Exam 2 Flashcards
(123 cards)
1
Q
What role do exposure techs/factors play in image quality?
A
Adequate signal to IR so software can do its job BUT not too much dose to patient
2
Q
mAs determines?
A
Quantity/intensity of radiation to the IR
3
Q
SID determines?
A
Quantity/intensity of radiation to the IR
Dose, magnification, etc.
4
Q
kVp determines?
A
Quality/penetration of beam through patient
Significant effect on final intensity of remnant beam at detector
5
Q
kVp and scatter: which has a primary influence on scatter production-patient size/collimation or kVp?
A
Patient size/collimation because volume of tissue irradiated “more tissue, more pinball”
6
Q
kVp as an exposure factor?
A
kVp as an exposure factor: experiments have demonstrated that 15% increase in kVp results in no to slight change in visible contrast. High kVp results in more penetration-reduction of subject contrast in latent image-processing software can reduce visible impact. Moral of story: increase kVp by 15% on all body parts, more may not be beneficial-may over penetrate
7
Q
How do you adjust mAs when you increased kVp by 15%
A
Reduce by ½. Experiments show little increase in quantum mottle
Chest images may show mottle, due to already high kVp and low mAs
8
Q
Patient skin and absorbed dose reduction?
A
15% kVp increase with 50% mAs decrease theoretically reduces: skin exposure by 67%. Absorbed dose by more-due to increased beam penetration
9
Q
Physics question: when you increase kVp by 15%, which type of electron-target interaction are you producing more of? Bremsstrahlung or Characteristic?
A
Bremsstrahlung-has more energy so can bend around more atoms
10
Q
kVp, image contrast, and subject contrast
A
a. Image contrast: kVp does not control. Computer software does. Rescaling modifies incoming image data. LUT application during gradation processing drives displayed contrast. Finally, windowing.
b. Subject contrast: kVp does influence. Beam penetration of body part very important. Must get enough signal to plate for adequate processing.
11
Q
Does kVp influence image contrast or subject contrast?
A
Subject contrast
12
Q
kVp and part penetration
A
a. better to slightly over penetrate with beam energy, not quantity, software can compensate for some over penetration.
b. Under penetrated images quickly display quantum mottle, 15% + decrease in kVp, loss of info, cannot replace lost info
13
Q
High and low kVp comparision
A
Difference in signal that reaches IR changes with beam energy, becomes more narrow at high energies-can see more anatomic data but risk increased scatter
14
Q
Scatter
A
Patient generated scatter during exposure can be compensated for during histogram created-s min and s max determined and dark tail is eliminated. Pre-exposure fog cannot: problem with CR, entire plate has minimal exposure, eliminates blank/white pixels shifting s min and s max to right, fog goes undetected
15
Q
Frequency processing to remove fog?
A
Use frequency processing to remove low frequency signal, eliminates certain low frequencies-fog and some image data
16
Q
Old rules that still hold true:
A
a. inverse square law and density maintenance formula
b. 4-cm rule for part thickness, double mAs or increase kVp by 15% for every 4 cm additional thickness or reverse
c. 15% rule for kVp adjustment and mAs compensation
17
Q
AEC tips
A
Use high kVp, usually no need to use + density settings. Have mottle? Increase kVp, want adequate signal to reach AEC detectors and IR, properly center body part over AEC cells
18
Q
Grid use
A
Scatter reduction to IR=one method of reducing image noise.
Anatomy up to 13cm thick can be non-grid, take out for small parts, peds.
Peds Chest x-ray can be non-grid, adult knees can be non-grid.
Beneficial to patient when grid eliminated? Positioning flexibility, especially for trauma, portables. Compare grid exam to non-grid exam, calculate mAs reduction with no grid, result: dose reduction 50-75%
19
Q
What thickness of a peds patient should a grid NOT be used?
A
Less than 13 cm. Can use grid if above 13 cm thick.
20
Q
Virtual grid software?
A
Does not actually prevent creation of scatter, uses noise reduction algorithms to remove certain sized structures from image: usually low frequencies, eliminates or smooths them. Then use contrast enhancement to high frequency layers. Note: applied to ALL image data-can influence image structures which are same size as scatter. Can lower patient dose
21
Q
Targeted area brightness correction?
A
Software which acts like compensating filter, targets specific, bright areas of image and performs brightness corrections. May eliminate need for compensating filters
22
Q
What is image quality?
A
The fidelity with which the body part being examined is imaged on the radiograph
23
Q
What does image quality include?
A
IR factors
Subject factors
Geometric factors
24
Q
Components of digital image quality?
