Nanotubes create CT images faster than traditional scanners

A new method that uses carbon nanotube x-rays to create CT images promises to make CT scanners work faster than traditional ones while using less peak power.

Multiplexing the carbon nanotubes to create multiple streams of x-rays and, consequently, multiple CT images simultaneously, makes the advantages possible, according to Otto Zhou, the Lyle Jones Distinguished Professor of Materials Science in physics and astronomy at the University of North Carolina at Chapel Hill.

Multiplexing was behind the development by Zhou and colleagues in 2005 of a scanner incorporating multiple x-ray sources. Unlike current mainstream CTs, the UNC prototype, called a multipixel scanner, required no mechanical motion. Instead, it switched rapidly among many x-ray sources, each taking an image of the object from a different angle in fast succession.

The team's latest innovation deploys this multisource x-ray approach through the use of carbon nantotubes, turning on all the x-ray sources at the same time to capture images from multiple views simultaneously.

"With multiplexing, we can have all the x-ray pixels on at the same time for maybe two seconds," Zhou said. "You still get all the images, only faster, and we need only about half of the original x-ray peak power."

Neither multiplexing nor x-ray nanotubes is particularly new. Multiplexing is widely applied, for instance, in cellular phones. Millions of cell phone signals travel along the same frequency band, then are separated into coherent messages at their destinations.

Zhou and colleagues demonstrated the utility of carbon nantotubes years ago, showing that these tubes, composed of layered carbon only a nanometer wide, can be excited by an electrical field to act like nano-electron guns, firing streams of x-rays.

In addition to increasing the speed of the scan, the nanotubes cut down on the heat generated during a scan, making the process more energy efficient. Whereas conventional x-ray tubes blast electrons into metal filaments inside a vacuum chamber, creating x-rays amid temperatures well over 1000° C, nanotubes operate at room temperature.

The key to speed and efficiency is the multiplexing of nanotubes, Zhou said.

"What makes a multiplexing CT scanner possible is the novel multipixel x-ray source we developed and the ability to program each pixel electronically," he said.

The first images produced by this combination of multiplexing and nanotubes was of an inanimate object, not a medical one. Zhou and colleagues took images of a computer circuit board, then compared the images to those generated by a traditional CT. The images showed little difference in resolution or clarity, but the prototype scanner got the job done faster.

"Our demonstration scanner gives only enough views to image a simple object," Zhou said. "Our next step is to develop a small CT scanner for small animal imaging."