Soft tissues such as organs and blood vessels are nearly impossible
to examine in X-ray images. To detect a narrowing or other changes in
coronary blood vessels, patients are therefore usually injected with an
iodinated contrast agent.
The most prevalent method for obtaining images of clogged coronary
vessels is coronary angiography. For some patients, however, the
contrast agents used in this process can cause health problems.
‘Monoenergetic X-rays would make it possible to decrease the required concentration of contrast agents by about one third with no loss of contrast.’
at the Technical University of Munich (TUM) has now demonstrated that
the required quantity of these substances can be significantly reduced
if monoenergetic X-rays from a miniature particle accelerator are used.
"The contrast agents can sometimes be hazardous to health. Particularly in patients with kidney insufficiency, complications may
arise, in some cases even kidney failure," explains Dr. Daniela Münzel,
an adjunct teaching professor for radiology at TUM's Klinikum rechts der
Isar. "That is why we are studying possibilities of using lower
concentrations of contrast agents."
One approach to reducing the dosage has now been developed by
scientists from the Department of Diagnostic and Interventional
Radiology at the Klinikum rechts der Isar, working in close cooperation
with the Chair of Biomedical Physics at TUM's Department of Physics.
method, which they have described in a paper published in Nature Scientific Reports
is not based on new contrast agents. Instead it relies on special
X-rays generated using the Munich Compact Light Source (MuCLS), the
world's first mini-synchrotron, which was officially inaugurated at TUM
at the end of 2015.
"Conventional X-ray sources generate a relatively broad range of
energy levels. By contrast, the energy of X-rays produced by the MuCLS
can be controlled much more precisely," says physicist Elena Eggl, the
first author of the paper.
Close to the absorption edge
Contrast agents such as iodine and gadolinium have an absorption
edge. That means that when the substance is exposed to X-rays of a
certain energy, the contrast of the final image of the marked organ is
particularly good. Below the absorption edge - about 30 kiloelectron
volts (keV) for iodine - the contrast deteriorates rapidly. The contrast
also becomes weaker at energies far above the absorption edge.
As a result, when using conventional broad-spectrum X-ray sources,
an adequate quantity of contrast agent must always be used in order to
offset this effect and obtain a sufficiently sharp image for a
diagnosis. The MuCLS can generate X-rays that have exactly the optimal
energy level. The capability of producing such monoenergetic X-rays has
existed for some time. In the past, however, this was possible only with
circular particle accelerators with a diameter of several hundred
meters. In contrast, the MuCLS is comparable in size to a car.
A significant improvement
The data shows that monoenergetic X-rays would make it possible to
decrease the required concentration of iodine by about one third with no
loss of contrast. For gadolinium, there would even be a somewhat
greater reduction. A lot more research is needed, however, before real
patients can be examined with monoenergetic X-rays.
"We're still at the very beginning of the development of this
technology," says Elena Eggl. The MuCLS is the very first machine of its
kind. Moreover, it is designed for fundamental research, and not for
examining patients. But with detailed computer simulations and tests
with a pig's heart, using blood vessels dyed with iodine, the
researchers were able to demonstrate feasibility of the method.
Franz Pfeiffer, professor of biomedical physics at TUM, sees the
team's results as a promising start for medical research with the
compact synchrotron: "The MuCLS offers numerous possibilities for
medical applications that we plan to continue researching with our
partners in medical fields."