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). There is a thin gelatin protective layer over the emulsion. Today polyester plastic is the base used for the film.

Types of Film There are four types of film that are used in radiography. They are: Dental Film Photoflourographic Film Non-screen Film Screen Film

Dental Film Small, lightweight & packaged in cardboard/plastic holders. Also used in radiographic badges to determine the amount of x-ray exposure technicians receive. People are allowed 5 rads/rems per year.

Photoflourographic Film This is the film used in cameras to take pictures of a fluoroscopic screen (barium study). It comes in rolls & is green or blue light sensitive. It has emulsion on only one side. It is used for mass screening as in the army.

Non-screen Film This is sensitive to x-rays but not to light. They are used mainly in extremity x-rays because the thicker body parts would require too much x-ray exposure We use extremity cassettes now instead of this film type Screens are used in cassettes with intensifying screens, because cardboard holders do not produce light.

Non-screen Film 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. The light from the screen would have no effect upon this type of film.

Screen Films Only film used for x-rays of the spine. It is sensitive to the light produced by the screens, but not to x-rays directly. Intensifying screens allow 40 times less patient exposure.

Screen Films Remember: X-rays hit the crystals in the intensifying screens, the crystals phosphoresce & emit light & the light exposes the film.

Film Holders Types: Cardboard Cassettes

Cardboard Holders Black cardboard envelopes that hold the film during the exposure. Non-screen film is used in these holders. The holder has a tube side so that we can expose the film correctly. 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.

Cardboard Holders These are used for extremities only. Nothing greater than 10 cm in thickness The same rule as with the grid, any thing greater than 10 cm we need a grid to prevent scatter. 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. Intensifying screens are coated with Ca++ tungstate which glows when exposed to x-rays, which in turn exposes the film. Today Gadolinium & Lanthanum are used instead of Ca++ tungstate ( Rare earth screens)

Cassettes Gadolinium& Lanthanum are rare earth crystals that are more sensitive to x-ray & give off more light, thereby reducing patient exposure further. intensifying screens are located on both sides of the cassette, so the film is sandwiched between the screens.

Cassettes 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. Screens come in a variety of speeds, depending upon the size & number of crystals.

Cassettes Larger crystals & thicker layers make faster screens but cause a loss of sharpness due to increased light spread. We put dye in screens now that help decrease the spread of light. Small crystals & less layers result in the best film quality.

Cleaning Mild soap solution and a wad of cotton is best. Make sure your screens are clean to increase film quality. Screens cost about $600.00 to replace.