Fluoroscopy Equipment Flashcards
(109 cards)
1
Q
Advantages of Tomography
A
Increase radiographic contrast
Increase subject contrast
Decrease superimposition
2
Q
Disadvantages of tomography
A
Increase patient dose
Increase image blur outside of the focal plane
3
Q
Advantage of computed tomography
A
Low contrast resolution (can see many shades of grey)
Data acquisition variability
Image reconstruction capabilities
3D imaging
4
Q
Primary Disadvantages of computed tomography
A
Increase patient dose
Artifacts (mainly due to patient motion)
Decrease spatial resolution
5
Q
Gantry house what CT components
A
Tube Detector array Generator Filtration Collimators DAS Slip rings
6
Q
X-Ray tube qualities and purpose
A
Designed for increased heat dissipation
Metal envelope helps with this
Anode is larger and thicker,
high rotation speed (allows for more heat dissipation)
smaller target angle (smaller focal spot size on anode generators more heat on a smaller area which increases the heat load on the tube)
Anode has 2 focal spot sizes
7
Q
Filtration purpose and 2 types
A
Removes long wavelength X-rays this creates a more uniform beam and beam hardening (absorbs low energy X-rays to create a more penetrating beam)
Decreases patient dose
Added filtration is b/w the patient and the tube
Inherent filtration is built into the tube
8
Q
Collimation purpose and how it affects image quality
A
Restrict the X-Ray beam before it passes through the patient
- in Conventional CT they control slice thickness
Reduces scatter to increase contrast resolution and decrease patient dose
9
Q
Attenuation principles
A
Z (atomic number)
Density
Energy - increase kVp decrease attenuation
Attenuation - is the reduction of the intensity (quantity) of a beam of radiation as it passes through and object
10
Q
what are Hounsfield units and other names for them
A
HU classifications are based on attenuation Water = 0 Air = -1000 Dense bone = +1000 Metal = +2000 Other names = CT numbers, density values
11
Q
what is the Operating console and its input factors
A
Consists of a computer, mouse, keyboard, and multiple monitors
Input factors = pt info, scan protocol, slice thickness, pitch, technical factors
12
Q
Bow tie filtration
A
Shape matches the beam divergence and the patient shape
13
Q
what is the DAS
A
Data acquisition system
Measures transmitted radiation beam
Converts measurements to binary data
Transmits digital data to the computer
14
Q
2 types of collimation
A
Pre - collimator in the X-Ray tube
Post - be/w the patient and detector, ensures the beam is the proper width as it enters the detector
Both decrease scatter and patient dose
15
Q
Detectors purpose
A
Detectors measure exit radiation
Ultimately converts the measurements into an electrical signal proportional to the radiation intensity
16
Q
Detector spacing
A
Width/spacing of detectors affect the amount of scatter that is recorded
Spacing bars - allows to detectors to be built in more of an arc
Distance measurements - measure from middle of one detector to the middle of another
Size - smaller detector is good for spatial resolution
Deep narrow detector will accept less scatter radiation than short wide detectors
17
Q
Detector characteristics (4)
A
- High efficiency QDE - transmitted photons must be captured, absorbed, and converted to an electrical signal
Influenced by size - wide captures more radiation
Spacing - tight spacing b/c radiation that hits the spacing bar is and lost and no info is added
Material - want high atomic number, increased density and thickness - High stability - detector response to radiation must be consistent
- Fast response time - no lag
- Wide dynamic range - wide variety of signals that can be captured and measured by the detector
18
Q
Xenon gas detector - advantages and disadvantages
A
Not used in MDCT
One step energy conversion
Advantages - cheaper, more stable (easier to calibrate), fast response time
Disadvantages - must remain under constant pressure in the aluminum casing, takes up a lot of space (tungsten plates), 50-87% DQE, aluminium casing will absorb X-rays
19
Q
solid state scintillation detectors - advantages and disadvantages
A
Used in MDCT
2 step energy conversion - light energy to electrical energy
Advantages - high absorption efficiency (94-100%, high X-Ray stopping power) due to high atomic number and increased density, high light output, low afterglow and fast response time
Disadvantages - afterglow (crystals emit light after being hit with X-rays), sensitive to temperature and moisture, spectral matching
20
Q
Single row detector array
A
Wide z axis Collimation controls slice thickness Largest allowable is less than the detector width 360 degree rotation = a single slice Used in SDCT
21
Q
Multidetector row systems
- 2 configurations
A
Collimation and number of detectors determine: the number of slice and slice thickness and decrease scan time
22
Q
Multislice detector advantages
A
More slice for 360 degree rotation
Increased volume coverage speed - decreased time for data collection, decreased scan time, patient motion and breath holding can have 4-320 slices per rotation
Anatomical coverage
