midterm Flashcards
(131 cards)
1
Q
responsible for processing and display program controls.
A
Display Console
2
Q
integration with dosimetric data.
A
Radiation Therapy Planning
3
Q
HU selection
A
Density Contouring
4
Q
two types of Reverse Display
A
directional reverse or Negative reverse
5
Q
how many Magnification – up to
A
x3 without distortion
6
Q
deletion of unwanted parts from reconstructed image.
A
Suppression
7
Q
They help ensure that the CT acquisition covers the correct anatomy
A
Ensure correct anatomy
7
Q
SCANNING PROGRAM
A
Display Console
Scanogram
Grid Application
Cursor
Density Contouring
Radiation Therapy Planning
Reverse Display
Magnification
- Suppression .
- Annotation
- Histograms
- 3D Imaging
7
Q
labeling and text adding
A
Annotation
7
Q
A radiographic technique used for showing true dimensions by moving a narrow orthogonal beam of x - rays along the length of the structure being measured.
A
SCANOGRAM
7
Q
Where you could also apply the particular planning for specific structures.
The first image you will see in the CT Images.
A
SCANOGRAM
7
Q
The first image you will see in the CT Images.
A
SCANOGRAM
8
Q
SCANOGRAM
A radiographic technique used for showing true dimensions by moving a WHAT
A
narrow orthogonal beam of x - rays along the length of the structure being measure
8
Q
They help determine the extent and location of the scan area, ensuring the target organs or regions are properly imaged.
A
Plan the scan
8
Q
THESE IMAGES, ALSO KNOWN AS CT LOCALIZER RADIOGRAPHS OR SURVIEW , ARE TAKEN BEFORE THE MAIN CT SCAN TO:
A
- Plan the scan
- Optimize radiation
- Ensure correct anatomy
9
Q
They allow the CT software to adjust the radiation dose and image quality settings for the main scan.
A
Optimize radiation
10
Q
The terms are all used interchangeably to describe this initial CT image.
A
” scout ,” “ topogram ,” “ scanogram ,” “ localizer ,” and “ surview “
11
Q
what is GRID APPLICATION
A
localizing the target area
12
Q
what is localizing the target area
A
GRID APPLICATION
13
Q
what is CURSOR
A
measurements, outlining area of interest, marker of area.
14
Q
measurements, outlining area of interest, marker of area.
A
CURSOR
15
Q
A tool used to pinpoint specific areas of interest on the image, allowing for precise analysis and measurement.
A
cursor
16
Q
in cursor A tool used to pinpoint specific areas of interest on the image, allowing for what
A
precise analysis and measurement.
17
Q
characteristics of cursor
A
- Locating features
- Performing measurements
- Navigating images:
18
use the cursor to identify and mark specific structures, lesions, or areas of interest within the CT scan images
Locating features
19
The cursor can be used to measure distances, areas, or volumes within the scanned region
Performing measurements
20
HISTOGRAM
HU analization by use of a what
bar graph.
21
In some cases, the cursor can be used to navigate through different slices or views of the CT scan data.
Navigating images
22
HU analization by use of a bar graph.
HISTOGRAM
23
is the numeric information contained in each pixel
CT number/Hounsfield unit
23
is a quantitative scale for describing Radiodensity.
The Hounsfield scale or CT numbers
24
The Hounsfield scale or CT numbers is a HWAT
a quantitative scale for describing Radiodensity.
24
values that represents the linear attenuation coefficient equivalent of various tissues
Tissue density
24
Tissue density values that represents the linear attenuation coefficient equivalent of various tissues.
CT NUMBER/HOUNSFIELD UNIT
24
Dense bone
3000 HU
25
Bone
1000 HU
26
Tissue density values that represents the
linear attenuation coefficient equivalent of various tissues
27
by use of a bar graph.
HU analization
28
what is CT number/Hounsfield unit
the numeric information contained in each pixel
29
Liver
40-60 HU
30
Muscle
50 HU
31
White matter
45 HU
32
Gray matter
40 HU
33
Kidney
30 HU
34
Blood
20 HU
35
CSF
15 HU
36
Water
0 HU
37
Fat
-100 HU
38
Lungs
-200 HU
39
Air
- 1000 HU
40
Scanning protocols includes the following parameters:
Section Interval and Section Thickness
Scan Arc
Exposure Factors
Algorithm
Scan Field Size (FOV/ROI)
41
is just the thickness of the detector
acquisition thickness
42
Larger body sections can be best visualized with thicker slices, smaller subjects should be imaged with thinner slices
SECTION INTERVAL AND THICKNESS
43
what size of teh bodysections can be best visualized with thicker slices
Larger body
43
what should be imaged with thinner slices
smaller subjects
43
thicker slice characteristics
Decreased image noise
Decrease detail
Fewer Slices
44
is the thickness of the images that we see on the screen
reconstruction slice thickness
44
The appropriate image reconstruction slice thickness depends on the anatomy being scanned.
