Enhancement of photoacoustic signal using a novel light illumination improvement device: In vivo feasibility animal study

A large portion of near infrared (NIR) laser energy is lost at the skin surfaces by reflection, for example 30% of the incident energy reflects off with incident angle of 20°. Retrieving the reflected light and redirecting it onto the skin surfaces will increase the effective excitation energy, resulting in an increased photoacoustic (PA) signal for the same light source without increasing power. Increased uniformity of light distribution on the skin is also expected due to multiple random light reflection inside a light retrieving and reflection device. In this study, we fabricated a relatively simple, but effective light illumination improvement device, called light catcher, and integrated it into a compact high frequency ultrasound transducer for small animal imaging. Using chicken breast tissues and a mouse cancer model, feasibility of the light catcher for PA imaging was demonstrated. When using the light catcher, PA signal intensity was increased by 33% (0.44 vs. 0.30) and 28% (0.57 vs. 0.41), and corresponding CNR was improved by 22% (2.66 vs. 2.18) and 23% (1.96 vs. 1.52) compared to without the light catcher for in vitro and in vivo study, respectively. This device might allow deep tissue PA imaging with improved CNR using the same laser power.