During shock wave therapy, a determination is made that a kidney stone has begun to fracture, and then to assess a progress of its fragmentation. This determination can reduce the number of shock waves used to disintegrate kidney stones, and thereby reduce dose-dependent tissue damage. The identification of fracture is possible through the detection and analysis of resonant acoustic scattering, which is the radiation caused by reverberations within a stone particle that is struck by a shock wave. The scattering frequency can provide both an indication that the kidney stone has fragmented, and an indication of the relative sizes of the fragments. Related concepts employ displacement measurements of kidney stones/fragments to provide both an indication that the kidney stone has fragmented, and an indication of the relative sizes of the fragments. Such techniques can be combined with vibro-acoustography based gating that better targets the stone.