Publications (19) View all
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Article: Quantitative 3D imaging of scattering media using structured illumination and computed tomography.
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ABSTRACT: An imaging technique capable of measuring the extinction coefficient in 3D is presented and demonstrated on various scattering media. The approach is able to suppress unwanted effects due to both multiple scattering and light extinction, which, in turbid situations, seriously hampers the performance of conventional imaging techniques. The main concept consists in illuminating the sample of interest with a light source that is spatially modulated in both the vertical and horizontal direction and to measure, using Structured Illumination, the correct transmission in 2D at several viewing angles. The sample is then reconstructed in 3D by means of a standard Computed Tomography algorithm. To create the adequate illumination, a novel "crossed" structured illumination approach is implemented. In this article, the accuracy and limitation of the method is first evaluated by probing several homogeneous milk solutions at various levels of turbidity. The unique possibility of visualizing an object hidden within such solutions is also demonstrated. Finally the method is applied on two different inhomogeneous scattering spray systems; one transient and one quasi-steady state.Optics Express 06/2012; 20(13):14437-50. · 3.59 Impact Factor -
Article: Low-order light scattering in multiple scattering disperse media
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ABSTRACT: Light scattering has been investigated in systems in which both single and higher order scattering occur. The Monte Carlo simulation technique for studying light scattering in randomly inhomogeneous, strongly scattering disperse media was employed. The reliability of the data obtained has been checked by comparing the results of the computer simulation with analytical calculations for the intensity of doubly scattered light. The first several scattering orders have been analyzed for different geometries of the optical experiment. It has been shown, in particular, that, depending on the detector aperture, the contribution of multiple scattering can vary by almost an order of magnitude.Optics and Spectroscopy 04/2012; 97(5):796-802. · 0.61 Impact Factor -
Article: Analysis of multiple scattering suppression using structured laser illumination planar imaging in scattering and fluorescing media.
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ABSTRACT: The accuracy, precision and limitations of the imaging technique named Structured Laser Illumination Planar Imaging (SLIPI) have been investigated. SLIPI, which allows multiply scattered light to be diminished, has previously demonstrated improvements in image quality and contrast for spray imaging. In the current study the method is applied to a controlled confined environment consisting of a mixture of water and monodisperse polystyrene microspheres. Elastic scattering and fluorescence are studied and the results obtained when probing different particle concentrations and diameters conclusively show the advantages of SLIPI for imaging within moderately turbid media. Although the technique presents both good repeatability and agreement with the Beer-Lambert law, discrepancies in its performance were, however, discovered. Photons undergoing scattering without changing their incident trajectory cannot be discriminated and, owing to differences in scattering phase functions, probing larger particles reduces the suppression of multiply scattered light. However, in terms of visibility such behavior is beneficial as it allows denser media to be probed. It is further demonstrated that the suppression of diffuse light performs equally well regardless of whether photons propagate along the incident direction or towards the camera. In addition, this filtering process acts independently on the spatial distribution of the multiply scattered light but is limited by the finite dynamic range and unavoidable signal noise of the camera.Optics Express 07/2011; 19(14):13647-63. · 3.59 Impact Factor -
Article: Extinction coefficient imaging of turbid media using dual structured laser illumination planar imaging.
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ABSTRACT: We demonstrate a technique, named dual structured laser illumination planar imaging (SLIPI), capable of acquiring depth-resolved images of the extinction coefficient. This is achieved by first suppressing the multiply scattered light intensity and then measuring the intensity reduction caused by signal attenuation between two laser sheets separated by Δz mm. Unlike other methods also able to measure this quantity, the presented approach is based solely on side-scattering detection. The main advantages of dual SLIPI is that it accounts for multiple scattering, provides two-dimensional information, and can be applied on inhomogeneous media.Optics Letters 05/2011; 36(9):1656-8. · 3.40 Impact Factor -
Article: Quantitative image contrast enhancement in time-gated transillumination of scattering media.
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ABSTRACT: Experimental work in turbid media has shown that trans-illumination images can be significantly improved by limiting light collection to a subset of photons which are minimally distorted by scattering. The literature details numerous schemes (commonly termed ballistic imaging), most often based on time-gating and/or spatially filtering the detected light. However, due to the complex nature of the detected signal, analysis of this optical filtering process has been heretofore limited to qualitative comparisons of image results. In this article we present the implementation of a complete system model for the simulation of light propagation, including both the scattering medium and all stages of the optical train. Validation data from ballistic imaging (BI) measurements of monodisperse scatterers with diameter, d = 0.7 µm, at optical depths 5, 10, and 14, are compared with model results, showing excellent agreement. In addition, the validated model is subsequently applied to a modified time-gated optical system to probe the comparative performance of the BI system used in validation and the modified BI system. This instrument comparison examines scatterers with diameters of 0.7 and 15 µm at optical depths 10 and 14, and highlights the benefits of each system design for these specific scattering conditions. These results show that the modified optics configuration is more suitable for particles which are much larger than the incident wavelength, d > λ, while the configuration employed in the validation system provides a better contrast for particle diameters on the order of the wavelength, d ~λ, where the scattering process exhibits a more homogeneous phase function. The insights and predictions made available by the full numerical model are important for the design of optimized imaging systems suited to specific turbid media, and make possible the quantitative understanding of both the effects of light propagation in the measurement and the performance of the complete imaging system.Optics Express 01/2011; 19(3):1866-83. · 3.59 Impact Factor
