GE changes digital x-ray landscape with debut of amorphous-silicon work

Milwaukee vendor has aggressive commercialization schedule

GE Medical Systems cleared up much of the mystery shrouding its work in digital x-ray detector technology with a news conference in Santa Clara, CA, last month, where the company announced its strategy for taking on what could be the next big leap in medical imaging technology. GE revealed that it is partnering with a division of high-technology conglomerate EG&G to develop amorphous-silicon-based detectors for a new generation of x-ray systems that the company hopes to have on the market in 1998.

GE and EG&G Amorphous Silicon combined their technology to develop the digital detector arrays, which will be manufactured at a new 74,000-square-foot EG&G plant in Santa Clara. GE has exclusive rights to the arrays, and will use the detectors to replace conventional screen-film cassettes and image intensifier tubes in x-ray systems. GE executives on hand at the press conference, including president and CEO Jeffrey Immelt, said the project was the end result of over 10 years of work and $100 million in R&D spending.

GE's announcement instantly changed the landscape of the rapidly developing direct digital detector segment, putting the Milwaukee company at the forefront of discussion about the technology. Although GE had been reticent to talk about its efforts until last month, the company's technology is at least as advanced as that of its competition, if not more so. The stakes involved are huge: GE and other firms hope that flat-panel digital detectors will revolutionize medical imaging by bringing the benefits of digital technology to the most widely used modality in the industry. Direct digital detectors will make it easier to bring x-ray systems into PACS networks and could confer a wide range of additional benefits in image quality and healthcare efficiency.

GE actually began working on digital detectors 10 years ago at its Corporate Research & Development center in Schenectady, NY, in the process winning 80 patents on its technology. About three years ago it began cooperating with EG&G, which itself had over 10 years of experience in amorphous-silicon technology. GE's research was transferred from Schenectady to EG&G, which put the finishing touches on the technology and began building a manufacturing facility for the arrays.

From the beginning, one of the biggest challenges faced by the companies was to build a single detector large enough to image the entire field-of-view of an x-ray study without resorting to tiling, in which the images from multiple arrays are stitched together to create a single image. The GE/EG&G arrays have 41 x 41-cm active areas without the use of tiling, which some other flat-panel and charge-coupled device (CCD) detector developers are using.

Each array is based on a glass substrate and consists of a cesium iodide scintillation layer, which captures x-rays and converts them to light; below that is an array of amorphous-silicon diodes, which take the light and convert it into an electrical signal. The signal is read through a matrix of thin-film transistors, and the digitized data can then be sent to a workstation for viewing.

The detectors have pixel sizes as small as 100 microns for demanding applications like full-field digital mammography, but for conventional x-ray, 200 microns is probably sufficient, according to Andres Buser, general manager of EG&G Amorphous Silicon. More important is the high dynamic range of the detectors, which at 16 bits is a major improvement over film.

"Spatial resolution is one thing, but the dynamics can help you resolve things much better than on a film-based system," Buser said.

Mammography systems will be the first products into which the detectors will be incorporated, according to Jeff Irish, general manager of global x-ray for GE. The vendor has built an 18 x 23-cm version of the detectors into its flagship Senographe DMR system, and will offer the detectors on new Senographe DMR and Senographe 800T systems. DMR and 800T systems in the field will also accept the detectors as a retrofit, Irish said. GE displayed images collected with the full-field digital version of DMR at last year's Radiological Society of North America meeting, although at the time it did not reveal the detector's origins (SCAN Special Report 12/96).

The full-field digital DMR has also been incorporated into a specially equipped van designed to demonstrate the utility of digital technology in bringing healthcare to remote areas. The Mobile Breast Care Center van was developed with funding from the U.S. government, and was demonstrated to Congress in March (SCAN 5/14/97). The van can collect mammography exams in the field, then send images via a T1 satellite link to a hospital for interpretation, according to Dr. Aiman Abdel-Malek, manager of the digital and networked systems program at GE CR&D in Schenectady. The van is one of several sites that have been collecting clinical data for submission to the Food and Drug Administration of a 510(k) application for the full-field digital DMR. GE expects to submit the application in the first half of 1998.

After mammography, the detectors will be adapted for other x-ray applications, including conventional x-ray, radiography/fluoroscopy, and angiography. The EG&G plant has the capacity to produce 10,000 detectors a year, and GE believes that it will have enough demand to use all that capacity, according to Irish.

At the Santa Clara press conference, GE displayed a mobile C-arm equipped with one of the detectors, resulting in a system lighter and less bulky due to the elimination of the image intensifier. The detectors are already capable of digitizing dynamic studies in real-time, an accomplishment that has yet to be accomplished outside of the R&D lab by some other developers of flat-panel digital detectors. The company also displayed dynamic cardiac cath images acquired with the panels.

What impact will GE's announcement have on the embryonic digital detector market, which is still waiting for the first products to appear? On the positive side, it will further legitimize the concept of flat-panel digital technology. On the other hand, GE's competitors may find that many potential customers would prefer to wait for a digital product from GE rather than buy an untested new technology from a company with a less storied history in the x-ray industry.

In any event, the market will soon be able to decide which offerings will win or lose. GE's timeline for a 1998 rollout of next-generation digital x-ray systems coincides with those of several flat-panel digital x-ray developers, such as Sterling Diagnostic Imaging; Siemens, Philips, and Thomson Tubes (through their Trixell joint venture); Canon; and dpiX and Varian.

GE, however, believes that it has the technology and the track record to dominate the digital detector segment as it has dominated the market for other medical imaging technologies. In fact, GE sees parallels between direct digital detectors and some of those other technologies, according to Immelt.

"We think that this will revolutionize (x-ray) much the same way that CT and MR revolutionized the industry more than 10 years ago," he said. "It facilitates great clinical value, it allows for speed and quality of images and diagnosis, it allows for the elimination of film, it facilitates electronic archiving. It really helps drive digital technology further into the healthcare industry, to the benefit of patients and doctors."