A
Brightness
Contrast
Spatial resolution
Noise
25
Factors independent of IR technology?
Size distortion
| Shape distortion
26
Digital image characteristics?
-Digital image receptors respond to wide range of x-ray energies
Large dynamic range
Under or over exposed images likely acceptable
-IR response is linear (film is nonlinear)
Can display wide range of “densities”
Easily visualize anatomy with large variations in attenuation
i.e. soft tissue, bone, calcified veins
27
What do you look for to eval your finished x-ray?
```
Positioning criteria
Patient motion
Markers present/missing
Collimation
Grid lines/grid cutoff
Ghosting
Double images
Tube/part alignment
Quantum mottle
EI number
```
28
Factors that cause image quality issues
```
Patient motion
Collimation
Grid cutoff
Ghosting
Double exposure
Tube/part alignment
Multiple images on one IR
Mottle
Excess scatter due to no collimation
```
29
Geometric factors:
```
Magnification
SID, OID
Distortion
Tube, part angle
Focal spot blur
```
What is the benefit?
Less part magnification
Better recorded detail
Reduces penumbra
30
Subject factors:
Anatomy being examined—size, shape, beam attenuating characteristics of anatomy i.e. subject contrast
kVp-Still influences the signal that reaches the IR
Motion blur
31
What needs to be adjusted if SID is changed?
mAs needs to be adjusted appropriately
32
What can cause distortion?
```
Alignment of:
CR
Part
IR
Tube angulation:
Degree
Direction
```
33
IR factors?
Type of receptor
Pixel size
Matrix size
Dynamic range (bit depth)
34
Image eval criteria?
```
Brightness
Contrast
Exposure Indicator
Image Noise
Image Blur
Positioning
```
35
Inherent and displayed brightness?
Displayed image brightness not an indicator for under or over exposure. Visual cues of exposure error don’t exist now
Displayed and inherent brightness independent of each other
Displayed—
LCD or CRT monitors
Monitor settings adjustable
36
Are inherent and displayed brightness dependent or independent of each other?
Independent
37
Image brightness in regard to a monitor?
In regard to a monitor: the amount of luminance of a display monitor
Area of decreased density displays bright
Area of increased density displays dark
Can be adjusted to see anatomy of interest
Density errors almost nonexistent
38
Inherent image brightness depends on:
Computer software that processed exposure data: Histogram analysis, LUT application, Window level, Postprocessing adjustment
Exposure level to IR- (Going backward…) exposure technique
39
Under vs over exposure
Under—
Increased quantum mottle
Loss of contrast in dense anatomy
Over–
Loss of contrast in skin & dense features
Overall loss of contrast
40
Signal to noise ratio? What is the "signal"?
Image forming, remnant radiation that reaches the IR
41
Which do we want, high signal to noise ratio or low? Why?
High signal; lower noise=allows for better contrast resolution
Thus we can see smaller objects
42
Which determines signal to noise ratio? kVp or mAs
mAs; as the number of photons created, it is your signal
| kVp; beam penetration-more photons reaching IR=more signal (DOUBLE CHECK IN BOOK THAT ITS BOTH)
43
**Image noise
Noise: “Uniform signal produced by scattered x-rays” “Grainy or uneven appearance of an image caused by an insufficient number of primary x-rays.” “undesirable input that interferes with the visibility of the subject of interest”
Scatter radiation: Principal source of noise
Quantum mottle: From inadequate number of photons reaching IR. Low beam penetration or low beam intensity, or very thick part. Limits visibility of soft tissue
Electronic noise
All limits contrast resolution
Material mottle: Phosphor crystals; CR, DR, II input phosphor, fiber-optic bundles
Off focus radiation
Aliasing artifacts
Algorithmic noise
Exposure artifacts: Grid lines, Extraneous objects, Superimposition of tissue-unwanted, Tomographic false images (streaks)
44
Exposure artifacts
Grid lines
Extraneous objects
Superimposition of unwanted tissue
Tomographic false images (streaks)
45
Spatial resolution per ARRT:
ARRT: The sharpness of the structural edges recorded in the image.
46
Spatial frequency:
Spatial frequency: number of line pairs that can be seen per a specified length (i.e. lp/mm)
Higher spatial frequency means smaller objects can be seen = higher spatial resolution
Smaller objects more difficult to image
47
Spatial resolution
DR has lower spatial res. than CR & film
Limited by pixel size
Cannot image anything smaller than a pixel
48
For spatial resolution: do you want a larger or smaller matrix? What about number of pixels-larger or smaller?
