In 1963 when I was first hired by Picker X-ray Corporation, the X-ray business, while being matured, was not yet making that quantum leap in technology that I was to see in the next 10 to 20 years. I think it really took the implementation of the Transistor to start the next positive movement in that chain of events. This event pushed the development of new technologies in other areas, such as X-ray film.
In the field of "X-ray Film" technology, Kodak and Dupont (as I remember) were the leaders. The Japanese and Europeans had not really entered the picture yet, but that was to change in later years. Both companies were well recognized, and their products were always under improvement or advancement. At that time Dupont had produced a certain film that the industry gave a speed rating of 100. The rating was and I think is still being used by the whole industry (100 speed), as a sort of measuring tool, by which other films could be compared to. There were other films that were than rated at 50 speed and some times lower. In other words, other companies could try to break the 100 speed by producing films with greater speed, and then use it as sort of a sales (bragging) tool. There was also a requirement that the competing film or films had to have as good or better definition. The definition was determined by what was called "line pairs". The test device used for this purpose was a special grid (Air Force Test Target) that was used in photography for determining image sharpness. The number of line pairs that could be seen with a magnifying glass would give the scientist an idea of how good the imaging qualities of the film was. In X-ray the same test was used except the grid or test target, which was made of very thin stainless steel or copper. It was placed on a film cassette and exposed to a given or test standard burst of X-radiation. Films were considered "fair" to "good" if you could see 6 or 8 line pairs. This was going to change!
X-ray films were produced with Film Emulsion (sensitive to X-ray and/or light) on only one side of the Polyester base, for special use studies, such as Mammography, because a "single" sided emulsion film could produce sharper images. This type of film usually took a greater X-ray exposure to produce a usable image. The film speed was usually rated at 50.
X-ray films were also produced with Film Emulsion on both sides of the polyester film base, because it had been discovered that the image could be produced in 1/2 the time required to produce an image on the single sided film. This was a speed advantage (100 over 50) but it did produce an image that was not as sharp. With a single sided emulsion film, you usually used a single intensifying screen, and with double sided emulsion, 2 screens were used.
X-ray intensifying screens, which played a crucial part in this system will be discussed in another part of this (see Cover Page) article. Improvements in X-ray intensifying screen technology was to force improvements in the X-ray film emulsion used to go with the new style "screens".
New emulsions were developed which not only decreased the use of drastic amounts of Silver Halide used in emulsions, but improved the perceived image sharpness by using improved "grain" size, along with an important increase in the "speed" of the film.
3M (Minnesota Mining and Mfg.) had been in the business of producing coating's for various products for many years. Their venture into the X-ray market was to be rather dramatic. Their first X-ray film products left some things to be desired, but as their experience grew, so did their stature in the Medical Imaging business. I have always said; If you want something done, let some one who doesn't know that it can't be done, work on the project. 3M soon came out with a film and system that was totally different than what had been tried before. It was called "High Lite". The film was not very sensitive to room light and less so to Yellow light. Yellow lights were installed in the X-ray room, and than for the most part, films could be handled in the open. No more dark room! The X-ray film processor could now be installed in the X-ray room in the vicinity of the patient, which left the technician able to care for the patient while performing the task of developing the exposed radiograph.
This system worked great for many years but was soon eclipsed by another and much more astounding invention by 3M. The new invention used Rare Earth technology (Gadolinium-oxysulfide) for a new style of intensifying screens which when struck with X-radiation, glowed GREEN. The screen technology is discussed in my article on intensifying screens.
Along with this Rare Earth screen technology came the invention of a totally new film which had been designed to be sensitive to light output in the Green region of the spectrum. The original reason for this invention was that the 3M scientists had discovered that the Green region of the spectrum allowed for a Dramatic increase in the speed of the system while using the same or less exposure. The speed of the film/screen system lead to speeds as high as 1600, which was well over the old 100 speed film/screen combinations that used Calcium Tungstate screen emulsion. Once again the patient was given a very large reduction in the X-ray exposure, in studies using the new technology.
One of the disadvantages noted in the new "Green" film technology, was an increase of what was termed "crossover". What happened was, when an X-ray exposure was made, the light emitted from the front intensifying screen (closest to the X-ray tube) would pass some of it's light through the emulsion on one side of the film to the emulsion layer on the other side. This action occurred in both directions, as both screens front and back) emitted light back and forth. The result was image halation, or image blurring. This was nothing new even to the "Blue" emitting screens and film systems, which also displayed this problem but to a lesser extent. But something happened that would help change this.
Along came a person (whose name I will not mention here) who joined 3M with a degree in nuclear physics. He had absolutely no experience in film emulsions. We had all been given to understand that film emulsion technology was a Black Art, and that you had to be gifted in order to work in this field!! He had an IDEA, and because he didn't know that it couldn't be done, he DID IT. He found a way to stop the "crossover" problem. He discovered that if you put a special colored dye, that would absorb the emitted light from the screens, on both sides of the polyester substrate before applying the film emulsion and other components, you could achieve a significant reduction of light crossover. His discovery lead to a dramatic gain in film image sharpness. The sharpest the World had ever seen.
One of our chemists who had come over from the U.K., before the announcement had been made, smugly said, "it can't be done because we tried it in the U.K"! Little did he know that my friend had already done it! The interesting thing about this effort was that my friend was from India, and his and my boss, was from Italy. Neither could understand the other very well, and as a result, my friend, because he couldn't make my boss understand, had to sneak or "bootleg" the project right under his nose. After our boss found out about the project and was shown an image, he recognized the talent and promoted my friend. Now they communicated!
Another outcome from this effort was when a noted radiologist and bone specialist from a Southern Hospital used the film on a child who had been abused by his parents. In a speech at 3M, the radiologist, with tears in his eyes, made note of the fact that without the use of this film to help detail bone fracture lines, he could have never proved to the Judge and Jury in Court, that abuse had occurred. The older style films that he had previously used could never have shown the detail that he now could reveal. He thanked my friend for what he had invented even when all odds were against him. To the radiologist, this meant he would now be able to do more to protect the children, that may have been abused, who came under his care.
Some years later Eastman Kodak Company came out with their own version of an anti-crossover film. They found that the halation problem could be stopped by using a film emulsion that was composed of micron sized "platelets". The platelets were "grown" by a technique used in emulsion making. This invention equaled the 3M anti-crossover system. It was another of those advancements that have made this an exciting business.
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Last updated on 14 January 2006