1. Unit 4 Radiographic Exposures Chapters: 32,19,20&22

2. Objectives
Compare various exposure systems and their advantages and disadvantages and how they work to obtain radiographic images.
Describe how AEC systems operate.
Describe how to develop a technique chart and how to use them in the clinical setting.
List and label on a diagram the components of radiographic film and intensifying screens.
Discuss film and screen handling, storage and artifacts.
Explain the steps in the processing procedure.
Describe two types of luminescence.

3. Chapter 32
Exposure Systems

4. Goals/ Purpose of Exposure Systems
Maintain a method of consistency for quality image production
Preprogramming of control panel based on exposure factors
Suggestions of starting points
Reduce repeat rates
Work as part of departmental quality assurance program

5. How they work Based on part thickness
Radiographer must measure part thickness for complete accuracy
Calipers – device used to measure body parts from central ray entrance to exit points

6. Types of exposure systems
Fixed kVp
Variable kVp
Anatomically programmed radiography systems

7. 1. Fixed Kilovoltage Systems
Developed by Fuchs in 1943 during WWII
Advantages:
Decrease patient dose
Provide more information on the image
Increase consistency of IR exposure
Lengthen exposure latitude
Reduce tube wear
Decrease time settings

9. 2. Variable Kilovoltage Systems
Proposed by Jerman in 1925
Advantages:
Permit small changes in exposure to compensate for variable body part thickness
2 kVp for every 1 cm tissue thickness
Produce higher contrast images
Enhance visibility of fine detail and perception of resolution

10. 3. Anatomically Programmed Radiography Systems
Completely computerized control units that combine AEC ( automatic exposure control) with anatomical procedures
Advantages:
Provides choice of anatomical procedures and suggested exposures
Can be modified but professional judgment must be used
mAs selection is eliminated

11. Creating an exposure control chart
Exposures of phantoms with optimal center of acceptance curve
Show images to radiologist to determine which images they prefer
Create technique chart for selected system used
Variable or fixed
Perform phantom testing
Perform clinical trials
Fine tune
Continue fine tuning as needed

12. AEC Systems AKA: Phototiming
Permit various combinations of ionization chambers
Usually 3 chambers- 2 outer , 1 center
Ionization Chamber- serve to measure the exposure to the receptor
Permit user to select mA and kVp- chambers eliminate TIME only
Permit density controls- -3 , -2, -1, 0, 1, 2, 3
Atomically add or subtract density
Used when part can’t be positioned properly over chamber
Should not be used to compensate for part thickness

13. Disadvantages Part must be aligned perfectly with chamber
Can cause under or over exposure if part not centered correctly

14. Back-up timers
Back up time ( max exposure) should be set to prevent overexposure
Should be set at 150% of the anticipated manual exposure
Laws regulate AEC shut off at 600mAs above 50 kVp and 2,000 mAs below 50kVp
When backup time is to short , underexposure will happen

15. Chapter 19 Radiographic Film

16. Terms Analog- image recorded on radiographic film
Aerial Image -x-ray beam that exits the patient that carries information about tissues and densities. Aerial image will be put on film to record the information
Latent image- the invisible image that exists on the film after the film has been exposed but before it has been processed
Manifest- the observable image that is formed when the latent image undergoes proper chemical processing- the visible image

17. Components of Film: Base
originally consisted of glass plate ex: flat plate abdomen
Must be flexible for handling- but tough enough and rigid to put on a viewbox and go through a processor
Must be uniformly lucent ( light can be transmitted without any additional artifacts being added)
1960’s- now made of polyester plastic
Blue dye added to tint film to reduce eyestrain for the radiologist
Magenta dye- to improve detail

18. Components of Film: Adhesive
Applied to the base material before emulsion
Acts as a “glue” to put emulsion and base together to prevent bubbles or other distortion when film is handled, processed, wet and heated

19. Components of Film: Emulsion
Consists of a gelatin, in which silver halide crystals are suspended
Gelatin purpose:
Neutral material that allows chemicals to react with silver halide
Distributes silver crystal evenly over film- no clumping
Gelatin must be clear to allow light to go through it
Must be flexible to allow bending without distorting the image
Silver halide crystals ( grains)
Silver bromide 95-98% of crystals
Silver iodide
Silver chloride
Removed during processing so light can get through film for viewing
Has an antihalation coating applied to back of film ( light absorbing coating)
Absorbs light coming from emulsion and prevents back scatter and visible light from degrading the image

