Research Interests:
Research Interests:
ABSTRACT
Research Interests:
Research Interests: Computer Science, Materials Science, Biomedical Engineering, Imaging, Medicine, and 15 moreMonte Carlo Methods, Humans, Models, Computer Simulation, Infrared spectroscopy, Diffusion, Animals, Biological, Light, Diffusion Model, Detector, Electrical And Electronic Engineering, Biomedical Application, Monte Carlo Method, and Human skin
Research Interests:
Research Interests: Mechanical Engineering, Physics, Computational Physics, Optics, Medicine, and 13 moreDiffusion, Spatial Scale, Asymmetry, Applied Optics, Optical physics, Irradiance, Scattering, Radiative Transfer, Boltzmann Transport Equation, Electrical And Electronic Engineering, Nonlinear Optimization, Turbid Media, and Optical Absorption
Research Interests:
Research Interests: Applied Mathematics, Computer Science, Physics, Biomedical Engineering, Reciprocity (Social and Cultural Anthropology), and 8 moreMonte Carlo Simulation, Inverse Problems, Monte Carlo Methods, Optical physics, Optometry and Ophthalmology, Radiative Transfer, Monte Carlo Method, and Biological Applications
Research Interests: Mechanical Engineering, Materials Science, Optics, Optical Tomography, Optical coherence tomography, and 15 moreMedicine, Biomedical Optics, Broadband, Computer Simulation, Diffusion, Light, Connective tissue, Optical Properties, Applied Optics, Optical physics, BioSilico, Electrical And Electronic Engineering, Nephelometry and Turbidimetry, Diffuse Reflection, and Optical Absorption
ABSTRACT
Research Interests:
Research Interests:
Research Interests:
Research Interests:
ABSTRACT We present a method for performing quantitative spectroscopy of superficial tissue volumes. We have employed a two-layer model, for which the upper, high-scattering layer's optical properties are known, to recover the... more
ABSTRACT We present a method for performing quantitative spectroscopy of superficial tissue volumes. We have employed a two-layer model, for which the upper, high-scattering layer's optical properties are known, to recover the optical properties of phantoms.
Research Interests:
ABSTRACT We present a method for performing quantitative spectroscopy of superficial tissue volumes. We investigate the performance of this technique over a range of optical properties and by varying the top layer thickness of two-layer... more
ABSTRACT We present a method for performing quantitative spectroscopy of superficial tissue volumes. We investigate the performance of this technique over a range of optical properties and by varying the top layer thickness of two-layer phantoms.
Research Interests:
Research Interests: Bioinformatics, Physics, Light Scattering, Life Sciences, Quantum Monte Carlo, and 14 moreStatistical Physics, Medicine, Transport, Biomedical Research, Optical Properties, Reflectance Spectroscopy, Collection, In Vivo, Scattering, Monte Carlo Method, Probes, Turbid Media, mammalian cells, and phantoms
Research Interests:
Research Interests: Engineering, Optics, Biomedical Engineering, Image Processing, Monte Carlo Simulation, and 15 moreMedicine, Optical Imaging, Biomedical Optics, Brain, Humans, Mice, Animals, Optical physics, Diffuse Optical Spectroscopy, Optometry and Ophthalmology, Photon, Diffuse Optics, Equipment Design, Monte Carlo Method, and Computer Assisted
Research Interests:
Research Interests:
Laser speckle imaging (LSI) enables visualization of relative blood flow and perfusion in the skin. It is frequently applied to monitor treatment of vascular malformations such as port wine stain birthmarks, and measure changes in... more
Laser speckle imaging (LSI) enables visualization of relative blood flow and perfusion in the skin. It is frequently applied to monitor treatment of vascular malformations such as port wine stain birthmarks, and measure changes in perfusion due to peripheral vascular disease. We developed a computational Monte Carlo simulation of laser speckle contrast imaging to quantify how tissue optical properties, blood vessel depths and speeds, and tissue perfusion affect speckle contrast values originating from coherent excitation. The simulated tissue geometry consisted of multiple layers to simulate the skin, or incorporated an inclusion such as a vessel or tumor at different depths. Our simulation used a 30x30mm uniform flat light source to optically excite the region of interest in our sample to better mimic wide-field imaging. We used our model to simulate how dynamically scattered photons from a buried blood vessel affect speckle contrast at different lateral distances (0-1mm) away from the vessel, and how these speckle contrast changes vary with depth (0-1mm) and flow speed (0-10mm/s). We applied the model to simulate perfusion in the skin, and observed how different optical properties, such as epidermal melanin concentration (1%-50%) affected speckle contrast. We simulated perfusion during a systolic forearm occlusion and found that contrast decreased by 35% (exposure time = 10ms). Monte Carlo simulations of laser speckle contrast give us a tool to quantify what regions of the skin are probed with laser speckle imaging, and measure how the tissue optical properties and blood flow affect the resulting images.
