Oxygen saturation mapping during reconstructive surgery of human forehead flaps with hyperspectral imaging and spectral unmixing

Abstract

Background: Optical spectroscopy is commonly used clinically to monitor oxygen saturation in tissue. The most commonly employed technique is pulse oximetry, which provides a point measurement of the arterial oxygen saturation and is commonly used for monitoring systemic hemodynamics, e.g. during anesthesia. Hyperspectral imaging (HSI) is an emerging technology that enables spatially resolved mapping of oxygen saturation in tissue (sO₂), but needs to be further developed before implemented in clinical practice. The aim of this study is to demonstrate the applicability of HSI for mapping the sO₂ in reconstructive surgery and demonstrate how spectral analysis can be used to obtain clinically relevant sO₂ values.

Methods: Spatial scanning HSI was performed on cutaneous forehead flaps, raised as part of a direct brow lift, in eight patients. Pixel-by-pixel spectral analysis, accounting for the absorption from multiple chromophores, was performed and compared to previous analysis techniques to assess sO₂.

Results: Spectral unmixing using a broad spectral range, and accounting for the absorption of melanin, fat, collagen, and water, provided a more clinically relevant estimate of sO₂ than conventional techniques, where typically only spectral features associated with absorption of oxygenated (HbO₂) and deoxygenated (HbR) hemoglobin are considered. We demonstrate its clinical applicability by generating sO₂ maps of partially excised forehead flaps showed a gradual decrease in sO₂ along the length of the flap from 95 % at the flap base to 85 % at the flap tip. After being fully excised, sO₂ in the entire flap decreased to 50 % within a few minutes.

Conclusions: The results demonstrate the capability of sO₂ mapping in reconstructive surgery in patients using HSI. Spectral unmixing, accounting for multiple chromophores, provides sO₂ values that are in accordance with physiological expectations in patients with normal functioning microvascularization. Our results suggest that HSI methods that yield reliable spectra are to be preferred, so that the analysis can produce results that are of clinical relevance.

Keywords: Hyperspectral imaging; Oxygen saturation; Reconstructive surgery; Spectral unmixing.