A contrast imaging method and related apparatus which provides the ultrasound irradiation of an aqueous medium and the photoemission of sonoluminescence of micro- or nanoparticles dispersed in said aqueous medium, capable of producing, according to the ultrasound conditions used, a light emission spectrum with specific optical peculiarities to highlight a particular cellular region or tissue or organ especially in the oncology field. The contrast agent comprises micro and/or nanoparticles of zinc oxide (ZnO) which range from 1 nm to 500 nm, which allows obtaining, already at a low intensity of US irradiation, without toxicity contraindication, a luminous signal with a characteristic emission spectrum determined by the presence of said semiconductor material, without needing the presence of noble gases, such as Ar and He, which are not biologically present in human tissues.