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CT > CT Basics And Model > Flashcards

CT Basics And Model Flashcards

1
Q

What are the 3 segments of CT imaging?

A
  1. Data acquisition
  2. Image recons
  3. Image display
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2
Q

What is data acquisition?

A

X-rays passing through the patient and hitting the detector

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3
Q

What is the gantry?

A

Ring shaped frame of the CT scanner.

It may be tilted forward or backward depending on patient or exam type.

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4
Q

What are slip rings?

A

Help the gantry frame continuously rotate for helical scans via electronically powered communication

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5
Q

What is the generator?

A

Power the scanner that control the exposure factors and are:
- High frequency
- High voltage
- High beam energy
- High penetrating ability
- High patient dose

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6
Q

What exposure technique helps to extend generator life?

A

High kV and low mAs

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7
Q

What are cooling systems?

A

Cool the scanner due to high heat from producing x-rays and include…
- blowers
- filters
- oil to air heat exchange

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8
Q

What material is the x-ray source usually made from?

A

Tungsten because it has a high atomic number and high melting point

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9
Q

What size focal spot is better for image quality and why?

A

A SMALLER focal spot produces sharper images because it reduces penumbra

(Heat concentrates on smaller portion of anode —> cannot tolerate as much heat)

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10
Q

What is a flying focal spot?

A

Multiple focal spots that create 2 beams and overlap directed at the same single detector array

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11
Q

What role does filtration have and what are the benefits?

A
  1. Filters out low energy x-rays
  2. Shapes the beam

Reduced patient dose and less image artefact

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12
Q

What filter is commonly used for body imaging?

A

Bow tie filter (thicker to lessen the beam for the body periphery)

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13
Q

What benefits does collimation have?

A
  1. Reduce scatter radiation
  2. Lower patient dose
  3. Increases image quality
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14
Q

What does collimation do?

A

Determine slice thickness and dose profile

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15
Q

What are detectors?

A

Array/collection of detectors that capture data from x-rays after passing through the patient

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16
Q

What are optimal characteristics of detectors?

A
  1. High detector efficiency
  2. Low/no afterglow
  3. High scatter suppression
  4. High stability
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17
Q

What type of detector was and is used?

A

Past: xenon gas

Now: solid-state crystal

18
Q

What are different types of detector arrays?

A
  1. Matrix array - evenly sized elements
  2. Hybrid array - most elements the same size with smaller rows in the middle
  3. Adaptive array - smaller elements in the middle and progressively getting larger the farther it goes out
19
Q

What determines the scanner generation?

A

Tube and detector configuration

20
Q

What is the 1st generation scanner generation?

A

Thin linear beam over the patient with a single detector opposite to the tube

21
Q

What beam style is used for a 1st gen scanner generation?

A

Pencil beam

22
Q

What is the 2nd generation of the scanner?

A

Fan shaped beam that is linear over the patient before rotating with single detector array opposite tube

23
Q

What is the 3rd generation of scanner?

A

Fan shaped beam travels linearly over patient with detector array opposite to the tube.

Both tube and detectors rotate in the gantry.

24
Q

What is another name for the 3rd gen scanner?

A

Rotate rotate scanner

25
Q

What are pros of 3rd gen scanners?

A
  1. Shorter scan time
  2. Less artefacts
  3. More collimation ability
  4. Reduced scatter
  5. Better image quality
26
Q

What are cons of 3rd gen scanners?

A

Increased ring artefact because same detector is overused and misalignment occurs

27
Q

What is the 4th generation scanner?

A

Tube is fixed and detector array moves 360 degrees in the gantry with a wide fan shaped beam

28
Q

What are pros of 4th gen scanners?

A

Really quick scan times

29
Q

What are cons of 4th gen scanners?

A
  1. More motion artefact
  2. Increased patient dose because of overscanning and tube closer to the patient
30
Q

What is incrementation?

A

Table movement during scanning

31
Q

What is the full length the table can move?

A

Scannable range

32
Q

What units are used for helical scan table movements?

A

mm/sec

33
Q

What is the pre patient collimation and what does it determine?

A

Between the x-ray source and patient

Limits the beam that hits and exposes the patient, determines slice thickness and patient dose

34
Q

What is the post patient collimation and what does it determine?

A

Between the patient and detector array

Restricts the area that the beam can hit the detector array, determines slice thickness and reduces scatter

35
Q

What is automatic tube modulation?

A

Adjusts the tubes current to maintain image quality while reducing patient dose

36
Q

How are images produced?

A

Raw data (no pixels or HU assigned) —> recon (pro or retrospective) —> image data

37
Q

How are images produced from the source?

A
  1. Tube produces x-ray photons
  2. Filters will filter out low energy photons
  3. Beam passes through the collimator to shape it
  4. Beam passes though the patient
  5. Beam hits and absorbed by the detector array
  6. Photons are converted to electronic signal
  7. Photons are absorbed and converted to digital signals by an analog to digital converter as raw data
  8. Digital data is assigned HU values
  9. The computer applies filters to remove artefacts and better visualise the subject
38
Q

What is window width?

A

The number of HU of pixels in an image

Quantity

39
Q

What is window length?

A

Centre of HU in an image

Range

40
Q

What is the SFOV?

A

Area within the gantry from which raw data are collected

41
Q

What is DFOV?

A

Amount of raw data that creates an image

42
Q

_FOV cannot be larger than _FOV…

A

DFOV; SFOV

CT (7 decks)

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