A thermoacoustic imaging system is provided for use in combination with an ultrasound imaging system for imaging features of tissue, the ultrasound imaging system including an ultrasound imaging probe including a transmit-receive transducer array with a plurality of transmit-receive array elements. The thermoacoustic imaging system includes a receive-only transducer array with a plurality of receive-only array elements, registered with the plurality of transmit-receive array elements. The transmit-receive transducer array is housed in an ultrasound imaging probe, and the receive-only transducer array is housed in a thermoacoustic imaging probe. The thermoacoustic imaging probe is mechanically joined to the ultrasound imaging probe, e.g., as a sleeve fitted to the ultrasound imaging probe. A combined ultrasound transducer system including the ultrasound imaging probe and an thermoacoustic imaging probe may be used in composite imaging of tissue based upon the registration of the receive-only array elements with the transmit-receive array elements.
