Correlation transfer equation for multiply scattered light modulated by an ultrasonic pulse

Abstract

We develop a temporal correlation transfer equation (CTE) and a Monte Carlo algorithm (MC) for multiply scattered light modulated by an ultrasonic pulse propagating in an optically scattering medium, where the ultrasound field can be nonuniform and the medium can have spatially heterogeneous distribution of optical parameters. The CTE and MC can be used to obtain the time-varying specific intensity and the spatial distribution of the time-dependent power spectral density, respectively, of ultrasound-modulated light. We expect the CTE and MC to be applicable for estimation of contrast and resolution in a wide spectrum of conditions in ultrasound-modulated optical tomography of soft biological tissues.

Highly parallel Monte-Carlo simulations of the acousto-optic effect in heterogeneous turbid media

“…This could potentially be implemented in the style of Sakadžić's voxelized CPU simulation. 13 Further analysis of the relative validity of the explicit and numerical integration methods may allow the program to determine automatically the appropriate technique based upon the form of the supplied acoustic field.…”

“…A diffusion approximation (DA) is presented in a subsequent work, 12 and later the CTE is reformulated to account for an ultrasonic pulse. 13 Recently Bratchenia et al 14 developed sensitivity maps of the acousto-optic technique based upon a pair of coupled diffusion equations accounting for the unmodulated and modulated distributions of light. Throughout the initial theoretical investigations of the technique, a number of CPU-based Monte-Carlo (MC) models were demonstrated to support the analytical solutions under development.…”

“…Previous CPU-based simulations reported in the literature 11,13 have implemented a similar level of flexibility by the use of a voxelized simulation domain for the spatial distribution of the optical and acoustic parameters. Here we will demonstrate the implementation of optical heterogeneity via a mesh-based system which avoids the deleterious effects of a voxelized geometry, 19 and exploits the computational power of the GPU to avoid approximations in the treatment of the AO phase shifts demonstrated in previous work.…”

Ultrasound-mediated optical tomography: a review of current methods

“…Analytical models of the effect of the mechanisms described in the previous section on UOT signals have previously been developed for different ultrasound conditions, including continuous wave ultrasound [36], pulsed ultrasound [37], non-uniform continuous ultrasound [38] and non-uniform pulsed ultrasound [39]. These models can provide insight concerning the effects of ultrasound parameters on modulated optical signals.…”

Implications of ultrasound beam shape on the modulation of diffuse light: analysis using spatio-temporal perturbation of the refractive index

“…For a given wavelength of optical excitation, the continuous layer may be characterized by the absorption coefficient (μ a ), and the reduced scattering coefficient (μ s ) [8]. One of the effects of ultrasonic modulation in such media, is the phase change of light scattered from the suspended particles, that undergo infinitesimally small displacements due to the acoustic pressure field [7,9]. The phase changes can result in the generation of speckles when measured by a small detector aperture at successive time points along an ultrasound cycle.…”