May 2010

Crystal Clear — Diffraction-Enhanced Imaging Seeks
X-Rays With Less Radiation

By Kathy Hardy

Radiology Today
Vol. 11 No. 5 P. 16
Understanding the difference between absorption x-ray and diffraction-enhanced imaging (DEI) is as easy as looking at a drop of water. “You can see a drop of water clearly,” says, Zhong Zhong, PhD, a physicist with the National Synchrotron Light Source at Brookhaven National Laboratory in Upton, N.Y. “It’s not absorbing any light. The light is diffracted through the water rather than absorbed. The same is true with clouds, which are made up of drops of water. Light travels through clouds, diffracted and bent in different directions.”

Taking the physics that makes water visible, Zhong and his colleagues thought the same theory could work for clinical x-ray technology.

Reducing Dose
“With DEI, light from the x-ray is diffracted as it travels through the area of the body being imaged,” he says. “It’s not absorbed, and therefore the amount of radiation left behind in the body is less.”

That’s where DEI enters the radiology community as a potential 2D imaging mechanism for finding details such as tears in tendons and cartilage and tumors in breast tissue. While these are normally the realm of MRI, CT, or ultrasound imaging, DEI could become a less costly modality that requires 1%  of the radiation dose of a conventional x-ray. While DEI generates MRI-like images, Zhong says, images produced with DEI have better resolution because of the x-ray.

“With imaging,” he says, “if the thing being imaged is transparent to x-ray, like the water drop, it’s not taking any increased radiation dosage. If the x-ray goes through, there’s no dose. We’re taking advantage of this difference for imaging purposes. There is significantly less radiation deposited in the body, but you can still see the image.”

Reduced doses of radiation are a big reason why work continues on making DEI available for clinical use. Development of a 2D DEI machine is under way, due in part to work done by Zhong and Etta Pisano, MD, vice dean for academic affairs at the University of North Carolina (UNC) School of Medicine.

“I believe that with the quality of diffraction-enhanced imaging, it will eventually be used in place of absorption radiography,” Pisano says. “Not only is the image quality superior, but the imaging can be done with a lower dose of radiation.”

Women and Children First
When considering the potential clinical uses for DEI, Pisano notes that research shows the technology is intended for use across all applications. However, she says rather than choosing a condition best suited for DEI, the question is more about for who DEI is best suited, given its ability to create clear tissue images with less radiation.

“Children are where this should be applied first,” she says. “They are most affected by radiation exposure. It’s not so much about what’s being imaged as it is about who is being imaged.” The application of DEI to breast and other imaging modalities will come down the road, she says.

Research conducted within the past 10 years shows evidence of the role DEI could potentially play in providing safe, effective imaging alternatives. In a study published in 2000 and coauthored by Pisano and Zhong, six out of seven cases of breast cancer specimens examined with DEI and compared with digital radiographs of the same specimens showed enhanced visibility of surface spiculation that correlated with biopsy information, including extension of a tumor into surrounding tissue. At that time, all existing imaging systems depended on the depiction of x-ray absorption to define the differences between normal and abnormal tissues. However, researchers found the refractive properties inherent with DEI improved the x-ray beam properties for enhanced contrast and available digital mammography detectors could increase early detection of breast cancer.

Three years later, Zhong participated in a study of radiography of soft tissue in the foot and ankle, which reported that DEI allows high-contrast imaging of noncalcified soft tissues such as ligaments, tendons, adipose tissue, and cartilage. The study’s intent was not to compare DEI with other imaging modalities but rather to discover the capabilities of radiography for soft tissue imaging.

Keeping It Simple
One drawback in these early studies was how to translate large-scale synchrotron sources, ideal environments for developing imaging technologies, to more conventional x-ray sources found in a laboratory or clinical setting. According to Zhong, at that time it was thought DEI images could be produced only with a large synchrotron facility. However, he points out that DEI is actually a simple process.

“It’s important that you keep the concept simple,” he says. “For new technology to be accepted, it needs to be simple to work.”

On a large scale, DEI uses the intense x-ray beams available at synchrotron sources, which are significantly brighter than those produced by conventional x-ray tubes. These beams provide enough monochromatic x-ray flux for imaging even after the selection of a single wavelength.
As Zhong explains, bone is dense, making it easier to see with traditional x-ray. Something that thick absorbs light well and you get a clear image on the other side. Soft tissue and tumors, however, are not as thick and don’t absorb light as well. Therefore, they are more difficult to image. The result is various shades of gray because different tissues absorb different amounts of radiation.

“To capture small differences between a tumor and surrounding regular tissue with x-ray would require higher dosages of radiation,” he says. “This can be an issue with breast imaging. Breast tissue absorbs so much radiation that it’s better to use a lower dosage for breast imaging.”

With DEI, what’s important is how the x-rays that pass through the tissue bend and scatter. These properties vary more subtly among different types of tissue. DEI provides information on the refraction of light through tissues using three sources of imaging contrast: refraction, scatter, and absorption. To analyze matter with DEI, a silicon crystal is placed between the sample and the image detector. As x-rays pass through the sample, they refract and scatter different amounts of light depending on the composition of the sample tissue. When those bent rays pass through the sample and strike the crystal, they are diffracted by different amounts. The silicon crystal helps convert the subtle differences in scattering angles produced by the different tissues into intensity differences that can be readily detected by a conventional x-ray detector. The result is extremely detailed images that are sensitive to soft tissue types such as tumors and cartilage. According to Zhong, it’s the analyzer that makes DEI unique.

“Conditions for diffraction must be met,” he says. “There is a relationship between wavelength of the x-ray and the target material. Filtering is required to produce monochromatic x-rays needed for diffraction. If wavelengths deviate, the crystal won’t diffract.”

When considering DEI for clinical imaging purposes, Zhong and his associates began by combining the x-ray tube and the analyzer to see how they could image tissue without increasing levels of radiation.

“We did this to convince ourselves and others that this is not just a dream,” he says. “We could really do this.”

Need for Speed
The next step was to set up a prototype of the system they would need to create images. One thing they learned was that by increasing the power of the x-ray tube, they could create images faster. The prototype was built using an off-the-shelf x-ray tube and detector, Pisano says. While this was sufficient for demonstrating soft tissue imaging quality, there’s a long way to go before it’s ready for the clinic.
“What we have now is only a 1-kW machine, so it takes two hours to make an image,” she says. “Optimally, it should take 1 second to capture the image.”
The UNC family has jumped into the business side of DEI development as a student team from the university’s Kenan-Flagler Business School received worldwide recognition for its business plan for a company called NextRay, of which Pisano and Zhong are cofounders. The university granted NextRay an exclusive license to develop and commercialize DEI technology, and patent applications have been filed. The company’s plan calls for acquiring funding and a manufacturing partner within the next two years, followed by clinical trials and full-scale production and distribution within four years.

NextRay is not alone in its efforts to commercialize DEI for clinical use. According to Zhong, there are now about a dozen separate projects worldwide that focus on the technology, and he welcomes the increased attention.

“This has good potential,” he says. “As more people get involved, there will be more acceptance of the technology.”

— Kathy Hardy is a freelance writer based in Phoenixville, Pa. She is a frequent contributor to Radiology Today.