Clinically translatable integrated ultrasound and photoacoustic imaging system

Due to the high scattering coefficient of tissue over the wavelength range used for photoacoustic (PA) imaging, most studies employ bulky, low repetition rate lasers to provide sufficient pulse energies at depth to image within the body. The size and cost of these lasers has impeded integration of photoacoustics into conventional, routinely-used ultrasound (US) scanners. Here, we present an approach leveraging the capabilities of modern, high repetition rate fiber lasers to produce a clinically translatable system providing integrated US/PA images at frame rates > 30 Hz. The system uses a portable, low-cost, low pulse-energy (1 mJ/pulse), high repetition rate (1 kHz), 1064 nm laser and is designed for integrated US/PA imaging of the peripheral vasculature or any relevant diseased region, such as a tumor. Using a rotating galvo-mirror system, the incident laser beam is quickly scanned over the imaging area. Multiple PA images covering the scan area are integrated to form a single PA image. Additionally, ultrasound firings are integrated into the scan sequence to provide an US image reconstructed over the same frame period. We acquired PA images of a 1.5-mmdiameter cylindrical absorber (absorption coefficient 5 cm-1) embedded in a tissue-mimicking gelatin phantom at 6-cm depth. A 2 cm × 1 cm (depth × lateral) area was reconstructed. We obtained a signal-to-noise ratio of more than 30 dB, comparable to conventional PA methods using high energy, low repetition rate lasers. The current system produces an integrated US/PA frame at a 32 Hz rate, and 100 Hz frame rates are possible with our present approach.