Research Interests:
Laser speckle imaging (LSI) enables measurement of relative blood flow in microvasculature and perfusion in tissues. To determine the impact of tissue optical properties and perfusion dynamics on speckle contrast, we developed a... more
Laser speckle imaging (LSI) enables measurement of relative blood flow in microvasculature and perfusion in tissues. To determine the impact of tissue optical properties and perfusion dynamics on speckle contrast, we developed a computational simulation of laser speckle contrast imaging. We used a discrete absorption-weighted Monte Carlo simulation to model the transport of light in tissue. We simulated optical excitation of a uniform flat light source and tracked the momentum transfer of photons as they propagated through a simulated tissue geometry. With knowledge of the probability distribution of momentum transfer occurring in various layers of the tissue, we calculated the expected laser speckle contrast arising with coherent excitation using both reflectance and transmission geometries. We simulated light transport in a single homogeneous tissue while independently varying either absorption (.001-100mm^-1), reduced scattering (.1-10mm^-1), or anisotropy (0.05-0.99) over a range of values relevant to blood and commonly imaged tissues. We observed that contrast decreased by 49% with an increase in optical scattering, and observed a 130% increase with absorption (exposure time = 1ms). We also explored how speckle contrast was affected by the depth (0-1mm) and flow speed (0-10mm/s) of a dynamic vascular inclusion. This model of speckle contrast is important to increase our understanding of how parameters such as perfusion dynamics, vessel depth, and tissue optical properties affect laser speckle imaging.
Research Interests:
Research Interests: Materials Science, Optics, Monte Carlo Simulation, Light Scattering, Monte Carlo, and 15 moreOptical Spectroscopy, Medicine, Diffuse Optical Imaging, Diffusion, Optical Properties, Optical physics, Image Enhancement, Light Propagation, Fiber Optic Technology, Diffusion Model, Equipment Design, Equipment Failure Analysis, Electrical And Electronic Engineering, Nephelometry and Turbidimetry, and Monte Carlo Method
Laser speckle imaging (LSI) enables visualization of relative blood flow and perfusion in the skin. It is frequently applied to monitor treatment of vascular malformations such as port wine stain birthmarks, and measure changes in... more
Laser speckle imaging (LSI) enables visualization of relative blood flow and perfusion in the skin. It is frequently applied to monitor treatment of vascular malformations such as port wine stain birthmarks, and measure changes in perfusion due to peripheral vascular disease. We developed a computational Monte Carlo simulation of laser speckle contrast imaging to quantify how tissue optical properties, blood vessel depths and speeds, and tissue perfusion affect speckle contrast values originating from coherent excitation. The simulated tissue geometry consisted of multiple layers to simulate the skin, or incorporated an inclusion such as a vessel or tumor at different depths. Our simulation used a 30x30mm uniform flat light source to optically excite the region of interest in our sample to better mimic wide-field imaging. We used our model to simulate how dynamically scattered photons from a buried blood vessel affect speckle contrast at different lateral distances (0-1mm) away from the vessel, and how these speckle contrast changes vary with depth (0-1mm) and flow speed (0-10mm/s). We applied the model to simulate perfusion in the skin, and observed how different optical properties, such as epidermal melanin concentration (1%-50%) affected speckle contrast. We simulated perfusion during a systolic forearm occlusion and found that contrast decreased by 35% (exposure time = 10ms). Monte Carlo simulations of laser speckle contrast give us a tool to quantify what regions of the skin are probed with laser speckle imaging, and measure how the tissue optical properties and blood flow affect the resulting images.
Research Interests:
ABSTRACT We present a method for performing quantitative spectroscopy of superficial tissue volumes. We investigate the performance of this technique over a range of optical properties and by varying the top layer thickness of two-layer... more
ABSTRACT We present a method for performing quantitative spectroscopy of superficial tissue volumes. We investigate the performance of this technique over a range of optical properties and by varying the top layer thickness of two-layer phantoms.
