Improved utilization of frequency-domain data for optical tomographic imaging of the human brain

Abstract

Frequency-domain (FD) optical tomography instruments modulate the intensity of the light source at a radio frequency and measure the amplitude and phase shift of the detected photon density wave. The differing spatial sensitivities of amplitude and phase to the optical properties of tissue suggest that inclusion of phase data can improve the image reconstruction accuracy. This study describes our methodology for improved use of FD data in conjunction with a Monte Carlo (MC) forward solver (Monte Carlo eXtreme; MCX) and a voxel-based model of a two-year-old child’s head. The child participated our previous study where subjects were stimulated with affective (slow brushing) and non-affective touch (fast brushing) to their right forearm, and the responses were measured from the left hemisphere with our in-house 16-channel high-density FD system. We implemented the computation of the FD sensitivity profiles to the MCX photon simulation software, and validated the output against our in-house MC code. We used simulated and the real experimental touch response data to observe the effects of including both FD data types to the image reconstruction instead of amplitude data alone. For the simulated and experimental case, we observed that the inclusion of phase data increases the reconstructed contrast in the brain. The individual touch responses showed similarity to the group-level results in our original publication with 16 subjects and amplitude data alone, and other literature.