Design enables slice thickness manipulation (partial volume, and retrospective slice thickness)
23
Q
1st generation CT scanner
A
Motion of system - translate rotate (move in straight line = 1 slice rotate 1 degree and go again)
Shape or geometry of beam - parallel narrow pencil beam
Path of tube travel - 180 degree rotation
Detectors - no array 1-2 max
Scan time - 4.5 -> 5.5 minutes
24
Q
2nd generation CT scanner
A
Motion of system - translate rotate
Shape of beam - narrow fan beam
Path of tube travel - 180 degree rotation
Detectors - linear array max 30 detectors
Scan time - 20 sec to 3.5 mins
25
3rd generation CT scanner
The most commonly used
Motion of system - continuously rotating, rotate rotate
Shape of beam - wide fan beam
Path of tube travel - rotate rotate 360 degree
Detectors - curved detector array about 256 detectors 30-40 degree arc
Scan time - a few seconds
26
4th generations CT scanners
```
Motion of system - rotate fixed
Shape of beam - wide fan beam
Path of tube travel - 360 rotation
Detectors - circular single row, single row of 4800 detectors
Scan time - very short scan time
```
27
Modulation Transfer Function
The ratio b/w image accuracy in comparison to the actual object
Most commonly used method of describing of system spatial resolution capabilities
0= the worst image you can get, blank
1= perfect image reproduction of the object scanned
28
Spatial Frequency
The size of the object
Increasedsf = small object (image more at once)
Decreased sf = large objects (image less at once)
It is harder to get accurate images of smaller objects
29
What is contrast resolution
Differentiating structures that vary only slightly in density
1% variability = 10HU
Contrast detail response = for a given technique the level of contrast that is visible will decrease as the object size decreases
30
Uncoupling Effect
Dose is no longer related to image quality b/c of automatic rescaling
Quantum mottle occurs
Overexposed/underexposed images still look good
31
Automatic tube current modulation
Adjusts the mAs during each gantry rotation to compensate for large variations in X-Ray attenuation
Similar to AEC in general radiography
Has a fixed kVp and variable mAs
32
Tube voltage kVp
Typical setting are 120-140 and 80 kVp
kVp doesn't alter contrast as directly in CT as general radiography
Increase kVp increase beam energy and penetrability
33
Tube current - filaments and mAs
Small filament = decrease penumbra and increase image quality
Large filament = for larger body parts, decreases spatial resolution and requires higher mA settings
mA settings range from 20->800 mA
Increase mA for abdomen, decrease mA for lungs
mAs = mA and scan time define the X-Ray quantity (multiple variations can be used to achieve the same mAs)
34
what is Scan time and how does it affect mAs
The length of time required for the X-Ray tube to complete a full rotation NOT defined by the number of slices acquired
Cardiac imaging is very fast
Rules that apply to mAs
- reciprocity = increase mAs decrease time
- tissue thickness and density = increase density increase mAs
- manipulation = east to manipulate the scan time
35
What is pitch and what does it affect
Changes the amount of thickness covered for each slice
Increase pitch you increase slice thickness and decrease image quality
Slice thickness and image quality
36
Partial volume averaging
Occurs when tissues of widely different absorption are encompassed on the same CT voxel a beam attenuation proportional to the average value of these tissues
37
how does Slice thickness affect image quality
Increase acquisition slice thickness you decrease image quality due to partial volume averaging
Increase slice thickness = decrease in contrast and increase in SNR
Decrease slice thickness = increase in contrast due to less partial averaging
38
What it DFOV and how does it affect IQ
Determines amount of raw data used for reformatting and affects the spatial resolution
Pixel size determines accuracy of objects imaged
- decrease pixel size = decrease in contrast (the smaller the pixel the less likely a photon will interact with that pixel)
Matrix controls pixel size
39
What are reconstruction algorithms and how they affect IQ
Changes how the raw data is manipulated to reconstruct an image
Improves image quality by balancing noise and detail
Algorithm chosen depends on what should be enhanced/suppressed to optimize the image for diagnoses
Bone = increase spatial resolution increase noise and decrease contrast
Soft tissue = increase contrast and decrease spatial resolution
Changes how the raw data is manipulated to reconstruct an image
40
Window function and how it affects IQ
Manipulates contrast resolution
Wide ww= decrease low contrast, bone
Narrow ww= increase low contrast, brain tissue (fewer shades of grey)
41
Windowing post processing
Basic Post processing function
Most common function
Adjusting shades of grey that are seen
42
Distance measurement post processing
Determines the site of pathology -> reports the size of the abnormality
Grids are used to measure distances (acts like a map)
Acts as a guide for needle placement/treatment
43
Image annotation post processing
Words arrows ect..