Research Interests:
The determination of optical properties of heterogeneous tissues over length scales з 0.1-3mm is a subject of ongoing research. 1, 2 These length scales lie in the transport regime which is intermediate between the coherent regime,... more
The determination of optical properties of heterogeneous tissues over length scales з 0.1-3mm is a subject of ongoing research. 1, 2 These length scales lie in the transport regime which is intermediate between the coherent regime, covered by confocal and optical coherence microscopies, for which the wave properties of light are preserved, and the diffuse regime, covered by conventional photon migration techniques, for which the light propagation is dominated by multiply scatttered photons (и 5mm). The focus in the literature within the transport ...
Research Interests:
Research Interests:
Research Interests: Mathematics, Physics, Optics, Microscopy, Confocal Microscopy, and 15 moreMedicine, Computer Simulation, Focused Ion Beam, Light, Artifacts, Optical physics, Theoretical Models, Optometry and Ophthalmology, Image Enhancement, Scattering, Electric Field, Electrical And Electronic Engineering, Amplitude, Superposition principle, and Finite Difference Time Domain Method
An overview is presented of recent trends in coherent anti-Stokes Raman scattering (CARS) microscopy. We briefly discuss the influence of tissue scattering on the CARS signal, methods for controlling the CARS emission and prospects for... more
An overview is presented of recent trends in coherent anti-Stokes Raman scattering (CARS) microscopy. We briefly discuss the influence of tissue scattering on the CARS signal, methods for controlling the CARS emission and prospects for surface-enhancement of the CARS radiation.
Research Interests:
Research Interests: Biomedical Engineering, Light Scattering, Computer Aided Design, Medicine, Biomedical Optics, and 15 moreHumans, Models, Computer Simulation, Infrared spectroscopy, Diffusion, Animals, Biological, Infrared, Dermoscopy, Diffusion Model, Detector, Equipment Design, Equipment Failure Analysis, Frequency Domain, and diffusion equation
Research Interests:
Research Interests:
Research Interests: Algorithms, Physics, Computational Physics, Optics, Monte Carlo Simulation, and 15 moreInverse Problems, Medicine, Humans, Computer Simulation, Animals, Light, Optical Properties, Inverse Problem, Optical physics, Epithelium, Length scale, Light Propagation, Electrical And Electronic Engineering, Nephelometry and Turbidimetry, and Monte Carlo Method
We introduce a robust method to recover optical absorption, reduced scattering, and single-scattering asymmetry coefficients (μ_a, μ′ _s, g_1) of infinite turbid media over a range of (μ′ _s/μ_a) spanning 3 orders of magnitude. This is... more
We introduce a robust method to recover optical absorption, reduced scattering, and single-scattering asymmetry coefficients (μ_a, μ′ _s, g_1) of infinite turbid media over a range of (μ′ _s/μ_a) spanning 3 orders of magnitude. This is accomplished through the spatially resolved measurement of irradiance at source-detector separations spanning 0.25–8 transport mean free paths (l*). These measurements are rapidly processed by a multistaged nonlinear optimization algorithm in which the measured irradiances are compared with ...
Research Interests:
Due to its simplicity and low cost, laser speckle imaging (LSI) has achieved widespread use in biomedical applications. However, interpretation of the blood-flow maps remains ambiguous, as LSI enables only limited visualization of... more
Due to its simplicity and low cost, laser speckle imaging (LSI) has achieved widespread use in biomedical applications. However, interpretation of the blood-flow maps remains ambiguous, as LSI enables only limited visualization of vasculature below scattering layers such as the epidermis and skull. Here, we describe a computational model that enables flexiblestudy of the impact of these factors on LSI measurements. The model uses Monte Carlo methods to simulate light and momentum transport in a heterogeneous tissue geometry. The virtual detectors of the model track several important characteristics of light. This model enables study of LSI aspects that may be difficult or unwieldy to address in an experimental setting, and enables detailed study of the fundamental origins of speckle contrast modulation in tissue-specific geometries. We applied the model to an in-depth exploration of the spectral dependence of speckle contrast signal in the skin, the effects of epidermal melanin cont...
Research Interests:
We present a polarization-sensitive, transport-rigorous perturbation Monte Carlo (pMC) method to model the impact of optical property changes on reflectance measurements within a discrete particle scattering model. The model consists of... more
We present a polarization-sensitive, transport-rigorous perturbation Monte Carlo (pMC) method to model the impact of optical property changes on reflectance measurements within a discrete particle scattering model. The model consists of three log-normally distributed populations of Mie scatterers that approximate biologically relevant cervical tissue properties. Our method provides reflectance estimates for perturbations across wavelength and/or scattering model parameters. We test our pMC model performance by perturbing across number densities and mean particle radii, and compare pMC reflectance estimates with those obtained from conventional Monte Carlo simulations. These tests allow us to explore different factors that control pMC performance and to evaluate the gains in computational efficiency that our pMC method provides.
