Noncontact, frequency-domain measurements of diffusely reflected light are used to quantify optical properties of two-layer tissuelike turbid media. The irradiating source is a sinusoidal intensitymodulated plane wave, with modulation frequencies ranging from 10 to 1500 MHz. Frequencydependent phase and amplitude of diffusely reflected photon density waves are simultaneously fitted to a diffusion-based two-layer model to quantify absorption ͑ a ͒ and reduced scattering ͑ s Ј͒ parameters of each layer as well as the upper-layer thickness ͑l ͒. Study results indicate that the optical properties of two-layer media can be determined with a percent accuracy of the order of Ϯ9% and Ϯ5% for a and s Ј, respectively. The accuracy of upper-layer thickness ͑l ͒ estimation is as good as Ϯ6% when optical properties of upper and lower layers are known. Optical property and layer thickness prediction accuracy degrade significantly when more than three free parameters are extracted from data fits. Problems with convergence are encountered when all five free parameters ͑ a and s Ј of upper and lower layers and thickness l ͒ must be deduced.

Collimated light sources in turbid media are difficult to describe within the diffusion approximation, because they do not meet the requirement of near isotropy. For precise calculation of light intensities close to the source, alternative descriptions of the light source are necessary. In this paper the transition of collimated light into diffusivity is studied by Monte Carlo simulations. On the basis of these simulations and the diffusion approximation a hybrid approach is designed and used to analyze approaches based on analytic source terms. The influence of boundaries to air is studied. The benefits of increased approximation orders are investigated. It is shown that, even in the presence of strong absorption, the diffusion approach can give satisfactory results if only the source terms are suitably chosen.

. Quantifying the absorption and reduced scattering coefficients of tissuelike turbid media over a broad spectral range with noncontact Fourier-transform hyperspectral imaging. Applied Optics, 39(34), 6487-6497. DOI: 10.1364/AO.39.006487General rights Copyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal Absorption ͑ a ͒ and reduced scattering ͑Ј s ͒ spectra of turbid media were quantified with a noncontact imaging approach based on a Fourier-transform interferometric imaging system ͑FTIIS͒. The FTIIS was used to collect hyperspectral images of the steady-state diffuse reflectance from turbid media. Spatially resolved reflectance data from Monte Carlo simulations were fitted to the recorded hyperspectral images to quantify a and Ј s spectra in the 550 -850-nm region. A simple and effective calibration approach was introduced to account for the instrument response. With reflectance data that were close to and far from the source ͑0.5-6.5 mm͒, a and Ј s of homogeneous, semi-infinite turbid phantoms with optical property ranges comparable with those of tissues were determined with an accuracy of Ϯ7% and Ϯ3%, respectively. Prediction accuracy for a and Ј s degraded to Ϯ12% and Ϯ4%, respectively, when only reflectance data close to the source ͑0.5-2.5 mm͒ were used. Results indicate that reflectance data close to and far from the source are necessary for optimal quantification of a and Ј s . The spectral properties of a and Ј s values were used to determine the concentrations of absorbers and scatterers, respectively. Absorber and scatterer concentrations of two-chromophore turbid media were determined with an accuracy of Ϯ5% and Ϯ3%, respectively.

Abstract. The basic principles of a non-contact, near-infrared technique for the mapping of layered tissues are discussed theoretically and verified experimentally. The propagation properties of diffuse photon-density waves in tissues depend on the optical properties of the tissue. When a layered medium is irradiated by amplitude modulated light, the difference in optical properties between the layers is evident in the phase and amplitude of the diffuse reflection coefficient, which is a result of the interference of the partial waves propagating in the different layers. Thus, diffuse photon-density waves are applicable to the analysis of the structure of layered tissue. The probing depth is determined by the modulation frequency of the incident light. For modulation frequencies between several hundred megahertz and a few gigahertz, this allows us to analyse the properties of muscle tissue of up to 4-8 mm below the surface. Experimental results based on chicken breast muscle are given. As an example, the technique might be of use for evaluating the depth of necrosis and the blood volume fraction in deep burns.

No abstract

No abstract

No abstract

No abstract