| Used to help communicate with the radiologist
44
Multiple image display post processing
Viewing more images at once done on the workstation
45
Reference image post processing
Helps identify which viewed slice corresponds to specific anatomical landmarks
46
Image magnification post processing
Only can do this to image data
Is NOT the same as DFOV
Helps with accuracy of pathology measurements
47
Histogram Display post processing
Graph demos how often CT numbers occur in a specified ROI
48
Retrospective reconstruction
Uses raw data to create new images
Same plane as acquisition images
Can change following parameters = DFOV, image center, reconstruction algorithms
Changing the parameters retrospectively can enable/improve image reformatting
All images need to have the same DFOV to be reformatted into one image
49
Beam Hardening Artifact
- cause
- appearance
- how to fix
Natural filtration of the x-Ray beam by the scanned object
Attenuation causes the beam to harden
Done/dense objects increase this
Appearance = bands or streaks (shading artifacts)
How to fix = selecting the appropriate SFOV and beam hardening reducing software
50
Partial Volume Artifact
- cause
- appearance
- how to fix
Caused by more than I type or tissue contained within a voxel
Appearance = shading artifacts
How to fix = smaller pixel sizes (can't control this) use thinner slices (increases patient dose)
51
Motion
- cause
- appearance
- how to fix
Voluntary or involuntary motion
Appearance = shading streaking blurring
How to fix = better communication, immobilization, sedation, short scan time, built in features such as software correction and cardiac imaging
*most common artifact*
52
Metallic Artifact
- cause
- appearance
- how to fix
Partly b/c the density of the metal is beyond the range of HU values that a system is designed to handle
Appearance = streak
How to fix = new software improves HU range (beam hardening still occurs) proper changing instructions and higher kVp techniques to make a more penetrating beam and direct transmission
53
Out of field artifacts
- cause
- appearance
- how to fix
Anatomy that extends outside the SFOV
Appearance = streaks and shading
How to fix = move arms out of the way and increase SFOV
54
Cone Beam Artifacts
- cause
- appearance
- how to fix
Interpolation of data and misrepresents CT numbers on the image, can be misinterpreted disease, cone beam geometry, only happens with helical scans
Appearance = streaks or bright and dark areas of large density differences are more pronounced in outer row detectors
How to fix = use lower pitch whenever possible and cone beam reconstruction algorithms
55
Rings and Bands Artifacts
- cause
- appearance
- how to fix
Appear from malfunctioning or miscalibrated detector elements or caused by imperfect detector elements either faulty or out of calibration
Appearance = rings or bands
How to fix = eliminate by recalibrating the scanner or call service tech
*3rd generation scanner problem*
56
Noise Artifacts
- cause
- appearance
- how to fix
```
Quantum noise (scanner efficiency and patient size) inherent physical limitations (electronic noise in DAS) reconstruction parameters (high resolution reconstruction algorithms and increased noise)
Appearance = salt and pepper
How to fix = increase mAs, increase noises and decrease SNR, DAS impact (use newer lower DAS system) reconstruction algorithm (use a smoothing algorithm)
```
57
MDCT matrix array detector configurations
Aka Fixed array or uniform array
- isotopic
- goal is to improve spatial resolution
- slice thickness is symmetrical
58
MDCT adaptive array
Aka Uniform or Hybrid array
- anisotropic (different shapes and sizes)
- slice thickness is variable
- thinner in the center and wider at the periphery
59
Xenon detector characteristics
Highly stable
Aluminum casing causes decreases efficiency
No afterglow
60
Solid state detector characteristics
Can exhibit afterglow
High photon absorption
Sensitive to moisture and temp
61
Scan Parameters
```
Pitch
Slice thickness
DFOV
Reconstruction Alogrithms
Windowing
```
62
Overlapping Reconstructions and IQ
MDCT - can retrospectively combine slices in different ways to create thicker image slices
- thicker slices for reformatting require less space
- 50% overlap is common
Slice overlap - improves 2D and 3D reformatted IQ
- creates thinner image slice to decrease formatting artifacts
- not required if the voxel is at/near isotopic
-DFOV and slice thickness is small
63
Reformatting and IQ
Uses IMAGE DATA and improves display of anatomic relationships
Reformats Require Identical
- DFOV
- Image centre
- gantry tilt
- slices must be contiguous
The thinner the original slice the better the reformatted image (use thicker slices and overlap them, using many small ones takes up lots of space)
64
2D vs 3D Reformats
