HeNe Lasers Give X-Rays a New Lease on Life
Brent D. Johnson
Since 1895, when Wilhelm Roentgen performed the first x-ray of his wife's hand, this noninvasive technique has become one of the most effective diagnostic tools available. Used by physicians and engineers alike, it has changed very little over the past 100 years. However, storing and sharing the images can be a problem because there are few effective ways of copying x-ray film. And although filmless radiography has been around for some time, the expense and the size of the systems have limited their success at replacing film-based systems.
As a solution to this problem, Agfa-Gevaert AG has developed a technique that can produce multiple originals from a single exposure. The company's ADC Compact Phosphor Scanner employs a filmless method called computed radiography that uses an imaging plate impregnated with photostimulable storage phosphors such as rare-earth-doped barium fluoride bromide, which can store the energy of x-rays for several days. When a laser scanner stimulates this imaging plate, it converts the x-ray energy to visible light that can be processed as a digital signal.
However, to get the latent image back out of the phosphor sheet, a considerable amount of visible energy must be put back into it. After some investigation, the researchers discovered that an 1145P HeNe laser from JDS Uniphase gave them the power they needed.
This laser has an inline configuration with an internal glass tube and produces 22 mW. When the phosphor material is scanned with a flying spot scanner, it emits at a deep-blue 400 nm. It can undergo 500 expose/scan/erase cycles without degrading the image.
Ralph Thoma, manager of the basic R&D optics center at Agfa-Gevaert, said that some people asked him why he chose that old technology. He answered that there was no other reasonable way of doing it at that time. If the laser is not stable, you get artifacts, he said. Although the HeNe was the most economical solution to the problem, it did require some work. JDS Uniphase had to boost the power from 17 to 22 mW.
The result of the researchers' efforts is that they can produce x-ray images that can be read directly from a cathode-ray tube monitor, and stored, printed or e-mailed anywhere in the world.
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