1. A method for characterizing ultrasound scatterers in a medium, the scatterers including red blood cells and clusters of red blood cells in blood, the method comprising: detecting in vivo ultrasound data from a pulser-receiver and a wideband ultrasound transducer representing a region of interest comprising a plurality of scatterers in a medium, the plurality of scatterers including clusters of scatterer sub-units being clusters of red blood cells, the scatterers having a physical property value to be estimated and the scatterer sub-units having at least one known physical parameter value; modelling a backscatter coefficient of the ultrasound data using an at least second order function based on a Taylor expansion of a frequency dependence of a structure factor, the frequency dependence of the structure factor being related to a Fourier transform of a pair correlation function in a system of scatterers, the pair correlation function defining a probability of finding a scatterer at a determined distance from another scatterer; estimating the physical property value of the scatterers from ultrasound data as modelled and the at least one known physical parameter of the scatterer sub-units by a fitting regression of the backscatter coefficient as a function of frequency; and monitoring red blood cell aggregation in blood from the physical property value.