New gold standard for industrial CT

At the electron synchrotron facility in Grenoble, a globally unparalleled measuring station is being created for the non-destructive testing of large components. The computed tomography system offers a resolution of 25 micrometers, which puts it well ahead of the previous standard resolution of 100 micrometers. Through its Development Center X-ray Technology division (EZRT), Fraunhofer IIS is playing a leading role in the development of the measuring station.

Industrial requirements for component testing are constantly increasing. And this demand is coming from a wide variety of sectors: from automotive manufacturing to the aviation industry to manufacturers of wind turbines. These businesses want to use computed tomography (CT) for things like checking the welds on a car door or evaluating the structure of a fiber-reinforced plastic. The CT systems used in laboratories are coming up against their physical limits in trying to meet the demand for ever better resolution. These limits can only be overcome by X-ray systems that are operated at an electron synchrotron installation, such as the European Synchrotron Radiation Facility (ESRF) in Grenoble.

The ESRF possesses an electron storage ring with a circumference of 844 meters. In this storage ring, electrons are constantly circulating at close to the speed of light. The enormous energy of these electrons is used to generate X-rays. There are several installations at the storage ring that act as X-ray sources. From there, the radiation is guided tangentially away from the ring in straight tubes known as beamlines and used for a wide variety of scientific experiments.

“In the course of renovating the electron storage ring, the ESRF built new beamlines. One of them is the BM18 beamline, which we are expanding into a unique system for industrial CT,” explains Prof. Simon Zabler, head of the EZRT locations in Deggendorf and Passau and manager of the BM18 project. Zabler is a recognized expert in synchrotron imaging. He wrote his undergraduate degree and master’s theses in Grenoble over twenty years ago. “Together with the Universities of Passau and Würzburg, Fraunhofer is responsible for developing the detector technology, the IT hardware and the data processing,” the physicist reports. The project is being funded by the German Federal Ministry of Education and Research to the tune of 6.3 million euros.

© European Synchrotron Radiation Facility
X-ray image of a camera, two views.

Extremely sharp images with unique phase contrast

In the BM18 beamline, the X-ray beam generated in the electron storage ring is guided 200 meters through a vacuum tube before it arrives at the large experimental hall. Here it encounters the object, which rotates on a podium and is scanned successively. After passing through the object, the X-ray strikes the detector, which is up to 40 meters away. “Through the large distance of the object to the X-ray source and to the detector, we obtain extremely sharp images with a unique phase contrast,” Zabler says.

In order to capture these images, the researchers have developed an X-ray detector that sets new standards. Whereas the highest-resolution X-ray camera before now supplied around 8,000 pixels per line, the new detector achieves over 16,000 pixels per line. This makes it possible to scan a 40-centimeter-wide object with a resolution of 25 micrometers per pixel. The X-ray camera is based on XEye technology, which was developed at the Development Center X-ray Technology EZRT.

European Synchrotron Radiation Facility (ESRF)

Founded in 1994 in Grenoble at the edge of the French Alps, the ESRF is funded by 17 countries. The electron storage ring operated by the ESRF is the third largest of its kind in the world. It generates X-rays that are ten trillion times brighter than the X-rays used in medicine. Researchers from around the world use the beams for experiments around the clock.

Two gigabytes of data per second

The data volumes supplied by the X-ray cameras are huge. “In full operation, we generate two gigabytes of tomography data per second,” Zabler explains. To manage this deluge of data, the EZRT is working closely together with the chairs of Prof. Tomas Sauer in Passau and of Prof. Randolf Hanke in Würzburg. The main task here is to reconstruct the volumetric image of the object from the data of the individual scans.

Röntgenaufnahme einer Obstschale — © European Synchrotron Radiation Facility
X-ray image of a bowl of fruit.

“If we were to just save the raw data on the ESRF servers, the entire storage capacity of this major research institution would be full after only a month,” Zabler points out. Therefore, the project team is working on the loss-free compression of the image data. The basis for this is the JPEG 2000 standard, which Fraunhofer IIS was involved in developing. Compression makes it possible to open a data set that originally comprised 100 terabytes on a laptop.

Although the project was affected by the pandemic after its launch in the spring of 2020, the team managed to carry out the first sample measurements at the end of 2021. The team will use the year 2022 to optimize the system and scan sample objects that will illustrate the system’s potential as showcase pieces. In December 2022, measurements are to begin for industrial customers.

Measuring components up to 70 centimeters wide

“The customers we look after with the laboratory CT are showing great interest in the BM18 beamline,” says a delighted Zabler. “We can expand the field of view to 70 centimeters by doing a half-field scan, whereby we scan first one half and then the other half of the object.” For customers that want to X-ray a whole range of components, BM18 offers a huge advantage. “Analyses for which we need a week with the laboratory CT, we can complete in a few hours in Grenoble – and in much better quality, too,” Zabler promises. “Naturally, the EZRT handles the entire measuring process from start of finish.”

One-eighth of the beamtime of the BM18 beamline will be reserved for industrial customers. The remaining time will be available for scientific investigations. Already, many more researchers have applied for a slice of beamtime than can be accommodated. An independent jury will select the fortunate scientists. One project is already approved: the Human Organ Project. In this project, diseased and injured human organs will be scanned with tremendous precision and made available to the general public as an anatomical 3D atlas.