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Tiny Endoscope Images in 3-D

Photonics.com
Oct 2006
BOSTON, Oct. 19, 2006 -- By projecting multicolored light from a single optical fiber onto tissue, a newly developed tiny endoscope can for the first time produce three-dimensional, high-definition images of hard-to-reach areas of the body through a probe the width of a human hair.

The new type of miniature endoscope was developed by researchers at Massachusetts General Hospital (MGH), who said it may greatly expand the application of minimally invasive diagnostic and therapeutic procedures.

"This new ultraminiature endoscope is the first to allow three-dimensional imaging of areas inside the body," said Guillermo Tearney of the MGH Wellman Center for Photomedicine, senior author of a report on the research and associate professor of pathology at Harvard Medical School. "Its ability to go places that other imaging tools cannot reach opens new possibilities for medical diagnosis and eventually treatment."

Endoscope.jpg
The spectral-encoded miniature endoscope uses micro-optics and a single optical fiber to project various colors of light onto different portions of the subject. The light reflected back into the endoscope is measured and analyzed to produce a three-dimensional image. This illustration shows a time exposure of white light transmitted through the miniature endoscope, superimposed on a 3-D rendering of mouse metastatic ovarian tumor nodules obtained with this new technique. (Image: Wellman Center for Photomedicine, Massachusetts General Hospital)
Standard miniature endoscopic devices -- which give physicians access to hard-to-reach internal organs and structures -- use bundles of optical fibers to supply light to and transmit images from the areas of interest. Larger endoscopes that use image sensors to produce high-quality, 2-D images can be a centimeter or more in diameter. Existing miniature endoscopes using smaller fiber bundles may be more flexible but have difficulty producing high-quality images.

The new device developed at MGH-Wellman uses a technology called spectrally encoded endoscopy (SEE). Multicolored light from a single optical fiber -- introduced through a probe about the size of a human hair -- is broken into its component colors and projected onto tissue, with each color illuminating a different part of the tissue surface. The light reflected back is recorded, and the intensity of the various colors decoded by a spectrometer, which analyzes the wavelengths of light. Another device called an interferometer, which calculates structural information based on the interaction between two waves of light, provides the data required to create 3-D images.

In the Oct. 19 issue of Nature, the team from MGH-Wellman describe their prototype device and its use imaging metastatic ovarian tumors on the abdominal wall of a mouse. The SEE probe was passed into the abdominal cavity through a fine-gauge needle. The resulting 3-D image showed several raised areas of tumor nodules, the presence of which was confirmed by histologic analysis of the tissue.

"The most important feature of this new endoscope is the ability to obtain three-dimensional images, something we don't believe is offered by any commercially available miniature endoscope system," says Dvir Yelin, first author of the paper. "While the image resolution we achieved in this demonstration is similar to existing small-diameter endoscopes, with further optimization of the optics it is possible to obtain images with 10 times the number of pixels provided by other miniature endoscopes."

"This new technology will offer physicians and surgeons the capability to bring many more procedures into outpatient settings, reduce anesthesia requirements and minimize tissue damage," Tearney said. "The device's size and flexibility should allow safer navigation through such delicate structures as the salivary ducts, the fallopian tubes and the pancreatic duct. Fetal and pediatric procedures may also benefit from this tool. Eventually, SEE could give rise to new procedures that permit diagnosis and microsurgery in previously inaccessible areas of the body."

Tearney and his colleagues are working to adapt the SEE device for human studies in the near future. Additional co-authors of the report are Imran Rizvi, Matthew White, Jason Motz, Tayyaba Hasan and Brett Bouma, all of the Wellman Center. The research was supported by grants from the Center for the Integration of Medicine and Innovative Technology, the National Science Foundation and the Whitaker Foundation.

For more information, visit: www.massgeneral.org/news


GLOSSARY
endoscope
A medical instrument used to view inside the human body by inserting the instrument into a natural or created aperture. The endoscope may use a coherent fiber optic bundle or conventional optics to relay the image to the eye or a television camera. Illumination is provided by a concentric bundle of noncoherent fiber optics.  
image
In optics, an image is the reconstruction of light rays from a source or object when light from that source or object is passed through a system of optics and onto an image forming plane. Light rays passing through an optical system tend to either converge (real image) or diverge (virtual image) to a plane (also called the image plane) in which a visual reproduction of the object is formed. This reconstructed pictorial representation of the object is called an image.
interferometer
An instrument that employs the interference of lightwaves to measure the accuracy of optical surfaces; it can measure a length in terms of the length of a wave of light by using interference phenomena based on the wave characteristics of light. Interferometers are used extensively for testing optical elements during manufacture. Typical designs include the Michelson, Twyman-Green and Fizeau interferometers. The basic interferometer components are a light source, a beamsplitter, a reference...
optical fiber
A thin filament of drawn or extruded glass or plastic having a central core and a cladding of lower index material to promote total internal reflection (TIR). It may be used singly to transmit pulsed optical signals (communications fiber) or in bundles to transmit light or images.  
probe
Acronym for profile resolution obtained by excitation. In its simplest form, probe involves the overlap of two counter-propagating laser pulses of appropriate wavelength, such that one pulse selectively populates a given excited state of the species of interest while the other measures the increase in absorption due to the increase in the degree of excitation.
spectrometer
A kind of spectrograph in which some form of detector, other than a photographic film, is used to measure the distribution of radiation in a particular wavelength region.  
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