Tissue oximetry by diffusive reflective visible light spectroscopy: Comparison of algorithms and their robustness

It is essential to measure tissue oxygen saturation (StO₂ ) locally and in thin layers of tissue, for example, the bronchial mucosa, skin flaps and small bones. Visible light spectroscopy (VLS) with a shallow penetration depth is suitable method. Although several VLS algorithms have been developed and described, they have not yet been compared to each other. This hinders attempts to compare the clinical results obtained by different algorithms. To address this issue, we compared the algorithms of Harrison, Knoefel, Pittman-Duling, Sato and our OxyVLS oximeter, which applies the algorithm from Wodick and Lübbers, in a liquid phantom with optical properties of human tissue. We generally observed considerable differences between the algorithms, which were StO₂ dependent. Exceptions were OxyVLS and Sato, showing a high level of agreement with negligible StO₂ dependency. In spite of the considerable deviation between the other algorithms, the difference of StO₂ between them in clinically normal StO₂ was <10%. We did not observe any dependency of the algorithms on hemoglobin content of the phantom or temperature.