Evaluating hypoxia and vascular perfusion during pre-clinical wound healing using photoacoustic imaging

Our goal is to improve the assessment of cutaneous wound healing by quantitatively measuring biomarkers of vascular perfusion and hypoxia. Our research employs photoacoustic imaging (PAI), which is an outstanding imaging modality for interrogating the entire wound depth at 4-5 mm in pre-clinical models and eventually in patients. For comparison, optical imaging methods cannot reliably measure biomarkers deeper than 1-2 mm into tissues. To meet this goal, we have developed Dynamic Contrast Enhanced (DCE) PAI that can evaluate vascular perfusion in wounds. Our DCE PAI approach can quantitatively measure pharmacokinetics parameters of perfusion rates of the agent in the tissue. We have also adapted our Oxygen Sensitive (OS) PAI method for wound healing studies that can measure oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), total hemoglobin (HbT) and oxygensaturation (%sO2). We have shown that OS PAI and DCE PAI both detect early-stage wound healing which precedes a significant change in wound area. In an excisional model, showing the strong impact that OS- DCE PAI can provide. We will further refine OS-DCE PAI for imaging wound healing models. We will improve our methodology by performing DCE PAI with our advanced analysis method that avoids complications from variable light absorbance and scattering in deep tissues. We will investigate multiparametric analyses to demonstrate that combined measurements of oxygenation and vascular perfusion can improve wound healing diagnoses relative to a single parameter. We will also evaluate our DCE PAI method that uses a single absorbance wavelength relative to multi-wavelength imaging, which will expand our method to perform multislice PAI that can cover an entire wound. Imaging the entire wound will allow us to investigate the diagnostic utility of evaluating voxel distributions of our imaging measurements, and the utility of regional analyses. Each of these improvements is designed to improve the clinical translation of OS-DCE PAI. To demonstrate the strong impact of our research, we will use our OS-DCE PAI methodology to evaluate our excisional “punch” wound model, ischemic “crush” wound model, and burn model with normal mice and diabetic mice. Importantly, we have established each of these wound models in our research program. We will test diabetic mice to support eventual clinical translation, because diabetic patients with foot & leg ulcers and other wounds is a major chronic problem in current health care. Our deliverable is a new OS-DCE PAI method that will position us at the doorstep of clinical translation of our OE-DCE PAI method to monitor patients with burns, diabetic foot ulcers, and other wounds. Our top-ranked Burn and Wound Center at the University of Wisconsin is highly motivated to support clinical translation. The three manufacturers of clinical PAI instruments have expressed strong interest in our research with wound healing that can expand the market for clinical PAI.