Santa Clara, CA--New technology is changing the way x-ray images are acquired and viewed. As a result, patients are exposed to less radiation; computers speed analysis; and images can be archived, retrieved, or transmitted electronically.
The technology, amorphous silicon x-ray detectors, converts x-rays into digital data. Developed by GE Medical Systems (Milwaukee, WI) and manufactured by EG&G Inc., these large-format detectors give doctors more diagnostic information in a single exposure than can be obtained in multiple film-based x-ray images.
Millions of picture elements make up the detector. For each of these elements, incoming x-rays strike a cesium iodide "scintillator material" that converts the x-rays into light. The scintillator material also channels the light to a layer of amorphous silicon, which converts the light into electrons.
An array of electronic switches and signal lines capture the electrical signals. This results in a collection of digital data that describes precisely the x-ray intensity hitting each one of the tiny picture elements. That data is then used to produce a high-quality x-ray image.
Although other digital imaging technologies have been tried in diagnostic x-ray machines, their performance is compromised by the inherently small size of their detectors. Charge-coupled devices, for example, can only be manufactured up to a few centimeters on a side.
To capture a complete chest x-ray image, such detectors must either be tiled together or matched to bulky optics designed to downsize the image. Either technique introduces image losses that are unattractive to the medical community.
The new panel's large format and high pixel density eliminate the need for optical image reduction. Each pixel delivers up to 16 bits of dynamic-range (contrast) information. Thus the detectors produce images with resolution comparable to fine-grain film--but the images are instantly available and formatted for electronic storage or transmission. "Amorphous silicon technology gives us the ability to make full-scale detectors in one piece, " says Lewis Edelheit. "This differs significantly from other approaches that combine several smaller detectors to make a large one." Edelheit predicts the large-area digital detectors will serve "the whole spectrum of x-ray applications from mammography and radiography, to real-time fluoroscopy and angiography."
Electronic storage will save hospitals the enormous space and labor costs now needed to archive and retrieve x-ray films. Filmless x-rays will spur the growth of telemedicine, by which local hospitals can consult with large medical centers. Finally, digital images lend themselves to computer-aided diagnosis and even fully automated screening of routine x-rays such as mammograms. Systems using the new detector are currently limited to investigational use in the U.S.