An imaging system may include: a probe head including a light source for emitting light in at least one spectral waveband suitable to generate a photoacoustic response in tissue, and an ultrasound transducer having a transmit mode for transmitting ultrasound energy into the tissue and a receive mode for receiving the ultrasound energy reflected by the tissue and photoacoustic energy from the tissue； and a programmable system configured to actuate the light source and to actuate the ultrasound transducer between the transmit mode and the receive mode in response to a timing signal.