20. Emulsion – cont’d 1. Double Emulsion ( double coated)
AKA: Duplitized
All film utilized in the Bucky- most film for diagnostic radiology
2. Single Emulsion ( coating on one side)
Duplicating film ( copy film)
Fine detail film ( extremity)
Mammography

21. Components of Film: Supercoat
Layer of hard, protective gelatin
Prevents soft emulsion from being damaged by scratches, oil form hands, stacking the film
Makes it very hard to tear a radiograph
Staples and paperclips can damage the supercoat( scratches)
Reports go in separate file
Don’t paperclip requests to radiographs

22. Construction of Silver Bromide Crystals
All manufacturing of film takes place in total darkness
During manufacturing, silver nitrate and potassium bromide are combined in gelatin
Crystals are flat and somewhat triangular in shape
1 cubic mm in film emulsion contains over half billion crystals

23. Sensitivity Specks ( sensitization specks)
Silver sulfide or gold silver sulfide is added to each crystal
Development center of crystal
“Gurney and Mott theory” states that sensitivity specks are essential to the image formation process
Crystal usually contain :
1 or more sensitivity specks
Silver atoms
Bromide ions
Iodide ions
During exposure, photoelectrons and silver ions are attracted to these sensitivity specs, where they combine to form a latent image center of metallic silver

24. Latent Image Formation
“photographic effect” “ Gurney & Mott theory”
Latent image- image produced by the interaction of x-rays with the emulsion of a radiographic film prior to development
The process of ionizing silver and bromide ions having the ( +) cluster around the (-) speck to acquire an image
1. x-ray or light photon form intensifying screens interacts with a bromide or iodine ion in a crystal
2. An electron from the ion is ejected and is attracted to and trapped by a sensitivity speck
3. Speck becomes negatively charged
4. Negative charged speck attracts a positive silver ion inside the crystal and speck becomes neutralized
5. Process is repeated until clump of silver atoms becomes deposited at the speck
In the processor crystals convert to black metallic silver

25. Types of Film Direct exposure film ( nonscreen film )
Used in cardboard cassette- no screens
Thicker emulsion with more silver content ( 2-3 x thicker that screen film)
Rarely used due to high dose
Screen film ( intensifying screen film)
Used in a cassette with an intensifying screen
Thin emulsion- very sensitive to light of screens
Less radiation- less dose
Allows for shorter exposure times

26. Film Storage and Handling
If not performed properly, can be huge expense to dept
Age of film
has expiration date
Can be fogged over time
Use film with oldest exp date first
Heat
Store in cool/dry place (Moisture can cause water artifacts)
680 or lower
Humidity
Between %
Too low-dry- static marks
Too high- wet – water marks
Light
Light and moisture proof package
Film is twice as sensitive after exposure
Low intensity (7-15 watt) dark red light or orange-brown filter
Safe lights should be installed no closer than 4 feet from working are and feed tray

27. Film Storage and Handling-cont’d
Ionization radiation
Film storage should be lead-lined
Handling
Store on end- not flat ( pressure marks)
Don’t remove film quickly from box- abrasions , static
Careful handling when loading and unloading cassettes
Don’t slide onto feed tray
Chemical fumes:
Can cause film fog
Should not store film near cleaning solutions , formaldehyde, or other strong chemicals

28. Film Flasher
Used to put identification on film prior to processing

29. Chapter 20
Film Processing

30. Four Primary Steps
1. Developing 2. Fixing 3. Washing 4. Drying

31. Developing 1st step in wet process
Black Silver Halide is deposited at the latent image sites and image become visible
F for 90 sec
Primary agents
Two Reducing agents
Activator
Restrainer
Preservative
Hardener
and water as a solvent
Only solution that is effected by contamination
Can be caused by evaporation, splashing, improper cleaning and filling

32. Fixing Removes undeveloped silver halides from emulsion
Permanently “fixes” them image before exposure to light for viewing
Primary Agent
Clearing agent
Activator
Preservative
Hardener
Water as a solvent

33. Archiving- Washing and Drying
Protects from deterioration by chemicals, fading and physical forces
Washing
removes as much of the developer and fixer as possible- warm water is best but 3-5 lower than other chemicals
Chemicals can cause damage over time
Silver stains and yellowing
Drying
Final stage F
Shrinks and seals emulsion

34. Silver Recovery
Silver halide crystals that are removed during fixer time is recycled
Silver is more valuable after processing than before- 10 % of the purchase price can be recovered

35. Artifacts Guide shoe marks Entrance roller marks- Pi lines
occur when the guide shoes in the turnaround assembly of the processor are sprung or improperly positioned
Entrance roller marks-
occur if roller is wet / damp from cleaning
Pi lines
occur at intervals because of dirt or a chemical stain on a roller.
Roller marks
Dirty or warped rollers can cause emulsion pick-off & gelatin buildup. Artifacts appear as sharp areas of ↑ or ↓OD
Chemical fog
looks like light or radiation fog & is usually a uniform dull gray
Wet Pressure Sensitization
produced in the developer tank. Irregular or dirty rollers cause pressure during development & produce small circular patterns of ↑ OD.

