Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1998-06-16
2001-08-28
Smith, Ruth S. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S476000, C600S477000, C600S478000, C600S109000
Reexamination Certificate
active
06280386
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to diagnostic imaging and more particularly relates to methods and apparatus for optical imaging of tissue containing a luminous object, such as a section of diseased tissue with an applied contrast agent.
2. Description of the Related Art
In many current modalities for medical imaging (i.e. X-ray, PGT, and CAT tomography), contrast agents have been used to enhance image quality and the resulting volume of information. Contrast agents have been introduced in optical imaging to enhance the ability to take an image of an object hidden in a scattering medium or tissue and improve the resulting image quality. An object located inside a scattering medium, such as tissue, is made luminous and viewed using its emission light by introducing a fluorescence dye or inorganic phosphorescence agent. Improvement in the image quality is achieved due to the fact that the distance that the emitted light by the luminous object traverses from the object to the exit point of the scattering medium is shorter than the distance that the illuminating light has to traverse in transillumination techniques. Further improvement of the image quality has been demonstrated by selectively reducing the diffusive component of the emitted light by the luminous object reaching the detector by introducing an absorbing dye into the random medium or using polarization difference imaging.
When tissue is illuminated with light, a first portion of the light undergoes elastic scattering, a second portion of the light undergoes inelastic scattering and a third portion of the light is absorbed by the tissue. When a tissue molecule absorbs a photon, it acquires an amount of energy that it will release within a time interval of less than 1 second. The excess energy of the photo excited tissue molecules is released via nonradiative processes giving rise to generation of phonons or via radiative processes giving rise to light emission by the tissue.
FIG. 1A
shows native light emission by breast chicken tissue illuminated with a 632 nanometer (nm) source. The emissions from the tissue extend up to 950 nm covering a significant part of the “spectral window” that may be used for optical biomedical imaging (700-1200 nm). The temporal profile of the emission shown in
FIG. 1A
is shown in FIG.
1
B. The temporal profile extends to over 2 nanoseconds showing that the recorded light is due to emission by photo excited tissue molecules without any contrast agents.
Contrast agents for use in medical imaging are specifically selected to bind to molecules associated and/or involved in tumors, cancers, brain disorders, liver disorders or other disorders or diseases of the human body. The contrast agents may be injected into the human body to reach and concentrate mostly in the diseased part of the body. Optical images of the diseased part of the human body may then be attained provided that the diseased part of the body can be illuminated and the emitted light from the contrast agent can be recorded by a detection/imaging system.
When the concentration of the contrast agent located at the diseased part of the human body is very small (giving rise to very weak emission) or when the object is deep inside the tissue and it is difficult to illuminate and/or record the emitted light (due to the thickness of the tissue between the diseased tissue and the exterior of the tissue), the detection of the emitted light by the luminous object may be orders of magnitude less than the emitted native fluorescence light by the normal tissue. This effect makes the detection of the emission from the diseased part of the body very difficult or impossible.
Therefore, there remains a need for apparatus and methods that address these problems and enhance the visibility of a luminous object inside a sample of tissue.
SUMMARY OF THE INVENTION
In accordance with a first embodiment of the present invention, an imaging system which enhances the visibility of a luminous object located inside tissue is formed. The imaging system includes means to illuminate the tissue; means to detect a first image signal and a second image signal of the luminous object; and means to perform normalization and subtraction of said recorded image signals, whereby a new image signal is generated in which an image of the luminous object is enhanced.
In accordance with a first imaging method, a selected contrast agent is applied to a tissue specimen to be imaged. The tissue specimen is then illuminated with a light source operating a selected wavelength. Images are then recorded at a first imaging wavelength and at least a second imaging wavelength. The recorded images are then subtracted from one another to minimize the image component resulting from the tissue specimen and enhance an image component resulting from a luminous body within the tissue specimen.
The first and the second imaging wavelengths are preferably selected such that the emission characteristics of the tissue are substantially constant while the emission characteristics of the illuminated body change significantly.
In accordance with another imaging method of the present invention, a selected contrast agent is applied to a tissue specimen to be imaged. The tissue specimen is then illuminated with a light source operating at a first illumination wavelength and at least a second illumination wavelength. First image signals, resulting from excitation by the first illumination wavelength, and second image signals, resulting from excitation by the second illumination wavelength, are then recorded at a selected imaging bandwidth. The recorded image signals are then subtracted from one another to minimize an image component resulting from the tissue specimen and enhance an image component resulting from a luminous body within the tissue specimen.
The first and the second illumination wavelengths are preferably selected such that the absorption characteristics of the tissue are substantially constant while the emission characteristics of the illuminated body change significantly.
These and other objects, features and advantages of the present invention will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.
REFERENCES:
patent: 5042494 (1991-08-01), Alfano
patent: 5678550 (1997-10-01), Bassen et al.
patent: 5823942 (1998-10-01), Toida
patent: 5827190 (1998-10-01), Palcic et al.
patent: 5853370 (1998-12-01), Chance et al.
P. Stefan Anderson et al., “Multispectral System for Medical Fluorescence Imaging”, IEEE, J. Quantum Electronics, QE-23, pp. 1798-1805, Oct. 1997.
K. M. Zoo et al., “Imaging objects hidden in scattering media using a fluorescence-absorption technique”, Opt. Lett. 16, pp. 1252-1254, 1991.
Alfano Robert R.
Ali Jamal
Demos Stavros G.
Wang Wubao
Dilworth & Barrese LLP
Smith Ruth S.
The Research Foundation of the City University of New York
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