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term test 2 imaging > Imaging Topics To Study > Flashcards

Imaging Topics To Study Flashcards

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
Q

What is registration or similarity metric

A

Quantifies the degree to which the pair of imaging studies are aligned

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26
Q

What is rigid registration

A

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

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27
Q

What is affine registration

A

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

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28
Q

What is deformable registration

A

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

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29
Q

In treatment planning, with MR and CT which image is the moving image and which is the stationary image

A

MR: moving
CT: stationary

30
Q

In adaptive radiotherapy, how are stationary and moving images determined

A

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
Q

What terms define the registration

A

Dimensionality
Nature of transformation
Interaction
Nature of registration basis

32
Q

What is nature of registration basis

A
  • extrinsic, using frames, molds, fiducials or intrinsic, using image features or voxel properties
33
Q

What are the limitation and challenges for registration

A
  • rigid: leaves errors associated with deformable nature of soft tissue
  • deformable registration also assumes smooth deformation and is very constrained mathematically
34
Q

What are the sources of error for registration

A
  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
Q

What factors effect quality of CT image (scan parameters)

A

MA
Scan time
FOV
Reconstruction algorithm
KV
Pitch (helical mode)

36
Q

What are some image quality metrics

A

High contrast (detail) spatial resolution
Low contrast resolution (contrast detect ability)
Temporal resolution
CT number uniformity
Accuracy
Noise
Artifacts

37
Q

What is high contrast spatial resolution

A

Ability to resolve small high contrast objects that are close together

38
Q

How do we measure spatial resolution?

A

Directly: using line pairs phantom
Modulation transfer function (MTF)

39
Q

What is spatial frequency?

A

How frequently an object will fit into a given space

40
Q

What is the spatial frequency of large and small objects?

A

Large: low spatial frequency
Small: high spatial frequency

41
Q

What is spatial resolution MTF?

A

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
Q

What factors affect spatial resolution?

A

Matrix size
Pixel size CMV
Field of view
Slice thickness / voxel size
Reconstruction algorithm
Iterative reconstruction
Focal spot size
Pitch
Patient motion

43
Q

Nyquist sampling theorem

A

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
Q

What does filtered back projection result in?

A

Higher noise and higher dose can result in high spatial resolution or high contrast resolution but not both

45
Q

What does iterative reconstruction result in?

A

Enhance image quality with lower dose

46
Q

What is a drawback for initiative reconstruction

A

Image artefacts occur
Edges are enhanced artificial
Image become sharp sharper, soft tissue become smoother

47
Q

MBIR

A

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
Q

What is low contrast resolution

A

Ability to differentiate objects with slightly different densities

49
Q

When comparing film/screen to CT, which is better in spatial resolution and which is better in resolving small differences in tissue density

A

Film screen: spatial resolution
CT: small differences in tissue density

50
Q

What is the relation between density and noise?

A

Objects that are closer in density create more noise

51
Q

What is object size/attenuation in relation to contrast resolution

A

Larger objects are easily visualized
High attenuation object, objects are easily visualized

52
Q

What is LCD low contrast resolution detect ability

A

Defined as the smallest object that can be seen at a given contrast level end dose

53
Q

Visual object size depends on what three factors

A

Image noise
Level of contrast in the object
Window setting

54
Q

How does mA inversely related to noise

A

To decrease noise by 1/2 increase MAS by four times this will also result in those increased by four times

55
Q

How does bone algorithm affect contrast and spatial resolution?

A

Produces lower contrast, resolution, but better spatial resolution

56
Q

How does soft tissue algorithm effect contrast resolution spatial resolution?

A

Better contrast resolution, but lower spatial resolution

57
Q

How does patient size affect contrast resolution?

A

Larger patients attenuate more futons, hence higher noise and lower contrast resolution

58
Q

What does temporal resolution depend on and how is it controlled?

A

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
Q

What is a disadvantage and advantage of perspective gating

A

Advantage: reduced dose to the patient
Disadvantage: reliance on the regularity of the heart heartbeat

60
Q

What is perspective gating?

A

X-ray tube being turned off during non-acquisition times and create fewer artefacts

61
Q

What is the fastest rotation time available for temporal resolution?

A

0.275 seconds

62
Q

What is a CT number uniformity test?

A

Ability of the scanner to yield the same CT number, regardless of the location of a region of interest within a homogeneous object

63
Q

Placing several regions of interest within a phantom thus main CT number should be and what is the to

A

Number should be close to zero tolerance of two hound units

64
Q

For noise measurements ST of an ROI should not exceeded what number

A

10

65
Q

What are the sources of noise?

A

Quantum / mottle
Inherent physical limitations
Reconstruction parameters

66
Q

What is quantum noise and how is it influenced?

A

Quantum noise is x-ray flux or number of detected photons

It is influenced by scanning parameters, scanner, efficiency, and patient size

67
Q

What are inherent physical limitations?

A

Electronic noise caused by
Detector photodiode
Data acquisition system
Scatter radiation

68
Q

What are high resolution kernels?

A

Increase in noise level, noise presented, high frequency, signals, mainly these kernels enhance high frequency, contents in the production

69
Q

How do we verify external and internal lasers and ISO

A
  • incorporate into QA phantom
  • use a separate phantom
70
Q

What is a Jaszczak /ACR phantom

A

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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