Spatial Resolution Flashcards
1
Q
F/S recorded detail definition
A
The sharpness of the structural LINES as recorded in the radiographic image.
2
Q
Digital radiography spatial resolution definition ASRT
A
The sharpness of the structural EDGES recorded in the image.
3
Q
What effect will the following change
Have on recorded detail:
From 100 mA to 200 mA
A
Impacts visibility of detail only
4
Q
What effect will the following change
Have on recorded detail:
Change from 0.01 sec to 0.005 sec
A
Impacts visibility of detail;
And increases sharpness if motion is an issue.
5
Q
What effect will the following change
Have on recorded detail:
60 kVp to 50 kVp
A
No change to sharpness of detail (SR)
Only impacts visibility of detail
6
Q
What effect will the following change
Have on recorded detail:
8:1 grid to no grid
A
No change to sharpness of detail.
Impacts visibility of detail
7
Q
What effect will the following change
Have on recorded detail:
2” OID to 6” OID
A
⬇️ spatial resolution
8
Q
What effect will the following change
Have on recorded detail:
Large focal spot to small focal spot
A
⬆️ spatial resolution
9
Q
What effect will the following change
Have on recorded detail:
Patient is moving
A
⬇️ spatial resolution
10
Q
What effect will the following change
Have on recorded detail:
1mAs to 2mAs without changing time
A
Impacts visibility of detail only
11
Q
What effect will the following change
Have on recorded detail:
40” SID to 72” SID
A
Increases spatial resolution/sharpness of detail
12
Q
Define Focal Spot
A
The area of the target from which X-rays are emitted.
13
Q
The size of large focal spots
A
Range from 1.2 to 2.0 mm
14
Q
Size of small focal spots
A
0.1mm to 1.0mm
15
Q
Large focal spots are generally used for mA over
A
200-300
16
Q
Define ACTUAL FOCAL SPOT
A
The area of bombardment on the target where X-rays are produced.
17
Q
Define EFFECTIVE FOCAL SPOT
A
The area projected onto the patient and the IR. The size of the focal spot is identified here.
18
Q
Define LINE FOCUS PRINCIPLE
A
A design feature whereby the anode is angled, so that the effective focal spot is smaller that the actual focal spot.
19
Q
What is the function of the line focus principle
A
Improve detail
Improve heat capacity
20
Q
Diagnostic X-ray tubes have anode angles ranging from
A
5-17 degrees
21
Q
What is the one disadvantage of the line focus principle?
A
The Heel Effect/Anode Heel Effect
22
Q
Describe the Heel Effect
A
Because of the divergent beam, a portion of the useful beam, emitted towards the anode side of the tube is absorbed by the heel of the anode.
Thus there is reduced X-ray intensity on the anode side of the tube.
This difference can vary as much as 45%.
This can be useful when imaging body parts with uneven thickness. Positioning the cathode over the thicker part of the anatomy provides more uniform density.
23
Q
Extra focal radiation results when
A
Electrons bounce off the focal spot and land on other areas of the target generating X-rays outside of the focal spot
24
Q
Focal Spot Blooming is not constant. It broadens or blooms with: (3)
A
- Age and use
- Large mAs
- Decreasing kVp
25
How does large mAs influence fs blooming
Increase current to the cathode filament causes increased heat.
The hotter the filament, the larger the space charge, so the effective focal spot broadens. (Try to use lowest mA possible).
26
How does decreasing kVp influence f/s blooming
At lower kVps, the electrons flowing from the cathode to the anode tend to stray since the potential difference is not as great.
They hit a wider area of the anode and enlarge the effective focal spot.
27
Name Focal Spot QC tests
1. Pinhole camera
2. Resolution Test patterns: - star pattern resolution test
- line pattern test
28
The line-focus principle allows
High anode heating with small effective focal spots.
29
As the target angle decreases, what happens to the effective focal spot
Decreases
30
How can we purposely distort anatomy
Angle tube
| Oblique pt
31
To minimize distortion we can
Put part parallel to IR
32
What feature of X-ray equipment helps us minimize distortion
Detent
33
Two types of distortion we use in X-ray
Elongation
| Foreshortening
34
What does "distortion of position" mean
Where you place part under CR and angled.
35
How does a ⬇️ in OID effect MF
Decrease
36
How does ⬆️SID effect MF
Decrease
37
Spatial resolution means
Visibility and Sharpness
38
Factors that influence visibility
```
Are not IR specific
Contrast
Grid
Scatter
kVp
mAs
```
39
Factors that influence Sharpness
IR
Physical factors
Geometric factors
Motion
40
How can we control the physical factors influencing sharpness
We need to control motion:
1. Give good pt instruction
2. Immobilization
3. Short exposure time
41
Visibility means the image is in
Diagnostically useful range; density and contrast
42
Visibility factors for film screen IR
1. Intensifying screen type and speed
2. Film type and speed
3. Processing time and temperature
43
Digital IR visibility factors
Indirect IR
Direct IR
Processing
44
Film screen IR sharpness factors
Intensifying screen type and speed
Film type and speed
F/s contact
45
Digital IR sharpness factors
Indirect DR
Direct DR
Matrix size
Pixel size
46
If the matrix size increases, the pixel size
Decreases
47
⬆️matrix size gives
⬆️ resolution (sharpness only)
48
The type and speed of CR
| Influence
Visibility and Sharpness
49
How does the CR reader influence sharpness
The smaller the pinpoint of the laser, the better the sharpness
50
Why does direct DR influence visibility
Because there are no phosphors, so no spreading of light.
