Book contents
- Frontmatter
- Dedication
- Contents
- Preface
- 1Nomenclature
- 2Overview of tissue optical properties
- 3Introduction to biomedical statistics for diagnostic applications
- 4General concepts of tissue spectroscopy and instrumentation
- 5Autofluorescence spectroscopy and reporter fluorescence
- 6Raman and infrared spectroscopy of vibrational modes
- 7Elastic and quasi-elastic scattering from cells and small structures
- 8Diffuse reflectance spectroscopy at small source-detector separations
- 9Transport theory and the diffusion equation
- 10Continuous-wave methods for tissue spectroscopy
- 11Time-domain methods for tissue spectroscopy in the diffusion regime
- 12Frequency-domain methods for tissue spectroscopy in the diffusion regime
- 13Instrumentation and experimental methods for diffuse tissue spectroscopy
- 14Diffuse optical imaging and tomography
- 15In vivo applications of diffuse optical spectroscopy and imaging
- 16Combining light and ultrasound: acousto-optics and opto-acoustics
- 17Modern optical microscopy for biomedical applications
- 18Optical coherence tomography
- 19Optical tweezers and laser-tissue interactions
- Answers to selected problems identified by *
- Table of symbols
- Table of acronyms
- Index
- References
2 - Overview of tissue optical properties
Published online by Cambridge University Press: 28 May 2018
Book contents
- Frontmatter
- Dedication
- Contents
- Preface
- 1Nomenclature
- 2Overview of tissue optical properties
- 3Introduction to biomedical statistics for diagnostic applications
- 4General concepts of tissue spectroscopy and instrumentation
- 5Autofluorescence spectroscopy and reporter fluorescence
- 6Raman and infrared spectroscopy of vibrational modes
- 7Elastic and quasi-elastic scattering from cells and small structures
- 8Diffuse reflectance spectroscopy at small source-detector separations
- 9Transport theory and the diffusion equation
- 10Continuous-wave methods for tissue spectroscopy
- 11Time-domain methods for tissue spectroscopy in the diffusion regime
- 12Frequency-domain methods for tissue spectroscopy in the diffusion regime
- 13Instrumentation and experimental methods for diffuse tissue spectroscopy
- 14Diffuse optical imaging and tomography
- 15In vivo applications of diffuse optical spectroscopy and imaging
- 16Combining light and ultrasound: acousto-optics and opto-acoustics
- 17Modern optical microscopy for biomedical applications
- 18Optical coherence tomography
- 19Optical tweezers and laser-tissue interactions
- Answers to selected problems identified by *
- Table of symbols
- Table of acronyms
- Index
- References
Summary
In Chapters 5, 6, and 7, we will examine in detail the molecular transitions and microscopic-scale structural features of tissue that are responsible for its optical properties on any scale, and that afford opportunities for diagnostic assessment. In this chapter, however, we introduce the primary constituents and structures of tissue that are responsible for its bulk optical properties, with primary attention to the wavelength range of near-UV through visible to near-IR. Of course, the heterogeneity of tissue lends complexity to the interpretation of the interactions of light with tissue, but, prior to addressing the effects of the heterogeneity, it is instructive to understand the factors that govern the averaged optical properties on a macroscopic scale.
The two optical properties that govern light transport in tissue, and that must be understood thoroughly, are absorption and scattering.
Absorption is due to a variety of chromophores, compounds and fluids that absorb light at certain wavelengths and are commonly found in tissue. The word chromophore derives from the Greek chroma, for color. This would imply that a chromophore exhibits an optical absorption band in the visible range of wavelengths (400–700 nm), although common usage in biomedical optics includes the near-infrared (NIR) region as well. In mammalian tissue, the origins of optical absorption in the visible-NIR range are primarily due to broad absorption features of electronic transitions of π-electrons in large organic molecules and biomolecular constituents.
Scattering is due to gradients and discontinuities in the optical refractive index of the various architectural microstructures and sub-cellular components of tissue.
Other intrinsic optical properties of tissue that can affect light transport include birefringence and optical activity. These are subtle effects, however, that do not generally affect bulk transport properties of tissue, but can be relevant to microscopy based on phase contrast or differential interference contrast, which will be studied in Chapter 17 (Section 17.2).
Whether absorption or scattering dominates the propagation of light in tissue depends on the specifics of the tissue optical properties, which are generally a function of wavelength, and on their spatial distribution at microscopic and macroscopic levels. Figure 2.1 illustrates two cases, wherein either absorption or scattering dominates.
Absorption and scattering coefficients
We address the bulk optical properties, for which typical scale lengths are long compared to both the wavelength of light and the individual elements of tissue microstructure (cells, for example).
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- Quantitative Biomedical OpticsTheory, methods, and applications, pp. 19 - 59Publisher: Cambridge University PressPrint publication year: 2016
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