Analog and digital technologies are presented for precise measurement of propagation delay of photons from source and detector placed on portions of the human body. The goal of the apparatus design is to quantify absorption and scattering induced by biological pigments and biological structures, respectively. Body tissues are highly scattering with a mean distance between scatterers of less than a mm (at 700–850 nm). Significant absorption is mainly due to 5%–10% of the tissue volume occupied by blood. Measurement of and is done by both time and frequency domain equipment. This article focuses upon frequency domain equipment because of its simplicity, reduced noise bandwidth, versatility, and the strong analogy to very high frequency/ultrahigh frequency communication devices, particularly those using phase modulation. Comparisons are made of homodyne and heterodyne systems together with evaluation of single and multiple side band systems, with particular emphasis on methods for multiplexed optical and radio frequencies by frequency encoding or time-sharing technologies. The applications of these phase modulation systems to quantitative brain and muscle blood oximetry, functional activity of the forebrain, and other important problems of medical science, are presented.
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October 1998
Review Article|
October 01 1998
Phase measurement of light absorption and scatter in human tissue
B. Chance;
B. Chance
Department of Biochemistry/Biophysics, Johnson Research Foundation, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6089
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M. Cope;
M. Cope
Department of Medical Physics and Bioengineering, University College London, 1st Floor Shropshire House, London WC1E 6JA, United Kingdom
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E. Gratton;
E. Gratton
Department of Physics, Laboratory for Fluorescence Dynamics, University of Illinois at Urbana-Champaign, Urbana, Illinois 61802
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N. Ramanujam;
N. Ramanujam
Department of Biochemistry/Biophysics, Johnson Research Foundation, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6089
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B. Tromberg
B. Tromberg
Department of Surgery, Beckman Laser Institute & Medical Clinic, University of California, Irvine, Irvine, California 92715
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Rev. Sci. Instrum. 69, 3457–3481 (1998)
Article history
Received:
September 26 1997
Accepted:
July 10 1998
Citation
B. Chance, M. Cope, E. Gratton, N. Ramanujam, B. Tromberg; Phase measurement of light absorption and scatter in human tissue. Rev. Sci. Instrum. 1 October 1998; 69 (10): 3457–3481. https://doi.org/10.1063/1.1149123
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