51
3 geometric factors influencing sharpness
OID
SID
Focal spot size
52
⬆️ OID with ? Sharpness
⬇️ sharpness
53
⬇️ SID will ? Sharpness
⬆️ sharpness
54
⬆️ Focal spot size ? Sharpness
⬇️ sharpness
55
As focal spot decreases, what happens to geometric blur and to sharpness
Geometric blur decreases
| Sharpness increases
56
Which side of the image has more blur
The cathode side bc of the focal spot angle
57
If there is inherent OID due to anatomy, we repair it by
Increasing SID
58
Distortion
Misrepresentation of the size and shape of an object
59
Magnification is desirable, when?
When we are looking for borders of tiny areas
| Like in mammo for smooth or rough borders
60
With size distortion, we increase OID, which will --resolution
Decrease
61
Shape distortion is good when?
ImAging a 3-D object because the image is 2-D
We angle the tube
Or
Oblique part
62
Can distortion be totally avoided?
No bc anatomy is 3-D and image is 2-D
63
The further away the OID, how does it change the image size
Larger is the image size
64
Magnification Factor
How much bigger the image is, compared to the object.
65
3 qualities of an X-ray beam
1. Heterogenous divergent beam- spreads out through distance.
2. Heterogenous- made up of a variety of different energies
3. Randomly distributed- the X-ray photons come down in a random pattern.
66
Similar triangles mean
The 2 angles are the same size.
67
If you want to magnify an object 2 times,
put it 1/2 way in the SID
68
The decrease magnification:
Decrease OID
| Increase SID
69
Radiographic image quality
The accuracy that the anatomy being examined, is shown on the radiograph.
70
High quality radiograph
Precisely reproduces structure and tissues.
71
Spatial resolution
The ability to image small objects that have high subject contrast.
Such as bone-soft tissue interface
A breast micro calcification
Calcified lung nodule
72
Screen-film radiography has---spatial resolution.
Excellent
73
Spatial resolution --- as blur decreases
Improves
74
Spatial resolution aka
Detail
| Recorded detail
75
Visibility of detail refers to
The ability to visualize recorded detail when image contrast and optical density (OD) are optimized.
76
How does the speed of the image receptor influence spatial resolution
As IR speed increases:
Spatial resolution decreases
(High noise)
77
⬇️ IR speed will -- spatial resolution
⬆️ spatial resolution
78
What are FILM FACTORS that affect f/s radiographic quality
Characteristic curve:
1. Density
2. Contrast
3. Speed
4. Latitude
Processing:
1. Time
2. Temperature
79
What are GEOMETRIC FACTORS that affect f/s radiographic quality
1. Distortion
2. Magnification
3. Blur
80
What are SUBJECT FACTORS that affect f/s radiographic quality
Contrast:
1. Thickness
2. Density
3. Atomic number
Motion
81
As f/s development time ⬆️
Fog ⬆️
IR speed ⬆️
Spatial resolution ⬇️
Visibility ⬇️
82
As f/s development temperature ⬆️
Fog⬆️
IR speed ⬆️
Visibility and spatial resolution ⬇️
83
As OID ⬇️
Sharpness ⬆️
| SR
84
As SID ⬆️
Sharpness (SR) ⬆️
85
3 geometric factors that affect radiographic quality
Magnification
Distortion
Focal-spot blur
86
All images are larger than the object. This is a condition called
Magnification
87
Quantitatively, magnification is expressed by the
Magnification factor
88
Magnification Factor =
```
ImAge Size/ Object Size
Or
SID / SOD
OR
IMAGE SIZE/OBJECT SIZE=SID/SOD
```
89
2 factors that affect image magnification
SID
| OID
90
To minimize magnification
Large SID
| small OID
91
Shape distortion define
Unequal magnification of different portions of the same object
92
3 conditions contribute to image distortion
Object: thickness
Position
Shape
93
How does object thickness affect distortion
With a thick object, OID⬆️
So
Thick objects are more distorted.
94
The image is not distorted if the object plane and the image plane are
Parallel
95
The image is not distorted if the object plane and the image plane are
Parallel
96
How do you increase the amount of foreshortening; extent of reduction in image size
Increase the inclination of angle will increase foreshortening
97
What is the most important factor for determining spatial resolution
Focal-spot blur
98
Focal spot blur is small when
The OID is small
99
The focal-spot blur is small on the ---side and large on the ---side of the image.
