QSI was compared against conventional DWI and non-Gaussian diffusion models, namely diffusion kurtosis imaging (DKI) and stretched-exponential model (SEM) to evaluate diffusivity heterogeneity for profiling breast tumour cell diversity. We investigated whole breast tumours excised from surgery, with imaging performed overnight on the same day on a clinical system. Asymmetry in diffusivity distribution was quantified as histogram skewness, median and 25th-percentile. Correlation analysis was performed to compare QSI against other models. The skewness of diffusivity distribution derived from QSI was the highest among the models and provided a wider spread of values across cohort, allowing more sensitive clinical applications.