```
2D
- MRP
3D * only change image data*
- MIP
-MinIP
- SR
- VR
```
65
Multiplanar Reformations and IQ
Displays anatomy in various planes
- transverse, coronal, and Sagittal
- oblique and curved require manual setting
Can be programmed for automatic generation
No additional patient dose required
Reformatted images maintain the original HU values of the acquisition images
66
3D image reformatting
Provides depth perception
Can rotate and tilt
Original HU values not retained
Rendering adds lighting texture and colour to the 3D image
67
Maximum Intensity Projections and IQ
```
Voxel with highest value is displayed
- high contrast image
High attenuation structures
- contrast filled vessels
- bone
Minimize superimposition and eliminate structures that are not important
```
68
Minimum Intensity Projections and IQ
```
Lowest value is displayed
- height contrast image
Low attenuation structures
- bronchial tree
Minimize superimposition and eliminate structures that are not important
```
69
how are MIP and MinIP created
Using an entire dataset or a select portion
Sliding slab method
- deletes structure that are not of clinical interest
- minimizes superimposition
If the threshold is not accurate there is an inaccurate representation of anatomy
70
Surface Rendering
Aka shaded surface display
Images are created using threshold CT values
-voxels are excluded or included based on the threshold level
- threshold value determines image accuracy (anatomy can be concealed, remaining voxels are invisible)
Uses 10% of data
- displays the contour of an object
- all other voxels are excluded
Useful for surfaces or airways, colon, and blood vessels
71
Surface Rendering threshold values
If threshold value is too low
- structures can be excluded
If threshold values is too high
- other materials like fluid will be also displayed as tissue of interest
72
Volume Rendering and IQ
3D semi-transparent image
All voxels used and contribute to the image
- examines internal and external images
Displays multiple tissues and anatomical relationships
Used for endoluminal imaging
Pixels can be assigned a colour, brightness, and an amount of transparency
- attenuation based classification of structures
- adjusting window settings can remove the soft tissue from the VR setting
- can change transparency to only see skin, the skin and bone then only honey anatomy
73
Segmentation
Improves 3D imaging
Aka ROI editing
Removal of unwanted data for display purposes
- manual (most common) or automatic
Improves visualization of area of interest
Errors
- manual and automatic
- anatomy of interest is not displayed -> can be impossible ID (excludes stenosis or create false positives)
74
Artifacts and Reformatting
Artifacts degrade reformatted images
- motion is the most common and ruins everything
- metal causes streak artifacts
- asymmetrical voxels -> need to be the same size and shape or creates stair step appearance
75
Factors that affect contrast resolution
```
mAs/dose
Pixel size *want low contrast resolution*
Slice thickness
Reconstruction algorithm
Patient size
Windowing
- post processing
```
76
Factors that affect Spatial Resolution
```
Matrix size
DFOV
Pixel size
Slice thickness
Reconstruction algorithm
Focal spot size
Pitch
Patient motion
```
77
3 steps in creating CT image
Data acquisition -> scan data/raw data
Image reconstruction -> happens to raw data
Image Display -> image that can be manipulated
- image post processing and image storage
78
Scanning
Defined by the beam geometry used (size shape and motion of the beam during the scan)
79
Data Acquisition
Refers to the method by which the patient is scanned to provide us with enough info to construct the image
80
Gantry geometries
Defined by the arrangement of the X-Ray tube and detectors
81
Continuous vs stationary geometries
Continuous - detector follows the tube in a circle
| Stationary - detectors are built in a ring and only the tube moves
82
Axial scans
Step and shoot method
- X-Ray tube rotates around the patient and collects data slices then tube stops and the patient moves and the next slice is scanned
Before slip rings were invented
83
Axial scans advantages vs disadvantages
Advantages
- contiguous data (no gaps)
- gapped
- overlapped (not common adds no extra info)
Disadvantages
- scan time is long due to step and shoot method
- reconstruction capabilities (increase artifacts, decrease ability to scan contrast filled vessels)
84
Helical Scans
Aka spiral
Beam rotates around the patient as multiple projections are taken in a 360 degree sca
-scans a volume of tissue rather than one slice
Slip rings - no more cables and faster
Continuous movement
Volume scanning *helical scans leaves gaps in data*
85
Helical scans advantages and disadvantages
Ad
- Misregistration is reduced due to faster scans
