Varian digital-detector project delivers fluoro images in real-time

August 20, 1997

Company claims achievement is first in detector designThe image intensifiers that sit atop radiography-fluoroscopy, angiography, and cardiac cath systems are a giant step closer to obsolescence as the result of a milestone achieved by Varian

Company claims achievement is first in detector design

The image intensifiers that sit atop radiography-fluoroscopy, angiography, and cardiac cath systems are a giant step closer to obsolescence as the result of a milestone achieved by Varian Associates last month. Working with a flat-panel sensor fashioned from amorphous silicon, engineers at the Palo Alto, CA, company have built an intricate lattice of electronic switches and amplifiers to digitize x-ray fluoroscopy studies in real time.

"We have a panel running and we can make video with it," said Dave Gilblom, general manager of Varian Imaging Products, the Varian subsidiary working on the detectors. "You can wave your hand in front of it and make moving pictures."

While flat panels have for years been used to generate static images using x-rays, real-time fluoro had escaped the grasp of engineers, due to formidable engineering hurdles. For example, signals indicating the impact of x-rays on the flat-panel sensor are obtained through the use of some 3800 individual lines, half of which carry the actual signals while the other half control signal acquisition, Gilblom said. Because of the extraordinarily low power of these signals-just 1000 electrons are released with the strike of an x-ray-amplifiers are needed throughout the latticework of electrical connections.

"There were some questions about how the images would look when we finally got the thing running, because there was very little data on panels running at the speed that you need in order to do video," Gilblom said.

The real-time, 30-frame-per-second video images were acquired using Varian's Large Area Sensing Technology (LAST), an amorphous silicon panel measuring 7.5 x 9.5 inches. LAST was able to achieve a resolution of about two lp/mm, about one-fifth of the resolution commonly achieved in CT. But Gilblom notes that LAST's resolution will undoubtedly improve.

"The first thing was to make it work at all," he said. "Nobody's ever done this before."

The milestone was accomplished using a flat-panel sensor made by dpiX, a wholly owned subsidiary of Xerox in Palo Alto, which has allied with Varian to develop flat-panel sensors for medical and industrial applications. The electronics that made the fluoro images possible were the product of Varian engineers.

Gilblom predicts that commercial production of fluoro-capable sensors is near at hand. Varian is on track to deliver production subsystems, consisting of amorphous silicon detectors and control electronics, to equipment manufacturers and systems integrators in the fourth quarter of this year. The company is working with 10 medical and industrial equipment suppliers that are incorporating this new technology into their product lines.

The real-time capability demonstrated with a LAST detector, as well as panels being fabricated by companies including Sterling Diagnostic Imaging, Trixell, EG&G Amorphous Silicon, and Optical Imaging Systems, are expected to usher in a new generation of smaller, lighter, and more cost-effective imaging systems. By replacing the large 100-pound image intensifier and the TV camera connected to it with 15-pound amorphous silicon imagers, manufacturers can produce systems up to 90% smaller and 70% lighter than current offerings.