Laser based therapies are the standard treatment protocol for port wine stain in the United States, but complete removal is infrequently achieved. Intense pulsed light (IPL) offers a broadband light spectrum approach as a viable treatment... more
Laser based therapies are the standard treatment protocol for port wine stain in the United States, but complete removal is infrequently achieved. Intense pulsed light (IPL) offers a broadband light spectrum approach as a viable treatment alternative. Previous studies suggest that IPL can be more effective in treatment of port wine stain by utilizing multiple wavelengths to selectively target different peaks in oxy- and deoxy-hemoglobin. Our study objectives were to (i) determine a characteristic radiant exposure able to achieve persistent vascular shutdown with narrowband IPL irradiation, (ii) determine the degree to which narrowband IPL irradiation can achieve persistent vascular shutdown, and (iii) compare the effectiveness of narrowband IPL radiation to single wavelength pulsed dye laser (PDL) irradiation in achieving persistent vascular shutdown. We utlized either single pulse or double, stacked pulses in narrowband IPL experiments, with the IPL operating over a 500-600 nm wavelength range on the rodent dorsal window chamber model. We compared the results from our narrowband IPL experiments to acquired PDL data from a previous study and determined that narrowband IPL treatments can also produce persistent vascular shutdown. We ran Monte Carlo simulations to investigate the relationship between absorbed energy, wavelength, and penetration depth. For single and double pulse narrowband IPL irradiation we observed (i) little to no change in blood flow, resulting in no persistent vascular shutdown, (ii) marked acute disruption in blood flow and vascular structure, followed by partial to full recovery of blood flow, also resulting in no persistent vascular shutdown, and (iii) immediate changes in blood flow and vascular structure, resulting in prolonged and complete vascular shutdown. Monte Carlo modeling resulted in a 53.2% and 69.0% higher absorbed energy distribution in the top half and the total simulated vessel when comparing the composite narrowband IPL to the 595 nm (PDL), respectively. Our data collectively demonstrate the potential to achieve removal of vascular lesions using a 500-600 nm range. Additionally, the narrowband IPL was tuned to optimize a specific wavelength range that can be used to treat PWS, whereas the PDL can only operate at one discrete wavelength. Lasers Surg. Med. © 2015 Wiley Periodicals, Inc.
Research Interests:
ABSTRACT
Laser Speckle Imaging (LSI) is a simple, noninvasive technique for rapid imaging of particle motion in scattering media such as biological tissue. LSI is generally used to derive a qualitative index of relative blood flow due to unknown... more
Laser Speckle Imaging (LSI) is a simple, noninvasive technique for rapid imaging of particle motion in scattering media such as biological tissue. LSI is generally used to derive a qualitative index of relative blood flow due to unknown impact from several variables that affect speckle contrast. These variables may include optical absorption and scattering coefficients, multi-layer dynamics including static, non-ergodic regions, and systematic effects such as laser coherence length. In order to account for these effects and move toward quantitative, depth-resolved LSI, we have developed a method that combines Monte Carlo modeling, multi-exposure speckle imaging (MESI), spatial frequency domain imaging (SFDI), and careful instrument calibration. Monte Carlo models were used to generate total and layer-specific fractional momentum transfer distributions. This information was used to predict speckle contrast as a function of exposure time, spatial frequency, layer thickness, and layer ...
Research Interests:
Research Interests:
The focal field distribution of tightly focused laser beams in turbid media is sensitive to optical scattering and therefore of direct relevance to image quality in confocal and nonlinear microscopy. A model that considers both the... more
The focal field distribution of tightly focused laser beams in turbid media is sensitive to optical scattering and therefore of direct relevance to image quality in confocal and nonlinear microscopy. A model that considers both the influence of scattering and diffraction on the amplitude and phase of the electric field in focused beam geometries is required to describe these distorted focal fields. We combine an electric field Monte Carlo approach that simulates the electric field propagation in turbid media with an angular-spectrum representation of diffraction theory to analyze the effect of tissue scattering properties on the focal field. In particular, we examine the impact of variations in the scattering coefficient (µ(s)), single-scattering anisotropy (g), of the turbid medium and the numerical aperture of the focusing lens on the focal volume at various depths. The model predicts a scattering-induced broadening, amplitude loss, and depolarization of the focal field that corro...