1. Components of Radiographic Image Quality
Radiologic Technology 244
created: Fall 2005
Rev

2. Review handouts

3. Main Factors Affecting Recorded Detail
kVp & mAs
Technique Selection (Time)
Motion
Object Unsharpness
Focal Spot Size
SID (Source to Image Distance)
OID (Object to Image Distance)
Material Unsharpness/ Film Screen
Combo

4. Factors that affect Recorded Detail
Geometric unsharpness
OID SID SIZE SHAPE
Motion unsharpness (blurring)
Intensifying Screens
Film Speed / Composition
Film – Screen contact
Kvp & Mas (density / visibility)

5. GEOMETRIC QUALITIES
DETAIL
DISTORTION
MAGNIFICATION

6. The degree of sharpness in an object’s borders and structural details.
How “clear” the object looks on the radiograph

7. Recorded Detail Other names: -sharpness of detail -definition
-resolution
-degree of noise

8. What are these
What does they
measure?

11. Factors Affecting DENSITY
PATIENT THICKNESS,PATHOLOGY
MAS & KVP
SID

14. POOR
DETAIL
GOOD DETAIL

15. Motion Can be voluntary or involuntary
Best controlled by short exposure times
Use of careful instructions to the pt.
Suspension of pt. respiration
Immobilization devices

17. Decrease Motion Unsharpness
Instruct patient not to move or breath
Use Immobilization devices
Use Short exposure times
Lock equipment in place

18. NAME 4 CAUSES

19. Blurring of image due to patient movement during exposure.

20. Focal Spot Size Smaller x-ray beam width will produce a sharper image.
Fine detail = small focal spot (i.e. small bones)
General radiography uses large focal spot
Beam from penlight size flashlight vs. flood light beam

24. FOCAL SPOT ANGLE

25. Object Unsharpness
Main problem is trying to image a 3-D object on a 2-D film.
Human body is not straight edges and sharp angles.
We must compensate for object unsharpness with factors we can control: focal spot size, SID & OID

27. SID Source to Image Distance
The greater the distance between the source of the x-ray (tube) and the image receptor (cassette), the greater the image sharpness.
Standard distance = 40 in. most exams
Exception = Chest radiography 72 in.

28. SID
Shine a flashlight on a 3-D object, shadow borders will appear “fuzzy”
On a radiograph it’s called ______________
A true border – _____
Farther the flashlight from object = sharper borders. Same with radiography.

29. OID Object to Image Distance
The closer the object to the film, the sharper the detail.
OID , penumbra , sharpness 
OID , penumbra , sharpness 
Structures located deep in the body, radiographer must know how to position to get the object closest to the film.

31. Distortion Misrepresentation of the true size or shape of an object
MAGNIFICATION (size distortion)
TRUE DISTORTION (shape distortion)

32. Shape Distortion Misrepresentation of the shape of an object
Controlled by alignment of the beam, part (object), & image receptor
Influences: Central ray angulation & body part rotation

36. Elongation Foreshortened Normal

38. Distortion (x-ray beam not centered over object & film)
Distortion (object & film not parallel)

39. Central Ray Radiation beam diverges from the tube in a pyramid shape.
Photons in the center travel along a straight line – central ray
Photons along the beam’s periphery travel at an angle
When central ray in angled, image shape is distorted.

40. Distortion of multiple objects in same image (right) due to x-ray beam not being centered over objects.

41. Central Ray Angulation
Body parts are not always 90 degrees from one another
Central ray angulation is used to demonstrate certain details that can be hidden by superimposed body parts.
Body part rotation or obliquing the body can also help visualize superimposed anatomy.
NAME 3 EXAMPLES

42. MAGNIFICATION caused by:
TUBE CLOSE TO THE PART (↓SID)
PART FAR FROM THE CASSETTE
(↑ OID)
Compensate for MAG : ↑ OID by ↑ SID =
“increase SID 7” for every 1” OID”

43. Size Distortion & SID Major influences: SID & OID
As SID , magnification 
Standardized SID’s allow radiologist to assume certain amt. of magnification factors are present
Must note deviations from standard SID

