A catheter-based imaging apparatus comprising: a catheter having a proximal end and a distal end; an optical emitter configured to emit optical excitation signals from a distal portion of the catheter; at least two ultrasound transducers (86, 87) configured for: (a) transmission of acoustic excitation signals from the distal portion of the catheter; (b) detection of ultrasound response signals from an object of interest at or near to the distal portion of the catheter at frequencies which include for a first one of the ultrasound transducers a lower receive frequency range at least as low as 10 MHz and for a second one of the ultrasound transducers a higher receive frequency range at least as high as 35 MHz, the first one of the ultrasound transducers being operable in the lower frequency range and thereby configured to detect response signals comprising photoacoustic response signals from the object of interest in the lower receive frequency range and the second one of the ultrasound transducers being operable in the higher frequency range and thereby configured for high resolution ultrasound imaging of the object of interest in the higher receive frequency range. a catheter having a proximal end and a distal end; an optical emitter configured to emit optical excitation signals from a distal portion of the catheter; at least two ultrasound transducers (86, 87) configured for: (a) transmission of acoustic excitation signals from the distal portion of the catheter; (b) detection of ultrasound response signals from an object of interest at or near to the distal portion of the catheter at frequencies which include for a first one of the ultrasound transducers a lower receive frequency range at least as low as 10 MHz and for a second one of the ultrasound transducers a higher receive frequency range at least as high as 35 MHz, the first one of the ultrasound transducers being operable in the lower frequency range and thereby configured to detect response signals comprising photoacoustic response signals from the object of interest in the lower receive frequency range and the second one of the ultrasound transducers being operable in the higher frequency range and thereby configured for high resolution ultrasound imaging of the object of interest in the higher receive frequency range. (a) transmission of acoustic excitation signals from the distal portion of the catheter; (b) detection of ultrasound response signals from an object of interest at or near to the distal portion of the catheter at frequencies which include for a first one of the ultrasound transducers a lower receive frequency range at least as low as 10 MHz and for a second one of the ultrasound transducers a higher receive frequency range at least as high as 35 MHz, the first one of the ultrasound transducers being operable in the lower frequency range and thereby configured to detect response signals comprising photoacoustic response signals from the object of interest in the lower receive frequency range and the second one of the ultrasound transducers being operable in the higher frequency range and thereby configured for high resolution ultrasound imaging of the object of interest in the higher receive frequency range.