This study will include X-ray cassettes because of the intimate ties between film and cassettes.
1963 to 1993
From the year 1963, I was able to observe the progress made in X-ray Intensifying screen and cassette technology up to 1993.
When I was first introduced into the X-ray business, some offices or accounts were still doing non-intensifying screen patient studies with light tight envelopes that the X-ray film was placed in for the X-ray exposure. Most hospitals were using the same envelopes but were also placing single or double (2) X-ray intensifying screens in the envelope with the X-ray film placed in between the screens. The intensifying screen emulsion was Calcium-Tungstate which glowed a bright Blue when hit with X-radiation. The number of screens was dependent upon whether the film was a single or double sided emulsion type film. When you shoot a patient using a non-screen technique, the radiation exposure is out of this world! No one does it anymore! The patients must have thought they had a hole burned through them.
For the most part, hospitals were into using metal cassettes that had a front side (where the X-ray's entered) that had a kind of phenolic or other composition light tight "window". The outer construction of the cassette was usually aluminum or stainless steel, except for the front where it had to be somewhat non-opaque to the X-ray beam. There were many manufacturers in the business of making cassettes because this was one of the more important parts of the imaging chain that affected image sharpness. If a cassette did not compress the screens tightly and evenly across the entire film plane, the image would be blurred in some areas and sharp in others. It was almost a contest among manufacturers as to who could produce the cassette that would give an extremely sharp image over the whole film. So the cassettes played a very important part in the use of intensifying screens.
Kodak and Dupont companies were probably the major suppliers of intensifying screens and cassettes for the industry at that time. Several other companies including (eventually) 3M produced them. The screens in the beginning, were almost entirely produced with Calcium-Tungstate emulsion coated on one (1) surface of a very heavy poly-ester or other plastic "plate". Calcium-Tungstate glowed a bright BLUE when exposed to X-ray's. The X-ray film emulsion for the most part was "tuned" for the color Blue for maximum effectiveness.
As progress was made in increasing the overall speed of film and other parts of the X-ray system, intensifying screen emulsions were also improved for speed, intensity, and sharpness. Companies found that by playing with "grain" size, and by adding or subtracting various components of the emulsion, not only could the speed of the system be increased, but image sharpness could be improved upon. (This progression required the improvement of X-ray cassettes at the same time). Finer grain size in the film emulsion slowed the system down, but allowed for the production of a sharper image. These screens were used for studies requiring the best image that could be obtained, such as in Mammography and Extremities. Screens used for Chest X-rays and related studies could be made with emulsions that contained larger crystals (grain size), but allowed for a related increase in film/screen speed, thus reducing the X-ray exposure to the vital parts of the patient.
Eastman Kodak invented and produced what I consider the finest X-ray cassette on the market. It was produced by molding the major part of the cassette in one (1) part, which included the front, back, and hinge (plastic living hinge). The total cassette probably had less than 15 parts, but turned out to be a great advancement in the cassette industry. I would like to meet the design engineer or inventor that came up with this great invention. These cassettes were not without their growing up problems, but for the most part, fulfilled the requirements of the X-ray business, for a simple to use cassette that allowed excellent film/screen contact. With the invention of this cassette came an advantage for the intensifying screens that were being produced, along with a whole new line of films.
Along came 3M:
As told in another part of my article, 3M was somewhat of a late comer in the Medical Imaging business. In some ways they had to play catch up. The 3M scientists were looking for a better way or system to reduce the exposure to the patient. They discovered that certain other elements produced a greater reaction to X-ray than did the Calcium-Tungstate emulsions that were in use. They found that Gadolinium-Oxysulfide, which glowed brilliant GREEN, produced a greater intensity when exposed to X-ray's. There is some argument with in 3M over just which Department discovered this. I don't know! It goes with out saying that 3M did invent and produce the Worlds First "Rare Earth" intensifying screens for X-ray. Along with this invention had to come the invention of a film that was "tuned" to the green phosphor of the Rare Earth screens. This was also a 3M First! These screen/film combinations revolutionized the industry by speeding up the system by a factor of more than 16 times.
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Last updated on 15 January 2006