Nov. 1, 1997 CHAPEL HILL -- By creating significantly sharper, more detailed pictures of breast tissue, mice and other objects, a technical advance in radiography could dramatically improve mammography and other medical and materials imaging, new studies suggest. The ultimate goal will be to cut the number of breast cancer deaths by diagnosing tumors earlier.
A team of scientists from the University of North Carolina at Chapel Hill, the Illinois Institute of Technology in Chicago, Brookhaven National Laboratory in Upton, N.Y., and N.C. State University in Raleigh are developing the new imaging method using a single-energy X-ray source. Such sharply defined pictures have never been produced through conventional X-ray machines.
"Mammography presents difficult imaging problems because the densities of the tissues are similar, and the lack of contrast often masks tumors," said Dr. Etta Pisano, associate professor of radiology at the UNC-CH School of Medicine and the research team physician.
"With our new method, which we call defraction-enhanced imaging, or DEI, we have produced images showing improved detail of cancerous tumors in human breast tissue," said Pisano, also mammography chief at UNC-CH and a UNC Lineberger Comprehensive Cancer Center member. "The detail is just outstanding -- it's like casting a sharper shadow when the sun shines down on you.
"While much work remains to be done before we can use this with patients, we are absolutely excited about the possibilities," she said. "This has never been done before, and we know of no reason why it couldn't work on other parts of the body as well."
A report on the findings appears Friday (Oct. 31) as the lead article in the November issue of Physics in Medicine and Biology, a professional journal. Besides Pisano, authors of the report are Drs. Dean Chapman, director of the IIT's Center for Synchrotron Research and Instrumentation; Eugene Johnston and David Washburn of radiology at UNC-CH; William Thomlinson and Zhong Zhong of Brookhaven's National Synchrotron Light Source; and Dale Sayers of physics at N.C. State University.
Diffraction-enhanced X-ray imaging was pioneered at Brookhaven and improved at Argonne National Laboratory's Advance Photon Source, Chapman said.
In conventional mammography, differences in tissue densities and composition are shown through absorption as contrasting areas in the image, allowing doctors to see tumors or changes in tissue, he said. The problem is that differences between healthy and cancerous tissues are very small, and X-ray scattering can lead to lower contrast, making it difficult to detect small tumors.
With synchrotron radiation, the DEI method employs a single-energy fan beam of X-rays instead of the broad-energy beam of conventional radiography. The beam is passed through the object or tissue under study. Eventually, that will be a patient.
"This method of line-scan imaging reduces scatter and helps us visualize low-contrast areas that otherwise would be lost," Chapman said. "The key to the new method is an analyzer crystal placed in the beam of X-rays that has passed through the object on its way to the imaging plate detector."
The analyzer can differentiate angle differences much less than one microradian, equivalent to an ant viewed from a mile away. The refraction image shows changes in X-ray refraction, or bending, as it passes through a target and highlights the edges of structures in that target. Objects having little absorption contrast may have strong refraction properties, which the image will highlight.
An example is the fine, thread-like fibers extending from some malignant tumors. Normally difficult or impossible to detect, they are clearly visible in the refraction image.
The second of two images DEI creates -- the apparent absorption image -- appears similar to a normal X-ray of the object but shows improved contrast due to the scatter-free method. In studies of the American College of Radiology test object, or "phantom," used for quality control in mammography, researchers have observed better than 25-fold contrast enhancements.
"During recent experiments at the Advanced Photon Source, we also showed that our method is energy independent for the refraction image," Chapman said. "Imaging breast tissue samples at 30 keV produced the same high-quality images as at 18 keV, which is the energy used in conventional mammography. Imaging at a higher energy means less dose or absorbed radiation for the patient."
While the technology has not been used on patients, preliminary results from studies of human breast tissue also show markedly higher contrast than conventional images, Pisano said.
If the DEI method works as well in the future as current studies suggest it could, it might be used clinically within a decade, she said. Besides mammography, possible applications include non-destructive materials testing, airline baggage screening and defense.
The team is investigating medical and other applications of the technology. Early studies looking at defects in airplane parts also have produced significantly better pictures than conventional X-rays. The research is supported in part by a grant from the U.S. Army Breast Cancer Research Program, the U.S. Department of Energy and individual departments of research team members.
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