CT scan example (European Synchrotron Radiation Facility)
Researchers from France, Germany, and Switzerland have devised an X-ray imaging technique that can improve the contrast of computed tomography (CT) scans while reducing the radiation dose of those scans. The results of the team led by Irene Zanette of the European Synchrotron Radiation Facility in Grenoble, France will be published this week in the journal Proceedings of the National Academy of Sciences.
Zanette’s team, which includes participants from the Paul Scherrer Institute in Villigen, Switzerland, Karlsruhe Institute of Technology in Karlsruhe, Germany, and Synchrotron Soleil in Gif-sur-Yvette, France, aimed to improve on conventional methods for CT scans that project an X-ray beam on the investigated object and measure the transmitted intensity behind it. This technique, however, depends on variations in the absorption of X-rays by the different components in the target object. Thus, this method has limitations for medical imaging where cancerous and healthy soft tissue often do not show enough contrast to be clearly distinguished in the resulting X-rays.
A newer imaging technique called X-ray grating interferometry takes a different approach that increases the contrast through the interaction between X-rays and matter, rather than absorption of radiation. X-ray grating interferometry uses microstructures, called gratings, that serve as the optical elements for X-rays. This technique was first developed at Paul Scherrer Institute and Karlsruhe Institute of Technology, and has been perfected over the past decade.
X-ray grating interferometry can be combined with CT scanning to give virtual slice images and full 3D information of an object. In addition to measuring absorption of radiation, the technique measures X-ray phase changes to produce “differential phase contrast” images. The researchers report that density differences of only 0.5 milligrams per cubic centimeter can be discerned using grating-based phase contrast.
The research team devised an enhancement of this process to make it more applicable for clinical implementation. The “sliding window,” as they call their technique, reduces the radiation dose and acquisition time. It also makes grating interferometry compatible with the continuous rotation of the gantry used in clinical CT scans.
The researchers tested the technique on mammalian soft tissues, in this case with various body parts of rats. The 3-D images from the tests showed minute visible details, such as the individual seminiferous tubules, tiny tubes in which sperm cells are formed. “These structures are simply invisible in standard CT, even in high-resolution setups,” says Zanette, “not only because of their tiny size, but even more so because they hardly give any contrast.”
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