title: Feasibility of Direct Digital Sampling for Diffuse Optical Frequency Domain Spectroscopy in Tissue.
abstract: Frequency domain optical spectroscopy in the diffusive regime is currently being investigated for biomedical applications including tumor detection, therapy monitoring, exercise metabolism, and others. Analog homodyne or heterodyne detection of sinusoidally modulated signals have been the predominant method for measuring phase and amplitude of photon density waves that have traversed through tissue. Here we demonstrate the feasibility of utilizing direct digital sampling of modulated signals using a 3.6 Gigasample/second 12 bit Analog to Digital Converter. Digitally synthesized modulated signals between 50MHz and 400MHz were measured on tissue simulating phantoms at six near-infrared wavelengths. An amplitude and phase precision of 1% and 0.6 degrees were achieved during drift tests. Amplitude, phase, scattering and absorption values were compared with a well-characterized network analyzer based diffuse optical device. Measured optical properties measured with both systems were within 3.6% for absorption and 2.8% for scattering over a range of biologically relevant values. Direct digital sampling represents a viable method for frequency domain diffuse optical spectroscopy and has the potential to reduce system complexity, size, and cost.
authors.affiliation: Department of Biomedical Engineering, Boston University, 44 Cummington Mall, Boston, MA 02115 ; Laser Microbeam and Medical Program (LAMMP), Beckman Laser Institute and Medical Clinic, University of California, Irvine.
authors.forename: Darren
authors.initials: D
authors.lastname: Roblyer
authors.affiliation: Laser Microbeam and Medical Program (LAMMP), Beckman Laser Institute and Medical Clinic, University of California, Irvine.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: O'Sullivan
authors.affiliation: Laser Microbeam and Medical Program (LAMMP), Beckman Laser Institute and Medical Clinic, University of California, Irvine.
authors.forename: Robert V
authors.initials: RV
authors.lastname: Warren
authors.affiliation: Laser Microbeam and Medical Program (LAMMP), Beckman Laser Institute and Medical Clinic, University of California, Irvine.
authors.forename: Bruce
authors.initials: B
authors.lastname: Tromberg
keywords: diffuse optics; digital sampling; frequency domain; photon migration; spectroscopy