# Thermal Rejection Assessment: New Strategies for Early Detection

## TL;DR

This study shows that thermal assessments can detect early signs of transplant rejection before visible symptoms appear, potentially reducing the need for invasive biopsies.

## Contribution

The novel contribution is demonstrating that thermal assessment can detect early rejection in transplants, even with skin pigmentation challenges.

## Key findings

- Thermal assessments detected significant temperature differences as early as postoperative day 1.
- Thermal assessment can identify early signs of rejection before clinical symptoms appear.
- This approach may reduce the need for invasive biopsies in diagnosing transplant rejection.

## Abstract

Skin pigmentation can pose challenges for physicians to diagnose pathologies. In Vascularized Composite Allotransplantation (VCA), this increases the difficulty of diagnosing rejection by clinical observation, which could be improved by noninvasive monitoring, thereby completely avoiding or aiding in guiding location for invasive diagnostics. In this study, pigmented and non-pigmented allogeneic and non-pigmented syngeneic control transplant recipients underwent daily thermal assessment using infrared (IR) gun and forward-looking IR (FLIR) imaging of VCAs using a rodent partial hindlimb transplant model. Daily clinical assessment was performed, and biopsies were taken on postoperative day (POD) 1, 3, and 7. Clinical and histological assessments indicated signs of rejection on POD 3. In contrast, thermal assessment using the IR gun detected significant differences as early as POD 1, notably a decrease in temperature, when comp ared to syngeneic control transplants. This demonstrates the capability of thermal assessments to identify early signs of rejection before clinical symptoms become apparent. The findings suggest that thermal assessments can serve as a non-contact, objective adjunct tool for early detection of graft rejection, with consideration of skin pigmentation. This approach may reduce the need for invasive biopsies, thereby improving patient comfort and reducing potential complications associated with current diagnostic methods.