Enhanced deep-tissue photoacoustic imaging using extended-pulse LED illumination and a 5 MHz ultrasound probe

Photoacoustic (PA) imaging combines optical absorption contrast with ultrasonic resolution, offering a powerful modality for visualizing vascular structures and functional parameters such as oxygen saturation. While laser-based PA systems have demonstrated strong performance, their size, cost, and safety constraints limit widespread clinical and point-of-care adoption. LED-based PA imaging has emerged as a promising alternative, though its relatively low pulse energy has historically restricted imaging depth. In this study, we investigate an approach to extend the penetration depth of LED-based PA imaging by evaluating a newly developed 5 MHz ultrasound probe in combination with extended LED pulse widths using the AcousticX multispectral PA/US imaging system. Phantom experiments were performed to assess PA signal performance across different probe frequencies (5, 7, and 10 MHz) and LED pulse widths (30–100 ns), followed by in vivo imaging of peripheral vessels and breast vasculature in healthy human volunteers. By matching a 100 ns LED pulse width to the acoustic reception bandwidth of the 5 MHz probe and increasing optical pulse energy at 850 nm, a substantial improvement in PA signal detection from deeper tissue was achieved. The optimized configuration enabled visualization of carotid, jugular, and breast vasculature at depths up to 1.8 cm in vivo, along with real-time oxygen saturation mapping. These results demonstrate the feasibility of deep-tissue, real-time LED-based PA/US imaging using low-frequency probes and highlight a practical pathway toward portable, clinically relevant PA imaging systems.