Heavy water coupling gel for short-wave infrared photoacoustic imaging

Significance Changes in lipid, water, and collagen (LWC) content in tissue are associated with numerous medical abnormalities (cancer, atherosclerosis, and Alzheimer's disease). Standard imaging modalities are limited in resolution, specificity, and/or penetration for quantifying these changes. Short-wave infrared (SWIR) photoacoustic imaging (PAI) has the potential to overcome these challenges by exploiting the unique optical absorption properties of LWC > 1000 nm.Aim This study's aim is to harness SWIR PAI for mapping LWC changes in tissue. The focus lies in devising a reflection-mode PAI technique that surmounts current limitations related to SWIR light delivery.Approach To enhance light delivery for reflection-mode SWIR PAI, we designed a deuterium oxide (D2O, "heavy water") gelatin (HWG) interface for opto-acoustic coupling, intended to significantly improve light transmission above 1200 nm.Results HWG permits light delivery >1 mJ up to 1850 nm, which was not possible with water-based coupling (>1 mJ light delivery up to 1350 nm). PAI using the HWG interface and the Visualsonics Vevo LAZR-X reveals a signal increase up to 24 dB at 1720 nm in lipid-rich regions.Conclusions By overcoming barriers related to light penetration, the HWG coupling interface enables accurate quantification/monitoring of biomarkers like LWC using reflection-mode PAI. This technological stride offers potential for tracking changes in chronic diseases (in vivo) and evaluating their responses to therapeutic interventions.