Photon Transport In Turbid Media Research Articles

Neu(t)ralMC: energy-efficient open source Monte Carlo algorithm for assessing photon transport in turbid media.

Light propagation in turbid mediums such as atmosphere, fluids, and biological tissues is a challenging problem which necessitates accurate simulation techniques to account for the effects of multiple scattering. The Monte Carlo method has long established itself as a gold standard and is widely adopted for simulating light transport, however, its computationally intensive nature often requires significant processing power and energy consumption. In this paper a novel, open source Monte Carlo algorithm is introduced which is specifically designed for use with energy-efficient processors, effectively addressing those challenges, while maintaining the accuracy/compatibility and outperforming existing solutions. The proposed implementation optimizes photon transport simulations by exploiting the unique capabilities of Apple's low-power, high-performance M-family of chips. The developed method has been implemented in an open-source software package, enabling seamless adaptation of developed algorithms for specific applications. The accuracy and performance are validated using comprehensive comparison with existing solvers commonly used for biomedical imaging. The results demonstrate that the new algorithm achieves comparable accuracy levels to those of existing techniques while significantly reducing computational time and energy consumption.

Prediction of tissue optical properties using the Monte Carlo modeling of photon transport in turbid media and integrating spheres

Monte Carlo methods are an established technique for simulating light transport in biological tissue. Integrating spheres make experimental measurements of the reflectance and transmittance of a sample straightforward and inexpensive. This work presents an extension to existing Monte Carlo photon transport methods to simulate integrating sphere experiments. Crosstalk between spheres in dual-sphere experiments is accounted for in the method. Analytical models, previous works on Monte Carlo photon transport, and experimental measurements of a synthetic tissue phantom validate this method. We present two approaches for using this method to back-calculate the optical properties of samples. Experimental and simulation uncertainties are propagated through both methods. Both back-calculation methods find the optical properties of a sample accurately and precisely. Our model is implemented in standard Python 3 and CUDA C++ [J. Nickolls, I. Buck, M. Garland, and K. Skadron, ACM Queue 6, 40 (2008)] and is publicly available in Code 1.

Modeling photon transport in turbid media for measuring colloidal concentration in drops using the time-shift technique.

Colloidal drops-suspensions, dispersions, emulsions-are widespread in the process industry but are difficult to characterize by size, velocity, and concentration of particulate matter in the drop. The present study investigates the use of the time-shift (TS) technique for such measurements. Numerically, a model based on ray tracing is developed, incorporating interactions with randomly placed monodispersed scattering centers within the spherical drop. The model creates a random walk propagation trajectory, known from radiative transfer problems. The model approximates Mie scattering from each internal particle with a Gaussian distribution. Experiments are performed using a conventional TS instrument, first with water as a reference and for validation, and then with different concentrations of a milk/water emulsion. Comparison of the modeled and received signals exhibits very good agreement, confirming the possibility of measuring the colloidal concentration in drops using the TS technique.

Accelerating Monte Carlo simulations with an NVIDIA ® graphics processor

Modern graphics cards, commonly used in desktop computers, have evolved beyond a simple interface between processor and display to incorporate sophisticated calculation engines that can be applied to general purpose computing. The Monte Carlo algorithm for modelling photon transport in turbid media has been implemented on an NVIDIA ® 8800 gt graphics card using the CUDA toolkit. The Monte Carlo method relies on following the trajectory of millions of photons through the sample, often taking hours or days to complete. The graphics-processor implementation, processing roughly 110 million scattering events per second, was found to run more than 70 times faster than a similar, single-threaded implementation on a 2.67 GHz desktop computer. Program summary Program title: Phoogle-C/Phoogle-G Catalogue identifier: AEEB_v1_0 Program summary URL: http://cpc.cs.qub.ac.uk/summaries/AEEB_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 51 264 No. of bytes in distributed program, including test data, etc.: 2 238 805 Distribution format: tar.gz Programming language: C++ Computer: Designed for Intel PCs. Phoogle-G requires a NVIDIA graphics card with support for CUDA 1.1 Operating system: Windows XP Has the code been vectorised or parallelized?: Phoogle-G is written for SIMD architectures RAM: 1 GB Classification: 21.1 External routines: Charles Karney Random number library. Microsoft Foundation Class library. NVIDA CUDA library [1]. Nature of problem: The Monte Carlo technique is an effective algorithm for exploring the propagation of light in turbid media. However, accurate results require tracing the path of many photons within the media. The independence of photons naturally lends the Monte Carlo technique to implementation on parallel architectures. Generally, parallel computing can be expensive, but recent advances in consumer grade graphics cards have opened the possibility of high-performance desktop parallel-computing. Solution method: In this pair of programmes we have implemented the Monte Carlo algorithm described by Prahl et al. [2] for photon transport in infinite scattering media to compare the performance of two readily accessible architectures: a standard desktop PC and a consumer grade graphics card from NVIDIA. Restrictions: The graphics card implementation uses single precision floating point numbers for all calculations. Only photon transport from an isotropic point-source is supported. The graphics-card version has no user interface. The simulation parameters must be set in the source code. The desktop version has a simple user interface; however some properties can only be accessed through an ActiveX client (such as Matlab). Additional comments: The random number library used has a LGPL ( http://www.gnu.org/copyleft/lesser.html) licence. Running time: Runtime can range from minutes to months depending on the number of photons simulated and the optical properties of the medium.

