Feasibility of Using Low-Energy Pulsed Laser Diode on Clinical Ultrasound Platforms for Photoacoustic and Transrectal Ultrasound Guided Laparoscopic Prostatectomy

Abstract

Here we present a feasibility study of adding a low-cost, low-energy, and compact pulsed laser diode (PLD) system on clinical ultrasound (US) platforms for photoacoustic (PA) point marker imaging. The size of the PLD plus a driver is no larger than a hand-held US probe, and the energy per pulse of the PLD is in µJ level, which is 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> lower than conventional PA lasers. We tackled two major challenges in this work, one is the very low energy per pulse of the PLD, and the other is the inaccessible beamformer on clinical US machines. We investigated the laser pulse widths and the number of frames for averaging in synthetic-aperture based PA re-beamforming (SPARE). The phantom experiment showed that when the laser pulse width is no greater than 1 µs, wider pulses yield higher contrast to noise (CNR) ratio. Also averaging of US beamformed PA data for over 49 frames promises identifiable PA point marker for real-time tracking. The framework significantly lowers the cost and compacts the system for PA point marker imaging, and one potential clinical application is the real-time PA navigation for transrectal ultrasound (TRUS) guided laparoscopic prostatectomy.