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term test 2 imaging > Imaging Topics To Study > Flashcards

Imaging Topics To Study Flashcards

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1
Q

What is the advantage of temporarily stopping at inspiration for imaging practices (DIBH: deep inspiration breath hold)

A
  • reduce the volume of normal tissue in the high dose region on or can be used to move the target away from critical structures
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2
Q

What is the advantage of temporarily stopping at expiration for imaging practices (DIBH: deep inspiration breath hold)

A

More reproducible than inspiration

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3
Q

What part of the heart is a concern which is WHY we use inspiration breath hole

A

Left anterior descending coronary artery

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4
Q

What are some examples of reproducibility aids for Deep Inhale Breath Hold

A
  • Varian RPM (infrared camera)
  • bellows belt
  • goggles
  • watch shape of target - MRidian
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5
Q

What are some forms of visual coaching for DIBH

A

Goggles
Tablet
Light panel

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6
Q

What is the minimum breath hold for ABC

A

10-15s

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7
Q

How do you set a threshold for active breaching coordination

A

Multiply exhale / inhale by 0.8 and that will be the threshold for breath hold that the machine will set

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8
Q

What is documented during ABC appointment

A
  • breathing characteristics: inhale, exhale, deep inhale, deep exhale
  • consistency
  • max BH max repeatable Bh
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9
Q

What function on LINAC do you use for ABC

A
  • fluoro
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10
Q

Most _____ patients are treated in ______ breath regardless of laterality

A
  • Breast
  • inhale
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11
Q

How do we reduce respiratory motion

A
  • compression plate
  • abdominal compression band
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12
Q

How do we measure target motion

A

Model it with 4DCT
- compare it with HELICAL CT with motion artifact on

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13
Q

How are phases determined in the system for breath cycles

A
  • phased based sorting
  • amplitude based sorting
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14
Q

When sorting into bins for breathing phases, how many fully complete CT data sets are received

A

10 fully complete data sets

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15
Q

How is an ITV made with inhales and exhale scans

A

CTV inhale + CTV exhale = ITV

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16
Q

What is the formula for PTV

A

ITV + 1 cm = PTV

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17
Q

Which reproducibility aids can be used to gate treatment with reflective markers

A

RPM : real time position management

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18
Q

Which reproducibility aids can be used to gate treatment with surface monitoring

A

Catalyst

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19
Q

What is hysteresis

A

Modern TPD systems can autocontour the phases based on the contour of the reference phase

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20
Q

What is image registration

A
  • overlaying medical images in the same coordinate system
  • process that determines geometric transformation that relates the same points in two image sets
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21
Q

What is fusion

A

Result of registration where the images are aligned
Combined display of the mapped data from the moving data set with the stationary data set

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22
Q

Where do we use image registration

A

Target normal tissue delineation
Tumour monitoring
Image guidance
Image registration for treatment adaption

