Zelda L. Kravitz
Thomas Edison invented fluoroscopy in 1896. In contrast to conventional radiography, fluoroscopy allows the direct and dynamic visualization of moving body parts on a fluorescent screen (instead of film).
The fluoroscopy x-ray tube generates a very low current (0.5 to 5.0 mA) and thus produces fewer x-rays. These pass through the patient’s body and strike the fluorescent screen which is coated with a phosphor, zinc cadmium sulfide. This phosphor converts the x-ray energy into a yellowish-green light, an area of the spectrum that the human eye is especially sensitive to.
The light glowing from the fluorescent screen is incredibly dim—in fact, it is only 1/10,000th that of the light used to look at radiographs. How can the image be seen in such dim light: The answer lies in the functioning of the rods and cones of the eye. We use our cones in bright light to see a range of colors. At night, our cones are no longer effective and we depend on the rods instead, because they are able to perceive extremely dim light. However, the eye must become adapted to the dark first before the rods are maximally effective.
Twenty five years ago, radiologists would wear red glass goggles for 20 minutes or so before a fluoroscopic examination. They were causing their eyes to become adapted to the dark. Now, because of new advances in fluoroscopy, we no longer see doctors running around in their red goggles. New image intensifiers have been invented, which means that the image is bright enough to be viewed by the cones as well as the rods.
Another important advance is the television screen. This allows the doctor to view the moving image in another room from the patient, thus eliminating the unnecessary radiation danger caused when high energy scattered radiation due to the Compton effect leaves the patient’s body.
