Surgery – Truss – Pad
Patent
1991-08-29
1995-05-30
Sykes, Angela D.
Surgery
Truss
Pad
A61B 600
Patent
active
054193230
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to optical and laser spectroscopy and, in particular, laser induced fluorescence (LIF) spectroscopy which has recently been explored as a technique for medical diagnosis.
It is known that fluorescence spectroscopy can be used to diagnose the presence of atherosclerosis in human artery wall, emphasizing the use of empirically defined algorithms to determine tissue type from fluorescence spectra. For example, using 476 nm LIF spectroscopy, Kittrell et al., "Diagnosis of Fibrous Atherosclerosis Using Fluorescence", Applied Optics, 24, 2280 (1985), have demonstrated that such an empirical algorithm can be used to differentiate normal aorta and early atherosclerotic plaque in vitro. Fluorescence spectra of normal aorta and fibrous plaque were differentiated by the peak to valley ratio of the fluorescence intensity at 600 nm to the intensity at 580 nm.
Catheters employing optical fibers for the illumination, viewing and treatment of tissue are now used with sources of laser radiation for a variety of medical applications. Through the insertion of the catheter into a human artery or bodily cavity, laser radiation of a given wavelength can be used to illuminate tissue within the body such that the tissue fluoresces. Radiation generated by tissue fluorescence is then conveyed by one or more of the optical fibers to the proximal end of the catheter where it can be analyzed to yield information about the tissue under examination.
SUMMARY OF THE INVENTION
The method of the present invention relates to the diagnosis of tissue and particularly targeting of chromophores in soft tissue with optical radiation and analyzing returning radiation to determine the type and abundance of those chromophores. By utilizing the laser induced fluorescence of chromophores contained in the tissue the concentration of those chromophores yields significant diagnostic information about the tissue. The method provides a technique for rapid identification and diagnosis of tissue without the highly invasive procedures currently in use.
Chromophores that naturally occur in tissue respond to incident light by several processes. Absorption of light by the tissue will occur based on the characteristics of each of the chromophores that are present. Single or multiple wavelength excitation will provide a characteristic spectrum or profile of the tissue being illuminated. Some of the chromophores in the tissue will fluoresce depending upon the excitation wavelength or wavelengths so that the fluorescence emission will define a characteristic profile for that tissue.
Note that the emission also has a fluorescence lifetime which may be measured and analyzed to reveal important diagnostic information. In addition, the chemical moieties in the tissue exhibit inelastic or Raman scattering, which also provide useful spectral information.
The total spectrum is the sum of the individual contributions of the many chemical constituents of the tissue. When additional excitation wavelengths are used, chromophore excitation is also altered, some emitting at stronger intensities and some weaker. The overall profile changes as each individual contribution changes. The use of many excitation wavelengths assists in the identification of the chromophores present in the tissue.
In particular, tuning through the absorption edge of a chromophore at a particular wavelength can result in sharp changes in the emission spectrum. Tuning close to the edge allows the spectral profile to be adjusted like a dimmer switch relative to the other chromophore contributions to the spectrum.
Since different types of tissue have different chemical composition, spectroscopy can be used to identify different chromophores present in the tissue being diagnosed. By measuring the presence and amount of the chromophores, the tissue type can be more fully characterized. For increased accuracy in diagnosis, or to help distinguish between similar but non-identical tissues, several wavelengths can be used to target several chromophores.
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An Kyungwon
Baraga Joseph J.
Cothren Robert M.
Dasari Ramachandra R.
Feld Michael S.
Massachusetts Institute of Technology
Sykes Angela D.
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