Three-dimensional diffuse optical tomography of simulated hand joints with a 64 × 64-channel photodiodes-based optical system

Abstract

A continuous-wave (CW) diffuse optical tomography (DOT) system that is specifically designed for three-dimensional (3D) imaging of hand joints is described in this paper. This DOT system consists of eight diode lasers coupled with 64 source optic fibre bundles for light excitations and 64 receiving optic fibre bundles in conjunction with 64 silicon photodiodes for light detection. It has a large dynamic range, high stability and low detective noise equivalent power. In this system, the excitation and detection fibre bundles are arranged in four layers each with 16 excitation and 16 detection fibre bundles, forming a cylindrical imaging volume where an inserted finger is supported by a solid coupling medium. A series of tissue-mimicking experiments have been conducted to evaluate the system using a simple joint model consisting of two 'bones' and one layer of 'cartilage'. These experiments also serve to identify optimal experimental and computational configurations for hand joint imaging. Coupled with our 3D finite-element based reconstruction algorithm, the phantom results suggest that the supporting/coupling medium with proper absorption and scattering coefficients is one of the key factors for high quality image reconstruction. In addition, these phantom investigations show that an off-centre positioned object can be significantly better imaged than a centre placed object. Studies have also been performed to determine an optimal mesh size for 3D hand joint imaging.