French researchers are developing a new medical imaging technique that uses liquid xenon. In the future, imaging devices based on this rare gas could have many advantages for examining patients.
A new medical scanner, invented based on research into the detection of dark matter, is the research project of Subatech, the Laboratory for Subatomic Physics and Associated Technologies. This project, called Xémis, involves the Institut Mines-Télécom Atlantique, the CNRS, and the University of Nantes. “As a member of an international team, we are working to detect signals of dark matter from xenon in its liquid state,” explains Dominique Thers, researcher and head of a research team in this laboratory at ITM Atlantique. This rare gas occurs in the air with a density of 10-7 atoms per molecule of air. We had an idea to use it to develop a new medical imaging technique.
Better image quality
The scanner is shaped like a cylindrical bathtub in the shape of a tube, in which the patient can lie. The 12-centimeter thick walls of the tube are filled with xenon.
The device is directly inspired by positron emission tomography (PET), a technique in which a weakly radioactive tracer is injected into the blood. Fluorine18 is commonly used because it emits two diametrically opposite gamma photons when it decays. This property allows one to draw a line through the patient’s body and locate the area where the emission occurs, close to the area where the atom has settled. Algorithms then process all the points to reconstruct an image. “We use a different tracer: scandium 44, reveals the researcher. It has the special property of emitting a third photon that passes through the emission point, allowing direct triangulation of position and therefore better image quality.”
Another important difference is that liquid xenon works like a camera. It is not necessary to move a ring of sensors along the patient’s body, as is the case with current devices. Images are no longer displayed “in slices” but offer a homogeneous field of view in all directions. Again, with greater precision.
To obtain an image of the same quality as with current scanners, the researchers expect to have to use 100 times fewer radioactive drugs. Normally, several megabecquerels (MBq) are injected per kilogram of the patient. “Here, a few kilobecquerels (KBq) are enough, analyzes Dominique Thers. Patients will thus be exposed to much less radioactivity.” This is an advantage because the individual risk of such exposure is not zero and each imaging test must be carefully weighed against the expected benefit. Thus, this xenon scanner will allow multiple tests on the same patient. More tests will allow greater precision in the diagnosis and therapeutic follow-up practiced in oncology. Scan sessions should also take less time so that each machine can perform more examinations per day. Currently, it takes about 20 minutes for each patient. A few minutes should be sufficient here.
Testing on small mammals
This research project is now entering the testing phase. A first prototype will be installed at Nantes University Hospital and tests will begin on mice and rats.
The 24 cm tube will allow the entire body of these small mammals to be scanned at once. This new medical scanner comes directly from another field, the search for dark matter, and we are really breaking with the other avenues currently being explored,” says Dominique Thers. The goal of these trials will be to convince the medical imaging industry of the importance of this new technology. If all goes we a scanner the size of a human could be available as soon as the year 2025.
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