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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Tue, 14 Jul 2020 06:09:07 GMT2020-07-14T06:09:07ZAssessment of tissue optical parameters in a spherical geometry using three different optical spectroscopy methods: comparison based on a theoretical approach
http://hdl.handle.net/10985/10055
Assessment of tissue optical parameters in a spherical geometry using three different optical spectroscopy methods: comparison based on a theoretical approach
VAUDELLE, Fabrice; ASKOURA, Mohamed Lamine; L'HUILLIER, Jean-Pierre
The non-invasive research of information inside the biological tissues can be made by means of continuous, time dependent or frequency modulated light source, emitting in the visible or infrared range. Moreover, the biological structures such as brain, breast or fruits, can be seen as closer to a spherical shape than a slab. This paper focus on the retrieval of tissue optical parameters in a spherical geometry using fittings with an analytical solution adapted for semi infinite geometry. The data were generated using three different optical spetroscopy methods: frequency-resolved, spatially-resolved, and time-resolved. Simulations based on a Monte Carlo code were performed on a homogeneous sphere, with 18 spaced detectors located at the periphery. First, data are examinated in the frequency domain, then, they are treated with optimization algorithms to assess the optical coefficients. The computations show that the spatially resolved measurements are often more robust than those obtained by the frequency-resolved mode. In the temporal domain, errors on the estimates are also exhibited with the fitting by the Fourier transform of a solution based on the semi-infinite geometry. Furthermore, when the analytical solution is modified to take into account the sphere geometry, the retrieval of the coefficients is improved.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/100552015-01-01T00:00:00ZVAUDELLE, FabriceASKOURA, Mohamed LamineL'HUILLIER, Jean-PierreThe non-invasive research of information inside the biological tissues can be made by means of continuous, time dependent or frequency modulated light source, emitting in the visible or infrared range. Moreover, the biological structures such as brain, breast or fruits, can be seen as closer to a spherical shape than a slab. This paper focus on the retrieval of tissue optical parameters in a spherical geometry using fittings with an analytical solution adapted for semi infinite geometry. The data were generated using three different optical spetroscopy methods: frequency-resolved, spatially-resolved, and time-resolved. Simulations based on a Monte Carlo code were performed on a homogeneous sphere, with 18 spaced detectors located at the periphery. First, data are examinated in the frequency domain, then, they are treated with optimization algorithms to assess the optical coefficients. The computations show that the spatially resolved measurements are often more robust than those obtained by the frequency-resolved mode. In the temporal domain, errors on the estimates are also exhibited with the fitting by the Fourier transform of a solution based on the semi-infinite geometry. Furthermore, when the analytical solution is modified to take into account the sphere geometry, the retrieval of the coefficients is improved.Time-resolved optical fluorescence spectroscopy of heterogeneous turbid media with special emphasis on brain tissue structures including diseased regions: A sensitivity analysis
http://hdl.handle.net/10985/8511
Time-resolved optical fluorescence spectroscopy of heterogeneous turbid media with special emphasis on brain tissue structures including diseased regions: A sensitivity analysis
VAUDELLE, Fabrice; L'HUILLIER, Jean-Pierre
Fluorescence-enhanced optical imaging based on near-infrared light provides a promising tool to differentiate diseased lesions from normal tissue. However, the measurement sensitivity of the fluorescence signals acquired at the output surface of the tissue is greatly influenced by the tissue structure, the optical properties, the location and the size of the target. In this paper, we present a numerical model based on the Monte Carlo method that allows to simulate time-resolved reflectance signals acquired on the surface of the scalp of a human head model bearing a fluorescent diseased region (tumor, glioma). The influence of tumor depth, tumor size and tumor shape evolution on the computed signals are analyzed by taking into account the multi-layered tissue structure. The simulations show that the mean-time-of-flight and the difference between two mean-times acquired at two source–detector distances are both relevant to this problem type. Furthermore, the simulations suggest that the use of the difference between mean-flight-times may be interesting to probe scattering changes that occur in the cerebrospinal fluid (CSF).
