Dynamic OCE with acoustic micro-tapping for in vivo monitoring of skin graft surgeries

Abstract The goal of this project is a develop a non-contact, non-invasive clinical tool to characterize, image and monitor skin grafting procedures using quantitative, volumetric, sub-mm resolved maps of Young's modulus based on Optical Coherence Elastography (OCE). Factors related to or directly defined by skin's elastic properties (such as contractions and shearing forces) are

among the most common complications of full thickness skin graft (FTSG) procedures. In addition, the recipient site functions best when its elastic properties are matched by transplanted donor tissue. With tens of millions of aesthetic procedures performed every year in the USA alone, surgical cosmesis is clearly critical, especially

when procedures are performed on the face, neck or breast. Currently there are no clinical tools, or even methods, that can quantitatively map skin's Young's modulus and anisotropy in vivo. We propose to map these parameters in skin using a non-contact, fully non-invasive method, with sub-mm spatial resolution and

nearly in real time. We hypothesize that quantifying skin elasticity in vivo will enable significant innovation within all areas of plastic surgery, burn surgery, oncologic surgery, and dermatology that modify a patient's tissue quality and elastic properties through medical, radiologic, or surgical intervention.

To achieve our objective, we propose a new non-contact OCE method. Our approach is based on: (i) acoustic micro-tapping (AµT) using ultrasound propagating in air to launch mechanical waves in soft media with the highest efficiency and best resolution among all non-contact wave-excitation methods, (ii) state-of-the-art real-

time 4-D PhS-OCT imaging to track wave propagation, and (iii) reconstruction of volumetric maps of Young's modulus and anisotropy using imaged wavefields in skin analyzed with a transversally isotropic model. SA1 will focus on refining previously developed analytic and numerical models of mechanical wave

propagation in skin considering its layered anisotropic structure, and developing algorithms to reconstruct skin's moduli. Then, SA2 will develop a robotized AµT-OCE imaging system for in vivo skin measurements in a clinical environment. We will perform routine measurements of skin elastic moduli in vivo on healthy

volunteers to understand normal variability in skin elastic properties in a representative population of normal human subjects to help define the level of expected improvements possible in matching skin elastic properties in FTSG procedures. SA3 will focus on in vivo monitoring changes in grafted skin elastic properties during

grafting procedures in the clinic, including pre-operative mapping of skin's elastic properties in donor and recipient sites and mapping longitudinal changes in fundamental structural and elastic parameters of FTSGs and surrounding tissue over the reconstruction process. If successful, this project can be the starting point for

multiple continuation projects testing whether new methods and clinical protocols can be developed using information from OCE to help select the best donor tissue for grafting and guide post-surgery procedures.