Single-fiber reflectance spectroscopy system using unmodified clinical laser fibers for tissue optical property recovery for photodynamic therapy treatment planning.

SIGNIFICANCE: Estimation of tissue optical properties in workflow- and resource-constrained clinical settings is required to support photodynamic therapy (PDT) treatment planning, yet large-scale clinical translation remains limited by spectroscopy probe cost, complexity, and the need for probe-specific inverse models. Single-fiber reflectance (SFR) spectroscopy offers a simple and low-cost option, but previous implementations relied on customized angle-polished fibers. AIM: The objective was to develop a proof-of-concept SFR spectroscopy system employing an unmodified, United States Food and Drug Administration (FDA)-approved clinical optical fiber for quantitative optical property extraction. APPROACH: A semi-empirical photon pathlength model was used to recover the absorption spectra μ a ( λ ) and reduced scattering spectra μ s ' ( λ ) from tissue-mimicking phantoms containing methylene blue (MB) as the absorber and Intralipid-20% as the scatterer. RESULTS: Optical property retrieval from measurements acquired using three nominally identical fibers demonstrated clinically sufficient accuracy across fibers without requiring model adaptation. Across all fibers, MB concentration ( C MB ) was recovered with a root mean square error (RMSE) of 0.6 to 0.7    μ M ( p = 0.88 among fibers), while μ s ' ( 665    nm ) was recovered with an RMSE of 1.5 to 2.2    cm - 1 ( p = 0.68 among fibers). CONCLUSIONS: We demonstrate the potential of SFR spectroscopy using a standard clinical optical fiber as a scalable and clinically useful tool for tissue optical property estimation to support PDT treatment planning.