The low resolution of diffusion-weighted imaging (DWI) is the main limiting factor in screening breast MRI. Recently a method was proposed for one millimeter isotropic DWI covering the entire breasts. Based on a readout-segmented DW-EPI sequence, 3 stacks of thick slices (3 mm) are acquired with 1mm-shifts in the slice direction; then a 1x1x1 mm3 dataset is obtained using a super-resolution reconstruction (SRR). In this study we further validate the method using a commercial diffusion breast phantom, in terms of SNR, resolution and ADC values. Additionally, SMS acceleration is investigated to reduce the total scan time below 10 min.