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IMAGE QUALITY REVIEW

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IMAGE QUALITY REVIEW RT 244 2007 What affects DENSITY on the radiographic image? Factors Affecting mAs & Density Patient factors: size of pt., density / pathology of ... – PowerPoint PPT presentation

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Title: IMAGE QUALITY REVIEW


1
IMAGE QUALITY REVIEW
  • RT 244 2007

2
What affects DENSITYon the radiographic image?
3
Factors Affecting mAs Density
  • Patient factors
  • size of pt., density / pathology of tissue
  • kVp
  • Collimation
  • Distance
  • Grids
  • Film/Screen Combinations
  • Processing

4
Factors Affecting mAs
  • Patient factors size of pt., density of tissue,
    pt. compliance
  • kVp
  • Distance
  • Grids
  • Film/Screen Combinations
  • Processing

5
Influences technique density on image
Patients Body Habitus (size)
6
PATHOLOGY ?
7
Lung collapses No tissue in space Easy to
penetrate with x-ray photons
pneumothorax
8
LUNGCancer
9
DONT ! WE WANT YOU HEALTHY NOT SMELLY !
10
LUNG CANCER
11
Creating the Image
  • Scatter
  • Creates fog
  • Lowers contrast (more grays)
  • Increases as
  • kV increases
  • Field size increases
  • Thickness of part increases

12
Effects of collimation on scatter
13
  • Collimate to area of interest -reduces scatter
    and radiation dose to the patient

14
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

15
Grid is placedbetween patient (behind table or
upright bucky) cassetteIf placed BACWARDS CAN
CAUSE GRID ERRORS
16
GRIDS CAN LEAVE LINES ON THE IMAGE
17
DETAIL Quality How well we can see something
on the image
18
DETAIL
  • The degree of sharpness in an objects borders
    and structural details.
  • How clear the object looks on the radiograph

19
Recorded Detail
  • The degree of sharpness in an objects borders
    and structural details.
  • Other names
  • -sharpness of detail
  • -definition
  • -resolution
  • -degree of noise

20
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)

21
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)

22
Factors that affect the detail of an image
23
Factors that affectRecorded Detail
  • Geometric unsharpness
  • OID SID SIZE SHAPE
  • Motion unsharpness (blurring)
  • Intensifying Screens
  • Film Speed / Compostion
  • Film Screen contact
  • Kvp Mas (density / visibility)

24
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

25
GEOMETRIC QUALITIES
  • DETAIL
  • DISTORTION
  • MAGNIFICATION

26
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27
RESOLUTION TEST TOOLS
LINE PAIRS/ MM Depits how well you can see the
differences in structures More linesmore detail
28
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29
  • POOR
  • DETAIL
  • GOOD DETAIL

30
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

31
Decrease Motion Unsharpness
  • Instruct patient not to move or breath
  • Use Immobilization devices
  • Use Short exposure times
  • Lock equipment in place

32
Blurring of image due to patient movement during
exposure.
33
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36
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

37
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

38
The position of the tube (SID) to IR
Will influence how the structures appear on the
image The farther away the less magnified
?SID ? MAGNIFICATION
39
SID
  • Shine a flashlight on a 3-D object, shadow
    borders will appear fuzzy
  • -On a radiograph called Penumbra
  • Penumbra (fuzziness) obscures true border umbra
  • Farther the flashlight from object sharper
    borders. Same with radiography.

40
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41
OIDObject 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

42
The position of the structure in the body will
influence how magnified it will be seen on the
image The farther away the more magnified
43
Focal spot size determined by filament in
cathode surface area used at anode
44
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45
Distortion
  • Misrepresentation of the true size or shape of an
    object
  • -MAGNIFICATION (size distortion)
  • -TRUE DISTORTION (shape distortion)

46
MAGNIFICATION
  • TUBE CLOSE TO THE PART (SID)
  • PART FAR FROM THE CASSETTE (OID)

47
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48
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49
In terms of recorded detail and magnification,
the best image is produced with a small OID and a
large SID.
50
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51
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52
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53
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54
40 SID VS 72 SID
55
MAGNIFICATION PROBLEMS
  • SID
  • SOD
  • SID OID SOD

56
Size Distortion SID
  • Major influences SID OID
  • As SID ?, magnification ?
  • Standardized SIDs allow radiologist to assume
    certain amt. of magnification factors are present
  • Must note deviations from standard SID

57
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

58
A goodB C shape distortion
(elongation of part)
59
D E shape distortion (foreshortening of
part)
60
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

61
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

62
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63
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64
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65
Elongation Foreshortened Normal
66
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67
Distortion (x-ray beam not centered over object
film)
Distortion (object film not parallel)
68
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 beams periphery travel at an
    angle
  • When central ray in angled, image shape is
    distorted.

69
Distortion of multiple objects in same image
(right) due to x-ray beam not being centered over
objects.
70
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.

71
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

72
Factors Affecting mAs
  • Patient factors size of pt., density of tissue,
    pt. compliance
  • kVp
  • Distance
  • Grids
  • Film/Screen Combinations
  • Processing

73
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

74
ANODE
ANODE
75
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76
THE SMALLER THE BEAM TOWARDS THE PATIENT - THE
BETTER THE DETAIL OF THE IMAGE PRODUCED
77
FOCAL SPOT ANGLE
SMALLER ANGLE SMALLER BEAM AT
PATIENT
78
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79
REVIEWIntensifying Screensand Film
80
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

81
Fast screen vs Slower screen
82
QUANTUM MOTTLE Not enough PHOTONS can create a
mottled or grainy image - MORE COMMON IN CR
SYSTEMS
83
SAME TECHNIQUE CHANGE IN SCREEN SPEED
SLOWER FASTER
84
CASSETTES with Intensifying
Screens
  • The CASSETTE holds the film in a light tight
    container
  • It consist of front and back intensifying screens

85
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)

86
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89
Intensifying Screens
  • Located inside the cassette (film holder)
  • Contains Phosphors
  • Calcium Tungstate
  • Blue to purple light
  • Rare Earth
  • Green Ultraviolet light

90
CHANGING CR SPEED
91
F/S SPEED CHANGES
92
CR SPEED CLASS
93
WIDER LATITUDE DYNAMIC RANGE WITH CR
94
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96
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

97
Tight contact needed between film screens
98
WIRE MESHSCREEN CONTACT TEST
99
When there is a space between the contact of the
film to the intensifying screens, a larger amount
of light is allowed to reach the film causing
more density on fim
100
Lack of contact between film and cassette can
cause blurring of the image
101
LOADING FILM IN CASSETTE
102
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

103
PARALLAX each emulsion has an imagesingle
image overlaped
edges edge sharp
less sharp
104
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

105
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)

106
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

107
Goal Produce Optimal Images for diagnosis
108
Too dark too light
Out of focus good image
109
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