New medical imaging technique first to use low-dose X-rays to reveal soft tissue
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To look below the surface of the human body in search of deep-seated injury or disease, today's radiologists use an alphabet-soup of imaging techniques: computerized tomography, or CT; magnetic resonance imaging, or MRI; positron emission tomography, or PET; single photon emission computed tomography, or SPECT; whole body scanners; and ultrasound.
Despite the advancements in non-invasive medical imaging since 1895 -- the year in which Wilhelm Röntgen discovered a new, higher energy, shorter wavelength form of light able to penetrate solid objects which he called the x-ray -- 80 percent of radiology still involves the plain, old x-ray.
But x-ray imaging technology has not changed very much over the past 100-plus years, since the day that Röntgen made the world's first x-ray of his wife's hand, complete with wedding ring. For the most part, x-rays still produce an image that shows bone very clearly, but, if a contrast agent is not used, distinguishes poorly among non-calcified soft tissue, such as ligaments, cartilage, or blood vessels.
Now, thanks to researchers working at Brookhaven Lab, x-rays from the National Synchrotron Light Source (NSLS) are being employed for the first time in a new, low-dose experimental technique to visualize not only bone, but also soft tissue in a way that not is possible using conventional x-rays. Called diffraction enhanced imaging (DEI), the technique provides all the information provided by conventional x-rays, plus additional data on soft tissues that were previously accessible only using alternative methods such as MRI or ultrasound. Even compared to those images, DEI delivers a much sharper and more detailed view of soft tissue.
Once DEI is scaled down for clinical use, this new imaging technique may eventually greatly enhance mammography and be used in the search for breast cancer, as well as be employed for the detection of other soft-tissue pathologies such as osteoarthritis and lung cancer.
"We've previously shown that this technique can visualize tumors in breast tissue and cartilage in human knee and ankle joints, but this is the first time that we have shown it to be effective in visualizing a variety of soft tissue, such as skin, ligaments, tendons, adipose pads, and even collagen and large blood vessels," explains NSLS physicist Zhong Zhong (pictured, above), who heads this research project.
"The ability to use just one technique to visualize such a range of soft tissue as well as bone has many potential diagnostic applications." Performed with Rush Medical College, the research is funded by the National Institutes of Health, GlaxoSmithKline, Inc., and the U.S. Department of Energy.
Shades of Grey
DEI makes use of the special beams of x-rays available at synchrotron sources such as the NSLS. In contrast to x-rays from conventional sources, synchrotron x-ray beams are thousands of times more intense, as well as being highly collimated, or extremely concentrated into a narrow beam. In addition, synchrotron light can be tuned to be "monochromatic," or essentially of one wavelength or color.
To make a conventional radiograph, x-rays are beamed at, say, a hand that is placed between the x-ray source and a piece of x-ray film or a digital recorder. The density of the structures being pictured and, hence, their x-ray absorption determine what the radiograph looks like.
When the negative is developed, bone and other calcified structures appear clear, or white, and metallic objects, such as Anna-Bertha Röntgen's ring, are seen as bright white. Soft tissue, because it absorbs fewer x-rays than does bone but has small differences in density, is seen as shades of grey.
Instead of making use of absorption, DEI, as its name says, relies upon diffraction, which is the variation in the intensities of light after it scatters off structures of different densities and organization. Because DEI relies upon diffraction instead of absorption to produce contrast among various structures, the x-ray dose is lower, while the image quality is higher. "Because absorption is necessary to produce contrast in the image, the radiation dose received from traditional x-rays comes from the x-rays that are absorbed by the body," explains Zhong. "But in DEI, we do not need to use absorption as a contrast mechanism because we are only following the x-rays that pass through the tissue. Therefore, we can use higher-energy x-rays, which pass through with little absorption so the dose is lower."
To make a diffraction enhanced image, x-rays from the synchrotron are first tuned to one wavelength before being beamed at an anatomical structure, such as a hand or foot. As the monochromatic beam passes through, the tissue within the appendage scatters the x-rays at different angles and causes the x-rays to refract, or change directions. The subtle scattering and refraction are detected by what is called an analyzer crystal, which diffracts, or changes the intensity, of the x-rays by different amounts according to their scattering angles.
The diffracted beam is passed on to a radiographic plate or digital recorder, which documents the differences in intensity to show the interior details.
2-D and 3-D Technology
Because the technique itself produces good contrast, another advantage of DEI is that it does not require the use of contrast agents, which are chemicals injected into the body before imaging to distinguish among different tissue types. "For screening, contrast agents are often undesirable since they complicate the procedure and may have side effects," Zhong explains. Being free of the need for contrast agents, this makes DEI viable as a potential screening tool for breast cancer.
Since medical centers do not have synchrotrons, Zhong and his team are working on transferring two-dimensional DEI technology out of the Laboratory. To make three-dimensional images, they are developing a DEI computed-tomography method useful for making scans of more complex anatomy. But, even in its present form, "DEI provides far greater structural information than conventional radiography," concludes Zhong." And this new technology can only stimulate the further development of x-ray imaging."
Meet Zhong Zhong
During the ten years that physicist Zhong Zhong has been performing research at the National Synchrotron Light Source (NSLS), starting as a graduate student in 1993 and, since 1998, as an NSLS staff physicist, he has worked on projects that have produced two patents in the field of medical imaging.
In 1999, he and two NSLS colleagues received a patent for the new soft-tissue x-ray imaging technique called diffraction enhanced imaging (DEI), which, using x-rays, allows soft tissue to be viewed with more detail and clarity than conventional imaging methods. This year, the application of DEI to cartilage imaging was patented. Now, two additional patents are pending that will bring the new technique to medical centers. In the future, Zhong wants to continue other research that he has begun using crystals to improve the focusing of high-energy x-rays, studies that may lead to better synchrotron light sources.
Zhong earned his B.S. in physics from Beijing University, China, in 1990; received an M.S. in applied physics from Michigan Technological University in 1992; and, in 1996, took his Ph.D. in physics from Stony Brook University (SBU). Today, he serves an assistant adjunct professor in the Department of Radiology and an assistant professor in the Biomedical Engineering Department, both at SBU.
In addition to spending his free time with his wife and two daughters, he enjoys fixing up his house, working on his two old cars, and doing vegetable gardening.
More Information
Funding: National Institutes of Health, GlaxoSmithKline, Inc., and the U.S. Department of Energy
Paper: "Radiography of soft tissue of the foot and ankle with diffraction enhanced imaging," Journal of Anatomy, May 2003, volume 202, issue 5, pp. 463-70
Contact: Zhong Zhong, zhong@bnl.gov or (631) 344-2117
Web: www.bnl.gov/bnlweb/pubaf/pr/2003/bnlpr051303.htm