups.D_s and D were significantly lower in the IDC group than those in the DCIS group (Table 1). These results can be explained by the fact that the cellularity of IDC was increased compared with that of DCIS (Figure 1). D_p of the IDC showed a tendency to be higher, but not significant, than that of the DCIS. This result agreed with the previous report which has demonstrated stronger contrast enhancement in IDC than DCIS because of the higher tumor angiogenesis in IDC [6]. Moreover, there was no significant correlation between D_p and D_s (Table 2), suggesting that D_p and D_s do not necessarily provide the same kind of information. On the other hand, we found a positive correlation between D^* and D. These results indicate that triexponential analysis could extract independent diffusion information better than biexponential analysis.Triexponential analysis makes it possible to noninvasively obtain more detailed information on perfusion and diffusion in breast cancer, thereby assisting in the diagnosis.