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Lihong V Wang - One of the best experts on this subject based on the ideXlab platform.

  • dependence of optical Scattering from intralipid in gelatin gel based tissue mimicking phantoms on mixing temperature and time
    Journal of Biomedical Optics, 2014
    Co-Authors: Puxiang Lai, Lihong V Wang
    Abstract:

    Intralipid is widely used as an optical Scattering agent in tissue-mimicking phantoms. Accurate control when using Intralipid is critical to match the optical diffusivity of phantoms to the prescribed value. Currently, most protocols of Intralipid-based hydrogel phantom fabrication focus on factors such as Intralipid brand and concentration. In this note, for the first time to our knowledge, we explore the dependence of the optical Reduced Scattering Coefficient (at 532 nm optical wavelength) on the temperature and the time of mixing Intralipid with gelatin-water solution. The studied samples contained 1% Intralipid and were measured with oblique-incidence reflectometry. It was found that the Reduced Scattering Coefficient increased when the Intralipid-gelatin-water mixture began to solidify at room temperature. For phantoms that had already solidified completely, the diffusivity was shown to be significantly influenced by the temperature and the duration of the mixing course. The dependence of the measured diffusivity on the mixing conditions was confirmed by experimental observations. Moreover, the mechanism behind the dependence behavior is discussed.

  • Development of tissue-simulating optical phantoms: poly-N-isopropylacrylamide solution entrapped inside a hydrogel.
    Physics in medicine and biology, 1999
    Co-Authors: Guillermo Marquez, Lihong V Wang, Changjie Wang
    Abstract:

    The average turbid optical properties of the N-isopropylacrylamide (NIPA) polymer solution entrapped inside a polyacrylamide hydrogel (called an NIPA/PAAM gel system) were studied using a multiwavelength oblique-incidence reflectometer. The turbidity of such a system can be drastically changed by simply switching the temperature from below the low critical solution temperature of the NIPA, around 33°C, to above. The absorption Coefficient and the Reduced Scattering Coefficient were obtained as a function of wavelength for samples with selected NIPA and blue dextran concentrations. It is found that the Scattering of the optical phantom comes from the NIPA polymer chains and the absorption from the blue dextran. The turbid optical properties of an NIPA/PAAM gel system can be tuned to simulate biological tissues at a specific wavelength by varying compositions of NIPA and blue dextran and further modified by controlling the temperature.

  • Turbid acousto-optics and its potential for biomedical applications
    Proceedings of the 19th Annual International Conference of the IEEE Engineering in Medicine and Biology Society. 'Magnificent Milestones and Emerging , 1997
    Co-Authors: Lihong V Wang
    Abstract:

    Continuous-wave ultrasonic modulation of scattered laser light has been used to image objects in tissue-simulating turbid media for the first time. The modulated laser light collected by a photomultiplier tube reflected the local mechanical and optical properties in the modulation zone. Buried objects in 5-cm thick tissue phantoms were imaged with millimeter resolution by scanning and detecting alterations of the ultrasound-modulated optical signal. The tissue phantoms had the following optical properties: absorption Coefficient /spl mu//sub a/=0.1 cm/sup -1/, Reduced Scattering Coefficient /spl mu//sub s/'=10 cm/sup -1/, which are comparable with those of biological tissues in the visible and near IR range. This technique is merely a representation of a much broader discipline coined turbid acousto-optics, which means acousto-optics in turbid media.

  • Ultrasound-modulated optical tomography of absorbing objects buried in dense tissue-simulating turbid media
    Applied optics, 1997
    Co-Authors: Lihong V Wang, Xuemei Zhao
    Abstract:

    Continuous-wave ultrasonic modulation of scattered laser light was used to image objects buried in tissue-simulating turbid media. The buried object had an absorption Coefficient greater than the background turbid medium. The ultrasonic wave that was focused into the turbid media modulated the laser light that passed through the ultrasonic field. The modulated laser light that was collected by a photomultiplier tube reflected the local mechanical and optical properties in the zone of ultrasonic modulation. Objects buried in the middle plane of 5-cm-thick dense turbid media were imaged with millimeter resolution through the scanning and detecting alterations of the ultrasound-modulated optical signal. The optical properties of the dense turbid media included an absorption Coefficient of 0.1 cm-1 and a Reduced Scattering Coefficient of 10 cm-1 and were comparable with those of biological tissues in the visible and near-IR ranges. The dependence of the ultrasound-modulated optical signal on the off-axis distance of the detector from the optic axis and the area of the detector was studied as well.

