Image quality Flashcards
1
Q
recap: define density
A
- degree of blackening of image
2
Q
recap: density influenced by (5)
A
- mAs
- kV
- distance
- filtration
- scatter radiation
3
Q
recap: define contrast
A
- degree of diff in density btw 2 areas
4
Q
recap: contrast influenced by (3)
A
- kV
- filtration
- scatter radiation
5
Q
recap: define detail (sharpness)
A
- degree of sharpness of recorded lines on image
6
Q
recap: detail influenced by (4)
A
- distance
- focal spot size
- motion
- magnification
7
Q
recap: define distortion
A
- deviation of image of the true shape of object
8
Q
recap: distortion influenced by (2)
A
- positioning
- magnification
9
Q
recap: define artefacts
A
- appearance on film that is not normally present on film
- prod by artificial means
10
Q
recap: artefacts influenced by (3)
A
- external objects
- equipment
- processing
11
Q
xray beam: ways of xrays entering patient (3)
A
- absorbed
- scattered
- transmitted
12
Q
xray beam: exit radiation
A
- combo of transmitted + scattered radiation
13
Q
xray beam: type of radiation leaving patient in og trajectory? and prod?
A
- transmitted radiation
- prod diagnostic image
14
Q
scatter radiation: define
A
- secondary radiation emitted from interaction of xrays w matter
15
Q
scatter radiation: general features
A
- generally lower in energy
- changes direction
- no useful info for radiographic image
16
Q
scatter radiation: reflected scatter will (2)
A
- may be reflected off surrounding objects
- source of exposure to personnel
17
Q
scatter radiation: effect
A
- lead to reduction in radiation contrast
- increased density
18
Q
scatter radiation: best time to remove scatter
A
- before reaching image receptor
- greatly improve image contrast
19
Q
scatter radiation: solutions (3) before hitting receptor
A
- collimators
- grids
- air gap technique
20
Q
scatter radiation: list factors increasing scatter (3)
A
- size of object
- xray beam energy
- field size
21
Q
scatter radiation: features- size of object
A
- increase in tissue thickness increase amount of scatter = more possible interactions
22
Q
scatter radiation: features- xray beam energy
A
- the higher the energy (higher kV) = more scatter
- lower energy beams more likely to be absorbed vs. scattered
23
Q
scatter radiation: features- field size
A
- larger field sizes = more scatter
- more possible interactions
24
Q
scatter radiation: name (3) beam restricting devices
A
- collimators
- diaphragms
- cones
25
scatter radiation: features- beam restricting devices (3)
- restrict field size to area of interest
- limit patient exposure in unnecessary areas
- improve image contrast by decreasing scatter
26
scatter radiation: collimators
- present on all xray machines
- defines size, shape of 1˚ xray beam
- light beam outlines area of exposure
27
scatter radiation: diaphragms
- added to collimator: further limit exposed area
| - diaphragm changes rectangular shape -> circle (at point of exit of xray beam)
28
scatter radiation: cones
- added to collimator: further limit exposed area
| - cone brings point of exit of xray beam closer to patient (limit to circular shape= more effective at limiting scatter)
29
scatter radiation: pros of diaphragms/cones
- good for spot views where improved image contrast is necessary
30
grids: general features and comprised of
- dev by Bucky 1913 for greater image contrast
- modern grid: series of lead strips (grid material: radiopaque) alternated w plastic/Al strips (interspace material: radiolucent)
- reduces amount scatter radiation within exit radiation reaching film
31
grids: designed for
- allowing passage of transmitted radiation (xrays in straight direction from source)
- scattered xrays absorbed by grid matter
32
grids: improves?
- radiographic contrast
| - reduce scatter radiation
33
grids: cons- (3)
- absorbs portion of transmitted ('useful') radiation, reduced xray quantity and density
- grid lines prod in film, lessens diagnostic value of image
- may be prone to grid cut off
34
grids: cons- absorbed transmitted radiation solution
- maintain optical density: mAs increased = higher patient dose
35
grids: cons- grid lines prod in film lessening diagnostic value solution
- moving grid overcomes this
36
grids: cons- grid cut off solution
- needs to be correctly positioned w respect to image receptor
- centre of xray should be centre of grid
37
grids: grid cut off features
- undesirable absorption of 1˚ rays by grid
| - misalignment of transmitted beam, lead strips increases progressively toward edges of grid
38
bucky: features
- grid placed in front of bucky, in front of image receptor
39
grid ratio: determines? and depends on
- determines amount of scatter radiation removed by grid
| - depends on height of grid strip and distance btw grid strips
40
grid ratio: the higher the grid ratio? effectiveness
- more effective cleaning up scatter
| - angle of scatter allowed less than lower ratios
41
grid ratio: higher grid ratio- gap size?