SECTION INTERVAL AND THICKNESS
45
thinner slice s characrteitcs
Increased image noise
Increase detail
More Slices
46
is the distance between scan sections.
Section Interval
47
is the width of the volume of the tissue being examined (Voxel).
Section thickness
48
Section thickness is the width of the volume of the tissue being what
examined (Voxel).
49
The arcs of xray exposure. Travel of xray tube in the gantry.
halfscan (180), Fullscan (360), Overscan (>360).
SCAN ARC
50
EXPOSURE FACTORS
120 KVp – most common
KVp selectable (80, 120, 140)
30mA – 1000mA (manufacturer’s specs)
51
SCAN ARC
The arcs of xray exposure.
Travel of xray tube in the gantry.
halfscan (180), Fullscan (360), Overscan (>360).
52
for reformatting and targeting.
ALGORITHMS/Reconstruction Algorithms
53
ALGORITHMS
Reconstruction Algorithms for reformatting and targeting.
Reconstruction Algorithms for windowing and Filters.
54
Common CT Image Reconstruction Algorithms:
Filtered Back Projection (FBP)
Iterative Reconstruction (IR)
55
A traditional, relatively fast algorithm that uses a convolution filter to reduce blurring in the image.
FILTERED BACK PROJECTION (FBP)
56
While widely used, that can lead to noise and artifacts, especially at lower radiation doses.
FILTERED BACK PROJECTION (FBP)
57
FILTERED BACK PROJECTION (FBP)
A traditional, relatively fast algorithm that uses a WHAT to reduce blurring in the image.
convolution filter
58
A more recent approach , to refine the image, starting with an initial guess and making adjustments based on the measured data.
ITERATIVE RECONSTRUCTION (IR)
59
IR algorithms can potentially reduce noise and artifacts while maintaining image quality, even at lower radiation doses.
ITERATIVE RECONSTRUCTION (IR)
60
SCAN FIELD SIZE
also known as
Field of View (FOV) or Region of Interest (ROI) .
61
also known as Field of View (FOV) or Region of Interest (ROI) .
SCAN FIELD SIZE
62
must be set to accommodate the size of the part under examination.
SCAN FIELD SIZE
63
scan field size per body part
Head (25cm). Small bodies (35cm). Large bodies (48cm)
64
Capturing the raw data, which is then reconstructed into high - resolution images
DATA COLLECTION BASICS
65
X - ray source & detector must be in & stay in alignment
Beam moves (scans) around patient
many transmission measurements
DATA COLLECTION BASICS
66
which is then reconstructed into high - resolution images
Capturing the raw data
67
Collimated to pass only through slice of interest shaped by special bow tie filter for uniformity
PRE-PATIENT BEAM
68
Beam attenuated by patient
PRE-PATIENT BEAM
69
Detected photon intensity converted to electrical signal (analog)
PRE-PATIENT BEAM
69
Electrical signal converted to digital value
PRE-PATIENT BEAM
70
Digital value sent to reconstruction computer
PRE-PATIENT BEAM
70
Transmitted photons detected by scanner
PRE-PATIENT BEAM
71
PRE-PATIENT BEAM
- Collimated to pass only through slice of interest shaped by special bow tie filter for uniformity
- Beam attenuated by patient
Transmitted photons detected by scanner
Detected photon intensity converted to electrical signal (analog)
Electrical signal converted to digital value
A to D converter
Digital value sent to reconstruction computer
71
That part of beam falling onto a single detector
CT “RAY”
72
CT Ray attenuated by patient projected onto what
one detector
72
A to D converter
PRE-PATIENT BEAM
73
Each CT Ray attenuated by patient projected onto one detector
detector produces electrical signal
produces single data sample
73
attenuated by patient projected onto one detector
CT Ray
73
SPIRAL GEOMETRIES
- X - ray tube rotates continuously around patient
- Patient continuously transported through gantry
- No physical wiring between gantry & x - ray tube
- Requires “Slip Ring” technology
73
Number of simultaneously collected rays
CT VIEW
74
SPECIAL CONSIDERATIONS FOR SLIP RING TECHNOLOGY
Continuous scanning means
Heat added to tube faster
No cooling between slices
74
SPECIAL CONSIDERATIONS FOR SLIP RING TECHNOLOGY
Needs
more heat capacity
faster cooling
huge tubes
75
IMPROVING QUALITY AND DETECTION
Geometry
I
Smaller detectors
Smaller focal spot
Larger focus - detector distance
Smaller patient - detector distance
76
IMPROVING QUALITY AND DETECTION
Thinner slices
less patient variation over slice thickness distance
77
X - ray tube and detectors rotate around the patient, taking multiple measurements from various angles
Rotational Acquisition
77
DATA ACQUISITION PROCESS
Rotational Acquisition
Data Sampling
78
As the X - ray tube and detectors rotate, the patient moves through the scanner in small increments, allowing for the creation of multiple slices through different parts of the body.
