Accurate Simulation of Light Propagation in Complex Skin Tissues Using an Improved Tetrahedron-Based Monte Carlo Method

Understanding light transportation in skin tissues can help improve clinical efficacy in the laser treatment of dermatosis, such as port-wine stains (PWS). Patient-specific cross-bridge PWS vessels are structurally complicated and considerably influence laser energy deposition due to shading effects. The shading effect of PWS vessels is investigated using a tetrahedron-based Monte Carlo (MC) method with extended boundary condition (TMCE). In TMCE, body-fitted tetrahedra are generated in different tissues, and the precision of photon–surface interaction can be considerably improved via mesh refinement. Such improvement is difficult to achieve with the widely used voxel-based MC method. To fit the real physical boundary, the extended boundary condition is adapted by extending photon propagation to the semi-infinite tissue layers while restricting the statistics of photon propagation in the computational domain. Results indicate that the shading parameters, such as the cross angle, vessel distance, and geometric shadow (GS), of cross-bridge blood vessel pairs determine the peak characteristics of photon deposition in deep vessels by affecting the relative deposition of collimated and diffused light. Collimated light is shaded, attenuated, and partially transformed into diffused light due to the increase in vessel distance and GS of vessel pairs, resulting in difficulty in treating deep and shallow vessels with one laser pulse. The TMCE method can be used for the individualized and precise forecasting of laser energy deposition based on the morphology and embedding characteristics of vascular lesions.

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Computational Simulation of Temperature Elevations in Tumors Using Monte Carlo Method and Comparison to Experimental Measurements in Laser Photothermal Therapy

Journal of Biomechanical Engineering ◽

10.1115/1.4025388 ◽

2013 ◽

Vol 135 (12) ◽

Cited By ~ 16

Author(s):

Navid Manuchehrabadi ◽

Yonghui Chen ◽

Alexander LeBrun ◽

Ronghui Ma ◽

Liang Zhu

Keyword(s):

Monte Carlo ◽

Optical Properties ◽

Gold Nanorods ◽

Photothermal Therapy ◽

Energy Deposition ◽

Thermal Damage ◽

Laser Energy ◽

Simulated Temperature ◽

Laser Energy Absorption ◽

Laser Photothermal Therapy

Accurate simulation of temperature distribution in tumors induced by gold nanorods during laser photothermal therapy relies on precise measurements of thermal, optical, and physiological properties of the tumor with or without nanorods present. In this study, a computational Monte Carlo simulation algorithm is developed to simulate photon propagation in a spherical tumor to calculate laser energy absorption in the tumor and examine the effects of the absorption (μa) and scattering (μs) coefficients of tumors on the generated heating pattern in the tumor. The laser-generated energy deposition distribution is then incorporated into a 3D finite-element model of prostatic tumors embedded in a mouse body to simulate temperature elevations during laser photothermal therapy using gold nanorods. The simulated temperature elevations are compared with measured temperatures in PC3 prostatic tumors in our previous in vivo experimental studies to extract the optical properties of PC3 tumors containing different concentrations of gold nanorods. It has been shown that the total laser energy deposited in the tumor is dominated by μa, while both μa and μs shift the distribution of the energy deposition in the tumor. Three sets of μa and μs are extracted, representing the corresponding optical properties of PC3 tumors containing different concentrations of nanorods to laser irradiance at 808 nm wavelength. With the injection of 0.1 cc of a 250 optical density (OD) nanorod solution, the total laser energy absorption rate is increased by 30% from the case of injecting 0.1 cc of a 50 OD nanorod solution, and by 125% from the control case without nanorod injection. Based on the simulated temperature elevations in the tumor, it is likely that after heating for 15 min, permanent thermal damage occurs in the tumor injected with the 250 OD nanorod solution, while thermal damage to the control tumor and the one injected with the 50 OD nanorod solution may be incomplete.

