1. A method of thermoacoustic imaging of structures of tissue, comprising immersing said tissue in an acoustic coupling media for acoustically coupling said tissue to an acoustic sensor array, delivering to said tissue a fluorescent dye responsive to electromagnetic radiation, irradiating said tissue with a source of electromagnetic radiation at a first frequency to stimulate fluorescence of said dye and a thermoacoustic response thereto, detecting said thermoacoustic response and producing therefrom a dye-enhanced image of structures of said tissue.