3D Numerical modeling and its experimental verifications for an inhomogeneous head phantom using broadband fNIR system

Abstract

Modeling behavior of broadband (30-1000 MHz) frequency modulated near infrared photons through a multilayer phantom is of interest to optical bio-imaging research. Photon dynamics in phantom are predicted using three-dimension (3D) finite element numerical simulation and are related to the measured insertion loss and phase for a given human head geometry in this paper based on three layers of phantom each with distinct optical parameter properties. Simulation and experimental results are achieved for single, two, and three layers solid phantoms using COMSOL (COMSOL AB, Tegnérgatan 23, SE-111 40, Stockholm, Sweden) (for FEM) simulation and custom-designed broadband free space optical transmitter (Tx) and receiver (Rx) modules that are developed for photon migration at wavelengths of 680, 795, and 850 nm. Standard error is used to compute error between two-dimension and 3D FE modeling along with experimental results by fitting experimental data to the functional form of afrequency+b. Error results are shown at narrowband and broadband frequency modulation. Confidence in numerical modeling of the photonic behavior using 3D FEM for human head has been established here by comparing the reflection mode's experimental results with the predictions made by COMSOL for known commercial solid brain phantoms.

Diagnosis of Hand Tumors using fNIR Optical System

“…The first stage is dedicated to performing functionality measurements to monitor both absorption and scattering, while the second stage is dedicated to optical parameter extraction of the ganglion cyst tissue and lipoma fatty tumor. The first stage is performed while the patients is bending his wrist to measure photon backscattering as shown in Figure 2, while the second stage is performed using transmission mode optical parameter extraction [3][4][5] after the ganglion cyst fluid and fatty tumor are aspirated. …”

“…Commercial multi-physics based FEM software (COMSOL) is used as a robust numerical tool in this study to numerically predict the photon behavior in scattering media and to solve the inverse problem. The Helmholtz equation is used for numerical analysis [4] [16][17] as:…”

“…A typical computation time of 4 seconds for single 2D simulation and 24-28 second for single 3D simulation is experienced using an Intel Core i3 processor PC. These meshing element sizes are also recommended for interfaces, when multi-layer human head phantoms are modeled [4]. Table 2.…”

“…Dirichlet and Neumann boundary conditions are chosen appropriately for airdielectric (or dielectric-dielectric) and radiation conditions in regions surrounding biomaterials. The mathematical representation is expressed [4] as:…”

“…Amplitude and phase of both forward and back-scattered photons out of the biological media are measured as IL and IP of the radio frequency signal and then Diffusion Equation is employed for inverse problem solving of turbid biological media. The advantages of broadband measurements are already reported [3][4][5] and are due to high accuracy in extraction of optical parameters and imaging of inhomogeneous material represented as multilayer media.…”