  • use of a laser beam with an oblique angle of incidence to measure the Reduced Scattering Coefficient of a turbid medium
    Applied Optics, 1995
    Co-Authors: Lihong V Wang, Steven L Jacques
    Abstract:

    A simple and quick approach is used to measure the Reduced Scattering Coefficient (μs′) of a semi-infinite turbid medium having a much smaller absorption Coefficient than μs′. A laser beam with an oblique angle of incidence to the medium causes the center of the diffuse reflectance that is several transport mean-free paths away from the incident point to shift away from the point of incidence by an amount Δx. This amount is used to compute μs′ by μs′ = sin(αi)/(nΔx), where n is the refractive index of the turbid medium divided by that of the incident medium and αi is the angle of incidence measured from the surface normal. For a turbid medium having an absorption Coefficient comparable with μs′, a revision to the above formula is made. This method is tested theoretically by Monte Carlo simulations and experimentally by a video reflectometer.

Arjen Amelink - One of the best experts on this subject based on the ideXlab platform.

Steven L Jacques - One of the best experts on this subject based on the ideXlab platform.

  • in vivo determination of optical properties of normal and tumor tissue with white light reflectance and an empirical light transport model during endoscopy
    Journal of Biomedical Optics, 2005
    Co-Authors: Paulo R Bargo, Scott A Prahl, Teresa Tarnowski Goodell, R Sleven, G Koval, G Blair, Steven L Jacques
    Abstract:

    Determination of tissue optical properties is fundamental for application of light in either therapeutical or diagnostics proce- dures. In the present work we implemented a spatially resolved steady-state diffuse reflectance method where only two fibers (one source and one detector) spaced 2.5 mm apart are used for the deter- mination of the optical properties. The method relies on the spectral characteristics of the tissue chromophores (water, dry tissue, and blood) and the assumption of a simple wavelength dependent expres- sion for the determination of the Reduced Scattering Coefficient. Be- cause of the probe dimensions the method is suited for endoscopic measurements. The method was validated against more traditional models, such as the diffusion theory combined with adding doubling for in vitro measurements of bovine muscle. Mean and standard de- viation of the absorption Coefficient and the Reduced Scattering coef- ficient at 630 nm for normal mucosa were 0.8760.22 cm ˛1 and 7.8 62.3 cm ˛1 , respectively. Cancerous mucosa had values 1.8761.10 cm ˛1 and 8.462.3 cm ˛1 , respectively. These values are similar to data presented by other authors. Blood perfusion was the main variable accounting for differences in the absorption Coefficient between the studied tissues. © 2005 Society of Photo-Optical Instrumentation Engineers.

  • in vivo determination of optical properties of normal and tumor tissue with white light reflectance and an empirical light transport model during endoscopy
    Journal of Biomedical Optics, 2005
    Co-Authors: Paulo R Bargo, Scott A Prahl, Teresa Tarnowski Goodell, R Sleven, G Koval, G Blair, Steven L Jacques
    Abstract:

    Determination of tissue optical properties is fundamental for application of light in either therapeutical or diagnostics procedures. In the present work we implemented a spatially resolved steady-state diffuse reflectance method where only two fibers (one source and one detector) spaced 2.5 mm apart are used for the determination of the optical properties. The method relies on the spectral characteristics of the tissue chromophores (water, dry tissue, and blood) and the assumption of a simple wavelength dependent expression for the determination of the Reduced Scattering Coefficient. Because of the probe dimensions the method is suited for endoscopic measurements. The method was validated against more traditional models, such as the diffusion theory combined with adding doubling for in vitro measurements of bovine muscle. Mean and standard deviation of the absorption Coefficient and the Reduced Scattering Coefficient at 630 nm for normal mucosa were 0.87+/-0.22 cm(-1) and 7.8+/-2.3 cm(-1), respectively. Cancerous mucosa had values 1.87+/-1.10 cm(-1) and 8.4+/-2.3 cm(-1), respectively. These values are similar to data presented by other authors. Blood perfusion was the main variable accounting for differences in the absorption Coefficient between the studied tissues.

  • use of a laser beam with an oblique angle of incidence to measure the Reduced Scattering Coefficient of a turbid medium
    Applied Optics, 1995
    Co-Authors: Lihong V Wang, Steven L Jacques
    Abstract:

    A simple and quick approach is used to measure the Reduced Scattering Coefficient (μs′) of a semi-infinite turbid medium having a much smaller absorption Coefficient than μs′. A laser beam with an oblique angle of incidence to the medium causes the center of the diffuse reflectance that is several transport mean-free paths away from the incident point to shift away from the point of incidence by an amount Δx. This amount is used to compute μs′ by μs′ = sin(αi)/(nΔx), where n is the refractive index of the turbid medium divided by that of the incident medium and αi is the angle of incidence measured from the surface normal. For a turbid medium having an absorption Coefficient comparable with μs′, a revision to the above formula is made. This method is tested theoretically by Monte Carlo simulations and experimentally by a video reflectometer.

