Future of digital XR glimmers in advanced aps and smart tools

Low-dose digital products cater to cardiac, R/F markets

Digital radiography has to provide more than just digital images, developers of the technology agree. Advanced applications and smart tools, including computer-aided detection, must be in place for DR to supplant film-based x-ray. And that is exactly what the major developers of digital x-ray are doing.

"We believe that if you buy a flat-panel detector product, you should get more than you would if you simply digitized a piece of film," said Renaud Maloberti, manager of global radiography business for GE Medical Systems.

GE flat-panel systems offer good quality imaging at a dose greatly reduced from that of conventional film-based products, according to Maloberti. He cites low noise, good detection of low-contrast objects (high detective quantum efficiency, or DQE), and fast imaging as additional advantages. But these capabilities are only the foundation for what developers need to provide for DR to transcend a century-old film technology.

Digital detectors allow advanced applications, Maloberti said. With dual-energy subtraction, for example, the digital panel captures two images of the chest within 150 msec at two different energy levels. Subtraction provides one image of the bone structure, and another showing the soft tissue alone, making it easier to spot detail previously hidden by the skeleton. A tissue equalization feature is also available on GE digital radiography products.

The integration of smart software is next, specifically the addition of CAD to flat-panel systems. Radiography applications will likely be first, followed by radiography/fluoroscopy (R/F). The extension of this technology is a logical next step for GE, which sees itself as a key player in the DR market, with more than 500 flat-panel systems installed globally.

It's been a long road.

The company released its first digital x-ray flat-panel system dedicated to chest exams in 1999 (Revolution XQ/i), followed in 2000 by a full-field digital mammography system (Senographe 2000D) and a flat-panel product for the cardiac market (Innova 2000). A digital system for general radiographic exams (Revolution XR/d) was released in 2001. At the RSNA meeting in December, GE unveiled its latest development: a 41 x 41-cm flat-panel system for vascular work (Innova 4100).

GE flat panels rely on the indirect conversion of x-rays to digital data via a cesium iodide scintillator and a nontiled amorphous silicon detector. Development of the detector technology is split among R&D centers of excellence in the U.S., France, and countries in Asia, where efforts to tailor the x-ray systems to meet specific imaging applications are ongoing.

"When we designed our product, we wanted a flat panel that could be used across the board, from radiographic to dynamic imaging," Maloberti said. "We will eventually put flat panels everywhere."

Trixell, a European DR manufacturer, shares this confidence in flat-panel DR and has an unwavering commitment to cesium iodide/

amorphous silicon detector technology. Trixell was founded in 1997 as a joint venture between Thales Electron Devices (51%), Philips Medical Systems (24.5%), and Siemens Medical Solutions (24.5%), to develop high-tech digital detectors for the medical imaging market. Trixell's products are integrated into Philips' and Siemens' DR product lines.

Future of digital XR glimmers in advanced aps and smart tools

Production of a detector suitable for general radiography (Pixium 4600) started in 1999, reaching volume production levels in 2001. Trixell's next flat-panel detector, targeted to the cardiovascular market (Pixium 4800), first appeared at the start of 2002 and is now rolling off production lines at the rate of 20 per month. Workforce numbers at the company's site near Grenoble, France, have tripled over this period.

A prototype digital detector for vascular and R/F applications (Pixium 4700) is under development. Trixell's CEO, Gerard Daguise, regards the 30 x 40-cm flat panel as the first in a new family of intervention-friendly digital products. Subsequent family members are likely to feature smaller detectors, he said.

Flat-panel systems will not dislodge conventional systems from interventional applications anytime soon, Daguise said. But digital products will find a strong niche in this segment of the market.

Despite the comparatively late arrival to Trixell's product portfolio of an R/F detector, dynamic imaging has always been part of the joint venture's plans, just as amorphous silicon has always been the core technology for both static and dynamic imaging. Alternatives were considered, however. Early on, Trixell engineers investigated the potential of amorphous selenium, which enables direct conversion of x-rays into an electrical charge. It was ruled out as being less reliable for R/F, although recent developments by competitors seem to have proven the viability of this technology, Daguise said.

"We were absolutely certain that with amorphous silicon technology we could make digital detectors for fluoroscopy, whereas it was not so obvious we could do it with amorphous selenium," he said. "It seems now that it is feasible, but we were not so sure at that time."

Promise of a higher DQE than that provided by amorphous selenium could tip the scales, and an existing track record in image intensifier technology changed the balance overwhelmingly in favor of amorphous silicon, a decision that Trixell is more than happy about.

"For the coming years, we are going to stick with the technology," Daguise said. "We have some research to do, not to change the technology for the sake of change, but to do some technological leapfrogging, to bring in something with much better performance than the technology we have now."

But Rex Harmon, vice president of global marketing and PR manager for Swissray International, believes the top three medical imaging vendors may have backed the wrong horse. Eschewing the flat-panel path, Swissray is using CCD detectors to record x-ray images captured on a cesium iodide scintillator with its ddR range of products.

"CCD is the technology for high-tech imaging," Harmon said.

Swissray's digital radiography portfolio, developed and manufactured in Hochdorf, Switzerland, fares well against rival flat-panel systems, he said. Harmon points to the company's latest system (ddRModulaire plus), which has a low-dose detector, requires just two seconds for the detector to refresh between exposures, and produces a diagnostic image in less than five seconds after exposure. Because the Swissray detector setup relies on technology developed by external suppliers, the systems are regularly updated at little cost when new components come on the market.

"Swissray is a systems integrator," Harmon said. "Inventing our own semiconductor technology was way too expensive."

GE's experience indicates just how expensive that can be. The company makes no bones about having invested more than $150 million over the past 15 years to develop its detector technology. Advocates of amorphous silicon accept that their solution is far from cheap but remain confident that customers will recognize the potential rewards to be gained from the one-time investment.

"There is room for several types of technologies, several types of products," Daguise said. "We are not on the cheap side, because we are looking at high performance and reducing radiation dose."