Larger matrix, smaller pixels
49
Contrast resolution per ARRT:
ARRT: Grayscale: the number of brightness levels (or gray shades) visible on an image & is linked to the bit depth of the system
50
Contrast resolution
Dynamic range:
ARRT: range of exposures that may be captured by a detector
Bushong: number of gray shades that an imaging system can reproduce
Identified by bit depth of system
DR has better contrast resolution than film
Bit depth
Does contrast res change with increased mAs/dose?
No; DR systems respond in a linear manner, unlike film
Pixel saturation can happen though
51
Dynamic range per ARRT:
| Per Bushong:
ARRT: range of exposures that may be captured by a detector
Bushong: number of gray shades that an imaging system can reproduce
Identified by bit depth of system
52
Does contrast resolution change with increased mAs/dose?
No; DR systems respond in a linear manner, unlike film.
| Pixel saturation can happen though
53
Which has a better contrast ratio? Film or DR? Why?
DR, due to bit depth?
54
Contrast resolution factors:
```
Bit Depth
Subject contrast
Noise
Viewing conditions
Viewer capabilities
```
55
Contrast sensitivity depends on:
```
Number of bits used to represent each pixel
System gain
Inherent subject contrast
Noise
Image viewing conditions
Limitations of observer
```
56
An ___ (increase or decrease) in contrast resolution, ___ (increases or decreases) visibility of recorded image detail
Increase, increases
57
What can influence contrast resolution?
Dip depth
58
What does contrast resolution have the ability to do?
Ability of a system to distinguish between small objects that have similar attenuation characteristics
How easy it is to see small objects that are of similar make-up/composition
And thus display similar shades of gray
59
What can affect contrast sensitivity?
Not just object size in diameter, but also density of the object affects contrast sensitivity or resolution
60
What can alter subject contrast? kVp or mAs?
kVp
61
Modulation transfer function?
Ratio of the recorded contrast to the contrast of the real object
Is a spatial frequency response of an imaging system—inherent to the system
Contrast values of different sized objects are converted into contrast intensity levels
62
*What can limit contrast resolution?
Noise
63
Is contrast resolution (dependent or independent) or pixel size?
Contrast resolution is independent of pixel size (and thus spatial resolution)
Ex: imagine two systems with different pixel sizes. Use the same imaging technique (exposure factors, SID, OID, FSS) with both systems. The contrast resolution will be the same, but the system with the smaller pixel size will have better spatial resolution.
64
Exposure indicator
Partial replacement for film/screen visual cues
An EI that is outside the proper exposure range always indicates that I used the wrong technique. True or false? Why?
False, It may be caused by a histogram analysis error—other factors might have caused it
65
An EI that is outside the proper exposure range always indicates that I used the wrong technique. True or false? Why?
False, It may be caused by a histogram analysis error—other factors might have caused it
66
List causes of histogram analysis errors
```
Improper collimation
Improper exposure factors
Scatter
Background radiation fog
Extreme density differences
Exposure field recognition errors
Lack of symmetry when multiple images on one plate
```
67
Name some practices that will result in optimal images
```
Proper centering of part to middle of IR
2-4 sided collimation
Appropriate kVp
Maximum SID
Minimal OID
Selection of correct image menu
Use a grid if part > 13 cm thick
```
68
Define artifact
```
Unintended optical density on an image
False visual feature that simulate anatomy or obscure tissues
Excludes scatter & fog
Degrades image
May necessitate repeat exam
```
69
5 categories of artifacts
```
1. Image receptor artifacts
Imaging plate artifacts
2. Plate reader artifacts
3. Image processing artifacts
Histogram errors
Rescaling
Image compression
4.Printer artifacts
5. Object artifacts
Collimation
Backscatter
Patient positioning
```
70
Image plate artifacts
```
Cracks in imaging plate
Radiolucent (white) lines
Static causing hair to cling to plate
Backscatter artifact
Dark/black line artifacts
Dust, dirt, scratches
From imaging plate handling
Plate in & out of cassette, through CR reader
```
71
Plate reader artifacts
Dirt on optics (lenses, mirrors, light guide)
Appear as horizontal white lines
Along path of plate travel
Service engineers must clean
Insufficient erasure—residual image on plate
Overexposure
Bad erasure lamp
Moire artifact from grid placement
Will know its the plate reader and not the IR, when issues occur when using different IRs
72
Grid artifacts from CR reader
When grid lines are parallel to scanning laser in CR reader, a moiré effect can occur
Oscillating grids eliminate this
Higher frequency grids recommended
> 103 lines/in.
