Multiplexing CT scanner heads for center stage at AAPM meeting

July 20, 2007

The seeds for what could be a new and much faster way of CT scanning will be planted next week, when researchers from the University of North Carolina at Chapel Hill unveil an approach involving nanotube x-ray sources and multiplexed data transmission.

The seeds for what could be a new and much faster way of CT scanning will be planted next week, when researchers from the University of North Carolina at Chapel Hill unveil an approach involving nanotube x-ray sources and multiplexed data transmission.

In a presentation scheduled for the American Association of Physicists in Medicine meeting July 23, the research team will describe the development of a multiplexing CT scanner that simultaneously captures and transmits data obtained using multiple x-ray sources. This concept of multiplexing is widely used in telecommunications but not in CT, where the x-ray source and detector rotate around the patient in the serial acquisition process. The team includes Otto Zhou, Ph.D., the Lyle Jones distinguished professor of materials sciences and physics at the university.

Multiplexing involves the transmission of many signals simultaneously, which dramatically increases data rates. It has not been applied to CT mainly due to limitations of x-ray technology.

In its prototype, the North Carolina team leveraged carbon nanotube field emission x-ray technology. The key to their success is the way in which these nanotubes generate x-rays.

A conventional x-ray tube produces electrons when metal filament is exposed to temperatures around or above 1000°C. Those electrons bounce off another piece of metal to generate x-rays. Carbon nanotubes, however, emit electrons at room temperature under an externally applied electric field. Because high temperatures are not needed, neither is bulky insulation. This makes room for the multiple x-ray sources to be built around the perimeter of the gantry.

The team has built a 25-pixel multiplexing CT scanner as a proof of concept. The prototype requires no mechanical motion, instead relying on rapidly switched x-ray sources, each taking an image of the object from a different angle. The researchers combined this scanner with multiplexing techniques to manage the data.

Their approach holds the promise of boosting the speed of CT scans by a factor of 500, according to the researchers. But achieving such gains is still down the road. The 25-pixel scanner operating at the university is far less complex than the 1000-pixel device needed to compete with current mechanical CTs. The cost of building such a machine would not, however, be more than current models, according to the researchers.