Leonid N. Soms

Application of the photon average trajectories method to real-time reconstruction of tissue inhomogeneities in diffuse optical tomography of strongly scattering media

The possibility of application of the photon average trajectories (PAT) method to real-time reconstruction of tissue inhomogeneities in diffuse optical tomography of strongly scattering media has been substantiated. By this method, the inverse problem is reduced to solution of the integral equation with integration along a conditional PAT. Such an approach allows the standard fast algebraic algorithms commonly used in projection computed tomography to be applied to diffuse optical image reconstruction. To demonstrate the capabilities of the PAT method, a numerical experiment on cross-sectional reconstruction of cylindrical strongly scattering objects with absorbing inhomogeneities has been done. Relative shadows caused by inhomogeneities are simulated via numerical solution of the non-stationary diffusion equation. To solve the inverse problem, the QR-factorization least-squares algorithm and the multiplicative algebraic reconstruction technique are used. The results are compared with those obtained by a well-known software package for temporal optical absorption and scattering tomography based on multiple solution of the diffusion equation. It is shown that the PAT method allows reconstruction of the optical structure of objects with comparable accuracy while saving reconstruction time considerably.

Application of transform algorithms to high-resolution image reconstruction in optical diffusion tomography of strongly scattering media

The applicability of transform algorithms generally used in projection-computed tomography is substantiated for the case of medical optical diffusion tomography (ODT). To reconstruct tissue optical inhomogeneities, a new method based on a concept of an average statistical trajectory for transfer of light energy [photon average trajectory (PAT)] is proposed. By this method, the inverse problem of ODT is reduced to a solution of an integral equation with integration along a PAT. Within the internal zone of the object, well away from the boundaries, PATs tend to a straight line, and standard integral algorithms based on the inverse Radon transform may be used to restore diffuse optical images. To demonstrate the capabilities of the PAT method, a numerical experiment on cross sectional reconstruction of cylindrical strongly scattering objects with low-contrast absorbing inhomogeneities is conducted. To solve the time-domain ODT inverse problem, two filtered backprojection algorithms (of Radon and Vainberg) are used. The reconstruction results are compared with those obtained by a well-known software package for temporal optical absorption and scattering tomography, based on multiple solutions of a diffusion equation. It is shown that in important cases of low-contrast absorbing inhomogeneities, the PAT method using the Vainberg algorithm allows reconstruction of tissue optical inhomogeneities with a 20% gain in spatial resolution.

The possibility of increasing the spatial resolution in diffusion optical tomography

This paper discusses the possibility of increasing the resolution of diffusion optical tomography, using the method of average photon trajectories. It is shown that this method makes it possible to use fast reconstruction algorithms based on both iterative algebraic procedures and integral transformations with filtering of projections. The latter case not only suppresses the discretization noise but also substantially compensates the diffusion smearing of the reconstructed images.

Polychromatic dynamic holographic one-way image correction using liquid crystal SLMs

The paper describes the results of experimental study of real time dynamic holographic correction of lens distortions in a model telescope, imaging a remote object in incoherent non-monochrome radiation in the visible range of the spectrum. Dynamic correction in the scheme of one-way imaging was provided by the thin dynamic hologram of the lens distortions, recorded in the optically addressed liquid crystal spatial light modulator.

Laser transmission module with a switchable directional pattern for the rangefinder of the Phobos–Ground spacecraft

This paper describes the operating principle and lists the main characteristics of a laser transmission module for the rangefinder intended for use in the far-space expedition to the Martian satellite Phobos, intended to start in 2011. A distinguishing feature of the laser included in the transmission module is rapid, nonmechanical switching of the direction of the directional pattern for measuring oblique ranges and computing the normal to the surface.

Two-coordinate electrically controlled liquid-crystal optical phase wedge

Based on the capacity of a parallel-oriented layer of nematic liquid crystal to alter its birefringence under the influence of an applied electric field, a two-coordinate electrically controlled optical phase wedge has been developed.

Physical mechanisms of laser-induced shockwave lithotripsy in the microsecond range of laser pulse durations

Analysis of possible ways for organic minerals destruction by laser-induced shockwave is presented. Physical mechanisms describing lithotripsy with microsecond laser pulses are discussed. Theoretical considerations show that the most probable fragmentation mechanisms are connected with the existence of absorptive inclusions in the stone volume. We have shown that surface plasma flash may be considered as attendant phenomenon which does not necessarily play an important fragmentation role under our conditions of observation.

Application of photon average trajectories method for separate mapping of absorbing and scattering macroinhomogeneities using time-domain measurements technique

Theoretical analysis and numerical experiments show a significant difference in a temporal dynamics of shadows caused by absorbing and scattering macroinhomogeneities. This difference is especially noticeable at the leading front of the pulse passed through the scattering medium. This makes it possible to image absorbing and scattering inhomogeneities separately using shadows obtained at subsequent time moments.

Influence of fast reconstruction algorithms on spatial resolution of optical diffuse tomography by photon average trajectories method

The influence of three reconstruction algorithms on spatial resolution of optical diffuse tomography by Photon Average Trajecotries (PAT) method was investigated. The resolution was estimated using the model of spatially invariant linear filter by the conventient procedure usually used in CT. The resolution of absorbing inhomogeneities of model objects is shown to go for a theoretical limit of PAT method and the algorithms considered appears to reconstruct optical diffuse images without complementary limitations on spatial resolution.

Application of integral transform algorithms to high-resolution reconstruction of tissue inhomogeneities in medical diffuse optical tomography

The applicability of the transform algorithms generally used in projection computed tomography is substantiated for the case of medical diffuse optical tomography (DOT). To reconstruct tissue optical inhomogeneities, a new method based on a concept of an average statistical trajectory for transfer of light energy (photon average trajectory, PAT) is proposed. By this method, the inverse problem of DOT is reduced to solution of integral equation with integration along a PAT. Within the internal zone of the object, remote well away from the boundaries, PATs tend to a straight line, and standard integral algorithms based on the inverse Radon transform may be used to restore diffuse optical images. To demonstrate the capabilities of the PAT method, a numerical experiment on cross-sectional reconstruction of cylindrical strongly scattering objects with absorbing inhomogeneities has been conducted. To solve the DOT inverse problem, two filtered backprojection algorithms (of Radon and of Vainberg) were used. The reconstruction results are compared with those obtained by a well-known software package for temporal optical absorption and scattering tomography, based on multiple solution of diffusion equation. It is shown that the PAT method using the Vainberg algorithm allows reconstruction of tissue optical structure with a 20%-gain in spatial resolution.