Characterization of in vivo frostbite injury depth using a portable handheld terahertz spectroscopic scanner

Tissue damage from frostbite injury may not be apparent until several weeks post-injury; however, early assessment of injury depth is critical for guiding clinical treatment. Recently, we have demonstrated that terahertz (THz) spectroscopic imaging can determine the severity and predict healing outcome of thermal burns with high accuracy. In this work, we extend this work to frostbite and present THz images captured from an in vivo porcine frostbite model using our Portable HAndheld Spectral Reflection (PHASR) Scanner. We establish a standardized frostbite injury model using controlled liquid nitrogen exposure, as confirmed by histological assessments. We then analyze the THz spectra within 24 and 72 hours after frostbite induction and observe a significant difference (p<0.05) between partial- and full-thickness frostbite injuries, as well as healthy tissue using a physical double-Debye dielectric relaxation model. Finally, we employ a support vector machine for classification and demonstrate an area under the receiver operating curve of 0.94, 0.85, and 0.87 for healthy tissue, partial-, and full-thickness frostbite injuries, respectively. This work suggests the potential of THz time-domain spectroscopy for early, noninvasive assessment of frostbite depth.