45. In terms of recorded detail and magnification, the best image is produced with a small OID and a large SID.

46. What can be done to improve the detail with a large OID?

47. Use a smaller FS

48. 40” SID VS 72” SID

50. Size Distortion & OID
If source is kept constant, OID will affect magnification
As OID , magnification 
The farther the object is from the film, the more magnification

51. How can it be measured?

52. Measuring % of Magnification
SID
SOD

53. Measuring % of Magnification
What is the % of mag when you have a 72” SID and
4” OID?
DO the math…………

54. Material Unsharpness
Equipment used can contribute to image unsharpness
Fast film/screen combinations = decrease in image sharpness
Slower film/screen combinations = increase in image sharpness

55. Intensifying screens Lower patient dose Changes resolution of image
slow screens less LIGHT = better detail
Faster – less detail (more blurring on edges)

57. Intensifying Screens: Review
Located inside the cassette (film holder)
Calcium Tungstate
Blue to purple light
Rare Earth
Green & Ultraviolet light

58. POOR SCREEN CONTACT
FOAM BACKING HELPS TO PLACE INTENSIFYING SCREENS IN DIRECT CONTACT WITH THE FILM – NO GAPS
IF GAPS – MORE LIGHT CAN BE EMITTED IN SPACE, CAUSING THE IMAGE TO BE OF POOR DETAIL

60. WIRE MESH SCREEN CONTACT TEST

62. Screen Speed
Efficiency of a screen in converting x-rays to light is Screen Speed.

63. Spectral Matching (F/S)
What does it mean?
Name the two types of screen phosphors
What light spectrum do they emit?

64. Spectral Sensitivity
Film is designed to be sensitive to the color of light emitted by the intensifying screens.
Blue LIGHT– Conventional Calcium Tungstate screen
Green, Yellow-Green LIGHT
– Rare Earth screen

65. Spectral Matching (F/S systems)

66. Spectral Matching (F/S systems)
Red safe light

68. Safe lights
What wattage bulb?
Distance from counter top?

69. Review of Film Characteristics
Size of silver halide crystals & emulsion thickness determine speed of film and degree of resolution
Speed – the response to photons
Resolution – the detail seen

70. What are these
What are they made of

71. Film Speed / Crystal size
Larger crystals or Thicker crystal layer
Faster response= less detail, and
less exposure (chest x-ray)
Finer crystals / thinner crystal layer
=Slower response, greater detail, more exposure (extremity)

72. IMAGE ON FILM SINGLE EMULSION = BETTER DETAIL
DOUBLE EMULISON = LESS DETAIL
PARALLAX
With double emulsion – an image is created on both emulsions – then superimposed – slight blurring of edges

73. Extremity vs Regular cassettes

74. QUANTUM MOTTLE Film grain, or graininess, refers to the tiny black spots that make up the visible image, one grain from each silver halide crystal exposed MORE COMMON IN CR SYSTEMS NOW NOT ENOUGH PHOTONS TO CREATE IMAGE

75. Factors Affecting mAs
LIST 6 factors

76. Factors Affecting mAs
Patient factors: size of pt., density of tissue, pathology
kVp
Distance - how
Grids
Film/Screen Combinations
Processing

77. Technique /Denisty CHANGES

78. Log denisty H & D curve

79. a densitometer,
measures film blackness.
Film blackness is the relationship of the intensity of the light that hits the film from the view box (incident intensity) to the intensity of the light transmitted through the film (transmitted intensity).
These measurements plotted on a graph produce a characteristic curve. The limitations of the human eye determine the useful density range in diagnostic radiography.
The diagnostically useful range of densities is 0.25 to 2.5.
The later module on exposure calculation considers this in more detail.

80. Film latitude ? What does it mean how does it plot on the curve?

83. Main Factors Affecting Recorded Detail
kVp & mAs
Motion
Object Unsharpness
Focal Spot Size
SID (Source to Image Distance)
OID (Object to Image Distance)
Material Unsharpness/ Film Screen
Combo