Hyperspectral Imaging Coming to Medical Applications

Hyperspectral Imaging Coming to Medical Applications

A powerful color-based imaging technique is making the jump from remote sensing to the operating room—and a team of scientists* at the National Institute of Standards and Technology (NIST) have taken steps to ensure it performs as well when discerning oxygen-depleted tissues and cancer cells in the body as it does with oil spills in the ocean.

microarrayer

Microarrayer machines (A) now can mix colors and deposit them on microscope slides, which can be used to calibrate hyperspectral imagers (HSI) for use in medical applications. The finished slides can be custom-colored (B) to calibrate HSIs to find specific types of tumors or disease tissue. Close up, they resemble dot-matrix printwork (C).

Credit: Clarke/NIST

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The technique, called hyperspectral imaging (HSI), has frequently been used in satellites because of its superior ability to identify objects by color. While many other visual surveying methods can scan only for a single color, HSI is able to distinguish the full color spectrum in each pixel, which allows it to perceive the unique color “signatures” of individual objects. Well-calibrated HSI sensors have been able to discern problems from diseases in coral reefs to pollution in the atmosphere as determined by the distinct spectral signature at a location.

“Because diseased tissues and cells also have distinct spectra, scientists have been trying to use HSI for medical applications as well,” says NIST physicist Jeeseong Hwang. “But any time you tell a machine to scan for something, you need to be sure it is actually looking for what you want, and you have to make sure that the image analysis algorithm extracts the correct color information out of a complex multicolor data set. We decided to create a way to calibrate an HSI device and to test its algorithm as well.”

Matthew Clarke, a former National Research Council-supported postdoctoral fellow in Hwang’s group who is currently working in the National Gallery of Art in Washington, D.C., wrote new software for a device called a microarrayer, so named because it is capable of laying down hundreds of tiny sample droplets in specific places on a microscope slide’s surface. Normally a microarrayer creates DNA arrays for genetic research, but the team remade it into an artistic tool, programming it to select chemicals of different hues and lay them down on the slide’s surface.

The results, which look a bit like dot-matrix printing, can be used to calibrate medical HSI devices and image analysis algorithms. When combined with HSI in a medical imaging application, this effort could allow a surgeon to look for cells with a specific chemical makeup, as determined by the cells’ color.

“Scientists and engineers can create a custom slide with the exact colors representing the chemical makeup they want the HSI devices to detect,” Hwang says. “It could be a good way to make sure the HSI devices for medical imaging perform correctly so that surgeons are able to see all of a tumor or diseased tissue when operating on a patient.”

This project is part of a larger effort to evaluate and validate optical medical imaging devices, led by the NIST team members, David Allen, Maritoni Litorja, Antonio Possolo, Eric Shirley and Jeeseong Hwang. Hwang adds that the special issue** of Biomedical Optics Express in which the team’s findings appear is the output of a recent NIST-supported international workshop on the topic.

*M.L. Clarke, J.Y. Lee, D.V. Samarov, D.W. Allen, M. Litorja, R. Nossal and J. Hwang. Designing microarray phantoms for hyperspectral imaging validation. Biomedical Optics Express, Vol. 3(6), pp. 1291-1299 (June 2012), doi: 10.1364/BOE.3.001300.

The design and fabrication of custom-tailored microarrays for use as phantoms in the characterization of hyperspectral imaging systems is described. Corresponding analysis methods for biologically relevant samples are also discussed. An image-based phantom design was used to program a microarrayer robot to print prescribed mixtures of dyes onto microscope slides. The resulting arrays were imaged by a hyperspectral imaging microscope. The shape of the spots results in significant scattering signals, which can be used to test image analysis algorithms. Separation of the scattering signals allowed elucidation of individual dye spectra. In addition, spectral fitting of the absorbance spectra of complex dye mixtures was performed in order to determine local dye concentrations. Such microarray phantoms provide a robust testing platform for comparisons of hyperspectral imaging acquisition and analysis methods.

Hyperspectral imaging (HSI) is a technique that analyzes a wide spectrum of light coming into a camera. Instead of assigning individual pixels to primary colors (usually red, green, and blue), the light coming into individual pixels is broken down into many more bands, providing more information of what’s being observed. Hyperspectral imaging has particularly been useful for satellites monitoring the environment on Earth, but now researchers at the National Institute of Standards and Technology (NIST) are working on bringing this technology to image the human body for disease.

Until now the problem has been calibrating an HSI device so that it spots the specific color signature of whatever is being looked for. The NIST team developed a method, which uses something called a microarrayer, to do this calibration by depositing substances that have the precise color they’re looking for and calibrating the HSI device against that.

More info from NIST’s press release:

“Because diseased tissues and cells also have distinct spectra, scientists have been trying to use HSI for medical applications as well,” says NIST physicist Jeeseong Hwang. “But any time you tell a machine to scan for something, you need to be sure it is actually looking for what you want, and you have to make sure that the image analysis algorithm extracts the correct color information out of a complex multicolor data set. We decided to create a way to calibrate an HSI device and to test its algorithm as well.”

Matthew Clarke, a former National Research Council-supported postdoctoral fellow in Hwang’s group who is currently working in the National Gallery of Art in Washington, D.C., wrote new software for a device called a microarrayer, so named because it is capable of laying down hundreds of tiny sample droplets in specific places on a microscope slide’s surface. Normally a microarrayer creates DNA arrays for genetic research, but the team remade it into an artistic tool, programming it to select chemicals of different hues and lay them down on the slide’s surface.

The results, which look a bit like dot-matrix printing, can be used to calibrate medical HSI devices and image analysis algorithms. When combined with HSI in a medical imaging application, this effort could allow a surgeon to look for cells with a specific chemical makeup, as determined by the cells’ color.

Source : http://www.nist.gov/pml/div682/hsi-061212.cfm

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