February 9, 2022 — For the first time, a team of researchers from the Technical University of Munich (TUM) has integrated the darkfield X-ray method into a CT scanner suitable for clinical use. Darkfield imaging provides additional information to conventional X-ray imaging. With the new prototype, it is now possible to produce three-dimensional darkfield X-ray images.
Computed tomography (CT) is one of the most important clinical methods for accurate and rapid diagnosis. By combining several X-ray images, three-dimensional images of the patient are generated. Thanks to darkfield imaging, additional information about fine tissue structures, especially in the lungs, is now accessible. Until now, technical challenges have prevented the integration of this new technology into clinical CT scanners for examining patients.
A team of researchers working with Franz Pfeiffer, professor of biomedical physics and director of the Munich Institute of Biomedical Engineering at TUM, has now developed a CT scanner that combines the two X-ray technologies.
“For the first time, we have shown that darkfield X-ray technology can also be integrated into a clinical CT scanner. Although this technology is in its infancy, preclinical studies in mice have demonstrated the clear benefits of dark-field CT scans, especially for capturing images of lung tissue,” says Franz Pfeiffer, who led the study. The new CT prototype has already been used successfully with a thorax phantom, a human upper body model, and is large enough for intended applications with real patients.
Conventional X-ray imaging
With conventional X-ray equipment, X-rays are attenuated by the intervening tissue as they travel from the source to the detector. This effect is used to produce images based on the varying degrees of attenuation associated with different tissue types and structures. This is why bones and similar structures, which have a stronger attenuation effect, appear white on X-rays, while more transparent types of tissue such as the lungs produce darker images.
Darkfield X-ray Imaging
Darkfield imaging, on the other hand, uses small-angle scattering of X-rays. When X-rays interact with materials of different densities like the interface between lung tissue and air, they are scattered. Analysis of this scattering effect gives additional information about very fine tissue structures, which are not otherwise accessible with conventional X-ray images.
Network Technology for Darkfield Imaging
To detect X-ray scattering, a set of three optical gratings is needed. They are placed between the X-ray source and the detector. When X-rays pass through these gratings, a characteristic pattern is produced at the detector. When a sample or person is subsequently positioned in the beam path, this characteristic pattern is changed. These deviations are then used to analyze the structure of the sample or the person’s tissues.
New hardware and software for darkfield computed tomography
Implementing the darkfield method in a human-sized CT scanner poses various technical challenges. Until now, this has limited dark-field computed tomography devices to a much smaller scale than would be needed for human patients. Besides the size, the fast rotation of the scanning unit also creates special challenges for the engineering design.
The CT scan unit, known as the gantry, rotates at very high speeds. This causes vibrations that affect the finely tuned components inside the device. Based on a detailed analysis of these vibrations, the team was able to use them to implement the required lag between gratings needed for darkfield imaging. To analyze the scans, they developed new algorithms to filter out vibration effects based on reference scans.
Additional information for clinical diagnosis
“With the darkfield CT prototype, we can capture both conventional and darkfield x-ray images in a single scan. This gives additional information that could be used in the future not only to diagnose lung diseases, but also to differentiate between different types of kidney stones and tissue deposits,” said Manuel Viermetz, one of the first two authors of the study. In the next step, the researchers plan to further optimize the dark-field computed tomography prototype and prepare for the first scans of human patients.
For more information: https://www.tum.de/en/