1. Technical Aspects: the machine the image
LeeAnn Pack DVM

4. Exposure settings: 4 components
kVp
mAs
Time
Focal film distance (FFD)
All can be changed alone or in combination

5. Make it just right Make a film more black Make a film less black
Increase the kVp, mAs or time
Decrease the FFD
Make a film less black
Decrease the kVp, mAs or time
Increase the FFD

6. Questions to Ponder Is there adequate penetration of the part imaged?
How much contrast is needed on the film (some inherent?)?
Is motion a strong possibility during the exposure?
Does the tube move?

7. Inverse Square Law
Decrease distance by ½ intensity is increased by 4 times
Increase distance by ½ intensity is increased by 4 times
Technical applications
Radiation safety

8. Cassettes Contain single or double screen Plastic, cardboard, metal
Must be durable
Film placed between the screens in the cassette
Foam between cassette and screen
Keeps out unwanted light

10. Intensifying Screens Absorb X ray photons and convert them to light
Reduces amount of radiation needed
Contain phosphors
Calcium tungstate  blue light
Rare earth phosphors  green light
More efficient

11. Screen Speed
Determined by the efficiency of X ray absorption and conversion
Thicker phosphor layer and larger crystal produce a greater amount of light  faster
Slow  detail   photonsresolution
Medium  par  average
Fast less resolution but not as many photons needed

12. Screen Speed/Resolution
100,200,400,800
Smaller number being a slower high resolution screen and the higher numbers are a faster screen
Screen speed and resolution are inversely proportional

14. Screen Cleaning Keep free of debris Sharp white artifact
Screen cleaner
Soft lint free cloth
Never use soap and water
Stand on end to dry

15. Radiographic Film Composition Base supports the emulsion – blue
Adhesive – base to emulsion
Emulsion – gelatin with silver halide crystals which is sensitive to radiation
Protective coat protects from damage during handlin and processing

17. Radiographic Films Single or double emulsion Light sensitivity
Film speed
Film speed is inversely related to exposure needed to produce a given degree of blackness
50 speed is half as fast as a 100 speed

18. Radiographic Film Film latitude
Range of exposures which can be used to achieve an acceptable film density
Wide range = high latitude
Image contrast suffers
Narrow range = low latitude
Good image contrast

19. Radiographic Density Subject density Over exposed = film to black
Additive – thick parts absorb more
Summation – know definition
Relative
What are the surroundings?
Silhouette sign – know definition
Over exposed = film to black
Under exposed = film not black enough

20. Factors that affect film density
Subject density – we cant change this
mAs – biggest factor
kVp – increases the penetrability
Distance – ISL
Development time and temp
Scatter and fog

21. Radiographic Contrast
Difference of densities of the different parts on the image
Subject contrast
Film contrast
Scatter and fog

22. Turn that dial: Density
The rule
kVp by 20% will double film density
kVp by 16% will half film density
Double mAs  double density
Half mAs  half density
Combos:
Inc kVp by 20% and dec mAs by half
Dec kVp by 16% and double mAs

23. Contrast Short scale  lot of contrast few grey
High mAs and low kVp
Long scale  many shades of grey
Low mAs and high kVp
Low contrast = long scale = high latitude = low mAs = high kVp
High contrast = short scale = low latitude = high mAs = high kVp

24. Magnification Enlargement of the image relative to the actual size
Causes loss of detail and blurring
Subject film distance
Dec SFD  decreases magnification
Focal film distance
Inc FFD  decreases magnification

25. Distortion Image which does not represent the true shape of the object
Unequal projection of an object
Femurs
Location of an object within the beam
spine

26. Scatter radiation What is scatter? Scatter increases with:
Bounce around undergo numerous interactions
Scatter increases with:
Increased thickness of the patient
Increased X ray beam energy
Amount of patient exposed (collimate)

27. Beam Limiting Devices
Smaller fields = less scatter and less radiation expsoure
Cones, cylinders, shuttered collimators
They do not shape the beam only exclude the part we don’t want to use
Light to illuminate field

29. Filtration Inherent Added Polychromatic beam Reduces patient dose
Glass housing, oil and tub housing window
Filter only low energy photons
Added
Aluminum filter
Will not remove the high energy photons
Polychromatic beam
Reduces patient dose

30. Grids Used to keep scatter from hitting film
Perpendicular radiation gets through, off angle photons do not
Used on parts > 10-11cm
Film contrast is improved
Required more X ray exposure

31. Grid ratio Height of lead strips:width between the strips
The higher the GR, the greater the ability of the grid to remove scatter
4:1 – 16:1
Lines per inch
Good and bad

33. Grid Cutoff
Grid must be precisely under the center of the central ray of the X ray beam along the central axis of the grid
Know what the types of grid cutoff look like
Bucky-Potter moving grid

34. Fog Light fog Storage fog Safelight fog Chemical fog