Structured-light imaging systems and methods for determining sub-diffuse scattering parameters

Abstract

A method for determining sub-diffuse scattering parameters of a material includes illuminating the material with structured light and imaging remission by the material of the structured light. The method further includes determining, from captured remission images, sub-diffuse scattering parameters of the material. A structured-light imaging system for determining sub-diffuse scattering parameters of a material includes a structured-light illuminator, for illuminating the material with structured light of periodic spatial structure, and a camera for capturing images of the remission of the structured light by the material. The structured-light imaging system further includes an analysis module for processing the images to quantitatively determine the sub-diffuse scattering parameters. A software product includes machine-readable instructions for analyzing images of remission of structured light by a material to determine sub-diffuse scattering parameters of the material.

What is claimed is: 
     
         1 . A method for determining sub-diffuse scattering parameters of a material, comprising:
 illuminating the material with a spectral wavelength of structured light, the structured light having periodic spatial structure varying between brighter and darker regions, the structured light provided by a structured-light illuminator;   imaging, using an electronic camera, to capture images of remission by the material of the structured light;   temporally varying the periodic spatial structure of the structured light to each of a plurality of spatial frequencies and, for each spatial frequency, a plurality of spatial phase shifts;   the imaging comprising capturing a plurality of images including an image of the remission for each of the the plurality of spatial phase shifts associated with each of the plurality of spatial frequencies; and   determining, in an analysis module, from the captured images, wavelength-specific sub-diffuse scattering parameters of the material;   the plurality of spatial frequencies comprising:   a lower spatial frequency sufficiently low that the remission associated therewith is sensitive to a reduced scattering coefficient of the material; and   a higher spatial frequency sufficiently high that the remission associated therewith is sensitive to a backscatter likelihood of the material.   
     
     
         2 . The method of  claim 1  wherein the lower spatial frequency corresponds to interrogation depth, of the material, associated at least in part with diffuse scattering; and the higher spatial frequency corresponds to interrogation depth, of the material, associated at least in part with sub-diffuse scattering. 
     
     
         3 . The method of  claim 1  wherein the sub-diffuse scattering parameters determined include reduced scattering coefficient and backscatter likelihood (γ). 
     
     
         4 . A method for determining sub-diffuse scattering parameters of a material, comprising:
 illuminating the material with structured light at a sequence of wavelengths, the structured light incorporating periodic patterns of light and dark at a same wavelength of the sequence of wavelengths;   imaging remission by the material of the structured light; and   determining, from images captured in the step of imaging, sub-diffuse scattering parameters of the material;   the sub-diffuse scattering parameters including reduced scattering coefficient and backscatter likelihood;   the step of illuminating comprising temporally varying the patterns to produce a plurality of spatial frequencies and, at each of the plurality of spatial frequencies a plurality of spatial phase shifts;   the step of imaging comprising capturing a plurality of images including an image of the remission for each of the spatial phase shifts associated with each of the plurality of spatial frequencies;   the step of determining comprising processing the plurality of images to deduce wavelength-specific values of the reduced scattering coefficient and the backscatter likelihood;   the step of determining comprising:   for each of the plurality of spectral wavelengths, generating demodulated images respectively associated with the plurality of spatial frequencies, from t the plurality of images; and   fitting a wavelength-dependent model for demodulated remission, sensitive to (a) the wavelength-specific values of the reduced scattering coefficient and the backscatter likelihood and (b) spatial frequency of the periodic structure, to intensities in the demodulated images associated with all of the plurality of spectral wavelengths, to determine the wavelength-specific values of the reduced scattering coefficient and the backscatter likelihood for each of the plurality of spectral wavelengths.   
     
     
         5 . The method of  claim 4 ,
 the step of fitting comprising ascertaining, for each of the plurality of spectral wavelengths, the wavelength-specific value of the backscatter likelihood as γ=(1−g2)/(1−g1), wherein g1 and g2 are first and second Legendre moments, respectively, of scattering phase function of the material; and   in the step of fitting, the model specifying remission as a function of γ and product between (a) the wavelength-specific value of the reduced scattering coefficient and (b) spatial frequency of the structured light.