Radiographic Film

DMI 50BKyle Thornton

Some History

Photography began before x-rays were discoveredCertain silver compounds react to light making image production possibleThese images could be made permanent by treatment with certain chemicalsThis 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 artPhotographic film with a nitrocellulose base was already being marketed by George EastmanThe first x-rays were recorded on glass platesThese were coated with emulsion on one side onlyThe exposure dose was quite highGlass plates were used up until WWI

And, Finally

During WWI, nitrocelluose based film was found to be a more feasable choice for recording x-raysThis film was single-emulsionIt was later discovered that double-emulsion responded to x-rays fasterThe flaw with nitrocellulose-based film was its easy flammabilityIn 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 crystalsMainly by the photoelectric interactionThe energy deposited into the film is in the same pattern as the subject that was exposed to radiationThis invisible image is known as the latent image

The Manifest Image

By chemically processing the latent image it is made visibleCertain chemicals permanently fixate the image onto the filmCrystals that were not irradiated will be removed from the film during processingThese 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 TimeA certain amount of radiation in a certain amount of time will expose filmThis 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 sightA 15 watt bulb is used no closer than 5 feet from the work surfaceAn amber filter can be used for blue-sensitive film onlyA 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