Nanotube-Powered X-Rays

Tiny electron emitters inside an x-ray generator could improve medical imaging and cancer therapy.

Carbon nanotubes are at the heart of a new x-ray machine that is slated for clinical tests later this year at the University of North Carolina (UNC) Hospitals. The machine could perform much better than those used today for x-ray imaging and cancer therapy, say the UNC researchers who developed the technology. They have shown that it speeds up organ imaging, takes sharper images, and could increase the accuracy of radiotherapy so it doesn't harm normal tissue.

Capturing the heart: In a new scanner, carbon nanotubes fire electrons instantly to generate x-rays. This gives sharp, high-resolution pictures, such as this one of a fast-beating mouse heart. Credit: Otto Zhou, University of North Carolina

Conventional x-ray machines consist of a long tube with an electron emitter, typically a tungsten filament, at one end and a metal electrode at the other. The tungsten filament emits electrons when it is heated to 1,000 degrees Celsius. The electrons are accelerated along the tube and strike the metal, creating x-rays.

Instead of a single tungsten emitter, the UNC team uses an array of vertical carbon nanotubes that serve as hundreds of tiny electron guns. While tungsten requires time to warm up, the nanotubes emit electrons from their tips instantly when a voltage is applied to them.

The researchers presented work on their nanotube scanner at the meeting last week of the American Association of Physicists in Medicine.

Physics and materials science professor Otto Zhou cofounded a company called Xintek in Research Triangle Park, NC, to commercialize the technology. Xintek has teamed with Siemens Medical Solutions to form a joint-venture company, XinRay Systems, which has developed the prototype system that will be clinically tested this year.

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Taking clear, high-resolution x-ray images of body organs is much easier with the new multi-beam x-ray source, Zhou says. Conventional computerized tomography (CT) scan machines take a few minutes to create clear 3-D images using x-ray. "Because the radiation is coming from one point in space, the machine has to move the [electron] source and detector around the object," Zhou says. The x-ray emitter fires while the tube moves. The motion of the heart and lungs can blur images, so a CT scanner takes hundreds of pictures that are synthesized to reconstruct a 3-D image.