Building a Better CT Scanner

An adept creator of detailed 3D anatomical images (bones, soft tissues, organs), computed tomography (CT) scanning is better than standard X-rays for investigating complex injuries, cancers, and vascular issues. Yet there is still room for vast improvement with the technology.

The next generation of CT scanners is starting to use a new process called photon-counting computed tomography (PCCT), at the heart of which are special detectors that count individual X-ray photons and measure their energy. The sharper, higher-resolution images the new machines produce means better visualization of fine structures (e.g., bronchi) and tissue composition for more accurate—and possibly earlier—diagnosis in fields such as cardiology, neurology, and cancer screening. 

Researchers from the University of Victoria and a leading BC-based provider of X-ray imaging technology are using the Canadian Light Source at the University of Saskatchewan to find ways to improve the ultrathin metal layer (contact) on top of the detector, which play a critical role in its performance. 

“Any time you give medical professionals more detailed, accurate information about your body, it’s useful for diagnosis and better outcomes,” stated Dr. Tom Tiedje, professor emeritus in electrical engineering at the University of Victoria and the University of British Columbia.

Using the SGM beamline at the CLS, the researchers discovered that the contact material currently used (an oxide)—which is only a few atoms thick—“is kind of a complicated beast.”: It controls the extraction of electrons from the detector. Tiedje and his colleagues are now assessing the performance of an alternative material (a sulfide).

“I feel like we’re making progress,” he said. “I think there’s good potential for improving the device performance.”

Better contacts on X-ray detectors could help CT scanners improve the way they differentiate between body tissues of different densities. “X-rays have different wavelengths,” explained Tiedje, “and body tissues respond differently to X-rays.” Current scanners can distinguish, for example, bone from muscle but not muscle from blood vessels. Current scanners measure how bright the X-ray photons are as they pass through tissue. 

But next-generation detectors will count the photons “one by one, billions and billions of them,” and allow colors to be assigned to different wavelengths that can then distinguish different tissues of similar densities. The result is a more detailed picture. 

There’s still more work to be done, Tiedje noted. “But if you can detect a small thing like a growth that looks the same as surrounding tissue, you won’t have to wait until it gets big to see it on a CT scan, so that’s definitely an advantage.”

The research was funded in part by a Mitacs grant, which helps Canadian companies with limited research capacity to access the expertise of university scientists. Redlen Technologies makes photon-counting X-ray detectors for CT scanners.

The Canadian Light Source (CLS) is a national research facility at the University of Saskatchewan and one of the largest science projects in Canada’s history. More than 1,000 academic, government and industry scientists worldwide use the CLS annually in innovative health, agriculture, environment, and advanced materials research. The Canada Foundation for Innovation, Natural Sciences and Engineering Research Council, Canadian Institutes of Health Research, the Government of Saskatchewan, and the University of Saskatchewan fund CLS operations.