RADT W4 Xray Films and Radiation Characteristics

What are the 4 components of a Dental X-ray Film?

1. Film base → provides support for emulsion and strength

2. Adhesive Layer → attaches emulsion to the base

3. Film Emulsion → radiation absorption layer

4. Protective layer → protects emulsion from damage

What colour is the film base? Why?

Slight blue tint which is necessary for xray image quality

What does the film emulsion consists of? What is the fx of each?

Gelatin → suspense the crystals over the film base so film processing solution can react with crystals

Silver Halide Crystals → Absorbs radiation during x-ray exposure and store energy from radiation

*Halide is sensitive to light or radiation

Define Latent Image

Latent image is the invisible image on the emulsion that is formed from the stored energy within the silver halide crystals

What are the 3 types of dental x-ray films?

1. Intraoral → PA, BW, Occlusal

2. Extraoral → Pano, Cephalometric

3. Duplicating

When are Size 3 films used for BW?

For adults posterior teeth when 8’s are present

Describe Occlusal films

• Largest intraoral film

• 4x size 2

• Used to examine the max and mand arch.

Film speed is determined by…(3)

1. Size of silver halide crystals

2. Thickness of Emulsion

3. Radiosensitive dyes

Larger crystals = faster film

faster film = less radiation exposure

What are the 6 components of the Intraoral Film Packet?

1. Identification dot → on the film

2. Paper film wrapper → surrounds film and helps protect film from light

3. Lead Foil → found behind the film shielding film from scatter which results in FILM FOG

4. Outerpackage wrapping → vinyl or paper wrapper; protects film from light and saliva

5. Tube side → solid white and has ID dot

6. Label Side → flap used to open the film packet

What are the 2 types of Extraoral Film Type?

1. Screen films

2. Nonscreen films

Describe Screen films

• need a screen for exposure

• place between 2 special intensifying screens in a cassette

• Less radiation required to exposure film

Describe the Intensifying screens of Screen Films

• Smooth plastic sheet coated with tiny fluorescent crystals (phosphors)

• Phosphors emit blue/green light when exposed to x-rays

How are Nonscreen Films different to Screen films? Why are they not used in dentistry?

• Nonscreen films do not require intensifying screen for exposure.

• Film is directly expoused to xrays

• Emulsion on the film is sensitive to x-rays rather than fluorescent light

Not used in dentistry because it requires more exposure time vs screen films

Why is the cassette important for Screen Films?

They are light-tight allowing sharper images to be produced

What are duplicating films?

Duplicating film is a specialized type of X-ray film used to create exact copies of original radiographs (X-ray images).

• films may need to be duplicated for insurance companies, referrals to specialists, teaching aid, etc.

The emulsion side of a duplicated film must be…

contacting the radiograph during duplicating process.

• There is only one emulsion side on duplicating films.

How should unexposed films be stored?

50-70F, cool dry place

What controls the QUALITY of the central ray?

kVp = kilovoltage peak

higher kvp = more penetrating power, shorter wavelength

kV regulates speed and energy of electrons

What is the kVp range used in dental radiography?

65-100 kV

60-70 kV for digital

higher kV is used for areas that are thick or dense

Density of a radiograph is affected whenebver there is a change in …?

kVp or mA, and exposure time.

• higher kVp/mA = increased density = darker films.

• more electrons = darker films

Define Contrast in relation to Radiography

Contrast is how sharply dark and light areas are differentiated or separated on an image.

• aka difference in density

• low kVp = high contrast = black and white

• high kVp = low contrast = many shades of grey

Exposure time is measured in ___ rather than in ___. Why?

measured in impulses rather than a continuous stream

• because xrays are created in a series of bursts

• 1 impulse every 1/60th of a second =60 impulses per second

• inverse relationship w kVp

ex. if kVp decreases, exposure time increases

How do we increase the amount of electrons ?

increasing mA = increase temperature = more electrons released from cathode

mA range 7-15 mA

What is the relationship between mA and exposure time?

inversely related

• if mA increases , expsure time decreases

What are the 4 distances thaat must be taken into consideration when exposing a dental radiograph?

1. Target-Surface distance → distance between xray source and client skin

2. Target-object distance → distance between xray source and tooth

3. Target-Receptor distance → distance between xray source and film receptor

4. Object-film distance → distance between object and the film

If the distance between the xray tube ____ the intensity of the xray beam decreases. What is the name of this relationship?

increases; more distance, less intense

Inverse Square Law = relationship between distance and intensity

• think of a flashlight on a wall

What is the definition of Inverse sqaure law.

The intensity of the radiation is inversely proportional to the SQUARE of the distance from the source of radiation

Formula:

original intensity/new intensity = new distance²/original distance ²

How do we reduce the intensity of the xray beam?

with a half-value layer = aluminum filter

• placed in the path of the beam inside tube head to filter out the less penetrating, long wavelength radiation.