Prototype of a clinical CT device combines dark-field X-ray and conventional technology

New technology for clinical CT scans

With dark-field imaging now additional information on fine tissue structures, in particular in the lung, is accessible. Until now, technical challenges have prevented the integration of this new technology into clinical CT scanners to examine patients.

A team of researchers working with Franz Pfeiffer, Professor for Biomedical Physics and Director of the Munich Institute of Biomedical Engineering at TUM, has now developed a CT scanner that combines both X-ray technologies.

“For the first time, we showed that dark-field X-ray technology can also be integrated into a clinical CT scanner. Although this technology is in its early stages, pre-clinical studies with mice have demonstrated clear benefits from dark-field CT scans, especially for capturing images of lung tissue,” says Franz Pfeiffer, who headed the study.

The new CT prototype has already been used successfully with a thorax phantom, a model of a human upper body, and is large enough for the intended applications with real patients.

With conventional X-ray equipment, the 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. That is why bones and similar structures, which have a stronger attenuating effect, appear white in X-rays, while more transparent tissue types such as the lung produce darker images.

The implementation of the dark-field method in a human-size CT scanner poses various technical challenges. Until now, this has limited dark-field CT devices to a scale much smaller than would be needed for human patients. Apart from the size, the fast rotation of the scan unit also creates special difficulties for the technical design. 

The scanning unit of CT scanners, known as the gantry, rotates at very high speeds. This causes vibrations that affect the finely-tuned components in the interior of the device. Based on a detailed analysis of these vibrations, the team was able to use them to implement the required shift between the gratings needed for dark-field imaging. To analyze the scans, they developed new algorithms to filter out the vibration effects based on reference scans.