Abstract

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: $\sim\!0.01\,\,{\rm mm}^{ - 1}$, reduced scattering coefficient: $\sim\!1\,\,{\rm mm}^{ - 1}$). This result is a major advance over single-distance or single-slope data, which feature maximal sensitivity to shallow tissue ($ \lt\!{{2}}\,\,{\rm{mm}}$ for the intensity, $ \lt\!{{5}}\,\,{\rm{mm}}$ for the phase).

© 2019 Optical Society of America

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