A method and device for determining the depth and fluorophore concentration of a fluorophore concentration below the surface of an optically absorbing and scattering medium suitable for use in fluorescence-based surgical guidance such as in tumor resection is described. Long-wavelength stimulus light us used to obtain deep tissue penetration. Recovery of depth is performed by fitting measured modulation amplitudes for each spatial frequency to precomputed modulation amplitudes in a table of modulation amplitudes indexed by optical parameters and depth.