- smaller gap btw strips/ increased height of strips
42
grid ratio: needs increased/decreased mAs? to maintain density
- need increased mAs (higher patient dose)
43
grid ratio: define
- ratio of height of lead strips to dist btw lead strips (thickness of interspace)
44
grid ratio: formula
GR = h/D
| height, dist
45
grid ratio: typical range
from 5:1 - 16:1
46
grid ratio: cons
- while removing scatter is difficult to align properly
47
grid freq: define
- no. of lead strips per cm
48
grid freq: higher grid freq means? (2)
- thinner strips
| - less visible on radiographic image
49
grid freq: assoc w higher/lower grid ratio and better at?
- assoc higher grid ratio
- higher patient dose
- better reduction of scatter radiation
50
grid freq: typical range
24 - 80 lines/cm
51
bucky (grid) factor: features
- how much scatter removed by grid
| - technical factors adjusted to prod same optical density
52
bucky (grid) factor: scatter?
- accounts for sig portion of density of final radiograph
53
bucky (grid) factor: compensation
- increase exposure when removing scatter
| - compensates for decreased xrays hitting image receptor
54
bucky (grid) factor: B?
- ratio of mAs required w grid to mAs w/o grid
| = prod same optical density
55
bucky (grid) factor: B formula
mAs (grid) ÷ mAs (without grid)
56
bucky (grid) factor: always greater than?
1
57
bucky (grid) factor: typical range
3 - 5
58
bucky (grid) factor: the higher bucky factor, the higher?
higher grid ratio and freq
59
linear parallel grids: consists of
- parallel strips
60
linear parallel grids: effect
- high ˚ of grid cutoff (esp outer edges due to diverging xrays)
61
linear parallel grids: define grid cut off
- undesirable absorption of transmitted rays by grid
62
linear parallel grids: cut off features
- misalignment of transmitted beam + lead strips increases progressively towards edges of grid
- cut off at periphery (both sides)
63
linear parallel grids: cut off reduced by?
- increasing SID
| - less divergence of xray beam
64
linear parallel grids: tilted cut off
- xray beam not perpendicular to grid
- poor tube positioning
- cut of one half of image
65
linear focus grids: features
- grid material aligned to coincide w diverging beam
- allows less grid cut off, more expensive to prod
- take care when positioning grid compared to xray tube (due to geometric limitations)
- intended dist and side must face xray tube marked on grid (when backwards = extreme grid cutoff)
66
linear focus grids: cut off
- when correctly positioned: no cut off
| - incorrect SID: falls outside focal range of grid
67
cross parallel grids: features
- as parallel only clean up scatter one direction, crossed overcomes this
- 2 linear grids perpendicularly opposed
68
cross parallel grids: pros
- efficient scatter cleanup
- improves contrast
- positioning critical
69
cross parallel grids: central beam?
- central beam must coincide w centre of grid
70
cross parallel grids: can u use angle techniques?
- no
| - due to grid cutoff
71
crossed focused grids: features
- 2 linear focused grids opposed
72
crossed focused grids: need? (3)
- central beam positioned correctly
- correct dist
- correct placement of grid in bucky
73
moving/reciprocating grids: features
- reduces grid lines on image (grid vibrated during exposure
- heard as audible 'rattle'
- grid moved by bucky
74
air gap technique: features (2)
- alt method for reducing scatter grid
| - uses increased OID
75
air gap technique: approx gap used
10 - 15cm
76
air gap technique: used in eg.
- lateral cervical spine radiographs
| - shape of normal anatomy
77
air gap technique: cons
- increased magnification, focal spot blur
78
air gap technique: to maintain same optical density?
- increased mAs
79
air gap technique: increased mAs same as using what grid?
8:1 grid
80
image detail: define
- degree of sharpness of recorded lines on image
| - smallest separation of 2 lines/edges that can be recognised as separate objects on image
81
image detail: define spatial resolution
- quantification of image detail
| - measured: line pairs/mm
82
image detail: decreased image detail assoc w high/low contrast
- low contrast
83
image detail: features penumbra aka
- area of decreased image detail
| - aka geometric unsharpness
84
image detail: affected by (2)
- blur
| - magnification
85
image detail: blur factors (3)
- focal spot size
- distance
- motion
86
image detail: magnification factors (1)
- distance
87
focal spot: features
- xrays not emitted from point, rather from rectangular-shaped focal spot
- most xray tubes have 2 focal spot sizes
88
focal spot: changing spot size (w constant kV and mAs) does not change (2)
- xray quality or quantity
89
focal spot: does limit?
