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CSH059 Imaging > Computed Tomography > Flashcards

Computed Tomography Flashcards

1
Q

How is CT performed

A

Utilises an x-ray tube and a detector array rotating around the patient

Data collected is reconstructed into sectional (axial) images

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2
Q

Benefits of CT

A
  • Fast
  • Ideal for trauma and paediatrics
  • Well tolerated
  • Has replaced some conventional angiography
  • helical datasets = high quality 3D imaging
  • small attenuation differences visualised
  • good demonstration of soft tissue
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3
Q

What are the Uses of CT

A
  • No longer gold standard neuroimaging tool
  • Widely used in initial investigation for many symptoms
  • Complementary imaging with ultrasound
  • Interventional procedures
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4
Q

What are the benefits of photon counting CT

A
  • Allows smaller detector pixels -> improved spatial resolution
  • Eliminates electronic noise -> lower radiation dose
  • Allows spectral sensitivity-> Multi-energy information
  • Lower energy quanta included -> improved image contrast
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5
Q

CT image production process

A

Data acquisition -> raw data (numbers) -> image reconstruction process

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6
Q

How to minimise dose when performing CT

A

minimise scan length
perform scout scan to confirm patient position/anatomy

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7
Q

Types of Contrast Agent Applications

A

Intravenous
Gastrointestinal
Intracavity

Iodine Based or Barium Based

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8
Q

What are the benefits of contrast agents

A
  • Utilised to enhance the vasculature
  • Demonstrates function and identifies pathological processes.
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9
Q

Consent regarding contrast agent use

A
  • Informed consent to undergo contrast procedure
  • Requires sufficient information to make informed choice
  • Voluntary decision
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10
Q

Risks to Contrast Agent Use

A

Hypersensitivity to iodinated contrast media.
o Immediate
o Delayed

Acute Kidney injury – low risk in patients with eGFR > 45mL/min

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11
Q

What are algorithms and kernels

A
  • Mathematical formulas which are applied to the raw data to create an image

Can be manipulated to alter the image:
o Edge enhancement -> beneficial for lung imaging

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12
Q

Window Widths and Levels

A

Influence the displayed appearance of the image

Do not alter the CT numbers of the image

  • Same image may be photographed at a range of window
    widths and levels (centres)
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13
Q

Approx window levels and window lengths for Cerebral Tissue

A
  • ww = 100 - 150
  • wl = 40 - 60
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14
Q

Approx window levels and window lengths for Bone

A
  • ww = 2000 - 3000
  • wl = 300 – 400
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15
Q

Approx window levels and window lengths for Lung Windows

A

ww = 1500
Wl = -600

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16
Q

Volume Rendering

A

3D technique that creates a semitransparent representation of imaged
structures – all voxels contribute to
the image

17
Q

Roles of CT in oncology

A
  • Diagnosis
  • Staging - TNM
  • Simulation for RT Planning
  • Guidance for intervention
  • Monitoring response to treatment
  • Assessment during follow-up 3/12; 6/12; 12/12
18
Q

tools to enhance visualisation of image

A

Exposure
Slice widths
Window widths
Use of contrast
Field of view

19
Q

What is convolution filter

A

Mathematical approach to data representation in image (applied to raw data)
Manipulation of actual data

20
Q

Multiplanar reconstruction

A

Image reconstruction into other planes
Can be at operator console or separate workstation

21
Q

Maximum intensity projection

A

3D technique which displays the voxels of the highest value

22
Q

Shaded Surface Display

A

3D technique that displays voxels on the edge of a structure

23
Q

What is the purpose of protocol development

A

To accommodate and ensure consistency with patient factors (e.g., position, contrast)

For the application of effective post processing requirements

To limit and monitor radiation dose delivery

24
Q

Strategies of reviewing CT images

A

Multiplanar reconstruction
- image reconstruction into other plans

Max intensity projection
- 3D technique which displays the voxels of the highest value

Shaded surface display
- 3D technique that displays the voxels on the edge of a structure

Volume rendering
- 3D technique that createsa semi transparent representation of imaged structures - all voxels contribute to the image

25
Q

Impact of IV contrast on HU and how are they corrected in TPS

A

Increase attenuation of X rays therefore increased HU

This needs to be allocated normal tissue density as the patient will be treated without contrast

WITH CONTRAST -> density of structure increases
* following peripheral effusion in kidney -> continual increase with contrast

26
Q

Effect of dose modulation on radiation dose to the patient

A

Optimise image quality whilst reducing patient dose
CAREDOSE4D is turned on and Dose length product decreases by half and so is Eff mAs

27
Q

Impact of changing pitch

A

Decreasing pitch, increases scan time, decreases CTDvol (dose measure) and DLP as there is less image interpolation and more sliced being acquired
Increasing pitch decreases scan time and and increases CTD vol and DLP due to more interpolation

28
Q

Benefit of CAREDOSE4D

A

It allows for dose modulation, and results in the following:
* decrease effective mAs and DLP
* decrease dose delivered to patient

29
Q

Does the acquisition slice combination impact the projected radiation dose delivery? Why might the slice
combination be relevant?

A

Scan time and dose to patients increase

30
Q

What is the benefit of producing a coronal series with a larger slice interval?

A

Allows for the image to follow the vessels and organs
Allows for a summary of images -> faster review time

31
Q

How does attenuation occur in CT

A

Attenuation of the beam occurs as x-rays travel through the patient

Absorption and scattering occurs upon interaction with tissue

Differences in attenuation are collected by the detectors

This is what establishes the contrast between tissues on CT images

32
Q

Main steps in performing CT

A

Register the patient
Select protocol for body part
Select patient orientation
Acquire scout scan
Select scan area and scan
Acquire data
Computer generates image from data collected
View images and check all data is sufficient prior to patient leaving CT
Perform any post processing and transfer of data

33
Q

What is a scout scan

A

Low dose scan which be used to set scan parameters for higher dose scan

*verify patient position
*verify scan length
*verify patient anatomy

Provides low spatial and contrast resolution

34
Q

Provide a definition for Hounsfield Units

A

Numbers used to define relative attenuation coefficients for each pixel of tissue in an image as compared to the attenuation coefficient of water

35
Q

Provide a definition for Window Level

A

Determines the mid range CT number

This is the centre CT number value.

36
Q

Provide a definition for Window Width

A

Determines the upper and lower range of CT numbers displayed by the gray scale

CT number above the range -> displayed as white

CT numbers below the range -> displayed as black

37
Q

Impact of decreasing pitch

A

More mAs required for the same volume
Increase in image quality
Slower scan time

38
Q

Role of CT in RT planning

A

Accurate determination of heterogeneities
Provides 3D and 4D information for treatment calcs
Creation of DRR’s
Accurate structure identification, target and OAR localisation
Conebeam CT -> IGRT

CSH059 Imaging (8 decks)

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