Real-time interleaved photoacoustic/ultrasound (PAUS) imaging for interventional procedure guidance.

Ultrasound-guided photoacoustic imaging has shown great potential for many clinical applications including vascular visualization, detection of nanoprobes sensing molecular profiles, and guidance of interventional procedures. However, bulky and costly lasers are usually required to provide sufficient pulse energies for deep imaging. The low pulse repetition rate also limits potential real-time applications of integrated photoacoustic/ultrasound (PAUS) imaging. With a compact and low-cost laser operating at a kHz repetition rate, we aim to integrate photoacoustics (PA) into a commercial ultrasound (US) machine utilizing an interleaved scanning approach for clinical translation, with imaging depth up to a few centimeters and frame rates > 30 Hz. Multiple PA sub-frames are formed by scanning laser firings covering a large scan region with a rotating galvo mirror, and then combined into a final frame. Ultrasound pulse-echo beams are interleaved between laser firings/PA receives. The approach was implemented with a diode-pumped laser, a commercial US scanner, and a linear array transducer. Insertion of an 18-gauge needle into a piece of chicken tissue, with subsequent injection of an absorptive agent into the tissue, was imaged with an integrated PAUS frame rate of 30 Hz, covering a 2.8 cm × 2.8 cm imaging plane. Given this real-time image rate and high contrast (> 40 dB at more than 1-cm depth in the PA image), we have demonstrated that this approach is potentially attractive for clinical procedure guidance.