1. Dr Mohamed El Safwany, MD.
IMAGE QUALITY REVIEW
Dr Mohamed El Safwany, MD.

2. Intended learning outcome
The student should learn at the end of this lecture radiological image quality review .

3. What affects DENSITY on the radiographic image?

4. Factors Affecting mAs & Density
Patient factors:
size of pt., density / pathology of tissue
kVp
Collimation
Distance
Grids
Film/Screen Combinations
Processing

5. Influences technique & density on image
Patient’s Body Habitus (size)
Influences technique & density on image

6. Creating the Image Scatter Creates fog Lowers contrast (more grays)
Increases as
kV increases
Field size increases
Thickness of part increases

7. Effects of collimation on scatter

8. Collimate to area of interest -reduces scatter and radiation dose to the patient

9. Grids
A device with lead strips that is placed between the patient and the cassette
Used on larger body parts to reduce the number of scattering photons from reaching the image

10. Grid is placed between patient (behind table or upright bucky) & cassette If placed BACWARDS CAN CAUSE GRID ERRORS

11. GRIDS CAN LEAVE LINES ON THE IMAGE

12. Recorded Detail
The degree of sharpness in an object’s borders and structural details.
Other names:
-sharpness of detail
-definition
-resolution
-degree of noise

13. 2 principal characteristics of any image are Spatial & Contrast Resolution
Spatial resolution
Resolution is the ability to image two separate objects and visually distinguish one from the other
Spatial resolution is the ability to image small objects that have high subject contrast (eg. bone-soft tissue interface, calcified lung nodules)

14. 2 principal characteristics of any image are Spatial & Contrast Resolution
Spatial resolution
Determined by focal-spot size and other factors that contribute to blur
Diagnostic x-ray has excellent spatial resolution. It is measured in line pairs per mm. (CT measured in cm)

15. Factors that affect the detail of an image

16. 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

17. GEOMETRIC QUALITIES
DETAIL
DISTORTION
MAGNIFICATION

19. POOR
DETAIL
GOOD DETAIL

20. 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

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

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

23. 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.
*See page 74 in your book

25. 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.
*See page 74 in your book

26. Focal spot size – determined by filament in cathode & surface area used at anode

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

29. MAGNIFICATION TUBE CLOSE TO THE PART (SID)
PART FAR FROM THE CASSETTE (OID)

34. 40” SID VS 72” SID

35. 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

36. A = good B & C = shape distortion (elongation of part)

37. D & E = shape distortion (foreshortening of part)

38. 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

39. Image Distortion
When the part to be imaged – does not lay parallel with the IR (cassette)
If the Central Ray is not perpendicular to the part

43. Elongation Foreshortened Normal

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

46. 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.

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

48. 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.

49. 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

50. Factors Affecting mAs
Patient factors: size of pt., density of tissue, pt. compliance
kVp
Distance
Grids
Film/Screen Combinations
Processing

51. 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
*See page 73 in your book

52. ANODE
ANODE

54. THE SMALLER THE BEAM TOWARDS THE PATIENT - THE BETTER THE DETAIL OF THE IMAGE PRODUCED

55. FOCAL SPOT ANGLE
SMALLER ANGLE – SMALLER BEAM AT PATIENT

57. REVIEW Intensifying Screens and Film

58. “Fast” Screen Cassettes
Equipment used can contribute to image unsharpness
Fast film/screen combinations = decrease in image sharpness
Slower film/screen combinations = increase in image sharpness

59. Fast screen vs Slower screen

60. SAME TECHNIQUE CHANGE IN SCREEN SPEED
SLOWER FASTER

61. CASSETTES with Intensifying Screens
The CASSETTE holds the film in a light tight container
It consist of front and back intensifying screens

62. Intensfying screens Lower patient dose (less photons needed)
Changes resolution of image
Slow screens less LIGHT = better detail
Faster – less detail (more blurring on edges)

63. 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

64. Tight contact needed between film & screens

65. Lack of contact between film and cassette can cause “blurring” of the image

66. LOADING FILM IN CASSETTE

67. 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

68. Film Characteristics (more in week 9)
Film contains silver halide crystals
2 layers – emulsion & base
emulsion thickness determine speed of film and degree of resolution
Speed – the response to photons
Resolution – the detail seen

69. 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)

70. Processing Film (wk 10) Film contains silver crystals
If crystals exposed to photons – will convert to black after placed in processing chemicals
If not exposed – will remain clear on film

71. Goal : Produce Optimal Images for diagnosis

73. Text Book David Sutton’s Radiology
Clark’s Radiographic positioning and techniques

74. Assignment
Two students will be selected for assignment.

75. Question
Define motion unsharpness?

76. Thank You