Real-time photoacoustic imaging with freehand light delivery and augmented reality guidance

Photoacoustic-guided surgery benefits from precise co-alignment between detached light delivery and sound reception components. Misalignment can result in absent photoacoustic signals, potentially leading to critical structures incorrectly interpreted as absent. Augmented reality has the potential to provide real-time spatial registration and intuitive visualization through tracking of the laser and ultrasound transducer positions. We developed and validated a novel augmented reality guidance system that tracks a freehand light source and ultrasound transducer, rendering real-time virtual representations of the associated laser beam and ultrasound image to facilitate intuitive alignment. Quantitative evaluation demonstrated a 58% reduction in mean targeting error during a static alignment task, relative to a standard freehand approach implemented without augmented reality. The total variance of laser-image intersection distribution with augmented reality was 12.0 mm ${}^2$ , reduced from 45.9 mm ${}^2$ without augmented reality, indicating higher motion stability. In addition, the system successfully tracked complex motions, and photoacoustic signals from a blood vessel target hidden by tissue were spatially rendered on the tissue surface to demonstrate surgical guidance capabilities. This work establishes augmented reality as a promising approach to address anticipated challenges surrounding photoacoustic-guided surgery with light delivery separated from acoustic receivers.