Anode
| Cathode
100
How do you increase the amount of foreshortening; extent of reduction in image size
Increase the inclination of angle will increase foreshortening
101
What is the most important factor for determining spatial resolution
Focal-spot blur
102
Focal spot blur is small when
The OID is small
103
The focal-spot blur is small on the ---side and large on the ---side of the image.
Anode
| Cathode
104
Reduce motion blur by
Restrict pt motion
Use shortest exposure
Time possible
105
Small focal spots are used when?
1. For fine detail
2. For magnification studies
3. For extremities
106
Detail describes
The sharpness of appearance of small structures on the radiograph.
107
Sharpness of image detail refers to
The structural lines or borders of tissues in the image and the amount of blur of the image.
108
Factors that generally control the sharpness of image detail:3
Focal spot size
SID
OID
109
Sharpness of image detail is influenced by
Type of intensifying screen
Presence
Of motion
110
Key factors that provide the best visibility of image detail
Collimation
Grids
Other methods that prevent scatter
111
Distortion can be minimized by 3
Proper tube alignment
Proper part alignment
Proper IR alignment
112
What effect will the following change
Have on recorded detail:
2" OID to 6" OID
⬇️ spatial resolution
113
Resolution
Measure of the ability of a system to image 2 separate objects and visually distinguish one from another
114
In electronic imaging as digital image matrix size increases
Pixel size decreases
115
Pixel depth is directly related to shades of gray, called?
| And is measured in?
Dynamic range
| Bits
116
The greater the number of bits, the more?
Shades of gray
117
Is pixel depth related to resolution
No
118
A digital image is formed by a
Matrix of pixels in rows and columns
119
Field of view
Used to describe how much of the patient is included in the matrix
120
SID affects recorded detail in which way
1. Directly related
| 2. As SID increase, recorded detail increases
121
Why don't we always use an large SID?
Because it would require a higher radiation dose to the patient.
122
How does field size affect detail visibility
Because it decreases scatter radiation produced, it will result in improved detail visibility
123
Which has better partial resolution, F/S or CR?
Film Screen has three times better spatial resolution than CR.
124
4 acceptable ways to minimize motion unsharpness
1. Use shortest possible exposure time
2. Accurate patient instructions
3. Suspended respiration
4. Immobilization
125
Subject / object unsharpness can result from ? Name 3
1. Object shape does not coincide/conform with the shape of x-ray beam.
2. Object plane is not parallel wth x-ray tube and / or IR
3. Anatomic object is a distance from the IR
126
As matrix size increase, spatial resolution
Improves / increases
127
How does the size of the PSP affect spatial resolution?
Smaller phosphor size improves resolution, because there will be less spreading of light.
128
How does the size of the scanner laser affect spatial resolution
The smaller the laser beam, the better the spatial resolution
129
As FOV increases, how does it affect the pixels of a fixed matrix size? And affect the spatial resolution?
Size of each pixel increases.
| The spatial resolution decreases.
130
For the same FOV,spatial resolution will be improved using?
A larger matrix
131
If matrix size increases, and fixed FOV, than pixel size will
Decrease, and better spatial resolution
132
```
All the following are related to recorded detail except:
mA
Focal spot size
SID
OID
```
mA
133
Focal Spot blur is greatest towards the ---- end of the beam?
Cathode end
134
Focal spot blur / geometric blur is caused by
Photons emerging from a large focal spot.
135
Factors that determine recorded detail in digital imaging include? 3.
1. Motion
2. Geometric Factors (OID, SID, and focal spot size)
3. Spatial resolution
136
In analog systems, spatial resolution is related to the?
Speed of the system/ intensifying screen speed
137
The spatial resolution of direct digital system is?
Fixed
Related to the detector element (DEL) size of the thin film transistor (TFT).
Smaller DEL SIZE, better resolution
138
DEL size of 200 in general radiography provides a spatial resolution of
2.5 lp/mm
139
A 100 speed intensifying screen system offers a spatial resolution of
10 lp/mm
140
How is OID related to recorded detail?
Inversely
| As OID increases the detail decreases; magnification increases
141
In digital imaging as DEL sizes decreases, spatial resolution
Increases
142
Recorded detail is inversely related to
1. SID
2. OID
3. Part motion
OID
| Part motion
143
Does mAs affect recorded detail
No
144
What are the geometric factors that influence recorded detail
Focal spot
OID
SID
145
In film screen imaging spatial resolution is related to the
Speed of the imaging system / intensifying screen speed
146
The spatial resolution of direct digital systems is related to
Detector element size of the thin film transistor
147
When involuntary motion must be considered, the exposure time may be cut in half if the kilovoltage is?
Increased by 15%
148
The greatest enemy of resolution
Motion
149
Focal spot blur is related to
Focal spot size
150
Which focal spot size produce less Blur and better resolution
Smaller focal spots
151
What term is used to describe unsharp edges of tiny radiographic details
Geometric Blur
152
Recorded detail can be improved by decreasing which:
1. SID
2. OID
3. Part motion
OID
| Part motion
153
What units are used to express resolution
Line pairs per millimeter
