Patent Application
20060221335
Spectroscopic imaging combines digital imaging and molecular spectroscopy techniques, which can include Raman scattering, fluorescence, photoluminescence, ultraviolet, visible and infrared absorption spectroscopies. When applied to the chemical analysis of materials, spectroscopic imaging is commonly referred to as chemical imaging. Instruments for performing spectroscopic (i.e., chemical) imaging typically comprise image gathering optics, focal plane array imaging detectors and imaging spectrometers.
In general, the sample size determines the choice of image gathering optic. For example, a microscope is typically employed for the analysis of sub micron to millimeter spatial dimension samples. For larger objects, in the range of millimeter to meter dimensions, macro lens optics are appropriate. For samples located within relatively inaccessible environments, flexible fiberscopes or rigid borescopes can be employed. For very large scale objects, such as planetary objects, telescopes are appropriate image gathering optics.
Often the sample under study includes a plurality of species in a mixture. Thus, the chemical image of the sample characterizes the sample as a mixture of species. Each specie can be a pure element, a compound of said element with other elements or a compound. While the chemical image of the sample can identify each of the species by using color or some other indication, it fails to communicate the spectral image of each specie independent of the mixture. Thus, there is a need for a method and apparatus to interactively obtain the spectral image for the desired specie from the chemical image of the mixture.
The instant disclosure addresses the needs described above. In one embodiment, the disclosure relates to a method for obtaining a spectral image of a first specie from a frame of a plurality of pixels defining a composition of the first specie with a second specie, comprising (i) identifying, for each of the first and second species, an appropriate Raman wavelength; (ii) defining at least one background wavelength for the frame; identifying pixels defined only by background wavelength; (iii) identifying pixels defined only by the first specie or the second specie; (iv) identifying the remaining pixels, the remaining pixels defined by at least a combination of the first and second species; (v) identifying the contribution from each of the first and the second specie for each of the remaining pixels; and (vi) forming a spectral image for the first specie.
In another embodiment, the disclosure relates to a method for obtaining a spectral image of first specie from a chemical image of said first specie in combination with a second specie. The method includes (i) providing a chemical image of a mixture of the first and second specie, the chemical image defined by a frame having a plurality of pixels; (ii) identifying, for each of the first and second species, an appropriate Raman wavelength; (iii) defining a background wavelength for the frame; (iv) identifying pixels defined only by background wavelength; (v) identifying pixels defined by the peak Raman wavelength of the first specie or the second specie; (vi) identifying a plurality of remaining pixels, the remaining pixels identifying a combination of the first and second species; (vii) identifying the contribution from each of the first and the second specie to each of the remaining pixels; and (viii) forming a spectral image for the first specie.
In still another embodiment, the disclosure relates to an apparatus for obtaining a spectral image of a first specie from a chemical image of said first specie admixed with a second specie. The apparatus includes: an illumination source for illuminating the sample with a plurality of excitation photons to produce a plurality of interacted photons; an optical device for receiving and directing the plurality of interacted photons to an imaging device for forming a chemical image define by at least one frame having a plurality of pixels; and a processor in communication with the imaging device. The processor can be adapted to execute instructions to (i) identify, for each of the first and second species, an appropriate Raman wavelength; define at least one background wavelength for the frame; (ii) identify pixels defined only by background wavelength; (iii) identify pixels defined only by the first specie or the second specie; (iv) identify the remaining pixels, the remaining pixels defined by at least a combination of the first and second species; (v) identify the contribution from each of the first and the second specie for each of the remaining pixels; and (vi) form a spectral image for the first specie.
After identifying a characteristic Raman peak wavelength for each specie, the background wavelength for the frame should be defined. The background wavelength can be caused by intangibles of the optical devices such as signal-to-noise interference, and other common electro-optical losses. The background wavelength can also define a quantifiable intensity uniformly affecting all pixels in the chemical image frame 100. Once the intensity and the wavelength of background noise is identified, all pixels in the Chemical image frame that only relate to the background wavelength can be identified. Thereafter, all pixels defined by wavelength and intensity characteristics similar to that of the known Raman spectra of each specie can be identified.
Once the pixels directed exclusively to one of the first or second specie or the background have been identified, the remaining pixels can be attributed to identifying a combination of the first and the second species, thereby constituting a chemical interface of one or more species. Theses remaining pixels can be said to contain a contribution from each specie.
Once the function of each pixel in the frame is defined as one of background, first specie, second specie or a combination of first and second species, a spectral image can be constructed for one of the species by interactively subtracting contributions from the background and the other specie. In the exemplary embodiment of
The disclosed method and apparatus enable interactive visualization and comparison of different imaging modes. The interaction is direct and unobstructed. The embodiments disclosed here enable macro-to-micro image exploration as well as specific targeting of regions of interest. In addition, the ability to switch between imaging modes for the same regions allow comparisons that would otherwise not be possible, or alternatively, would be difficult and time consuming. These exemplary steps can be repeated to determine a spectra for the second specie. While the exemplary embodiments of
Moreover, the same principles can be extended to samples exhibiting a chemical interaction between the species.
Sample 420 can have a plurality of species (not shown.) Further, the sample can be any biological, organic or inorganic sample suitable for spectral studies. Optical device 430 can receive and direct interacted photons to imaging device 440. The illumination source can be positioned above, near or below the sample. Optical device 430 may include gathering optics, optical train, macro-scope and electromechanical devices needed for its operation. Imaging device 440 may include, for example, an optical train for gathering and focusing interacted photons; one or more optical filters for rejecting photons of undesired wavelengths; an LCTF for obtaining spectral images of the sample; and a charge-coupled device for devising a chemical image based on the spectral images of the sample. Imaging device 440 can communicate with peripheral network devices (not shown) such as printers, video recorders or internet communication systems.
Processor 450 communicates with imaging device 440 and can be used to implement interactive hyperspectral image subtraction steps disclosed above. For example, the processor can be programmed to: (1) identify, for each of the first and second species, an appropriate Raman wavelength; (2) define at least one background wavelength for the frame; (3) identify pixels defined only by the background wavelength; (4) identify pixels defined only by the first specie or the second specie; (5) identify the remaining pixels, the remaining pixels defined by at least a combination of the first and second species; and (6) form a spectral image for the first specie. These steps can be implemented substantially simultaneously or sequentially. In an optional embodiment, the step of identifying the contribution from each of the first and the second specie for each of the remaining pixels may be implemented.
Processor 450 may communicate with operator 460 for interactive subtraction. In addition, the processor may communicate with illumination source 410 in order to increase or decrease illumination wavelength λillum. in response to operator 460 request or in response to programmed instructions.
While the principles of the disclosure have been disclosed in relation to specific exemplary embodiments, it is noted that the principles of the invention are not limited thereto and include all modification and variation to the specific embodiments disclosed herein.