Ideal: grid lines are perpendicular to translation of laser
73
Moiré Pattern Artifacts
Lines on CR final image
74
IR artifacts
Stains from cleaning chemicals
Leakage into cassette
Wrong chemical used on IP
Anhydrous alcohol only
Pixel malfunction
Sampling errors
Bad pixels on flat panel detectors
Ghost images
Incomplete erasure
Incorrect erasure settings
75
Printer artifacts
Dirt in laser printer causes fine white lines
Service engineers must clean, calibrate
Easy to differentiate from plate reading artifacts
76
Software artifacts
Quantum mottle
What causes this?
Not enough radiation exposure to detector
How do you fix this?
Usually more mAS
77
Image processing artifacts
Exam menu selection
Wrong menu = wrong histogram
Incorrect sampling of image file
```
Poor Technique:
Collimation
Grid selection
Wrong exposure factors
Poor part positioning—on plate
```
78
Artifacts from operator error
Backward cassette
Grid pattern of cassette support seen over image
No collimation
Unattenuated radiation strikes IR
Alters histogram
Wrong size IR
Image appears small
79
Artifacts from improper or no collimation
```
Improper collimation =
(Too much or too little collimation)
Exposure field recognition errors =
Histogram analysis errors
Software cannot find VOI; result: rescaling error
Poor density, contrast on image
```
No collimation=
Too much exposure in histogram
Exposure indicator number reflects plate overexposure
But maybe it wasn’t overexposed!
80
Exposure field recognition errors
Preprocessing software cannot find exposure field edge
What is the result?
Scatter, off focus, unattenuated radiation included in histogram
This leads to:
Light, dark, or low contrast images
Incorrect exposure indicator number
81
Histogram/rescaling errors
If software cannot find borders, all image data included
Histogram applied to all image data, not just VOI
When rescaled, software cannot properly adjust image to reference histogram
LUT cannot properly apply contrast
Image may look dark or light, have little contrast latitude
Cannot window/level image
82
When the preprocessing software cannot distinguish the borders of an image, what type of error occurs?
Exposure field recognition errors
83
What can exposure field recognition errors lead to?
Histogram errors
84
When a histogram analysis error occurs, what happens to the image?
Very dark or light with little contrast
85
Histogram error that may not be your fault:
Unexpected area of increased/decreased attenuation in body
Artificial joint, Ba2SO4 in bowel, uneven lead shield border
Area of low lucency included in histogram
Oops! Software thinks image underexposed
Compensates with rescaling/LUT application
Image looks dark
86
What is it called when you put more than one image on a plate?
Partitioning. (Can really only be done on CR and film)
Symmetry is key:
4-sided collimation
Symmetric part placement
Appropriate technique
Software averages all image data
87
Flat panel artifacts
Dead pixels
Software interpolates data to fill in
Correction algorithms that assign values to dead pixels based upon values of adjacent pixels
Flat field correction
Incorrect gain calibration
Software corrects irregularities in AMA detector
Uniform response to uniform x-ray beam
Image lag—multiple reasons
Detector doesn’t clear image data before next image created
Overexposure
“double exposure”
Offset correction fixes this—determines baseline signal on detector array
88
Name the common types of digital image artifacts
Image plate artifacts, plate reader, image processing, printer, operator errors
89
How do backscatter artifacts appear on the image?
Black lines
90
What happens when the preprocessing software cannot find a collimated border?
All exposure data included in image, resulting in histogram analysis error
91
List the best practices for collimation
Collimate parallel to cassette borders
| 2 or 4 sided collimation
92
List some best practices for image creation
```
Use the appropriate size IR
Collimate on 2 or 4 sides
Select the proper exposure menu
Select kVp in the higher end of the range for body part imaged
One image per plate
Place part in center of IR
```
93
Define tomography
A radiographic process used to demonstrate anatomy on in one specific plane
94
What planes does tomography deal with?
Sagittal and coronal planes
95
How does tomography work?
Used to view specific anatomy without superimposition
Provides better contrast resolution
Movement of x-ray tube and image receptor in opposite directions, at same rate of speed
Blurs anatomy above & below image plane
96
Object/Focus plane:
Section being imaged
97
Fulcrum:
Pivot point around which the motion of the tube and IR are centered
98
Tomographic section:
Thickness of tissue imaged
99
Tomographic angle:
Arc of x-ray tube
100
Section interval
Distance between fulcrum levels
101
Tomographic angle and thickness of cut:
A large tomographic angle creates a small thickness of cut.
| A small tomo angle creates a large thickness of cut
102
Tomographic motion types:
```
Linear – along a single line
Curvilinear – with an arch
Circular – in a circle pattern
Elliptical – oblong circular pattern
Figure Eight
Trispiral – bulls eye type pattern
Hypocycloidal – small circle within a larger circle
```
103
What is trispiral?
