Extracting quantitative microstructure information of living-tissue by non-invasive imaging is an outstanding challenge for understanding disease mechanisms. We introduce a method to make selectively images of microstructure-sizes by probing molecule diffusion with MRI. It relies on designing dynamical control of nuclear spins to sense magnetization “decay-shifts” rather than the commonly used spin-echo decay-rates. The feasibility and performance of the method are illustrated with proof-of-principle experiments and simulations on typical size-distributions of white-matter in the mouse brain. These results position spin-echo decay-shifts as a promising MRI tool to perform non-invasive histology without assuming a microstructure distribution model.