Rotational Acquisition
79
Detectors collect data at different angles, they generate a set of projection data
Data Sampling
80
RECONSTRUCTION OF DATA
- FOURIER TRANSFORM AND BACK - PROJECTION
- FILTERED BACK - PROJECTION (FBP)
- ITERATIVE RECONSTRUCTION (IR)
80
is a process where the projection data is mathematically "reversed " to simulate the X - ray paths back through the body.
FOURIER TRANSFORM AND BACK - PROJECTION/ Back-projection
80
The process involves converting the raw projection data into interpretable images using specialized algorithms.
RECONSTRUCTION OF DATA
81
FOURIER TRANSFORM AND BACK - PROJECTION
Back-projection is a process where the projection data is mathematically WHAT to simulate the X - ray paths back through the body.
"reversed"
82
It tends to produce blurry images.
FOURIER TRANSFORM AND BACK - PROJECTION
82
Uses a filter to modify the back - projected data, reducing blurring and producing sharper images.
FILTERED BACK - PROJECTION (FBP)
82
Unintended optical density on a radiograph
COMPUTED TOMOGRAPHY ARTIFACTS
82
Systematic discrepancy in CT numbers/HU
COMPUTED TOMOGRAPHY ARTIFACTS
82
FACTORS AFFECTING DATA ACQUISITION
X - ray Tube and Detector Sensitivity
Slice Thickness
Scan Time
Radiation Dose
82
repeatedly refine the image through multiple iterations, improving the accuracy of the reconstructed image. Can significantly reduce noise and improve image quality while maintaining a lower dose of radiation.
ITERATIVE RECONSTRUCTION (IR)
82
Unwanted aberration on CT images
COMPUTED TOMOGRAPHY ARTIFACTS
83
More common in CT than in conventional radiographs
COMPUTED TOMOGRAPHY ARTIFACTS
83
The more projection angles and data points that are collected, the higher the image quality and resolution.
Data Sampling
83
COMPUTED TOMOGRAPHY ARTIFACTS
Types:
- Streaking
Shading
Rings
Distortion
84
due to an inconsistency in a single measurement
Streaking
85
due to a group of channels or views deviating gradually from the true measurement
Shading
86
due to errors in an individual detector calibration
Rings
87
due to helical reconstruction
distortion
88
COMPUTED TOMOGRAPHY ARTIFACTS
Four categories:
- Physics-based artifacts
Patient-based artifacts
Scanner-based artifacts
Helical and multisection artifacts
89
Caused by physical processes involved in the acquisition of CT data
Physics-based artifacts
90
Caused by Patient movement, Presence of metallic materials
Patient-based artifacts
91
Caused by imperfections in scanner function
Scanner-based artifacts
92
Caused by image reconstruction process.
Helical and multisection artifacts
93
PHYSICS-BASED ARTIFACTS
Beam hardening artifact
Cupping artifact
Streak artifact
Partial volume
Photon starvation
Undersampling
94
noise is influences partially by the number of photons that strike the detector. Photon starvation can occur as a result of poor patient positioning or poor selection of exposure techniques.
Noise (photon starvation)
95
Today modern scanners virtually eliminate this effect due to what
mA modulation
96
PATIENT - BASED ARTIFACTS
- Metallic materials
Patient motion
Incomplete projection
97
SCANNER - BASED ARTIFACTS
Ring Artifacts
98
HELICAL AND MULTISECTION CT ARTIFACTS
Cone beam effect (Helical)
Stair - step artifacts (MSCT)
Zebra or windmill artifacts (MSCT)
