Improved contrast in laser-diode-based photoacoustic images with short-lag spatial coherence beamforming

Abstract

Pulsed laser diodes (PLDs) enable photoacoustic imaging with lower cost, increased portability, and higher frame rates compared to conventional Q-switched Nd:YAG lasers. However, the main disadvantage of the PLD is its low peak power, which necessitates averaging thousands of photoacoustic signals to achieve signal-to-noise ratios that are comparable to those produced by an Nd:YAG laser. The averaging process degrades temporal resolution with minimal improvements to image contrast. This work is the first to investigate the use of a PLD and short-lag spatial coherence (SLSC) beamforming to display high-contrast photoacoustic images with minimal to no signal averaging required. The mean contrast in single photoacoustic images of targets as deep as 5–15 mm from the surface was improved by 11–17 dB with SLSC beamforming when compared to conventional delay-and-sum (DAS) beamforming of the same data. The SLSC correlation kernel was adjusted based on laser pulse lengths to demonstrate applicability to coded excitation. Results suggest that coherence-based beamforming can overcome current limitations with real-time PLD-based photoacoustic imaging.