Bulls eye type pattern
104
What is hypocycloidal?
Small circle within a larger circle
105
What is elliptical?
Oblong circular pattern
106
Tomography procedure
Scout image taken to identify location of anatomy within the body
Decide tomographic angle, fulcrum level, exposure factors
Align long edge of body part parallel to path of x-ray tube motion
The greater the tomographic angle, the thinner the slice of anatomy can be created
Had to use manual techniques and have a long exposure time anywhere from 1-3 seconds. Low mA
Thickness measured from tabletop-may include pad they are laying on
107
Technical factors for tomography
Technical Factors
Exposure time must match time required to complete one tomographic amplitude
Exposure amplitude and tomographic amplitude should match
< time = < blur due to motion of anatomy outside ROI
> time = < blur due to detail of anatomy outside ROI
Usually at least 3 – 6 seconds
mAs stations at 10 – 50, but mAs is higher due to OID required
kVp appropriate for penetration of ROI
108
Types of tomography
Zonography (Narrow-Angle Tomography)
<10°
Thick slice when ROI location is unknown or large structure
Wide-Angle Tomography
>10°
Small/thin structures or multiple slices of one structure
Panoramic Tomography
Curved IR
109
Advantages of tomography
Improved radiographic contrast
| Enhanced due to blur of structures outside focal plane
110
Disadvantages of tomography
Patient dose
X-ray tube activated for entire arc
Several exposures made for exam
One slice of kidneys could deliver 10mGyt dose (estimate-varies)
111
Tomosynthesis
About 10 static exposures are various CR angles through the anatomy
Post processing algorithm allows for reconstruction, contrast manipulation, blur filters, etc.
112
Tomosynthesis for mammo
FDA approved for breast cancer screening & diagnostic mammography in 2011
Improves breast cancer detection, esp in dense breasts
Better dense breast imaging
Reduces number of false-positives & recalls
113
Tomosynthesis image acquisition
Digital image capture & processing combined with conventional tomography
Requires minimum number of exposures, per manufacturer
Uses higher resolution flat panel detectors
aSe detector with aSi TFT
Must have high DQE @ low exposure levels
Special reconstruction algorithms
114
How images captured for tomosynthesis
Breast compressed
7-30 images taken of breast, centered over a ROI
Sweep Mode:
Tube moves over breast
Pulsed image at specific frame rate for detector
Step-and-shoot method:
Static exposures at slightly different CR angles
Detector may be stationary, or may move in tangent to x-ray tube
115
Tomosynthesis image creation
Larger tube motion = more projections & slices created
Increased angle = thinner slices, better depth resolution, less image blurring
116
Processing and viewing tomosynthesis
Graphic processing units (think video games) process data
Volumetric 3-D data
Images viewed individually, or as a loop
Data files large: each projection 20 Mb
```
Two types of algorithms:
Analytical algorithms
Filtered back projection; used in CT also
Iterative algorithms
Affect image noise, computing time
```
117
Two types of algorithms for tomosynthesis
Analytical algorithms
Filtered back projection; used in CT also
Iterative algorithms
Affect image noise, computing time
118
Tomosynthesis stats
Increases detection of invasive breast cancers by 40% in comparison to 2D mammography
Total cancer detection increased from 6.1 patients per thousand to 8.0 patients per thousand (a 27% increase)
False-positive readings reduced by 15%
Uncertain readings and patient call-backs reduced by 20-30%
119
Tomosynthesis problems
Tests take twice as long as mammography tests, resulting in slightly more radiation exposure.
Some calcification fields, which are precancerous indications, are more easily interpreted on 2-D mammograms
More expensive equipment and larger storage archives will be required
120
Computer Aided Detection & Diagnosis (CAD)
Tool used by radiologists to enhance diagnostic accuracy & image interpretation consistency
Software algorithms that analyze image data
Search for abnormal patterns
Or quantify image features as normal or abnormal
121
CAD uses
Common in Mammography
Chest radiography
Chest CT
Virtual colonography
122
Goal of CAD
Improve the quality and the productivity of the radiologist by improving the accuracy and consistency of radiologic diagnosis and reducing the time required to interpret images
123
What is CAD stand for?
Computer Aided Detection & Diagnosis
