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ENGINEERS from the University of South Carolina (USC) have developed a laboratory-scale device sensitively detects what are called"soft X-rays" – those on the lowest end of the X-ray energy scale. As the USC engineers reported in Applied Physics Letters, the soft X-ray detectorpotential applications in medical imaging.
According to Krishna Mandal, the associate professor of electrical engineering who led the team that built it, the detector offers tremendous potential in breast cancer detection and treatment. Soft X-ray devices are potentially less harmful to patients than those based on hard X-rays, he said.
"If you take mammography as an example, hard X-rays pose difficulties,"Professor Mandal said. "First,they have very high energy,and so we have to minimize exposure to them."
"And more importantly, the soft X-rays interact withcalcifications in the tissue," he added. "Hard X-rays do not –they just pass through calcium deposits."
In the breast, calcification can be an indicator of pathology. Not as opaque as bone to X-rays, calcium deposits represent a very promising target for detailed soft X-ray mapping.
Professor Mandal envisions the new soft X-ray detectors being at the forefront of a new way of imaging breast tissue, so that physicians can follow progression of calcification over time. "It's common for women even under 40 years of age to have calcifications. It's critical to know whether it exists in the tissue and especially whether it is spreading," he said. "But to see that,we need very high resolution detection systems, which is what we've made.These detectors are instantaneous, real-time and will be able to operate at room temperature with high resolution."
The USC engineers constructed the detector through epitaxial growth of silicon carbide on wafers of 4H-SiC. They were tested for response to soft X-rays at both the Los Alamos National Laboratory in New Mexico, and Brookhaven National Laboratory in New York.
The resulting detectors exhibited high sensitivity for soft X-rays (50 to 10,000 electron volts). There are no commercially available soft X-ray detectors covering this range, and comparison with an off-the-shelf ultraviolet detector showed a much more robust response for soft X-rays with the new device.
"There's nothing available on the market that covers this range of X-rays,"Professor Mandal said. "Nobody has explored this region, and there will be many innovations that will result from our being able to do so, particularly when it comes to medical imaging." (University of South Carolina)