-more data manipulation capabilities (change the plane in which you the view image by reformatting)
- use a smaller volume of contrast due to faster scan times -> contrast is hard on the kidneys and moves through the body quickly
Disadvantages
- 360 of data is not obtained for each helix -> needs interpolation or extrapolation
-image quality
86
DAS
Digital acquisition system
| - converts digital signal to analog signal
87
ADC
Analog to digital converter
88
Scan data or measurement data
Data measured by the detectors
| Preprocessed data
89
Image Data
Reconstructed Raw Data
Convolution -> filtering
Alogrithms applied to raw data to make image data
90
Alogrithms
Rules or directions used to get a specific output for a specific input
- filtered back projection -> removes blurring that occurs from smearing
- back projection -> blurring/smears
- iterative reconstruction
* changin the reconstruction algorithm will change the way the raw data is manipulated to create image data*
91
Data Processing in a nutshell
Raw data undergoes some form of processing
-The raw data is reconstructed meaning the data has been average and corrections are made
Image reconstruction
- raw data is converted into a digital image characterized by CT numbers
Image Data
- averaged for post processing and can be reformatted
92
SDCT slice thickness
Done with collimation
| Increase collimation decrease slice thickness
93
MDCT slice thickness
Pre-patient collimator width and detector configuration
94
Volume averaging
Affected by slice thickness
- increase slice thickness increase partial volume effect
Inaccurate pixel values hides pathologies
*the thicker the slice = more averaging*
95
Retrospective slice Incrementation
Done by post processing
Overlaps slices (done after the scan acquisition)
Can help decrease the partial volume affect
Can't change slice thickness with SDCT
Can change slice thickness with MDCT but they can't be smaller than the acquisition slices
96
Pitch
Used to describe the movement of the gantry throughout a helical scan
The tube is on for the entire length of a helical scan
*pitch doesn't change the slice thickness*
97
Pitch of 2
Increasing the pitch increases the amount of anatomy covered lengthwise for a total acquisition time
Increase extrapolation required (helical scans are gapped)
Increase acquisition speed (fast scan time)
Decrease resolution due to more partial volume averaging
98
Pitch of 0.5
Very bad for image quality
very slow scan
Increases the patient dose
Overlap is increased which gives more accurate extrapolation and data for reconstruction
99
Pitch of 1
Ideal for image quality
Decreases heat load on the tube with shorter scan time
Image sharpness has minimal loss
Most common pitch is between 1 and 1.5
100
Matrix
A 2D array of numbers that make up a digital images
| The larger the matrix size the smaller the pixel size for the same FOV which results in better spatial resolution
101
Voxel
Represents a volume of tissue and a section thickness
| Preferably isotopic
102
Pixel
Each pixel represents a single value
Brightness level is based on attenuation characteristics
Pixels can represent 1 of any 256 shades and is determined by the bit depth
Bit depth - contrast resolution and grayscale
103
Hounsfield Units CT Numbers and Density Values
Value based on linear attenuation coefficients of tissue
Each is assigned a shade on the bit depth scale
Water = 0
bone = 1000
Air = -1000
Metal = +2000
104
Window Width
Manipulates image data - done with post processing
Controls the contrast of the image
HU range controls CT # range
Wide window width = more grays
Narrow window width = less grays (darker image)
Max numbers of gray we will see in an image
105
Window Level
Manipulates image data and is done with post processing
Determines the brightness of the image
Determines the center value of the CT number range
Increase window level = decrease in brightness
106
SFOV
Determines the amount of space sued within the aperture during data acquisition
Selected before the exam begins
Must ensure the patient is in the isocenter
Number of detector cells depends on the scanner
If not correctly selected can cause out of field artifacts
107
DFOV
Will display a specific ROI in greater detail
Affects the pixel size (more magnified the larger the pixel size)
Spatial resolution (less partial volume averaging in each pixel so this is increased)
*DFOV can't be smaller than the SFOV*
*magnifying SFOV after scan will decrease spatial resolution*
108
Image Archiving
Occurs when the images have been reconstructed and image display is acceptable
PACS
DICOM
Dictation/viewing - allows for remote access to images
Images can be stored on optical disks or DVD
109
Slice thickness Vs Image thickness
Slice thickness = data acquisition
| Image thickness = data reconstruction
