New era of CT promises lower radiation dose

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A conventional cardiac CT scan images a larger portion of a patient's body and then extracts the data pertinent to the cardiac question. A new approach being researched portends to image only the heart, thus reducing radiation exposure to the patient.

With current CT scanners, the x-rays probe the patient along multiple wide beams focused on the patient including a region of interest, such as the heart, from various orientations. That is, the source of the x-rays rotate around the individual as he or she lies inside a large aperture, then a computer program reconstructs images from the exposures. This CT process increases radiation exposure but generates a lot of different views to be analyzed by physicians for diagnosis.

In many cases, like cardiac CT, the area of interest is a relatively small region within the larger body. "It was realized long before that one could reduce the radiation dose by sending x-rays just through the region of interest from different directions, and then reconstruct that region from resultant local data," said lead researcher Ge Wang, PhD, director of the biomedical imaging division of the Virginia Tech-Wake Forest University School of Biomedical Engineering & Sciences, located in Blacksburg, Va., and Winston-Salem, N.C., respectively.

Wang and colleagues have reportedly solved the "interior problem," which has held back finding a solution for decades. His group at Virginia Tech, in collaboration with others, developed the patented "Interior Tomography and Instant Tomography by Reconstruction from Truncated Limited-angle Projection Data."

"We assume a known sub-region within the region of interest–such as an air gap, a blood area, or an implant in the heart. With a known sub-region, we can solve the interior problem in a theoretically exact and mathematically stable fashion–we can produce an accurate image," said Wang.

Researchers have compared conventional CT image reconstructions, made from wide beams of x-rays, to datasets made from truncated x-rays, and the data look promising. "While medical CT can presently only perform global image reconstruction, we look forward to having precise local reconstruction from a highly truncated dataset," Wang said.

By applying interior tomography to medical CT, radiation exposure can be reduced, and a large patient can be accommodated because the focus will be on the region of interest and not the entire body.

Wang's group has envisions a multisource interior tomography concept. For example, the individual is surrounded by a half dozen or more x-ray tubes and detectors. X-rays are focused in narrow beams on the region of interest and the detectors are also small, not requiring much room. More than 10 views per second are possible, and interior tomography software can potentially provide accurate images of the beating heart.

Funding for the project has been provided by GE Global Research in Niskayuna, N.Y., and the National Institutes of Health.