Journal of the Optical Society of America A · 2019 · 60 citations · 32 references
Natural SciencesBiomedical EngineeringBiophysicsBiomedical OpticsBiophotonicsSpectroscopyAbsorption SpectroscopyLight-tissue InteractionOptical SpectroscopyScattering In TissueTissue Optical PropertiesTissue OpticsDiffuse Optical SpectroscopyDiffusion TheoryFrequency-domain SpectroscopyOptical Absorption CoefficientOptical PropertiesReduced Scattering CoefficientScatteringTissue Optical Diagnostics
Using diffusion theory, we show that a dual-slope method is more effective than single-slope methods or single-distance methods at enhancing sensitivity to deeper tissue. The dual-slope method requires a minimum of two sources and two detectors arranged in specially configured arrays. In particular, we present diffusion theory results for a symmetrical linear array of two sources (separated by 55 mm) that sandwich two detectors (separated by 15 mm), for which dual slopes achieve maximal sensitivity at a depth of about 5 mm for direct current (DC) intensity (as measured in continuous-wave spectroscopy) and 11 mm for phase (as measured in frequency-domain spectroscopy) under typical values of the tissue optical properties (absorption coefficient: ∼0.01mm−1, reduced scattering coefficient: ∼1mm−1). This result is a major advance over single-distance or single-slope data, which feature maximal sensitivity to shallow tissue (<2mm for the intensity, <5mm for the phase).
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