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23
Q

What are some image registration methods

A

Manual
Computer assisted manual
Computer assisted automatic

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24
Q

What is transformation

A

Function that is applied to the moving image to align it to the stationary image

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25
What is registration or similarity metric
Quantifies the degree to which the pair of imaging studies are aligned
26
What is rigid registration
Registration where the transformation preserves the distance between all points in the image A rigid registration can include translation in all directions as rotation sin all directions
27
What is affine registration
Includes the transformations from rigid registration and adds the additional transformations of scaling, shearing, and plane reflection. The distance between all points is not maintained as in rigid registration, however parallel lines remain parallel after the transformation
28
What is deformable registration
A registration transformation can also be variant where the number of degrees of freedom can be as large as three times the number of voxels in the source dataset
29
In treatment planning, with MR and CT which image is the moving image and which is the stationary image
MR: moving CT: stationary
30
In adaptive radiotherapy, how are stationary and moving images determined
CT may be the moving image and the mid treatment CT is the stationary image to enable the dose from the original CT to be mapped onto the new CT
31
What terms define the registration
Dimensionality Nature of transformation Interaction Nature of registration basis
32
What is nature of registration basis
- extrinsic, using frames, molds, fiducials or intrinsic, using image features or voxel properties
33
What are the limitation and challenges for registration
- rigid: leaves errors associated with deformable nature of soft tissue - deformable registration also assumes smooth deformation and is very constrained mathematically
34
What are the sources of error for registration
1. Input - artifacts 2. Registration - optimal selection of the similarity metric, transform ion model, optimizer can reduce errors here 3. Output - incorrect or invalid uses of contaminates downstream processes
35
What factors effect quality of CT image (scan parameters)
MA Scan time FOV Reconstruction algorithm KV Pitch (helical mode)
36
What are some image quality metrics
High contrast (detail) spatial resolution Low contrast resolution (contrast detect ability) Temporal resolution CT number uniformity Accuracy Noise Artifacts
37
What is high contrast spatial resolution
Ability to resolve small high contrast objects that are close together
38
How do we measure spatial resolution?
Directly: using line pairs phantom Modulation transfer function (MTF)
39
What is spatial frequency?
How frequently an object will fit into a given space
40
What is the spatial frequency of large and small objects?
Large: low spatial frequency Small: high spatial frequency
41
What is spatial resolution MTF?
Ability to accurately portray an object Varies by the size of the object The smaller, the object, the higher, the spatial frequency the more difficult to accurately depict the image
42
What factors affect spatial resolution?
Matrix size Pixel size CMV Field of view Slice thickness / voxel size Reconstruction algorithm Iterative reconstruction Focal spot size Pitch Patient motion
43
Nyquist sampling theorem
Because an object may not lay entirely within a pixel, the pixel should be half the size of the object to increase the likelihood of being resolved Reducing the pixel size will increase our chances of accurately representing the object
44
What does filtered back projection result in?
Higher noise and higher dose can result in high spatial resolution or high contrast resolution but not both
45
What does iterative reconstruction result in?
Enhance image quality with lower dose
46
What is a drawback for initiative reconstruction
Image artefacts occur Edges are enhanced artificial Image become sharp sharper, soft tissue become smoother
47
MBIR
Newest method that compares statistical projections to actual data, then modified to produce a temporary model after a series of iteration cycles. It will help to reduce the image noise. Results in reduced noise, reduced dose and reduced artifacts. Good for bariatric patients.
48
What is low contrast resolution
Ability to differentiate objects with slightly different densities
49
When comparing film/screen to CT, which is better in spatial resolution and which is better in resolving small differences in tissue density
Film screen: spatial resolution CT: small differences in tissue density
50
What is the relation between density and noise?
Objects that are closer in density create more noise
51
What is object size/attenuation in relation to contrast resolution
Larger objects are easily visualized High attenuation object, objects are easily visualized
52
What is LCD low contrast resolution detect ability
Defined as the smallest object that can be seen at a given contrast level end dose
53
Visual object size depends on what three factors
Image noise Level of contrast in the object Window setting
54
How does mA inversely related to noise
To decrease noise by 1/2 increase MAS by four times this will also result in those increased by four times
55
How does bone algorithm affect contrast and spatial resolution?
Produces lower contrast, resolution, but better spatial resolution
56
How does soft tissue algorithm effect contrast resolution spatial resolution?
Better contrast resolution, but lower spatial resolution
57
How does patient size affect contrast resolution?
Larger patients attenuate more futons, hence higher noise and lower contrast resolution
58
What does temporal resolution depend on and how is it controlled?
Depends on how rapidly data is required Controlled by gantry rotation, speed, and number of detector channels in the system The scanner’s ability to freeze motion of an object
59
What is a disadvantage and advantage of perspective gating
Advantage: reduced dose to the patient Disadvantage: reliance on the regularity of the heart heartbeat
60
What is perspective gating?
X-ray tube being turned off during non-acquisition times and create fewer artefacts
61
What is the fastest rotation time available for temporal resolution?
0.275 seconds
62
What is a CT number uniformity test?
Ability of the scanner to yield the same CT number, regardless of the location of a region of interest within a homogeneous object
63
Placing several regions of interest within a phantom thus main CT number should be and what is the to
Number should be close to zero tolerance of two hound units
64
For noise measurements ST of an ROI should not exceeded what number
10
65
What are the sources of noise?
Quantum / mottle Inherent physical limitations Reconstruction parameters
66
What is quantum noise and how is it influenced?
Quantum noise is x-ray flux or number of detected photons It is influenced by scanning parameters, scanner, efficiency, and patient size
67
What are inherent physical limitations?
Electronic noise caused by Detector photodiode Data acquisition system Scatter radiation
68
What are high resolution kernels?
Increase in noise level, noise presented, high frequency, signals, mainly these kernels enhance high frequency, contents in the production
69
How do we verify external and internal lasers and ISO
- incorporate into QA phantom - use a separate phantom
70
What is a Jaszczak /ACR phantom
Water phantom with spheres that can be filled with contrast / F-18 solution mix Used to calibrate CT PET

term test 2 imaging (3 decks)

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