This review describes the diffusion model for light transport in tissues and the medical applications of diffuse light. Diffuse optics is particularly useful for measurement of tissue hemodynamics, wherein quantitative assessment of oxy- and deoxy-hemoglobin concentrations and blood flow are desired. The theoretical basis for near-infrared or diffuse optical spectroscopy is developed, and the basic elements of diffuse optical tomography are outlined. We also discuss diffuse correlation spectroscopy, a technique whereby temporal correlation functions of diffusing light are transported through tissue and are used to measure blood flow. Essential instrumentation is described, and representative brain and breast functional imaging and monitoring results illustrate the workings of these new tissue diagnostics.

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Diffuse optics for tissue monitoring and tomography

First introduced in the 1980s, laser speckle contrast imaging is a powerful tool for full-field imaging of blood flow. Recently laser speckle contrast imaging has gained increased attention, in part due to its rapid adoption for blood flow studies in the brain. We review the underlying physics of speckle contrast imaging and discuss recent developments to improve the quantitative accuracy of blood flow measures. We also review applications of laser speckle contrast imaging in neuroscience, dermatology and ophthalmology.

/pdf/laser-speckle-contrast-imaging-in-biomedical-optics-1lk5nj5vp2.pdf

Laser speckle contrast imaging in biomedical optics

Visually opaque media are ubiquitous in nature. While some materials are opaque because they strongly absorb visible light, others, such as loam, white paint, biological tissue and milk, are opaque because photons traveling within them are predominantly scattered rather than absorbed. A vanishingly small number of photons travel straight through such substances. Instead, light is transported through these materials in a process similar to heat diffusion (figure 1).

Spectroscopy and Imaging with Diffusing Light

1. Introduction: mesoscopic physics 2. Wave equations in random media 3. Perturbation theory 4. Probability of quantum diffusion 5. Properties of the diffusion equation 6. Dephasing 7. Electronic transport 8. Coherent backscattering of light 9. Diffusing wave spectroscopy 10. Spectral properties of disordered metals 11. Universal conductance fluctuations 12. Correlations of speckle patterns 13. Interactions and diffusion 14. Orbital magnetism and persistent currents 15. Formulary Index.

/pdf/mesoscopic-physics-of-electrons-and-photons-3ycvopdvcp.pdf

Mesoscopic Physics of Electrons and Photons

Photon Upmanship: Why Multiphoton Imaging Is More than a Gimmick

We obtain useful information from the intensity autocorrelations of light scattered from systems which exhibit strong multiple scattering. A phenomenological model, which exploits the diffusive nature of the transport of light, is shown to be in excellent agreement with experimental data for several different scattering geometries. The dependence on geometry provides an important experimental control over the time scale probed. We call this technique diffusing wave spectroscopy, and illustrate its utility by studying diffusion in a strongly interacting colloidal glass.

Diffusing wave spectroscopy

Dynamic light scattering is extended to optically thick (opaque) media which exhibit a very high degree of multiple scattering This new technique, called diffusing-wave spectroscopy (DWS), exploits the diffusive nature of the transport of light in strongly scattering media to relate the temporal fluctuations of the multiply scattered light to the motion of the scatterers A simple theory of DWS, based on the diffusion approximation for the transport of light, is developed to calculate the temporal electric field autocorrelation functions of the multiply scattered light Two important scattering geometries are treated : transmission and backscattering The theory is compared to experimental measurements of Brownian motion of submicron-diameter polystyrene spheres in aqueous suspension The agreement between theory and experiment is excellent The limitations of the photon diffusion approximation and the polarization dependence of the autocorrelation functions are discussed for the backscattering measurements The effects of absorption of light and particle polydispersity are also incorporated into the theory and verified experimentally It is also shown how DWS can be used to obtain information about the mean size of the particles which scatter light

https://hal.archives-ouvertes.fr/jpa-00212514/document

E. Herbolzheimer

Papers

Diffusing wave spectroscopy

Diffusing-wave spectroscopy : dynamic light scattering in the multiple scattering limit