Journal
MEASUREMENT SCIENCE AND TECHNOLOGY
Volume 24, Issue 4, Pages -Publisher
IOP PUBLISHING LTD
DOI: 10.1088/0957-0233/24/4/045501
Keywords
diffuse optical spectroscopy; frequency domain; photon density waves; digital sampling; analog to digital conversion
Funding
- National Institutes of Health [P41RR01192, P41EB015890]
- Network for Translational Research [U54-CA136400]
- American College of Radiology Imaging Network (ACRIN) [ACR-50185-6691, NCI-2P30CA62203]
- University of California, Irvine Cancer Center Support Grant
- Arnold and Mabel Beckman Foundation
- DOD [W81XWH-10-1-0972]
- UCI [NCI-T32CA009054)]
- [R01-CA142989]
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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 has 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 50 MHz and 400 MHz were measured on tissue-simulating phantoms at six near-infrared wavelengths. An amplitude and phase precision of 1% and 0.6. were achieved during drift tests. Amplitude, phase, scattering and absorption values were compared with a well-characterized network analyzer-based diffuse optical device. 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.
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