Film

Question 1

Film Composition

Answer 1

• Inner paper
• Dental film
• Inner paper wrap
• Lead foil backing
  
  • has a spider web/ tire track pattern
  • Positioned behind the lead foil packet away from tube
  • Reduces radiation exposure to patient
  • Reduces back scatter
  • If film is positioned backward the tire track pattern will appear
• Outer package

Question 2

Inner Dental Film Composition

Answer 2

• Over coat- for protection
• Emulsion
• Base
  
  • Support emulsion
  • Fimness to handle processing
  • Flexible
• Emulsion
  
  • Main thing capturing the image
  • Contains silver halide grains
  • Vehicle
  • Dbl emulsion requires less radiation to make radiograph
• Overcoat

Question 3

Dot used for orientation

During exposure and viewing

Answer 3

• During exposure
  
  • Raised side to radiation source
  • Concave side toward tongue
• During viewing?
  
  • Convex side away
  • Concave up

Question 4

Extraoral Films

Answer 4

• Designed to be sensitive to visible light
  
  • UV light or blue light
  • Screen film placed between 2 itensifying screens

Question 5

Intensifying Screen

Answer 5

• On either side of film
• Screen absorb x-rays/photons and converts it to visible light
• Intensity of light proportional to x ray energy absorbed
• Taking 1 photon and turning it into 10-15 rays of light
• Advantage is we need less radiation
• Con is you took one signal and spread it out, less accurate
• This lowers spatial resolution bc boundaries are less defined

Question 6

How do x-rays chemically change silver halide crystals

Answer 6

• Silver bromide crystal
  
  • Sensitivity site
    
    • Physical irregularity caused by sulfur
  • Free positive silver ion
  • Photon hits bromide, ionizes it -> releases electron
  • Positive silver ion attracted to negative sensitivity site
  • Neutral atom of metallic silver is created

Question 7

Steps to develop a film

Answer 7

• Film immersed in developer
• Developer rinsed off in water bath
• Immense film in fixer
• Fixer washed in water bath
• Dry and mount for viewing

Question 8

Before and after exposure of silver bromide

What do the exposed silver bromide have

Answer 8

• Before exposure
  
  • Silver bromide crystals in emulsion
• After exposure
  
  • Exposed crystals contain neutral silver atoms at latent image

Question 9

Developer

Answer 9

• Converts silver bromide crystal to metallic silver grains
  
  • Silver is the catalyst that turns grain to metallic grain
• All or none effect
• Neutral silver in latent image site acts as catalyst
• If you left your image in developer for too long will convert all of it to metallic grain eventually

Question 10

Fixer

Answer 10

• Removes unexposed, undeveloped silver bromide crystals

Question 11

Optical Density of film

Answer 11

• Degree of darkening or oapcity of exposed film
• Measured by how much light transmitted
  
  • Light behind film initial intensity over the amount of light that travels through the film
  • If light had initial intensity of 100, and all light passed through, then 100/100=1
  • Take the log of 1= 0 optical density
  • OD 0, 100% transmitted
  • OD= 1, 10 % transmitted
  • OD=2 1% transmitted

Question 12

Film Density Factors

Answer 12

• Exposure
  
  • Increase in mA or kVp increases density
  • Bc it pushes the photons more inc permeability
  • Reducing the x-ray source to receptor distance increases the density
• Subject
  
  • Subject thickness- more attenuation with thicker subjects
  • Subject density- more attenuation with denser subjects
    
    • Dense objects= absorb x-rays=light area on film=radiopaque
    • Less dense objects=less absorption=dark=radiolucent

Question 13

Radiographic Contrast

Answer 13

• Difference in densities between light and dark region on radiograph
• High contrast= both light and dark areas
  
  • Short gray scale of contrast, few number of grays
• Low contrast= only light gray and dark gray
  
  • Long gray scale of contrast, large number of grays

Question 14

Short vs long gray scale

Answer 14

• Long scale
  
  • Low contrast image
  • Many shades of gray
  • Black and white are far from eachother
• Short scale
  
  • High contrast image
  • Black and white close to each other
• kVp affects this by changing contrast to delineate btw enamel and dentin
  
  • low kVp= higher contrast
  • High kVp- lower contrast
  • Usually set machine to 70kVp

Question 15

Radiographic speed

Answer 15

• Amount of radiation to produce an image of standard density
• Fast film requires less radiation to have density of 1
• Controlled by silver content in silver halide grains and size of the silver halide grains
• Speeds
  
  • D for faster
  • Most are E or F speed now

Question 16

Radiographic Sharpness

Answer 16

• The ability of a radiograph to define an edge precisely
  
  • Depends on size and number of silver grains in emulsion
  • Finer grain size=finer sharpness

Question 17

Radiographic Resolution

Answer 17

• Ability of a radiograph to record seperate structures that are close together
  
  • Inraoral 20 lp/mm
  • Extraoral 5 lp/mm