Diffuse photon remission along unique spiral paths on a cylindrical interface is modeled by photon remission along a straight line on a semi-infinite interface (original) (raw)
Related papers
OSA Continuum
Near-infrared optical techniques permit tissue diagnosis by surface measurement. However, the geometrical shape of this interface profiles the intensity of the surface measurement, which is found to have an iso-pathlength (IPL) point allowing for absorption identification independent of tissue scattering. The IPL point was projected in Monte Carlo (MC) simulation, validated experimentally in cylindrical tissues, but remains underappreciated through analytical approaches. In this work, we present an analytical solution of an IPL point for steady-state diffusion based on the extrapolated zero-boundary condition. The same IPL points were found when comparing this solution to 3-D MC simulations for a tissue radius range of 5-8mm.
Steady-state diffuse reflectance associated with a center-illuminated-area-detection (CIAD) geometry has shown potentials for tissue assessment and elucidating the patterns of single-fiber reflectance (SFR) via a simple scaling of the photon remission between the two geometries. Part I has demonstrated a new algebraic model approach to the steady-state diffuse photon remission associated with the CIAD geometry, by means of area-integration of a radially resolved diffuse photon remission projected by a master-slave dual-source scheme. This Part II proposes a model of time-dependent diffuse photon remission for the CIAD geometry, by virtue of area-integration of the radially resolved time-dependent diffuse photon remission formulated with the master-slave dual-source scheme. Monte Carlo (MC) simulations, limiting to only the Heyney-Greenstein scattering phase function, are used to examine the outputs of the terminally algebraic model of the time-dependent photon remission associated w...
Controlled Monte Carlo method for light propagation in tissue of semi-infinite geometry
Applied Optics, 2007
The controlled Monte Carlo method is generalized to model photon migration in turbid media of arbitrary geometries. Its implementation for the reflection geometry is exemplified in this paper. The most probable diffuse direction of light is used as the local attractive vector that serves as the basis of biased sampling of scattering angles. Consequently, path-length resolved photon trajectories can be generated with a significantly improved efficiency. We report a more than 29 times reduction in simulation time for early arriving photons in a typical configuration.
Estimation of quasi-straightforward propagating light in tissues
Physics in Medicine and Biology, 1999
We have developed a controlled Monte Carlo (CMC) method to calculate the timedependent transmittance of light through a thick tissue, especially for evaluation of the contribution from early arriving photons. Quasi-straightforward propagating trajectories are favoured according to a selection mechanism, so adequate trajectories of interest can reach the detector, improving the statistics dramatically. Simulations were conducted for tissue models with a thickness of 3-5 cm, and with optical properties similar to human breast tissue. Temporal profiles of early transmittance were obtained with satisfactory convergence. In addition, comparison was made with the conventional Monte Carlo approach to verify our scheme when applied to cases of optically thin tissues.
Journal of the Optical Society of America, 2012
This is Part III of the work that examines photon diffusion in a scattering-dominant medium enclosed by a "concave" circular cylindrical applicator or enclosing a "convex" circular cylindrical applicator. In Part II of this work Zhang et al. [J. Opt. Soc. Am. A 28, 66 (2011)] predicted that, on the tissue-applicator interface of either "concave" or "convex" geometry, there exists a unique set of spiral paths, along which the steady-state photon fluence rate decays at a rate equal to that along a straight line on a planar semi-infinite interface, for the same line-of-sight source-detector distance. This phenomenon of steady-state photon diffusion is referred to as "straight-lineresembling-spiral paths" (abbreviated as "spiral paths"). This Part III study develops analytic approaches to the spiral paths associated with geometry of a large radial dimension and presents spiral paths found numerically for geometry of a small radial dimension. This Part III study also examines whether the spiral paths associated with a homogeneous medium are a good approximation for the medium containing heterogeneity. The heterogeneity is limited to an anomaly that is aligned azimuthally with the spiral paths and has either positive or negative contrast of the absorption or scattering coefficient over the background medium. For a weak-contrast anomaly the perturbation by it to the photon fluence rate along the spiral paths is found by applying a well-established perturbation analysis in cylindrical coordinates. For a strong-contrast anomaly the change by it to the photon fluence rate along the spiral paths is computed using the finite-element method. For the investigated heterogeneous-medium cases the photon fluence rate along the homogeneous-medium associated spiral paths is macroscopically indistinguishable from, and microscopically close to, that along a straight line on a planar semi-infinite interface.
