Dogancan Kuyel, Zhongmin Zhu, Brianna Hajek, Sinisha Stojanovski, Anamarija Jankulovska, Igorce Djikovski, Risto Colanceski, Imran Ferati, Natasha Toleska Dimitrovska, Ilir Vela, Despot Despotovski, Nexhati Jakupi, Darko Angjushev, Magdalena Bogdanovska Todorovska, Goran Kondov, Borislav Kondov, Fumihiro Kawano, Shuming Nie, Claudius Conrad, Viktor Gruev
Wavelength-dependent fluorescence spread profiles across NIR-I and NIR-II can encode depth information for subsurface ICG targets, providing a wide-field, single-fluorophore, single-excitation approach compatible with emerging multispectral surgical imaging platforms.
SIGNIFICANCE: Wide-field fluorescence-guided imaging is inherently depth ambiguous. Multispectral imaging across NIR-I and NIR-II may encode depth because longer-wavelength fluorescence undergoes less diffuse broadening in tissue.
AIM: The study aims to determine whether wavelength-dependent radial spread profiles of subsurface indocyanine green (ICG) fluorescence can be used to estimate depth from a single excitation wavelength.
APPROACH: ICG phantoms (1 to 50 μ M ) were imaged through ex vivo chicken breast under 785 nm excitation using four emission bands spanning NIR-I and NIR-II. Radial spread profiles from high-dynamic-range images formed a multispectral dictionary, and depth was estimated with an inverse model evaluated leave-one-thickness-out across 2.2 to 6.0 mm under concentration-matched and concentration-randomized conditions, randomized exposure subsets, and spectral-band ablations, and compared with analytical and empirically calibrated scalar dual-emission fluorescence-ratio baselines of Leblond et al. Two ICG-localized sentinel lymph nodes from a breast cancer specimen were analyzed ex vivo.
RESULTS: Longer-wavelength channels produced more compact spread profiles, and full width at 20% peak intensity increased linearly with tissue thickness for all filters ( R 2 = 0.94 to 0.95). The NIR-II-only subset (940 and 1070 nm) yielded sub-millimeter root mean square error at every held-out thickness under both concentration conditions (0.32 to 0.66 mm), whereas the analytical and empirical scalar-ratio baselines yielded 1.58 to 5.24 and 1.13 to 2.74 mm. Clinical sentinel lymph nodes preserved the wavelength-dependent profile narrowing, with phantom-to-clinical normalized-width RMSE of 3.3% to 8.5%.
CONCLUSIONS: Wavelength-dependent fluorescence spread profiles across NIR-I and NIR-II can encode depth information for subsurface ICG targets, providing a wide-field, single-fluorophore, single-excitation approach compatible with emerging multispectral surgical imaging platforms.