- limits max possible xray quantity
90
focal spot: sml/lrg spot used for normal imaging? features (2)
- lrg spot
- allows sufficient mAs for denser body parts
- assoc w decreased image detail
91
focal spot: sml/lrg spot used for fine detail imaging? and features (3)
- sml spot
- areas don't need v high mAs to penetrate
- able to get improved image detail
- extremity radiography
92
focal spot blur: combo
- combo of xray beam, rectangular size of focal spot = focal spot blur
93
focal spot blur: larger the focal spot, more/less focal spot blur?
- more spot blur
94
focal spot blur: most vital factor for?
- spatial resolution
95
focal spot blur: eg. poor resolution (less detail) w smaller/larger focal spot
- larger focal spot
96
anode heel effect: features
- angles anode prod xray beam w more intensity on cathode side
97
anode heel effect: why less intense on anode side?
- xrays running parallel to anode angulation absorbed by anode, giving decreased intensity
98
anode heel effect: focal spot blur greater on anode/cathode side xray tube?
- cathode
| - decreased xrays on anode side -> smaller effective focal spot, less blur
99
focal spot blur: divergence of beam (interacting w object) will increase/decrease when increase SOD (source to image dist)?
- divergence decreases w increased SOD
100
focal spot blur: increasing SOD increase/decrease focal spot blur
- will decrease spot blur
101
focal spot blur: SOD increased/decreased by increasing SID?
- increased SID (source to image dist)
102
focal spot blur: divergence of transmitted radiation (exiting from an object) will increase/decrease when increase OID (object to image dist)?
- divergence increases w increased OID
103
focal spot blur: decreasing OID will increase/decrease focal spot blur?
- decrease spot blur
104
focal spot blur: increased/decreased SOD by increasing SID?
- increased SOD (?)
105
focal spot blur: decreased by- list (4)
- smaller focal spot
- larger SID (larger SOD): if change SID need to consider image density affected
- smaller OID (larger SOD)
- anode side of tube
106
motion blur: define and is major cause of?
- blur caused by patient moving during xray exposure
| - one of major causes: repeat radiographs
107
reducing motion blur: list (2)
- time
| - stabilisation
108
reducing motion blur: time and controls what movement?
- shortest possible exposure times
| - controls for involuntary movement of heart and lungs
109
reducing motion blur: stabilisation and controls what movement?
- restrict patient motion by instrument, restraining device
| - controls for voluntary movement
110
linear tomography: features
- xray tube deliberately moved during exposure time while image receptor is moved in opp direction
- used to blur structures on either side of plane of interest (see slice of subject vs. structures superimposed)
- position of fulcrum determines object plane
111
linear tomography: greater angle = the thicker/thinner slice
- thinner the slice
112
magnification: define
- enlargement of object on resultant image
113
magnification: due to
- divergence of xray beam
114
magnification: measured by?
- magnification factor (MF)
| - ratio of image size to object size
115
magnification: formula
MF = i ÷ O
image size : object size
116
magnification: magnification of 1 means?
- same size as object
117
magnification: MF is also proportional to? (when object size is unknown helpful)
- SID to OID
118
magnification: MF formula using SID, OID
MF = SID ÷ SID-OID
119
magnification: how to minimise
- min divergence of beam:
- larger SID
- smaller OID
120
magnification: at 100cm MF approx?
1.1
121
magnification: at 180cm MF approx?
1.05
122
magnification: formula to find size of og object (O) using image (i), SID, OID
O = i(SID-OID) ÷ SID
123
decreased image detail assoc w: list (7)
- decreased SID
- decreased SOD
- increased OID
- increased focal spot size
- cathode side of xray tube
- increased motion
- increased magnification
124
distortion: define
- unequal magnification of diff portions of same object
125
distortion: depends on (3)
object:
- thickness
- position
- shape
126
distortion: object thickness
- thicker = more distortion
127
distortion: object position- depends on
- depends on relative position of object, image receptor, central xray beam
128
distortion: object position- (2) eg.
- object plane vs image plane not parallel (increased OID in some areas)
- objects positioned off central ray beam (more xray divergence)
129
distortion: object position- shape distortion? (2)
- elongation
| - foreshortening
130
distortion: object position- patient positioning
- important to prevent distortion and magnification as possible
131
distortion: object shape
- irregular objects produce irregular distortion
132
image assessment: check (5)
- contrast
- density
- detail
- distortion
- artefacts
