"This new ultraminiature endoscope is the first to allow three-dimensional imaging of areas inside the body", stated Guillermo Tearney, MD, PhD, of the MGH Wellman Center, the report's senior author. "Its ability to go places that other imaging tools cannot reach opens new possibilities for medical diagnosis and eventually treatment."
Standard miniature endoscopic devices - which give physicians access to hard-to-reach internal organs and structures - utilize 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, two-dimensional 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). Multicoloured light from a single optical fiber - introduced through a probe about the size of a human hair - is broken into its component colours and projected onto tissue, with each colour illuminating a different part of the tissue surface. The light reflected back is recorded, and the intensity of the various colours decoded by a spectrometer, which analyses 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 three-dimensional images.
To demonstrate the device's application in a live animal, the researchers used the system to image metastatic ovarian tumours on the abdominal wall of a mouse. The SEE probe was passed into the abdominal cavity through a fine-gauge needle. The resulting three-dimensional image showed several raised areas of tumour 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", stated Dvir Yelin, PhD, first author of the Nature 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 anaesthesia requirements and minimize tissue damage", Dr. Tearney added. "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. Foetal and paediatric 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."
The spectral encoded miniature endoscope uses micro optics and a single optical fiber to project various colours of light onto different portions of the subject. The light reflected back into the endoscope is measured and analysed to produce a three-dimensional image. This illustration shows a time exposure of white light transmitted through the miniature endoscope, superimposed on a three-dimensional rendering of mouse metastatic ovarian tumour nodules obtained with this new technique. (Photo by courtesy of the Wellman Center for Photomedicine, Massachusetts General Hospital)
Dr. Tearney is an associate professor of Pathology at Harvard Medical School. He and his colleagues are working on adapting the SEE device for human studies in the near future. Additional co-authors of the Nature report are Imran Rizvi, Matthew White, MD, Jason Motz, PhD, Tayyaba Hasan, PhD, and Brett Bouma, PhD - 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.
Massachusetts General Hospital, established in 1811, is the original and largest teaching hospital of Harvard Medical School. The MGH conducts the largest hospital-based research programme in the United States, with an annual research budget of nearly $500 million and major research centres in AIDS, cardiovascular research, cancer, computational and integrative biology, cutaneous biology, human genetics, medical imaging, neurodegenerative disorders, regenerative medicine, transplantation biology and photomedicine. MGH and Brigham and Women's Hospital are founding members of Partners HealthCare HealthCare System, a Boston-based integrated health care delivery system.