36. Chapter 22 Intensifying Screens and Film/Screen Combination

37. Cassettes
Film holders use to protect film from light before, during and after the exam
It creates a light-proof case for the film to utilize the intensifying screens to their best advantage
Construction
Aluminum and stainless steel frame or plastic frame
Front- uniformly radiolucent to eliminate artifacts
Back is usually colored side with a hinge opening- latch
Have lead foil in back to absorb excess radiation to prevent back scattering and fogging
Intensifying screens will be mounted inside the front and back of the cassette.
Should be mounted on a foam pressure pad to provide good contact between screens and film

38. Intensifying Screens
Location- inside the cassette, one on each side fro double emulsion film
Purpose- when making an exposure, screens convert x-ray energy to light.
Screen will emit a Luminescence
Formation of the latent image
From 98-99% of the light of the intensifying screens
1-2 % formed directly from x-rays striking the film
Inventor- Thomas Edison 1896

39. BASE
Made of polyester plastic 1 mm thick- previously made of cardboard and metal
Acts as a support for the active layer of the screen
Characteristics:
Rugged, tough and flexible
Moisture resistant
Not damaged by radiation
Will not discolor with age or exposure to air
Chemically inert so that it will not interfere with the phosphor layer and interfere with the conversion of x-rays to light
Cannot obtain impurities that would be imaged by x-rays : uniformly radiolucent

40. Reflective Layer Located between the phosphor and base layers
Made of magnesium oxide or titanium dioxide
25 micrometers thick
Purpose is to reflect light towards the film, which increases the efficiency of the screen
Can help to reflect twice as much light towards the film- helps to create latent image and reduce dose to pt.
Layer may have a dye incorporated into it, which absorbs longer wavelength light that would decrease detail on the film

41. Phosphor layer The active layer of the screen
micrometers thick, depending on the speed of the screen
Contains phosphors which are materials that absorb x-ray energy and emit ligh photons

42. Protective coating Protective coating for screen
Made of protective plastic or cellulose
25 micrometers thick
Purpose is to protect the phosphor layer from abrasions and stains during the loading and unloading of films
repeated trauma to screens, such as scratches, can remove this coating
Removal of phosphors in next layer can cause white line artifacts from no exposure
Coating must be transparent to light, so the phosphor light reaches the film to make an image
Provides a surface that is durable enough to tolerate cleaning
Helps prevent production of static electricity

43. Phosphor Characteristics
High atomic number
Will increase the probability of an x-ray interaction, called quantum detection efficiency ( DQE)
High atomic number is needed to permit photoelectric and Compton interactions
Conversion efficiency
The ability of the phosphor to emit as much light per x-ray photon interaction as possible
As conversion efficiency increases, pt dose decrease- fewer x-rays are needed to make image

44. Phosphor Characteristics
3. Spectral Emission
An indication of the precise wavelength of light emitted by the phosphor
Spectral emission should match the sensitivity of the film to obtain the maximum latent image formation
4. Luminescence
The ability of a material to emit light
Screen image will represent the aerial image ( exit radiation from pt) in the form of light
When x-rays hit phosphor in screen:
Parts that are better penetrated in body will be brighter on screen
Results in darker areas; more exposure in these areas on radiograph

45. Types of Luminescence
Fluorescence: light emitted promptly after x-rays strike the crystal
Instantaneous emission
Occurs within seconds
Phosphorescence
Delayed emission of light
After x-ray has dissipated, phosphor continues to emit light for a period of time
Known as “ screen lag” or “ afterglow”
Occurs after seconds
if this occurs, the film may be removed before the latent image is completely formed
If another film is loaded immediately in the cassette, it may be faintly exposed to a previous image
This type of luminescence is more common in older screens and in fluoroscopic screens

46. Luminescence – Cont’d
Maximum fluorescence and minimal phosphorescence is ideal for screens
Normal life of a screen is 5-7 years
As screens age their phosphors decrease in activity
Recommended that all screens in a department get replaced simultaneously so all phosphor activity level will be the same.

