Chapter 9 Film Film Holders Film Xray film
- Slides: 21
Chapter 9 Film & Film Holders
Film X-ray film consists of a transparent, blue -tinted base (cellulose acetate with 3% nitrocellulose), covered on both sides with an emulsion composed of gelatin containing silver bromide, silver chloride & silver iodide (halides). n There is a thin gelatin protective layer over the emulsion. n Today polyester plastic is the base used for the film. n
Types of Film n There are four types of film that are used in radiography. n They are: Dental Film Photoflourographic Film Non-screen Film Screen Film
Dental Film n Small, lightweight & packaged in cardboard/plastic holders. n Also used in radiographic badges to determine the amount of x-ray exposure technicians receive. n People are allowed 5 rads/rems per year.
Photoflourographic Film n This is the film used in cameras to take pictures of a fluoroscopic screen (barium study). n It comes in rolls & is green or blue light sensitive. n It has emulsion on only one side. n It is used for mass screening as in the army.
Non-screen Film This is sensitive to x-rays but not to light. n They are used mainly in extremity xrays because thicker body parts would require too much x-ray exposure n We use extremity cassettes now instead of this film type n Screens are used in cassettes with intensifying screens, because cardboard holders do not produce light. n
Non-screen Film n If we put non-screen film in a cassette with intensifying screens, there would be some x-ray penetration, but not enough to give a good image. n The light from the screen would have no effect upon this type of film.
Screen Films n Only film used for x-rays of the spine. n It is sensitive to the light produced by the screens, but not to x-rays directly. n Intensifying screens allow 40 times less patient exposure.
Screen Films n Remember: X-rays hit the crystals in the intensifying screens, the crystals phosphoresce & emit light & the light exposes the film.
Film Holders n. Types: Cardboard Cassettes
Cardboard Holders Black cardboard envelopes that hold the film during the exposure. n Non-screen film is used in these holders. n The holder has a tube side so that we can expose the film correctly. n The back side of the holder has a lead sheet in it to prevent scatter from bouncing off the table and double exposing the film. n
Cardboard Holders n These are used for extremities only. n Nothing greater than 10 cm in thickness n The same rule as with the grid, any thing greater than 10 cm we need a grid to prevent scatter. n Remember that extremity cassettes are available today rather than cardboard holders.
Cassettes Light tight holders made of hinged metal & bakelight frames that hold the film during exposures, with intensifying screens inside. n Intensifying screens are coated with Ca++ tungstate which glows when exposed to x -rays, which in turn exposes the film. n Today Gadolinium & Lanthanum are used instead of Ca++ tungstate ( Rare earth screens) n
Cassettes n Gadolinium& Lanthanum are rare earth crystals that are more sensitive to x-ray & give off more light, thereby reducing patient exposure further. n intensifying screens are located on both sides of the cassette, so the film is sandwiched between the screens.
Cassettes n The tube side screen is thinner than the back side to allow less absorption of the x-rays, allowing more rays to hit the screen on the other side, increasing the exposure to the film. n Screens come in a variety of speeds, depending upon the size & number of crystals.
Cassettes n Larger crystals & thicker layers make faster screens but cause a loss of sharpness due to increased light spread. n We put dye in screens now that help decrease the spread of light. n Small crystals & less layers result in the best film quality.
Cleaning n Mild soap solution and a wad of cotton is best. n Make sure your screens are clean to increase film quality. n Screens cost about $600. 00 to replace.
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