Novel Application of Photoacoustic Ultrasound (PAUS) and Near-Infrared Dye Imaging for In Vivo Assessment of Tendon Compositional and Biological Changes During Injury and Healing
Description
Tendon injury and healing induce substantial changes in tissue biology and composition. Conventional techniques often necessitate animal sacrifice or tissue destruction, thereby restricting the assessment of dynamic alterations in tendons, encompassing treatment response, disease development, rupture risk, and healing progression. Changes in tendon composition, specifically modified glycosaminoglycan (GAG) content, can profoundly influence tendon mechanics and function. Analyzing these compositional changes usually demands ex vivo techniques involving animal sacrifice or tissue destruction. In vivo evaluation of tendons is crucial for longitudinal assessment. We employed photoacoustic ultrasound, a hybrid imaging modality that combines ultrasound and laser-induced photoacoustic signals to create detailed and high-resolution images of biological tissues, to identify components within the tissue in vivo. This technique has solely been applied to an in vivo rat tendon model, targeting hemoglobin. In this study, we assessed an exogenous near-infrared dye, Cy5-DPA-Zn, for imaging GAGs throughout injury and healing. We hypothesized that Cy5-DPA-Zn measures distinct differences in GAG content due to tendon injury and throughout tendon healing. The results indicate that Cy5-DPA-Zn exhibited a correlation with toluidine blue staining, particularly in the hypercellular regions of the healing tendon, suggesting the dye's potential localization in the more vascular areas of the tissue. This study supports the use of exogenous photoacoustic ultrasound for in vivo tendon assessment and represents the initial effort to image these targets in the rat Achilles tendon in vivo.