47. Calcium Tungstate vs Rare Earth Screens
used by Thomas Edison & considered one of the best phosphors until the late 1970s
conversion efficiency of approximately 5 % (5% of x-ray energy is converted to light energy)
emits blue light - need blue-sensitive film to match

48. Calcium Tungstate vs Rare Earth Screens
infrequently found in nature and these elements are more difficult to separate from the earth & most have atomic numbers between 57-71
conversion efficiency of approximately 20 % (4 times more efficient than calcium tungstate phosphors)
have the advantage of having fast speed but retaining good detail
more expensive than calcium tungstate
require less exposure to obtain a given density; therefore, pt dose is decreased
less exposure will lengthen the life of the x-ray tube
mostly emits green light, although some rare earths are blue-emitters
different speed levels like calcium tungstate
Each level is approximately twice as fast as a similar calcium tungstate screen but detail is not lost

49. Screen Speed
Definition - the ratio of the exposure needed to produce a density on a film using screens compared to the exposure required to produce the density without screens
also known as the relative speed, intensifying factor or intensification factor

50. Factors determining screen speed
Intrinsic factors
factors built into the screen; under the control of the manufacturer (inherent)
1. Phosphor conversion efficiency
how well the phosphor can absorb photons
how well the phosphor converts the absorbed energy to light
rare earth (20%), calcium tungstate (5%) rare earth more efficient
screen efficiency
The ability of light emitted by the phosphor to escape the screen & expose a film (a typical screen will absorb 50 % of the light; the other 50 % will expose the film)

51. Factors determining screen speed
2. Thickness of active layer (layer of crystals)
the thicker the layer, the faster the screen
more crystals are available in a thicker layer; therefore, more light is emitted
thicker layers produce more blur on the image due to light spread
3. Size of phosphor crystal (just like film)
the larger the crystals, the faster the screen
more light is emitted due to the crystal receiving more photons
larger crystals increase screen efficiency (will scatter less light within the active layer)

52. Factors determining screen speed
4 Reflectance of backing of screen
the more light that is reflected from the backing to the active layer, the faster the screen
5. Presence of dyes in reflecting layer
dyes help reduce the amount of scattering long wavelength light photons
dyes will increase detail
dyes will decrease speed
6. Concentration of phosphor crystals
the higher the concentration of crystals in an area, the higher the screen speed

53. Factors determining screen speed
Extrinsic factors
conditions under which screens are used; under the control (somewhat) of the technologist
1. Temperature
as room temperature increases (over 1000 F), screen speed decreases and film speed increases (technique should be increased)
screens emit more light at lower temperatures, so technique would need to be decreased
only of concern in extreme climates or outdoor radiography

54. Factors determining screen speed
2. Kilovoltage
an increase in kVp will cause an increase in some screen speeds
phosphors have high atomic numbers, so higher kVps can increase the probability of light production from the phosphors

55. Screen Speed Classifications
Intensification factor system
exposure without screens compared to exposure with screens
Descriptive rating system
“Slow” speed
Fine detail, high resolution
Requires more rad’n to get a given density
Best detail next to using a cardboard cassette holder
“Medium” speed
Par speed, average or universal speed
“High” speed
Fast speed, most blur
Small amount of rad’n required to get a given density on a film

56. Relative speed number system (RS)
Fine detail RS (less than 100)
Medium detail RS
High speed RS (more than 100)

57. Screen Contact
If film-screen contact is not perfect, blurring of structures will occur. This is due to light diverging out instead of being projected straight down to the film.
test used is the “wire mesh test”
film-screen contact is usually better in smaller cassettes, where the screens are more uniformly compressed compared to larger cassettes

58. Causes of poor film-screen contact:
1. Warped cassette front 2. Cracked/twisted cassette frame 3. Loose, bent or broken hinges or latches 4. Presence of a foreign body under a screen 5. Worn contact felt 6. Warped screens due to excessive moisture

59. References sheet for all documents
Care of Screens
1. Keep cassette closed except when loading/unloading and cleaning.
2. Use screen cleaner with soft gauze pads; cleaner is also “antistatic”.
3. Some manufacturers recommend soap and tap water because cleaners can wear out the screens.
4. Do not dig the film out with finger nails.
5. Clean screens often depending on use; dusty environments, such as construction areas will require more cleaning, whereas 1-3 months may suffice for regular use.
6. Let screens dry thoroughly before loading with film; film could leave a permanent stain on the screen due to purple dye in film.
7. Fingernail polish, including clear coats, should not be worn when handling film or screens because permanent marks can be left on the screens; if screen cleaner and isopropyl alcohol do not remove the stain, the screen is ruined; will show up as a white streak on image.
References sheet for all documents

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