Creating a Portable X-Ray Machine

A startup company is developing a flat-panel source of x-rays that could help make the imaging technique portable. The company’s panels are made using techniques commonplace in the semiconductor industry and would be combined with flat-panel image sensors to make a briefcase-sized x-ray machine powered by a laptop battery. Such a system might be used in the field by the military or instead of bulky bedside systems used in hospital intensive-care units. Early research also suggests it might expose patients to less radiation.

The company behind the x-ray source, Radius Health, was spun out of the University of California, Los Angeles last year. It is developing a commercial version of a flat-panel x-ray source developed by physicists at the university. The company will make its first complete x-ray imager in three to four months and says it will have a full-scale prototype in a year.

The x-ray machines used in hospitals today employ a high-energy source of the radiation. A tungsten filament at one end of a long vacuum tube emits electrons when heated and those accelerate down the tube until they hit a metal electrode, causing it to produce x-rays.

Many groups are working to develop more compact and robust x-ray sources, says Dieter Enzmann, chair of radiological sciences at the University of California, Los Angeles Health System. Enzmann was not involved with the development of the new x-ray source but serves on Radius Health’s advisory board.

A key advantage of Radius Health’s system is that it uses an array of emitters, rather than a single source. “There is some potential to reduce the x-ray dose if you can control hundreds or thousands of x-ray sources independently,” says Enzmann. This lower dose would be especially attractive for pediatric imaging, Enzmann says, adding “if you have a portable, thin design that generates good images, it could be used both in the field and within the hospital.”

Radius Health’s x-ray sources work through pyroelectricity–the ability of some materials to produce electrical fields when they’re either heated or cooled–and uses an approach developed at the University of California, Los Angeles for controlling the emission of electrons by pyroelectric crystals.

Chemical etching is used to carve wafers of pyroelectric crystals into small tiles, which are then arrayed on top of a resistive heater. “We pattern the surface of the crystal with fine points that allow electrons to leave only at those points,” says Gil Travish, a researcher in the university’s particle beam physics laboratory and one of the company’s cofounders. This ensures a steady beam of electrons that can then be used to generate aligned x-rays suitable for imaging. The crystals used include lithium niobate and lithium tantalate crystals, which are found in telecommunications devices and sensors. “We don’t need unusual materials,” says Travish.

The tiled wafers are topped with a metal foil that emits x-rays when bombarded by electrons from the crystal beneath. A conventional x-ray tube produces a cone-shaped beam of radiation with a hot spot in the middle, which means radiologists must place patients farther away from the x-ray source to get an image of a larger area–to make up for the loss in intensity over distance, the energy of the radiation has to be increased. The new system produces uniform, parallel rays that should have advantages when imaging large areas, says Travish.

Another company, Xintek, is developing a novel x-ray source that uses bundles of carbon nanotubes. The company is farther along in development, having brought its technology to clinical testing with Siemens. But Enzmann says the advantage of Radius Health’s technology is that the panels can be readily fabricated over large areas using methods already employed in the microchip industry.