Radiographic Film DMI 50B Kyle Thornton

Some History Photography began before x-rays were discovered Certain silver compounds react to light making image production possible These images could be made permanent by treatment with certain chemicals This phenomenon was applied to x-ray procedures

More History In 1812, silhouettes were recorded on glass plates In 1819, the solvent action of sodium thiosulfate on silver chloride was discovered In 1839, the phenomenon of development was discovered by Louis Daguerre One year later, it was discovered that treating exposed silver chloride paper with sodium chloride would make the image permanent

Even More History By the time x-rays were discovered, photography was already an art Photographic film with a nitrocellulose base was already being marketed by George Eastman The first x-rays were recorded on glass plates These were coated with emulsion on one side only The exposure dose was quite high Glass plates were used up until WWI

And, Finally During WWI, nitrocelluose based film was found to be a more feasable choice for recording x-rays This film was single-emulsion It was later discovered that double-emulsion responded to x-rays faster The flaw with nitrocellulose-based film was its easy flammability In 1924, cellulose acetate replaced the nitrocellulose based film

Modern Radiographic Film Components Transparent base Provides a surface and support for the emulsion It must have strength, but be flexible Most film bases are composed of polyester This can withstand higher temperatures and is more fireproof The base is usually tinted blue to reduce light glare The amount of tint varies per specifications of different manufacturers

Modern Radiographic Film Components Emulsion Layer This is the active layer It contains fine crystals of silver bromide These crystals are evenly dispersed into a gelatin Silver bromide is made by dissolving silver metal in nitric acid creating silver nitrate This is then combined with potassium bromide creating silver bromide The gelatin acts as a suspension agent and prevents the crystals from adhering to one another

Film Construction

Latent Image Formation Remnant radiation interacts with the silver halide crystals Mainly by the photoelectric interaction The energy deposited into the film is in the same pattern as the subject that was exposed to radiation This invisible image is known as the latent image

The Manifest Image By chemically processing the latent image it is made visible Certain chemicals permanently fixate the image onto the film Crystals that were not irradiated will be removed from the film during processing These areas will remain clear

Film Characteristics Spectral matching Matching color sensitive film to the screen that emits that color Speed The sensitivity of film to light Influencing factors:  Emulsion thickness  Crystal size and dispersion Contrast The difference between two adjacent densities Film displays high or low contrast characteristics

Crystal Size and Dispersion

Film Characteristics Detail The sharpness of the image The degree to which the smallest structural lines of anatomy can be recorded Depends on grain size The use of screens also affect detail Latitude The range of exposure techniques that will produce an acceptable image Inversely proportional to contrast Crossover Light emitted from each screen crossing over the film base Reduced by an anticrossover layer and tabular grain emulsions

Crossover

Comparison of Low and High Contrast

Silver Halide Crystals

Comparison of Visibility of Detail Between Speeds

Film Resolution Tests – It’s all about the number of line pairs/mm

The Exposure/Development Process

The Reciprocity Law Exposure = Intensity X Time A certain amount of radiation in a certain amount of time will expose film This law can fail with screen film Usually with short or long exposures Increasing technique can overcome reciprocity law failure

Safelights Lamps with colored filters that do not expose the film but allow sufficient light for sight A 15 watt bulb is used no closer than 5 feet from the work surface An amber filter can be used for blue-sensitive film only A red filter must be used for green-sensitive film Also can be used for blue-sensitive film

Film Handling and Storage Each of the following can have a negative effect upon film contrast Improper handling  Causes artifacts Heat and humidity  Too much humidity can cause the emulsion to swell  Too little humidity can cause static to develop  Too much heat can fog film Light and radiation  Exposure to each can fog film decreasing contrast Shelf life  Film loses speed, contrast and begins to fog with age

Film Types Direct Exposure Used without intensifying screens Used mainly for extremities, previously for mammography Requires 10 – 100 times more the exposure dose The emulsion is thicker than screen film Renders excellent detail

Direct Exposure Image – Enjoy the Resolution

Film Types Mammography Film Single emulsion Fine grain Video Film Exposes images displayed on a video monitor Can format to present up to 16 images on one film

Film Types Laser film Uses a laser printer Provides excellent image quality Sensitive to red light Must be processed in complete darkness Duplication film Single emulsion film Used for producing copies of radiographs

Film Types Subtraction film A type of single emulsion film used with angiography One type prepares a positive copy of the image The other type enhances subject contrast and detail

Film Types Cine film Used with cardiac catheterization Produced in 16 and 35mm sizes Also used for radiography of the esophagus Spot film Produced in 70 and 105mm sizes Used in fluoroscopy with a spot film camera