Giovanni Zaccanti - One of the best experts on this subject based on the ideXlab platform.

  • effect of dependent Scattering on the optical properties of intralipid tissue phantoms
    Biomedical Optics Express, 2011
    Co-Authors: Paola Di Ninni, Fabrizio Martelli, Giovanni Zaccanti
    Abstract:

    The calibration of optical tissue-simulating phantoms remains an open question in spite of the many techniques proposed for accurate measurements of optical properties. As a consequence, a reference phantom with well known optical properties is still missing. As a first step towards a reference phantom we have recently proposed to use dilutions of Intralipid 20%. In this paper we discuss a matter that is commonly ignored when dilutions are prepared, i.e., the possibility of deviations from the simple linear relationships between the optical properties of the dilution and the Intralipid concentration due to the effects of dependent Scattering. The results of an experimental investigation showed that dependent Scattering does not affect absorption. As for the Reduced Scattering Coefficient the effect can be described adding a term proportional to the square of the concentration. However, for concentrations of interest for tissue optics deviations from linearity remain within about 2%. The experimental investigation also showed that the microphysical properties of Intralipid are not affected by dilution. These results show the possibility to easily obtain a liquid diffusive phantom whose optical properties are known with error smaller than about 1%. Due to the intrinsic limitations of the different techniques proposed for measuring the optical properties it seems difficult to obtain a similar accuracy for solid phantoms.

  • calibration of Scattering and absorption properties of a liquid diffusive medium at nir wavelengths time resolved method
    Optics Express, 2007
    Co-Authors: Lorenzo Spinelli, Fabrizio Martelli, Antonio Pifferi, Andrea Farina, Alessandro Torricelli, Rinaldo Cubeddu, Giovanni Zaccanti
    Abstract:

    In this paper, a general method to calibrate the absorption Coefficient of an absorber and the Reduced Scattering Coefficient of a liquid diffusive medium, based on time-resolved measurements, is reported. An exhaustive analysis of the error sources affecting the estimation is also performed. The method has been applied with a state-of-the-art time-resolved instrumentation to determine the intrinsic absorption Coefficient of Indian ink and the Reduced Scattering Coefficient of Intralipid-20%, with a standard error smaller than 1% and 2%, respectively. Finally, the results have been compared to those retrieved for the same compounds by applying a continuous wave method recently published, obtaining an agreement within the error bars. This fact represents a cross validation of the two independent calibration methods.

  • Calibration of Scattering and absorption properties of a liquid diffusive medium at NIR wavelengths. CW method.
    Optics Express, 2007
    Co-Authors: Fabrizio Martelli, Giovanni Zaccanti
    Abstract:

    In spite of many progresses achieved both with theories and with experiments in studying light propagation through diffusive media, a reliable method for accurate measurements of the optical properties of diffusive media at NIR wavelengths is, in our opinion, still missing. It is therefore difficult to create a diffusive medium with well known optical properties to be used as a reference. In this paper we describe a method to calibrate the Reduced Scattering Coefficient, μs, of a liquid diffusive medium and the absorption Coefficient, μa, of an absorbing medium with a standard error smaller than 2% both on μs and on μa. The method is based on multidistance measurements of fluence into an infinite medium illuminated by a CW source. The optical properties are retrieved with simple inversion procedures (linear fits) exploiting the knowledge of the absorption Coefficient of the liquid into which the diffuser and the absorber are dispersed. In this study Intralipid diluted in water has been used as diffusive medium and Indian ink as absorber. For a full characterization of these media measurements of collimated transmittance have also been carried out, from which the asymmetry factor of the Scattering function of Intralipid and the single Scattering albedo of Indian ink have been determined.

  • measurements of optical properties of high density media
    Applied Optics, 2003
    Co-Authors: Giovanni Zaccanti, Samuele Del Bianco, Fabrizio Martelli
    Abstract:

    Measurements of optical properties (Scattering Coefficient μs, absorption Coefficient μa, Reduced Scattering Coefficient μs′, and asymmetry factor g) have been carried out up to a volume particle concentration of ρ = 0.227. The results for μs and μs′ show significant deviations from the linear dependence on ρ as expected when the independent Scattering assumption is fulfilled. The asymmetry factor also changed significantly. In contrast, the dependence of μa remained linear even at the largest concentration investigated. The simple linear dependence of absorption on the chromophore concentration expected from the independent Scattering assumption is thus applicable also to spectroscopic measurements of dense media. A comparison with an approximate theoretical model based on the Foldy-Twersky equation is also reported. The model provides a good description of the dependence of μs on particle concentration.