Optical propagation in tissue with anisotropic scattering
IEEE Transactions on Biomedical Engineering, 1988
Understanding the distribution of light in tissue is necessary for dosimetry in photodynamic therapy of malignant tumors. The Dunning R3327-AT rat prostate solid tumor model was the specific tissue chosen for experimental and theoretical studies of optical propagation at 630 nm. Goniometric measurements on tissue sections showed strongly forward-peaked scattering and a scattering coefficient of 270 Em-'. An average absorption coefficient of 0.49 cm-' was derived from direct absorbance measurements obtained using an integrating sphere technique. Optical intensity distributions for a pencil beam, emitted from an optical tiber implanted in excised solid tumors, were obtained with fiber optic probes in various orientations. The relative light intensities at the same radial distance from the pencil beam source were found to depend on the polar angle, being highest in the direction of the beam and lowest in the backwards direction. Tissue light distributions were modeled using the transport approximation to the Boltzmann equation. The analysis yielded a value between 0.97 and 0.98 for the mean cosine of the angular scattering phase function. The theoretical model showed good agreement with experimental attenuation constants as well as absolute values of optical intensity within tumors.
1989
Abstruct-Using optical interaction coefficients typical of mammalian soft tissues in the red and near infrared regions of the spectrum, calculations of fluence-depth distributions, effective penetration depths and diffuse reflectance from two models of radiative transfer, diffusion theory, and Monte Carlo simulation are compared for a semi-infinite medium. The predictions from diffusion theory are shown to be increasingly inaccurate as the albedo tends to zero andlor the average cosine of scatter tends to unity.
IEEE Transactions on Biomedical Engineering, 1989
Abstruct-Using optical interaction coefficients typical of mammalian soft tissues in the red and near infrared regions of the spectrum, calculations of fluence-depth distributions, effective penetration depths and diffuse reflectance from two models of radiative transfer, diffusion theory, and Monte Carlo simulation are compared for a semi-infinite medium. The predictions from diffusion theory are shown to be increasingly inaccurate as the albedo tends to zero andlor the average cosine of scatter tends to unity.
Model for photon migration in turbid biological media
Journal of the Optical Society of America A, 1987
Various characteristics of photon diffusion in turbid biological media are examined. Applications include the interpretation of data acquired with laser Doppler blood-flow monitors and the design of protocols for therapeutic excitation of tissue chromophores. Incident radiation is assumed to be applied at an interface between a turbid tissue and a transparent medium, and the reemission of photons from that interface is analyzed. Making use of a discrete lattice model, we derive an expression for the joint probability r(n, p)d 2 p that a photon will be emitted in the infinitesimal area d 2 p centered at surface point p = (x, y), having made n collisions with the tissue. Mathematical expressions are obtained for the intensity distribution of diffuse surface emission, the probability of photon absorption in the interior as a function of depth, and the mean path length of detected photons as a function of the distance between the site of the incident radiation and the location of the detector. We show that the depth dependence of the distribution of photon absorption events can be inferred from measured parameters of the surface emission profile. Results of relevant computer simulations are presented, and illustrative experimental data are shown to be in accord with the theory.
Light dosimetry at tissue surfaces for small circular fields
Proceedings of SPIE, 2003
Small circular light fields (≤ 2 cm diameter) are sometimes used for photodynamic therapy of skin and recurrent breast cancers on the chest wall. These fields have lateral dimensions comparable to the effective mean free path of photons in the turbid medium, which causes reduced light fluence rate compared to that of a broad beam of uniform incident irradiance. We have compared Monte-Carlo simulation with in-vivo dosimetry for circular fields (R = 0.25, 0.35, 0.5, 0.75, 1, 2, 3, and 8 cm) in a liquid phantom composed of intralipid and ink (µ s ' = 4-20 cm −1 and µ a = 0.1 cm −1) for wavelengths between 532 and 730 nm. We used anisotropy g = 0.9 and the index of refraction n = 1.4 for all Monte-Carlo simulations. The measured light fluence rate agrees with Monte-Carlo simulation to within 10%, with the measured value lower than that of the Monte-Carlo simulation on tissue surface. The ratio of the peak fluence rates between a circular beam and a broad beam under tissue is 0.58-0.96 or 0.84-1.00 for R between 0.5-2 cm and µ eff = 1.1 or 2.0 cm −1 , respectively. The ratio of peak fluence rate and incident irradiance for the broad beam is 5.9 and 6.4 for µ eff = 1.1 and 2.0 cm −1 , respectively. The optical penetration depth δ varies from 0.34-0.48 cm for R between 0.5 and 2 cm, with the corresponding δ = 0.51 cm for a broad beam. The ratio of fluence rate and incident irradiance above tissue surface is 1.4-1.8 or 1.9-2.2 for R between 0.5-2 cm and µ eff = 1.1 or 2.0 cm −1 , respectively. At depth of 0.2 cm inside tissue, Offaxis ratio OAR, defined as the ratio of fluence rate at off-axis distance r to that on the central axis, varies between 0.91-0.54 or 0.93-0.52 for off-axis distances r between 0.6 and 1.0 cm and µ eff = 1.1 or 2.1 cm −1 , respectively. In conclusion, in-vivo light dosimetry agrees with Monte-Carlo simulation for small field dosimetry provided the isotropic detector is corrected for the blind spot. The light fluence rates for small circular fields are substantially lower than that of the broad beam of the same incident irradiance.