Tue, 01 Jan 2013 00:00:00 GMThttp://hdl.handle.net/10985/85112013-01-01T00:00:00ZVAUDELLE, FabriceL'HUILLIER, Jean-PierreFluorescence-enhanced optical imaging based on near-infrared light provides a promising tool to differentiate diseased lesions from normal tissue. However, the measurement sensitivity of the fluorescence signals acquired at the output surface of the tissue is greatly influenced by the tissue structure, the optical properties, the location and the size of the target. In this paper, we present a numerical model based on the Monte Carlo method that allows to simulate time-resolved reflectance signals acquired on the surface of the scalp of a human head model bearing a fluorescent diseased region (tumor, glioma). The influence of tumor depth, tumor size and tumor shape evolution on the computed signals are analyzed by taking into account the multi-layered tissue structure. The simulations show that the mean-time-of-flight and the difference between two mean-times acquired at two source–detector distances are both relevant to this problem type. Furthermore, the simulations suggest that the use of the difference between mean-flight-times may be interesting to probe scattering changes that occur in the cerebrospinal fluid (CSF).Assessment of the effective attenuation coefficient of scattering media illuminated by a LED array : Effect of the beam size
http://hdl.handle.net/10985/10054
Assessment of the effective attenuation coefficient of scattering media illuminated by a LED array : Effect of the beam size
LE POMMELLEC, Jean-Yves; PIRON, Vianney; ASKOURA, Mohamed Lamine; L'HUILLIER, Jean-Pierre
The knowledge of the light fluence rate distribution inside a biological tissue irradiated by a Laser (or LED) is fundamental to achieve medical treatments. In this paper, we present a semi-analytical model based on the 2-D Fourier Transform of the diffusion equation. This method can be applied to any irradiation source (cylindrically symmetric or not) at the surface of the tissue. Two particular beam shapes are studied: planar irradiation and flat beam with finite radius. The total fluence rate along the depth in tissues was computed by adding the collimated and the diffuse components. The analytical solution was also used to study the effect of the beam radius on the light attenuation. Measurements were performed using a tank filled with a liquid-simulating medium (Milk), illuminated with a LED array (660 nm, 100mm×100mm). Several circular diaphragms were used to obtain uniform circular beams with well defined radii. An optical fibre (with an isotropic tip) was used to measure the fluence rate inside the medium. Preliminary experimental results are in agreement with theoretical predictions.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/100542015-01-01T00:00:00ZLE POMMELLEC, Jean-YvesPIRON, VianneyASKOURA, Mohamed LamineL'HUILLIER, Jean-PierreThe knowledge of the light fluence rate distribution inside a biological tissue irradiated by a Laser (or LED) is fundamental to achieve medical treatments. In this paper, we present a semi-analytical model based on the 2-D Fourier Transform of the diffusion equation. This method can be applied to any irradiation source (cylindrically symmetric or not) at the surface of the tissue. Two particular beam shapes are studied: planar irradiation and flat beam with finite radius. The total fluence rate along the depth in tissues was computed by adding the collimated and the diffuse components. The analytical solution was also used to study the effect of the beam radius on the light attenuation. Measurements were performed using a tank filled with a liquid-simulating medium (Milk), illuminated with a LED array (660 nm, 100mm×100mm). Several circular diaphragms were used to obtain uniform circular beams with well defined radii. An optical fibre (with an isotropic tip) was used to measure the fluence rate inside the medium. Preliminary experimental results are in agreement with theoretical predictions.Analyse théorique et expérimentale de la diffusion de la lumière générée par une diode électroluminescente dans des répliques tissulaires
http://hdl.handle.net/10985/8471
Analyse théorique et expérimentale de la diffusion de la lumière générée par une diode électroluminescente dans des répliques tissulaires
LE POMMELLEC, Jean-Yves; L'HUILLIER, Jean-Pierre
The knowledge of the spatial distribution of light within a biological tissue exited by a light source (LASER or LED) is fundamental to achieve optimal photodynamic treatment. In this paper, we develop an analytical model relative to the diffuse fluence rate within a tissue-like medium irradiated by a continuous-wave light emitting diode (LED). The model is based on the two dimensional Fourier transform and applied to a homogeneous tissue slab. The total fluence rate along the axis of the medium was computed by adding the collimated and the diffuse components. The analytical solution was also used to study the depth evolution of the photon fluence rate as functions of the finite source beam size and the tissue optical parameters. Measurement results were performed using a tank filled with a liquid-simulating turbid medium (milk) illuminated with a LED beam. The experimental behaviour results agree with the theoretical predictions.
