The invention: A complex electronic device that increases the intensity of the light in X-ray beams exiting patients, thereby making it possible to read finer details.

The people behind the invention:

Wilhelm Conrad Rontgen (1845-1923), a German physicist Thomas Alva Edison (1847-1931), an American inventor W. Edward Chamberlain, an American physician Thomson Electron Tubes, a French company

Radiologists Need Dark Adaptation

Thomas Alva Edison invented the fluoroscope in 1896, only one year after Wilhelm Conrad Rontgen’s discovery of X rays. The primary function of the fluoroscope is to create images of the internal structures and fluids in the human body. During fluoroscopy, the radiologist who performs the procedure views a continuous image of the motion of the internal structures.
Although much progress was made during the first half of the twentieth century in recording X-ray images on plates and film, fluoroscopy lagged behind. In conventional fluoroscopy, a radiologist observed an image on a dim fluoroscopic screen. In the same way that it is more difficult to read a telephone topic in dim illumination than in bright light, it is much harder to interpret a dim fluoroscopic image than a bright one. In the early years of fluoros-copy, the radiologist’s eyes had to be accustomed to dim illumination for at least fifteen minutes before performing fluoroscopy. “Dark adaptation” was the process of wearing red goggles under normal illumination so that the amount of light entering the eye was reduced.
The human retina contains two kinds of light-sensitive elements: rods and cones. The dim light emitted by the screen of the fluoroscope, even under the best conditions, required the radiologist to see only with the rods, and vision is much less accurate in such circumstances. For normal rod-and-cone vision, the brightness of the screen might have to be increased a thousandfold. Such an increase was impossible; even if an X-ray tube could have been built that was capable of emitting a beam of sufficient intensity, its rays would have been fatal to the patient in less than a minute.


In a classic paper delivered at the December, 1941, meeting of the Radiological Society of North America, Dr. W. Edward Chamberlain of Temple University Medical School proposed applying to fluoroscopy the techniques of image amplification (also known as image intensification) that had already been adapted for use in the electron microscope and in television. The idea was not original with him. Four or five years earlier, Irving Langmuir of General Electric Company had applied for a patent for a device that would intensify a fluoroscopic image. “It is a little hard to understand the delay in the creation of a practical device,” Chamberlain noted. “Perhaps what is needed is a realization by the physicists and the engineers of the great need for brighter fluoroscopic images and the great advantage to humanity which their arrival would entail.”
Chamberlain’s brilliant analysis provided precisely that awareness. World War II delayed the introduction of fluoroscopic image intensification, but during the 1950′s, a number of image intensi-fiers based on the principles Chamberlain had outlined came on the market.
The image-intensifier tube is a complex electronic device that receives the X-ray beam exiting the patient, converts it into light, and increases the intensity of that light. The tube is usually contained in a glass envelope that provides some structural support and maintains a vacuum. The X rays, after passing through the patient, impinge on the face of a screen and trigger the ejection of electrons, which are then speeded up and focused within the tube by means of electrical fields. When the speeded-up electrons strike the phosphor at the output end of the tube, they trigger the emission of light photons that re-create the desired image, which is several thousand times brighter than is the case with the conventional fluoroscopic screen. The output of the image intensifier can be viewed in an undarkened room without prior dark adaptation, thus saving the radiologist much valuable time.
Moving pictures can be taken of the output phosphor of the intensifying tube or of the television receiver image, and they can be stored on motion picture film or on magnetic tape. This permanently records the changing image and makes it possible to reduce further the dose of radiation that a patient must receive. Instead of prolonging the radiation exposure while examining various parts of the image or checking for various factors, the radiologist can record a relatively short exposure and then rerun the motion picture film or tape as often as necessary to analyze the information that it contains. The radiation dosage that is administered to the patient can be reduced to a tenth or even a hundredth of what it had been previously, and the same amount of diagnostic information or more can be obtained. The radiation dose that the radiologist receives is reduced to zero or almost zero. In addition, the combination of the brighter image and the lower radiation dosage administered to the patient has made it possible for radiologists to develop a number of important new diagnostic procedures that could not have been accomplished at all without image intensification.


The image intensifier that was developed by the French company Thomson Electron Tubes in 1959 had an input-phosphor diameter, or field, of four inches. Later on, image intensifiers with field sizes of up to twenty-two inches became available, making it possible to create images of much larger portions of the human anatomy.
The most important contribution made by image intensifiers was to increase fluoroscopic screen illumination to the level required for cone vision. These devices have made dark adaptation a thing of the past. They have also brought the television camera into the fluoro-scopic room and opened up a whole new world of fluoroscopy.
See also Amniocentesis; CAT scanner; Electrocardiogram; Electroencephalogram; Mammography; Nuclear magnetic resonance; Ultrasound.

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