Research & Development Center, General Electric Co.Schenectady, N.Y.

Amorphous silicon X-ray detector

Doug Bartholomew, Samuel Greengard, Glenn Hasek, John Jesitus, Scott Leibs, Kristin Ohlson, Robert Patton, Barb Schmitz, Tim Stevens, and John Teresko contributed to this article. They say it looks like a pizza box and replaces equipment that resembles a beer barrel, but, then again, General Electric researchers have reason to be lighthearted: Their digital X-ray detector has emerged from a year of clinical trials with kudos from physicians. Its amorphous silicon technology also has created dramatic new opportunities to extend the effectiveness of X-ray imaging in nonmedical applications. The new device is a solid-state detector that takes the place of photographic film in X-ray systems and will be the basis for a new line of medical-imaging systems to be announced next year. GE is also exploring industrial applications and is already using amorphous-silicon imaging to examine aircraft-engine blades in its own manufacturing process. Amorphous silicon is used in a variety of devices, such as solar-powered calculators and laptops. Other companies also have been trying to develop detectors using amorphous silicon, but GE's is the only clinically usable detector that captures the same area as a sheet of photographic film -- up to 16 inches square -- all on a single piece of material, as opposed to smaller pieces tiled together. GE's system produces images that are as good as those created by film, while offering a host of additional features. The detector contains millions of pixels. Incoming X-rays that have passed through the anatomy first hit a special "scintillator material" (cesium iodide) that converts the X-rays to light. The resulting light passes through the pixels, striking an underlying layer of another material, amorphous silicon, that converts the light into electrical signals. Those signals are transformed by computer into digital data that become a digital image that can be stored, transmitted, and analyzed using a variety of techniques. The advantages of having digital instead of photographic images are immense. Digital images can be easily transmitted around the world via satellite, enabling physicians at one location to consult electronically with far-flung experts. Digital images also lend themselves to computer-aided diagnosis and screening, an option that health-care centers are exploring to improve accuracy of diagnosis and decrease costs. Unlike film-screen images, which require large-capacity storage facilities and cumbersome retrieval procedures, digital images can be stored electronically and retrieved as easily as any other computer file. In fact, specialists in different parts of a hospital can retrieve and view the images simultaneously. And unlike film-screen images, the digital images are produced without chemicals or plumbing, thus without hazardous waste. Another critical advantage is enhanced sensitivity. "This means less radiation is required to create an image," explains Bruce Griffing, manager of the R&D Center's Industrial Electronics Laboratory. "Reducing the dose of radiation can be a real advantage for both physicians and patients. This is the case in balloon angioplasty -- even though there's only a small amount of radiation, it adds up for the doctor, who does this procedure over and over. But since our system is capable of better resolution, the doctor can see what's going on better, with less radiation. In other procedures, the patient is on the table for hours being exposed, and a lower dose is also important. In cases like mammography, physicians might instead choose to give patients the same dose of radiation as before, but get better images and maybe detect cancer sooner." The latter application has already led to new imaging strategies among doctors participating in clinical trials. "Our experience has been that you can do so many more things with digital imaging that it far outperforms film-screen mammography," says Daniel Kopans, director of the Breast Imaging Div. at Massachusetts General Hospital and associate professor of radiology at Harvard Medical School. Kopans has been working on new techniques such as digital tomosynthesis, in which images of the breast are taken from many different angles and then electronically combined. Physicians can then look at any plane within the breast while blurring out the other planes. "The breast is a complex organ with a lot of structures," says Kopans. "When we look for a cancer, it's a lot like looking for a tree in a forest. With this technology, we can make it look like a tree in a clearing."

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