Sat, 01 Jan 2011 00:00:00 GMThttp://hdl.handle.net/10985/84712011-01-01T00:00:00ZLE POMMELLEC, Jean-YvesL'HUILLIER, Jean-PierreThe knowledge of the spatial distribution of light within a biological tissue exited by a light source (LASER or LED) is fundamental to achieve optimal photodynamic treatment. In this paper, we develop an analytical model relative to the diffuse fluence rate within a tissue-like medium irradiated by a continuous-wave light emitting diode (LED). The model is based on the two dimensional Fourier transform and applied to a homogeneous tissue slab. The total fluence rate along the axis of the medium was computed by adding the collimated and the diffuse components. The analytical solution was also used to study the depth evolution of the photon fluence rate as functions of the finite source beam size and the tissue optical parameters. Measurement results were performed using a tank filled with a liquid-simulating turbid medium (milk) illuminated with a LED beam. The experimental behaviour results agree with the theoretical predictions.Influence of the size and skin thickness of apple varieties on the retrieval of internal optical properties using Vis/NIR spectroscopy: A Monte Carlo-based study
http://hdl.handle.net/10985/10053
Influence of the size and skin thickness of apple varieties on the retrieval of internal optical properties using Vis/NIR spectroscopy: A Monte Carlo-based study
VAUDELLE, Fabrice; L'HUILLIER, Jean-Pierre
Visible/near-infrared spectroscopy is a well-established method to measure optical properties of tissues, assuming that a light propagation model can be used to recover absorption and reduced scattering coefficients from non-invasive probing. Spectroscopic measurements have achieved success in non-destructive assessment of apple optical properties and quality attributes. However, the spectroscopy of apples must consider the size of the fruit and the presence of the thin skin layer that surrounds the flesh, to correctly read the signals acquired on the boundary. In this research, the fruit was modelled as a two layer spherical structure with various radii and finite thickness of the upper skin layer. Monte Carlo computations were performed to generate time-resolved reflectance and spatially-resolved reflectance measurements. Simulated data were then fitted using a procedure based on Levenberg–Marquardt algorithm with specific semi-infinite models. The errors in the retrieved optical properties of the flesh (absorption coefficient μa, and reduced scattering coefficient μ′s) were studied as functions of apple radius, skin thickness, and source–detector distance, for given optical parameter sets assigned to the flesh and the skin. The results suggest that the time-resolved reflectance spectroscopy may probe optical properties of the flesh regardless of the skin layer, when a sufficient source–detector distance (15 mm) is used for the measurements. Similar results were found in case of using the spatially resolved spectroscopy, because measurements extend up to 15–29 mm by steps of 1 mm or 2 mm. The computations also show that the curvature of the boundary has noticeable effect on the errors in the retrieved optical coefficients of the flesh. However, results from time-resolved spectroscopy are more influenced by the size of apples, compared with the spatially-resolved spectroscopy.