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A Numerical Analysis of the Hemodynamic Functionality of Human Coronary Stenosis Under Different Physiologic Conditions and Boundary Condition Formulations

Volume 2: Computational Fluid Dynamics ◽

10.1115/ajkfluids2019-4820 ◽

2019 ◽

Author(s):

Iyad Fayssal ◽

Fadl Moukalled

Keyword(s):

Boundary Condition ◽

Boundary Conditions ◽

Functional Significance ◽

Diffusion Flux ◽

Computational Effort ◽

Patient Specific ◽

Computational Domain ◽

Artery Disease ◽

Outflow Boundary

Abstract Coronary artery disease (CAD) is among the foremost causes for human death worldwide. This study aims at investigating the performance of different boundary condition model types to characterize CAD functional significance. In addition, alternate models to estimate FFR using any different combination of boundary conditions at inlet and outlet were analyzed. In the first type of boundary condition, an outflow resistance model is used combined with a fixed pressure at inlet. In the second model of boundary conditions, constant pressure values are imposed at the domain inlet and outlet/s sections. In the third model, a zero diffusion flux is applied at outlet with a pre-specified flow rate at inlet. Numerical simulations performed on healthy and stenosed idealized and physiological arterial models revealed the superiority of the first type of boundary condition to directly capture the level of ischemia in diseased arteries. However, in this model, special numerical treatment at the outflow boundary is needed to dampen pseudo numerical reflections entering the computational domain. Alternative simple methods are developed to tackle the problem incurred in the second and third types of boundary condition types. The alternate models are effective for carrying extensive parametric studies with minimal computational effort. The new developed methods allow results generated via generic simulations under any specified boundary condition type to correctly estimate CAD functional significance. The obtained surrogate models account for the effects of the patient-specific physiologic parameters and can be easily incorporated without modifying existing CFD codes. Moreover, where it is unfeasible to experimentally incorporate the downstream effects of a given diseased arterial segment, an important aspect the alternative models provide is that they can be easily adopted by experimentalists through building in-vitro arterial models to assess the functional significance of the obstruction caused by the disease and its relation to any given patient specific physiologic parameter.

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Cyclic Breathing Simulations: Pressure Outlet Boundary Conditions Coupled With Resistance and Compliance

Volume 2: Fora ◽

10.1115/ajkfluids2015-26569 ◽

2015 ◽

Author(s):

Xiao Wang ◽

Keith Walters ◽

Greg W. Burgreen ◽

David S. Thompson

Keyword(s):

Boundary Condition ◽

Interstitial Fibrosis ◽

Flow Patterns ◽

Simulation Software ◽

Scale Model ◽

Whole Body ◽

Patient Specific ◽

Computational Domain ◽

Alveolar Pressure ◽

Geometry Model

A patient-specific non-uniform pressure outlet boundary condition was developed and used in unsteady simulations of cyclic breathing in a large-scale model of the lung airway from the oronasal opening to the terminal bronchioles. The computational domain is a reduced-geometry model, in which some airway branches in each generation were truncated, and only selected paths were retained to the terminal generation. To characterize pressure change through airway tree extending from the truncated outlets to pulmonary zone, virtual airways represented by extended volume mesh zones were constructed in order to apply a zero-dimensional airway resistance model. The airway resistances were prescribed based on a precursor steady simulation under constant ventilation condition. The virtual airways accommodate the use of patient-specific alveolar pressure conditions. Furthermore, the time-dependent alveolar pressure profile was composed with the physiologically accurate pleural pressure predicted by the whole-body simulation software HumMod, and the transpulmonary pressure evaluated based on lung compliance and local air volume change. To investigate airway flow patterns of healthy and diseased lungs, unsteady breathing simulations were conducted with varying lung compliances accounting for healthy lungs, and lungs with emphysema or interstitial fibrosis. Results show that the simulations using this patient-specific pressure boundary condition are capable of reproducing physiologically realistic flow patterns corresponding to abnormal pulmonary compliance in diseased lungs, such as the hyperventilation in lungs with emphysema, and the demand of more mechanic work for breathing in lungs with fibrosis.

