Fig. 1.

Real-time integrated photoacoustic and ultrasound (PAUS) system used in these studies. The ultrasound system programmably controls the laser, motor controller, and US transducer. The motor controller synchronizes emission with the centers of 20 fibers in the bundle, delivering a trigger to the US system when properly aligned for each fiber. The US system then externally triggers the compact laser, transmitting a pulse at about a 1 $\text{k}\text{H}\text{z}$ repetition rate with a wavelength switchable from pulse-to-pulse over the range from 700 $\text{n}\text{m}$ to 900 $\text{n}\text{m}$. With absolute position control, a precise rate is not needed for external laser triggering, ensuring maximal light delivery to each fiber. Motor speed variations only slightly alter the overall frame rate of 50 $\text{H}\text{z}$. A total of 20 fibers are arranged on two sides of the linear array US transducer, as shown in the zoomed front view in the bottom right corner. The system mixes laser beam and focused US transmissions for interleaved PA spectroscopic imaging and US B-mode imaging.