Stephen C Kanick - One of the best experts on this subject based on the ideXlab platform.

  • dual channel red blue fluorescence dosimetry with broadband reflectance spectroscopic correction measures protoporphyrin ix production during photodynamic therapy of actinic keratosis
    Journal of Biomedical Optics, 2014
    Co-Authors: Stephen C Kanick, Brian W Pogue, Scott C Davis, Yan Zhao, Tayyaba Hasan, V Edward M D Maytin, Shane M Chapman
    Abstract:

    Dosimetry for aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) photodynamic therapy of actinic keratosis was examined with an optimized fluorescence dosimeter to measure PpIX during treatment. While insufficient PpIX generation may be an indicator of incomplete response, there exists no standardized method to quantitate PpIX production at depths in the skin during clinical treatments. In this study, a spectrometer-based point probe dosimeter system was used to sample PpIX fluorescence from superficial (blue wavelength excitation) and deeper (red wavelength excitation) tissue layers. Broadband white light spectroscopy (WLS) was used to monitor aspects of vascular physiology and inform a correction of fluorescence for the background optical properties. Measurements in tissue phantoms showed accurate recovery of blood volume fraction and Reduced Scattering Coefficient from WLS, and a linear response of PpIX fluorescence versus concentration down to 1.95 and 250 nM for blue and red excitations, respectively. A pilot clinical study of 19 patients receiving 1-h ALA incubation before treatment showed high intrinsic variance in PpIX fluorescence with a standard deviation/mean ratio of >0.9. PpIX fluorescence was significantly higher in patients reporting higher pain levels on a visual analog scale. These pilot data suggest that patient-specific PpIX quantitation may predict outcome response.

  • quantification of the Reduced Scattering Coefficient and phase function dependent parameter γ of turbid media using multidiameter single fiber reflectance spectroscopy experimental validation
    Optics Letters, 2012
    Co-Authors: Ute A Gamm, Stephen C Kanick, Dominic J Robinson, H J C M Sterenborg, Arjen Amelink
    Abstract:

    Multidiameter single fiber reflectance (MDSFR) spectroscopy is a method that allows the quantification of μs′ and the phase-function-dependent parameter γ of a turbid medium by utilizing multiple fibers with different diameters. We have previously introduced the theory behind MDSFR and its limitations, and here we present an experimental validation of this method based on phantoms containing a fractal distribution of polystyrene spheres both in the absence and presence of the absorber Evans Blue.

  • method to quantitate absorption Coefficients from single fiber reflectance spectra without knowledge of the Scattering properties
    Optics Letters, 2011
    Co-Authors: Stephen C Kanick, Henricus J C M Sterenborg, Dominic J Robinson, Arjen Amelink
    Abstract:

    This study presents a methodology to accurately extract the absorption Coefficient from single fiber reflectance spectra measured in turbid media without a priori knowledge of either the Reduced Scattering Coefficient or the phase function. This novel approach accounts for the interrelated effects these properties have on the photon path length, yielding estimates of an absorption Coefficient on average within <7.5% of true values over a wide range of biologically relevant optical properties.

  • measurement of the Reduced Scattering Coefficient of turbid media using single fiber reflectance spectroscopy fiber diameter and phase function dependence
    Biomedical Optics Express, 2011
    Co-Authors: Stephen C Kanick, Henricus J C M Sterenborg, Ute A Gamm, M Schouten, Dominic J Robinson, Arjen Amelink
    Abstract:

    This paper presents a relationship between the intensity collected by a single fiber reflectance device (RSF) and the fiber diameter (dfib) and the Reduced Scattering Coefficient ( μs′) and phase function (p(θ)) of a turbid medium. Monte Carlo simulations are used to identify and model a relationship between RSF and dimensionless Scattering ( μs′dfib). For μs′dfib > 10 we find that RSF is insensitive to p(θ). A solid optical phantom is constructed with μs′ ≈ 220 mm−1 and is used to convert RSF of any turbid medium to an absolute scale. This calibrated technique provides accurate estimates of μs′ over a wide range ([0.05 – 8] mm−1) for a range of dfib ([0.2 – 1] mm).