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Correction: Dual-pulse laser energy deposition for the flow control in a supersonic flow

AIAA Aviation 2019 Forum ◽

10.2514/6.2019-3355.c1 ◽

2019 ◽

Author(s):

Daniel W. Hartman ◽

Albina Tropina ◽

Rajib Mahamud

Keyword(s):

Supersonic Flow ◽

Flow Control ◽

Pulse Laser ◽

Energy Deposition ◽

Laser Energy ◽

Pulse Laser Energy

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QMC integration errors and quasi-asymptotics

Monte Carlo Methods and Applications ◽

10.1515/mcma-2020-2067 ◽

2020 ◽

Vol 26 (3) ◽

pp. 171-176

Author(s):

Ilya M. Sobol ◽

Boris V. Shukhman

Keyword(s):

Monte Carlo ◽

Error Estimate ◽

Numerical Experiments ◽

Probable Error ◽

Quasi Monte Carlo ◽

Integration Error ◽

Asymptotic Error ◽

Dimensional Cube ◽

Integration Errors ◽

Mc Method

AbstractA crude Monte Carlo (MC) method allows to calculate integrals over a d-dimensional cube. As the number N of integration nodes becomes large, the rate of probable error of the MC method decreases as {O(1/\sqrt{N})}. The use of quasi-random points instead of random points in the MC algorithm converts it to the quasi-Monte Carlo (QMC) method. The asymptotic error estimate of QMC integration of d-dimensional functions contains a multiplier {1/N}. However, the multiplier {(\ln N)^{d}} is also a part of the error estimate, which makes it virtually useless. We have proved that, in the general case, the QMC error estimate is not limited to the factor {1/N}. However, our numerical experiments show that using quasi-random points of Sobol sequences with {N=2^{m}} with natural m makes the integration error approximately proportional to {1/N}. In our numerical experiments, {d\leq 15}, and we used {N\leq 2^{40}} points generated by the SOBOLSEQ16384 code published in 2011. In this code, {d\leq 2^{14}} and {N\leq 2^{63}}.

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Prediction on Geometrical Characteristics of Laser Energy Deposition Based on Regression Equation and Neural Network

IFAC-PapersOnLine ◽

10.1016/j.ifacol.2021.04.085 ◽

2020 ◽

Vol 53 (5) ◽

pp. 89-96

Author(s):

Changhui Song ◽

Lisha Liu ◽

Yongqiang Yang ◽

Changwei Weng

Keyword(s):

Neural Network ◽

Energy Deposition ◽

Laser Energy ◽

Regression Equation ◽

Geometrical Characteristics

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Stereoscopic particle image velocimetry of laser energy deposition on a mach 3.4 flow field

Experiments in Fluids ◽

10.1007/s00348-021-03142-6 ◽

2021 ◽

Vol 62 (2) ◽

Author(s):

Arastou Pournadali Khamseh ◽

Ramez M. Kiriakos ◽

Edward P. DeMauro

Keyword(s):

Particle Image Velocimetry ◽

Flow Field ◽

Energy Deposition ◽

Particle Image ◽

Laser Energy ◽

Stereoscopic Particle Image Velocimetry ◽

Image Velocimetry

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Pressure Waves in Microscopic Simulations of Laser Ablation Leonid

MRS Proceedings ◽

10.1557/proc-538-491 ◽

1998 ◽

Vol 538 ◽

Cited By ~ 67

Author(s):

V. Zhigilei ◽

Barbara J. Garrison

Keyword(s):

Boundary Condition ◽

Laser Ablation ◽

Laser Energy ◽

Scale Up ◽

Boundary Region ◽

Dynamics Simulation ◽

Pressure Waves ◽

Absorption Region ◽

Organic Solids ◽

Direct Laser

AbstractLaser ablation of organic solids is a complex collective phenomenon that includes processes occurring at different length and time scales. A mesoscopic breathing sphere model developed recently for molecular dynamics simulation of laser ablation and damage of organic solids has significantly expanded the length-scale (up to hundreds of nanometers) and the time-scale (up to nanoseconds) of the simulations. The laser induced buildup of a high pressure within the absorbing volume and generation of the pressure waves propagating from the absorption region poses an additional challenge for molecular-level simulation. A new dynamic boundary condition is developed to minimize the effects of the reflection of the wave from the boundary of the computational cell. The boundary condition accounts for the laser induced pressure wave propagation as well as the direct laser energy deposition in the boundary region.

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