TRINITY: A three-dimensional time-dependent radiative transfer code for in-vivo near-infrared imaging. (January 2022)

• Record Type: Journal Article
• Authors: Yajima, Hidenobu; Abe, Makito; Umemura, Masayuki; Takamizu, Yuichi; Hoshi, Yoko
• Is Part Of: Journal of quantitative spectroscopy & radiative transfer. Volume 277(2022)
• Publication Date: 2022-01
• Subjects: Radiative transfer simulations -- Diffuse optical tomography -- Forward modelling -- Numerical simulations; Spectrum analysis -- Periodicals; Radiation -- Periodicals; Analyse spectrale -- Périodiques; Rayonnement -- Périodiques; Radiation; Spectrum analysis; Periodicals; 543.0858
• DOI: 10.1016/j.jqsrt.2021.107948
• Languages: English
• ISSNs: 0022-4073

Abstract

Highlights: In-vivo diffuse optical tomography needs an accurate model of light propagation. A new radiative transfer code, TRINITY, is described. TRINITY reproduces the pulse experiments for a medium mimicking biological tissue. TRINITY handles an inhomogeneous medium with different refractive indices. Abstract: We develop a new three-dimensional time-dependent radiative transfer code, TRINITY (Time-dependent Radiative transfer In Near-Infrared TomographY), for in-vivo diffuse optical tomography (DOT). The simulation code is based on the design of long radiation rays connecting boundaries of a computational domain, which allows us to calculate light propagation with little numerical diffusion. We parallelize the code with Message Passing Interface (MPI) using the domain decomposition technique and confirm the high parallelization efficiency, so that simulations with a spatial resolution of ∼ 1 millimeter can be performed in practical time. As a first application, we study the light propagation for a pulse collimated within θ ∼ 15 ∘ in a phantom, which is a uniform medium made of polyurethane mimicking biological tissue. We show that the pulse spreads in all forward directions over ∼ a few millimeters due to the multiple scattering process of photons. Our simulations successfully reproduce the time-resolved signals measured with eight detectors for the phantom. We also introduce the effects of reflection and refraction at the boundary of medium with a different refractive index and demonstrate the faster propagation of photons in an air hole that is an analogue for the respiratory tract.