Using phase contrast tomography, researchers at the University of California, Los Angeles, and their colleagues have produced high-resolution 3D images of breast tissue with radiation exposure that is less than that from today's 2-dimensional screening mammograms.
Computerized tomography (CT) can produce high-resolution, 3-dimensional (3D) images of the breast or other parts of the body. However, using CT scanning for screening would be a Pyrrhic victory: The high radiation exposure needed to get those images would pose a significant cancer risk.
A research team led by scientists at the California NanoSystems Institute (CNI) at the University of California, Los Angeles, has reported results that might take the “Pyrrhic” out of the victory. By combining phase contrast tomography with an algorithm developed by Jianwei Miao, PhD, they have produced high-resolution 3D images of breast tissue with radiation exposure that is less than that from today's 2-dimensional screening mammograms (PNAS 2012;109:18290–4).
Standard CT scans depend on differences in radiation absorption to distinguish one type of tissue from another. Phase contrast tomography (PCT) distinguishes tissue types by how the electromagnetic waves of X-rays oscillate through them. The X-rays used in PCT have higher energy than those used clinically, but because less radiation is absorbed, the patient's radiation dose is actually smaller.
Getting a high-resolution PCT image requires many X-rays from different angles, commonly referred to as views or projections. With CNI's approach, far fewer views are needed because Miao's “extra sloped tomography” (EST) algorithm accurately fills in the data that more views would ordinarily provide. As a result, Miao and his colleagues reported that the radiation dose is reduced by 74%. When 5 radiologists, blinded to the techniques, rated the resolution of images from a mastectomy specimen, they saw no difference between those created with more views and those that used the EST algorithm and fewer views.
However, this approach has hurdles to clear before it becomes a clinical reality. The experiment was conducted at the mammoth European Synchrotron Radiation Facility in Grenoble, France, which is about a half mile in circumference. Various groups are building more compact, room-sized synchrotrons capable of producing the same type of high-energy X-rays, but the machines aren't available yet to hospitals and imaging centers. Given those engineering challenges and the need for patient trials of PCT mammography, Miao estimates that the approach may not be adopted by clinics for a decade or more.
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