Spectrometer Looks for Cancer
Brent D. Johnson
Breast cancer is the second leading cause of death among women, with 700,000 new cases diagnosed every year. X-ray mammography remains the most important means of diagnosing the disease, but its sensitivity depends on the size of the tumor. Consequently, medical researchers are investigating alternative techniques, including optical spectroscopy.
Researchers are using optical translation spectroscopy to analyze the physiological changes that precede the development of breast cancer. Their system employs a multichannel spectrometer that features a volume-phase holographic transmission grating. Courtesy of P&P Optica Inc.
Lothar Lilge of the Ontario Cancer Institute at Princess Margaret Hospital said that the risk factors for breast cancer typically are not considered until women reach the age of 40. However, he noted that cancer can take up to two decades to develop, so the scientists at the facility are looking at people in their early 20s to attempt to understand the preconditions for its onset. Using optical translation spectroscopy, they are analyzing the physiological changes that precede cancer formation so that these factors can be correlated.
The system features a multichannel spectrometer developed for the application by P&P Optica Inc. that incorporates a volume-phase holographic transmission grating. Standard gratings, explained Olga Pawluczyk, vice president of the company, have grooves on the surface of a substrate with which the light interacts. This grating, however, features a photosensitive gel with a periodic index of refraction, which presents fewer physical edges and thereby reduces scattering.
In other spectrometers, the interaction of light takes place at the surface of the grating. With this holographic grating, in contrast, refraction occurs throughout the volume of the gel, permitting more light to enter the detector. This results in a high spectral efficiency, with a peak above 80 percent and a spectral range from 500 to 1100 nm.
In application, broadband illumination passes through the breast over several centimeters of tissue and is measued at several points. The radiation leaving the breast is collimated onto the grating, and a CCD collects spectral information from each point of light.
Using nonionizing radiation offers the same results as high-energy, ionizing radiation, so the technique offers a less dangerous alternative to x-ray mammography. It also allows the scientists to image several channels simultaneously.
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