Systems and methods for tomographic image reconstruction
Optical tomography systems that provide light of multiple distinct wavelengths from a plurality of sources are described. The systems direct light into mammalian tissue, and light from the mammalian tissue is collected at a plurality of reception points. Collected light from each reception point is separated according to its wavelength, and received by a photodetector to produce path attenuation signals representing attenuation along paths between the source locations and the reception points. An image construction system generates a tomographic image of the mammalian tissue from the path attenuation signals. One embodiment of an optical imaging system includes an optical coherence tomography-near infrared probe. The systems and methods may utilize a spectral derivative approach that provides insensitivity to the boundary and boundary artifacts in the signal, thereby improving the quality of the reconstructed images.
1. A tomography system, comprising:
a plurality of lasers of a first group, each laser of the first group for generating light of a distinct wavelength within a first wavelength band;
apparatus for simultaneously applying the light from lasers of the first group to mammalian tissue at a plurality of stimulus locations, such that the apparatus is configured to apply light from a first laser of the first group to a first stimulus location but not to a second stimulus location, and configured to apply light from a second laser of the first group to the second stimulus location but not the first stimulus location, the first stimulus location differing from the second stimulus location;
a plurality of lasers of a second group, each laser of the second group for generating light of a distinct wavelength within a second wavelength band not overlapping the first wavelength band, the lasers of the second group operable simultaneously with the lasers of the first group;
wherein the apparatus for applying light to mammalian tissue is further configured to apply light from a first laser of the second group to the first stimulus location but not to the second stimulus location, and configured to apply light from a second laser of the second group to the second stimulus location but not to the first stimulus location;
apparatus for collecting light from the mammalian tissue at a plurality of reception points;
apparatus for separating light received from the apparatus for collecting light according to a wavelength of the received light;
apparatus for generating path attenuation signals encoding received light amplitude information for each path from a stimulus location to each reception point at each wavelength corresponding to each laser of the plurality of lasers; and
image construction apparatus for receiving the path attenuation signals and for reconstructing a tomographic image of the mammalian tissue corresponding to oxygenation of the mammalian tissue.
2. The tomography system of claim 1 wherein the image construction apparatus comprises a processor configured to perform an image reconstruction procedure selected from the group consisting of Direct Chromophore Spectral Reconstruction (DCSR) and Spectral Derivative Image Reconstruction (SDIR).
3. The tomography system of claim 2 wherein the image reconstruction procedure is SDIR, and further is based upon differences in logarithms of detected intensities at each wavelength at each reception point.
4. The tomography system of claim 1 , wherein the first wavelength band is of bandwidth less than one percent, and a center wavelength of the first wavelength band is separated from a center wavelength of the second wavelength band by between five and ten percent.
5. The tomography system of claim 4 , wherein the apparatus for generating a path attenuation signal further comprises a diffraction grating, a fiber-optic distributor, and a plurality of photomultiplier tubes.
6. The tomography system of claim 4 , wherein the first wavelength band is within the range 750 to 860 nanometers and wherein the apparatus for generating a path attenuation signal further comprises a diffraction grating and a charge-coupled device (CCD) image sensor.
7. The tomography system of claim 6 , wherein the apparatus for generating a path attenuation signal further comprises an image intensifier tube for amplifying light separated according to wavelength by the diffraction grating and for providing amplified light to the CCD image sensor.
8. The tomography system of claim 1 , wherein the first wavelength band is near infrared between 620 and 1000 nanometers.
9. The tomography system of claim 8 , wherein the first wavelength band is within the range 750 to 860 nanometers.
10. The tomography system of claim 8 , wherein the first wavelength band is of bandwidth less than two percent of its center wavelength.
11. The tomography system of claim 10 , wherein the apparatus for separating light further comprises a diffraction grating and the apparatus for generating a path attenuation signal further comprises a fiber-optic distributor, and a plurality of photomultiplier tubes.
12. The tomography system of claim 10 , wherein the apparatus for separating light further comprises a diffraction grating and the apparatus for generating a path attenuation signal further comprises a charge-coupled device (CCD) image sensor.
13. The tomography system of claim 12 , wherein the apparatus for generating a path attenuation signal further comprises an image intensifier tube.