Posted: August 14, 2006

CT imaging gets boost from carbon nanotubes

(Nanowerk News) Scientists at the >Carolina Center for Cancer Nanotechnology Excellence have developed a new method to create computed tomography (CT) images using carbon nanotube x-rays. This new method, which works much faster than traditional scanners and uses less peak power, represents a step toward developing scanners for medical imaging and homeland security that are smaller, faster, and less expensive to operate.
Otto Zhou, Ph.D., of the University of North Carolina at Chapel Hill, leads the team developing carbon nanotube x-ray sources for use in cancer imaging applications, among others. Carbon nanotubes are able to produce x-rays without the use of the high temperatures used with conventional x-ray sources. The Carolina team published its findings in the journal Applied Physics Letters ("Multiplexing radiography using a carbon nanotube based x-ray source").
"The current CT scanners take images sequentially, which is slow and inefficient,” said Zhou. “Using the nanotube x-ray technology, we show in this paper the feasibility of multiplexing – taking multiple images at the same time."
Traditional CT scanners use a single x-ray source that takes approximately 1,000 images from multiple angles by mechanically rotating either the x-ray source or the object being scanned at high speed. Last year, Zhou and colleagues created a scanner with multiple x-ray sources, called a multipixel scanner. The machine required no mechanical motion but switched rapidly among many x-ray sources, each taking an image of the object from a different angle in fast succession.
The team's newest innovation combines this multiple-x-ray-source innovation with a principle called multiplexing, in which all the x-ray sources are turned on simultaneously to capture images from multiple views at the same time.
"Let's take a simple case where suppose you need 10 images," Zhou said. "Let's say each view takes one second. In the conventional step-and-shoot method used for the current CT scanners, you take one shot, and the first pixel stays on for one second. Then we turn on the second pixel, and that stays on for one second." The whole process would take 10 seconds.
"With multiplexing, we can have all the x-ray pixels on at the same time for maybe 2 seconds,” Zhou said. “You still get all the images, only faster, and we need only about half of the original x-ray peak power."
Multiplexing is a known concept used by, for instance, cellular phones. Millions of cell phone signals travel along the same frequency band, and are then separated into coherent messages at their destinations.
"What makes the multiplexing CT scanning possible is the novel multi-pixel x-ray source we developed and the ability to program each x-ray pixel electronically," Zhou said. Because of their small size and electronic properties, carbon nanotubes fit the bill perfectly as a source of pixel-sized, programmable x-ray sources.
In this study, Zhou and colleagues took images of a computer circuit board using a prototype multiplexing scanner, then compared the images to those generated by a traditional x-ray scanner. The images showed little difference in resolution or clarity, but the prototype multiplexing scanner got the job done faster.
"For this paper we built a prototype or demonstration scanner that gives a limited number of views, to image a simple object," Zhou said. "Our next step is to develop a small CT scanner for small animal imaging."
Source: National Cancer Institute