A microwave imaging system comprising: a microwave antenna array comprising a transmitting antenna and a plurality of receiving antennas, wherein the transmitting antenna is configured to transmit microwave signals over a range of frequencies so as to illuminate a body part of a patient and the receiving antennas are configured to receive the microwave signals following scattering within the body part and acquire data representing the received microwave signals affected by scattering arising from objects within the body part; and a processor; characterised in that the processor is configured to: process the acquired data to determine a plurality of sets of scattering parameters for a plurality of points within the body part, wherein each set of scattering parameters represents the scattered field, at respective frequencies across the range of frequencies, from a corresponding point within the body part; generate an output indicative of the internal structure of the body part, using the plurality of sets of scattering parameters, to identify a region of interest within the body part; and classify the region of interest based on a type of tissue therein by analysing the change of the scattering parameters, in a set of scattering parameters corresponding to the region of interest, over the range of frequencies. a microwave antenna array comprising a transmitting antenna and a plurality of receiving antennas, wherein the transmitting antenna is configured to transmit microwave signals over a range of frequencies so as to illuminate a body part of a patient and the receiving antennas are configured to receive the microwave signals following scattering within the body part and acquire data representing the received microwave signals affected by scattering arising from objects within the body part; and a processor; characterised in that the processor is configured to: process the acquired data to determine a plurality of sets of scattering parameters for a plurality of points within the body part, wherein each set of scattering parameters represents the scattered field, at respective frequencies across the range of frequencies, from a corresponding point within the body part; generate an output indicative of the internal structure of the body part, using the plurality of sets of scattering parameters, to identify a region of interest within the body part; and classify the region of interest based on a type of tissue therein by analysing the change of the scattering parameters, in a set of scattering parameters corresponding to the region of interest, over the range of frequencies. process the acquired data to determine a plurality of sets of scattering parameters for a plurality of points within the body part, wherein each set of scattering parameters represents the scattered field, at respective frequencies across the range of frequencies, from a corresponding point within the body part; generate an output indicative of the internal structure of the body part, using the plurality of sets of scattering parameters, to identify a region of interest within the body part; and classify the region of interest based on a type of tissue therein by analysing the change of the scattering parameters, in a set of scattering parameters corresponding to the region of interest, over the range of frequencies.