Fluorescence quenching by polystyrene microspheres in UV-visible and NIR tissue-simulating phantoms

Tissue-simulating phantoms are widely used for controlled studies of photon transport in turbid media. Here, we describe how polystyrene microspheres, which are often used to simulate optical scattering in such phantoms, can reduce fluorophore quantum yield via collisional quenching. We report studies on UV-visible (fluorescein-based) and NIR (IR125-based) phantoms with differing fluorophore and scatterer concentrations, as well as differing microsphere sizes. Results consistent with the Stern-Volmer relation suggest that the fluorophore intrinsic excited-state lifetime decreased due to collisional quenching from polystyrene microspheres and that the quenching efficiency was dependent on the concentration ratio of fluorophores to microspheres. Lifetime decreases ranging from 10-35% (20%) were measured for fluorescein-based (IR 125-based) phantoms. Since polystyrene microspheres are commonly used in tissue-simulating phantoms for quantitative studies of fluorescence light propagation, their quenching effects on fluorescence intensities may be difficult to separate from intensity losses attributed to optical absorption and scattering in the phantom unless fluorescence lifetime measurements are performed simultaneously.

Diffusion coefficient for photon transport in turbid media

Light propagation in a turbid medium is considered using the linear transport equation. The existence of a diffusion length is proved for the Henyey–Greenstein scattering kernel for all absorption ratios. Numerical methods are given that allow accurate computation of the diffusion coefficient quite easily.

Transient Photon Transport in Turbid Media with an Irregularly Shaped Foreign Object

A finite-volume method for the modeling of transient photon propagation in turbid media with an irregularly shaped foreign object is presented. The procedure can account for non-rectangular foreign object. Body-fitted coordinates are used to discretize the spatial domain. Absorbing, anisotropic scattering non-homogenous medium can be modeled. The procedure is validated using existing numerical results for a homogenous medium. The procedure produces physically possible trends for different optical properties of the foreign object.

Multiple processor version of a Monte Carlo code for photon transport in turbid media

Although Monte Carlo (MC) simulations represent an accurate and flexible tool to study the photon transport in strongly scattering media with complex geometrical topologies, they are very often infeasible because of their very high computation times. Parallel computing, in principle very suitable for MC approach because it consists in the repeated application of the same calculations to unrelated and superposing events, offers a possible approach to overcome this problem. It was developed an MC multiple processor code for optical and IR photon transport which was run on the parallel processor computer CRAY-T3E (128 DEC Alpha EV5 nodes, 600 Mflops) at CINECA (Bologna, Italy). The comparison between single processor and multiple processor runs for the same tissue models shows that the parallelization reduces the computation time by a factor of about N , where N is the number of used processors. This means a computation time reduction by a factor ranging from about 10 2 (as in our case where 128 processors are available) up to about 10 3 (with the most powerful parallel computers with 1024 processors). This reduction could make feasible MC simulations till now impracticable. The scaling of the execution time of the parallel code, as a function of the values of the main input parameters, is also evaluated.

Effective source term in the diffusion equation for photon transport in turbid media

The Green's function for the diffusion equation is widely used to describe photon transport in turbid media. We have performed aseries of spectroscopy experiments on a number of uniform turbid media with different optical properties (absorption coefficient in the range 0.03-0.14 cm(-1), reduced scattering coefficient in the range 5-22 cm(-1)). Our experiments have been conducted in the frequency domain, where the measured parameters are the dc intensity (I(dc)), ac amplitude (I(ac)), and phase (?) of the light intensity wave. In an infinite medium, the Green's function predicts a linear dependence of ln(rI(dc)) and ? on the source-detector separation r. Our measurements show that the intercepts of these straight lines predicted by the Green's function do not agree with the experimental results. To reproduce the experimental results, we have introduced an effective photon source whose spatial extent and source strength depend on the optical properties of the medium. This effective source term has no effect on the slopes of the straight lines predicted by the Green'sfunction at large values of r.