What happened on November 8, 1895, late one Friday evening in the Physics Institute of the University of Würzburg can doubtless be described as one of the most revolutionary developments in the history of medicine. Wilhelm Conrad Röntgen discovered a “new type of radiation” that seemed able to penetrate matter with ease, and he quickly recognized how useful this type of radioscopy  would be for medicine. Two days before Christmas, he succeeded in making the first “X-ray photograph”: it was an image of his wife’s hand, in which not only the wedding ring but also the bones were clearly visible. The fact that Röntgen was awarded the first Nobel Prize in Physics in 1901 was only a logical consequence of his extraordinary achievement.

And it wasn’t long before the first commercial products appeared. On March 24, 1896, just three months after Röntgen’s discovery, the company Siemens&Halske obtained a patent for a new X-ray tube that was “especially suited to transillumination of the entire body of adult persons.” And to this day, Siemens has remained faithful to diagnostic radiology. The company offers a whole range of solutions, from mobile devices to fully digital systems to CT scanners for 3D images.

Over 90 percent of all medical imaging examinations worldwide now rely on X-rays. But the technology is still based on the fundamental principle that was used 120 years ago: electrons that are generated in a cathode and accelerated to high energies collide with a fixed anode — usually made of the heavy metal tungsten — and thereby release X-rays. The X-rays, in turn, are absorbed to a greater degree by bone than by soft tissue. The bones therefore appear dark in an X-ray image, and the soft tissues appear light.

Despite the success of this technique in medical engineering, it does have a few drawbacks. For example, the electrons that collide with the anode produce mainly heat. No more than one percent of the energy is converted to X-rays — a huge waste of energy. There are also many applications, such as tumor diagnostics, in which physicians want to be able to distinguish among various soft tissues more easily. But if  contrast is increased, the patient is exposed to a higher dose of X-ray radiation — which should be avoided, because high radiation doses can damage body tissue. In X-ray examinations involving cardiovascular diseases, on the other hand, contrast agents are often needed in order for the angiography systems to be able to make blood vessels visible in X-ray light — but nearly one out of ten patients suffers allergic reactions to these substances, which can lead to shock and kidney failure. A technique that uses smaller quantities of contrast agent, or even none at all, would therefore be beneficial to millions of people.

“The technology that we’re currently developing at Siemens could help us overcome all these challenges,” says Prof. Oliver Heid, head of the Global Technology Field of Healthcare Technology and Concepts at Siemens Corporate Technology. Heid is a medical doctor and holder of approximately 300 patents in a large variety of fields, from high-frequency technology to superconductivity, materials science, accelerators and software solutions. “We’re in the process of completely rethinking everything and changing everything: the method by which X-rays are generated as well as the technique used for detecting them. If everything goes well with our next-generation X-ray system, it will be another revolution in medical diagnostics,” says Dr. Heinrich Kolem, CEO for Angiography and Interventional X-Ray Systems at Siemens Healthcare.

This multi-year R&D project, which is scheduled to run until 2017, brings together just the right innovators: alongside Heid and Kolem, they also include the team of Components and Vacuum Technology at Siemens Healthcare lead by its CEO Dr. Peter Molnar, researchers from Siemens Corporate Technology in Russia, external partners from institutions such as Oxford University, as well as Prof. Alessandro Olivo of University College London, whose contribution to the development team includes both scientific expertise and insights from clinical practice. Molnar, whose business unit produces approximately 22,000 X-ray tubes per year for CT machines, angiography systems, and X-ray equipment from Siemens, underscores the value of this cooperation. “Our shared objective is to commercialize the new system in a competitive form and successfully launch it on the market. Only then does a good idea become a true innovation,” he says.

What is being changed exactly? It starts with the cathode. Here, the team is no longer using 2,000-degree Celsius filaments to emit electrons. Instead, they are using a ring-shaped “cold cathode” of nanostructured carbon that operates at a high voltage and at room temperature. The advantage of this approach is that it uses less energy than the previous cathodes.

The electrons no longer collide with a fixed target of tungsten, but with a new device invented by Siemens researchers that they’ve named LiMA, which stands for “liquid metal jet alloy” target. In other words, the electron target is a jet of liquid metal as thin as a human hair. The metal consists of 95 percent lithium and 5 percent heavy elements such as bismuth or lanthanum. The latter produces short wavelength X-rays, the former acts as a coolant. The energy of electrons leaving the liquid-metal-jet anode can potentially be reclaimed and fed back into the energy cycle. The result is that the X-ray tube requires less than half the electricity and cooling of previous devices, which greatly reduces total energy demand.

Significantly more important, however, is the fact that the tube can achieve a much higher energy density at the target. At the same light intensity, the focus of the new X-ray source is 400 times smaller than in conventional X-ray tubes – “at the focal point, this X-ray radiation is four billion times brighter than the sun on the surface of the earth,” says Heid, “which results in a 20-fold higher imaging resolution.”

That, in turn, is the prerequisite for an entirely new imaging technique, one that scientists around the world have been working on for years: phase-contrast X-ray imaging. Whereas conventional radiography simply records whether X-rays penetrate a certain tissue or not, phase-contrast imaging measures the effect that passing through bodily tissue has on the wave phase – i.e. the sequence of wave crest and trough. This same physical phenomenon can be seen in the light effects on the bottom of a water-filled swimming pool on a sunny day. This phase shift is highly revealing, since it varies depending on the refractive power of the tissue through which the radiation passes. The approach described here would make it possible to distinguish different soft tissues, in particular fat from water or iron levels in blood, which is essential for being able to easily differentiate a tumor in an early stage of growth from healthy tissue.

“To be able to measure these phase shifts, we’re also working on a completely new component on the detector side,” says Dr. Andreas Geisler, project manager for the new X-ray system on Heid’s team. To this end, a wavefront sensor of the kind used in optics or astronomy, for example, is to be used for the first time for X-ray light. The sensor consists of millions of concave metallic or silicon lenses that generate a matrix of focal points on the detector. Through the displacement of these focal points, the refraction in the object can be calculated. This is not possible today with conventional detectors alone.

“So not only will these next-generation X-ray systems be very efficient to operate, they will also do a good job of registering contrasts among soft tissues at a relatively low radiation dose,” says Geisler. Blood vessels could be made visible in this way without contrast agents; tumors could be more clearly recognized thanks to the 20-fold higher resolution and phase-contrast X-ray imaging; and the new technology would be ideal for minimally invasive surgery too. “We want to guide and navigate catheters using magnetic fields, for example, and know at any time via the X-ray imaging where exactly they are located in the body,” says Heinrich Kolem. That isn’t possible with conventional X-ray tubes, because they are sensitive to magnetic fields – “the next-generation X-ray systems won’t have this drawback, and at the same time, they’ll be able to provide images that are more useful diagnostically.”