Thu, 01 Jan 2015 00:00:00 GMThttp://hdl.handle.net/10985/100532015-01-01T00:00:00ZVAUDELLE, FabriceL'HUILLIER, Jean-PierreVisible/near-infrared spectroscopy is a well-established method to measure optical properties of tissues, assuming that a light propagation model can be used to recover absorption and reduced scattering coefficients from non-invasive probing. Spectroscopic measurements have achieved success in non-destructive assessment of apple optical properties and quality attributes. However, the spectroscopy of apples must consider the size of the fruit and the presence of the thin skin layer that surrounds the flesh, to correctly read the signals acquired on the boundary. In this research, the fruit was modelled as a two layer spherical structure with various radii and finite thickness of the upper skin layer. Monte Carlo computations were performed to generate time-resolved reflectance and spatially-resolved reflectance measurements. Simulated data were then fitted using a procedure based on Levenberg–Marquardt algorithm with specific semi-infinite models. The errors in the retrieved optical properties of the flesh (absorption coefficient μa, and reduced scattering coefficient μ′s) were studied as functions of apple radius, skin thickness, and source–detector distance, for given optical parameter sets assigned to the flesh and the skin. The results suggest that the time-resolved reflectance spectroscopy may probe optical properties of the flesh regardless of the skin layer, when a sufficient source–detector distance (15 mm) is used for the measurements. Similar results were found in case of using the spatially resolved spectroscopy, because measurements extend up to 15–29 mm by steps of 1 mm or 2 mm. The computations also show that the curvature of the boundary has noticeable effect on the errors in the retrieved optical coefficients of the flesh. However, results from time-resolved spectroscopy are more influenced by the size of apples, compared with the spatially-resolved spectroscopy.Use of steady-state imaging setup for assessing the internal optical properties of non-spherical apple samples
http://hdl.handle.net/10985/17256
Use of steady-state imaging setup for assessing the internal optical properties of non-spherical apple samples
ASKOURA, Mohamed Lamine; VAUDELLE, Fabrice; L'HUILLIER, Jean-Pierre
The aim of this paper was to retrieve the absorption (µa) and reduced scattering (µ's) coefficients of whole apples which exhibit a complex shape. The effect of the local boundary curvature on the retrieved optical properties was investigated by means of numerical simulations and measurements carried out at the wavelength of 633 nm. A first attempt was made by performing Monte Carlo simulations on an apple-like spheroid model covered with a thin skin layer of thickness 80 µm. Monte Carlo data were then analyzed to depict the changes of photon densities, diffusively reflected images and optical properties as a function of the light source location over the surface of such target. Second, spatially-resolved backscattered images were acquired from 207 ‘Royal Gala’, and the values of µa and µ's were retrieved using an inverse algorithm to fit the scattering profiles with a diffusion theory model, in a selected fitting range of 2.8–10 mm. The results confirm the theoretical prediction and show that the absorption coefficient µa may be overestimated, while the reduced scattering coefficient µ's is slowly changed when the measurements are performed on these apple species. Finally, experiments carried out on 200 apples still show that µ's is negatively correlated to the fruit firmness with a correlation coefficient (r) of 0.63. The spatially-resolved technique provides an efficient means for measuring the optical properties of fruits, and may be also useful for assessing the apple firmness.
Tue, 01 Jan 2019 00:00:00 GMThttp://hdl.handle.net/10985/172562019-01-01T00:00:00ZASKOURA, Mohamed LamineVAUDELLE, FabriceL'HUILLIER, Jean-PierreThe aim of this paper was to retrieve the absorption (µa) and reduced scattering (µ's) coefficients of whole apples which exhibit a complex shape. The effect of the local boundary curvature on the retrieved optical properties was investigated by means of numerical simulations and measurements carried out at the wavelength of 633 nm. A first attempt was made by performing Monte Carlo simulations on an apple-like spheroid model covered with a thin skin layer of thickness 80 µm. Monte Carlo data were then analyzed to depict the changes of photon densities, diffusively reflected images and optical properties as a function of the light source location over the surface of such target. Second, spatially-resolved backscattered images were acquired from 207 ‘Royal Gala’, and the values of µa and µ's were retrieved using an inverse algorithm to fit the scattering profiles with a diffusion theory model, in a selected fitting range of 2.8–10 mm. The results confirm the theoretical prediction and show that the absorption coefficient µa may be overestimated, while the reduced scattering coefficient µ's is slowly changed when the measurements are performed on these apple species. Finally, experiments carried out on 200 apples still show that µ's is negatively correlated to the fruit firmness with a correlation coefficient (r) of 0.63. The spatially-resolved technique provides an efficient means for measuring the optical properties of fruits, and may be also useful for assessing the apple firmness.