Methods and are provided for determining, monitoring or detecting particle size distribution of a medium. An example method includes comparing a measured ultrasound attenuation spectrum of the medium with a calculated attenuation spectrum, where the calculated attenuation spectrum is obtained by accounting for the scattering of ultrasound waves into the receiver. The methods of the present invention can be used to determine particle size distribution in a dense suspension of particles in the intermediate wavelength regime. In other aspects, methods of the present invention may also be used to monitor changes in particle size distribution, infer the shape of particles, provide feedback to a process involving a change in particle size, and determine the completion of a dissolution process.