Robustness of tissue oxygenation estimates by continuous wave space-resolved near infrared spectroscopy

SIGNIFICANCE: Continuous wave near infrared spectroscopy (CW-NIRS) is widely exploited in clinics to estimate skeletal muscles and brain cortex oxygenation. Spatially resolved spectroscopy (SRS) is generally implemented in commercial devices. However, SRS suffers from two main limitations: the a priori assumption on the spectral dependence of the reduced scattering coefficient [[Formula: see text]] and the modeling of tissue as homogeneous. AIM: We studied the accuracy and robustness of SRS NIRS. We investigated the errors in retrieving hemodynamic parameters, in particular tissue oxygen saturation ([Formula: see text]), when [Formula: see text] was varied from expected values, and when layered tissue was considered. APPROACH: We simulated hemodynamic variations mimicking real-life scenarios for skeletal muscles. Simulations were performed by exploiting the analytical solutions of the photon diffusion equation in different geometries: (1) semi-infinite homogeneous medium and constant [Formula: see text]; (2) semi-infinite homogeneous medium and linear changes in [Formula: see text]; (3) two-layered media with a superficial thickness [Formula: see text] , 7.5, 10 mm and constant [Formula: see text]. All simulated data were obtained at source-detector distances [Formula: see text] , 40, 45 mm, and analyzed with the SRS approach to derive hemodynamic parameters (concentration of oxygenated and deoxygenated hemoglobin, total hemoglobin concentration, and tissue oxygen saturation, [Formula: see text]) and their relative error. RESULTS: Variations in [Formula: see text] affect the estimated [Formula: see text] (up to [Formula: see text]), especially if changes are different at the two wavelengths. However, the main limitation of the SRS method is the presence of a superficial layer: errors strongly larger than 20% were retrieved for the estimated [Formula: see text] when the superficial thickness exceeds 5 mm. CONCLUSIONS: These results highlight the need for more sophisticated strategies (e.g., the use of multiple short and long distances) to reduce the influence of superficial tissues in retrieving hemodynamic parameters and warn the SRS users to be aware of the intrinsic limitation of this approach, particularly when exploited in the clinical environment.