Both the Economist and the Technology Review are reporting this week on a newly-developed technology for generating X-rays, which employs some of the results of nanotechnology research. Since X-rays were first discovered by Wilhelm Röntgen in 1895, they have been generated using vacuum tube techology. An electron emitter, usually a tungsten filament, is heated to about 1000°C, and the emitted electrons are accelerated through the tube to strike a metal target. The energy transferred from the electrons’ impact causes X-rays to be produced.
The new technology, developed by Dr. Otto Zhou of the University of North Carolina, uses an array of carbon nanotubes as electron guns by a process called electron-field emission. This permits the X-ray source to be much smaller, potentially leading to higher-resolution images.
The result is a compact source of X-rays that can be controlled with great precision. Such sources can then be built into an array, each element of which is programmed to fire whenever required.
The individual electron guns can be switched on and off rapidly, since they don’t require time to warm up, as a filament emitter does.
Dr. Zhou has formed a joint venture, XinRay Systems, with Siemens Medical Solutions, to develop, test, and market new X-ray imaging devices based on this technology. While clinical trials still have to be conducted, the method has considerable potential to improve the quality of medical images. For example, in an existing CT (CAT) scanner, a single X-ray source is moved around the patient, capturing a succession of images from different angles, which are then re-assembled by computer. Since it is effectively impossible for the patient to remain completely motionless for the few minutes that this takes, some blurring of the resulting composite image is inevitable. The nanotube-based technology can use an array of sources, each of which can be switched on and off rapidly, to get a considerably sharper image:
The new machine, by contrast, turns multiple nanotube emitters on and off in sequence to take pictures from different angles without moving. Because the emitters turn on and off instantaneously, says Daniel Kopans, director of breast imaging at Massachusetts General Hospital, the system should be able to take more images every second. This faster exposure, Kopans says, should reduce blur, much as a high-speed camera captures ultrafast motion.
The technology also has potential uses in display applications. Traditional cathode ray tube (CRT) displays, as used in televisions, for example, used a tungsten filament to emit electrons. The electron beam was “steered” by electromagnets around the tube, and the image was produced when the beam struck phosphor dots on the display surface, causing them to emit light. As in the case of X-rays, the nanotube electron guns can be used to replace the filament:
Companies such as Samsung and Motorola are making displays based on nanotube emitters that promise to consume less power than liquid-crystal displays or plasma screens while providing the brightness and sharpness of bulky cathode-ray-tube TVs because they work on the same principle: shooting electrons at a screen coated with red, green, and blue phosphors.
I’ve been fascinated by the work being in done in nanotechnology, and it’s nice to see it producing some tangible results.