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CT & MRI > CT Principle 1 > Flashcards

CT Principle 1 Flashcards

1
Q

Unlike X-rays, CT reconstructs ____ of internal structures according to ____ for almost every region in the body

A

cross sectional images; x-ray attenuation coefficients (tissue density)

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2
Q

CT was previously known as

A

Computed Axial Tomography (CAT Scan)

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3
Q

What imaging technique was used to visualize the brain before the invention of CT?

A

radiography

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4
Q

Which mathematician introduced the transformation operator that laid the foundation for tomographic reconstruction?

A

Johann Radon

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5
Q

After the injection of air in pneumoencephalography, the patient was rotated, somersaulted or placed in a ___________ position to depicts the entire ventricular system and subarachnoid spaces

A

Decubitus

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6
Q

Who validated Allan Cormack’s work by building the first prototype CT scanner?

A

Sir Godfrey Hounsfield

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7
Q

which gen uses pencil beam

A

1st Gen

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8
Q

which gen uses narrow fan beam

A

2nd Gen

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9
Q

which gen uses wide fan beam

A

3rd, 4th, 6th

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10
Q

which gen uses electron gun firing beam

A

5th

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11
Q

which gen uses cone beam

A

7th

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12
Q

which gen uses translate-rotate

A

1st, 2nd

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13
Q

which gen uses rotate-fixed

A

4th

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13
Q

which gen uses rotate-rotate

A

3rd, 6th, 7th

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14
Q

which gen uses stationary-stationary electron beam

A

5th

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15
Q

which gen uses rotate-rotate (helical/spiral)

A

6th, 7th

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16
Q

which gen uses slip ring technology

A

3rd, 6th, 7th

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17
Q

What is the main advantage of CT over conventional radiography?

A

Elimination of superimposition of structures

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18
Q

The first generation of CT scanners used which motion for scanning?

A

Translate – rotate

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19
Q

In CT, what does the term ‘voxel’ refer to?

A

A volume element in 3D space

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20
Q

pre-patient collimators is place between

A

filter & patient

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21
Q

post-patient collimators is placed

A

on top of detector

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22
Q

purpose of pre-patient collimators

A

lowers dose & over beaming

23
Q

purpose of post-patient collimators

A

reduces scatter, penumbra

defines slice thickness

24
Q

what are slip rings

A

alternatives to cabling system; power & control signals comms via rotating frame through slip ring

25
Q

what is the main benefit of slip rings

A

Allow scan frame to rotate continuously with no need to stop between rotations to rewind system cables

26
Q

CT Detector Image Formation Process

A
  1. x-rays generates radiation
  2. x-rays penetrate body & attenuated by tissue
  3. attenuated x-rays processed by detector
  4. detector converts radiation into electrical signals
  5. converts digital data into high res images
27
Q

GOS

A

Gadolinium Oxysulfide

28
Q

Pr

A

Praesodynium-doped

29
Q

UFC

A

ultra fast ceramic

30
Q

CsI

A

Cesium Iodide

31
Q

Solid scintillator layer converts ___

A

x-ray photons to light photons

32
Q

photodiode converts __

A

light photons to electrical signals

33
Q

properties of solid state detectors

A
  1. high detection
  2. high geometry
  3. small size of DELs
34
Q

DELs are important for

A

spatial resolution

35
Q

high detection & high geometry are important for

A

radiation dose

36
Q

what does beam shaping filtering do

A

Hardens x-ray by removing low energy x rays that do not contribute to image formation but increase patient dose

37
Q

as the x-ray energies become narrower, the beam becomes more ___

A

monochromatic

38
Q

what is the common beam filter used

A

bow-tie filter

39
Q

what happens if the iso-centering is off

A

off iso-centering > need to increase x-ray output due to filtering mismatch > increases dose

40
Q

what is related to couch top speed

A

pitch

41
Q

sequential scans are when the patient moves ___

A

gradually layer-by-layer through gantry during scan

42
Q

spiral scans are when the patient moves ___

A

continuously through gantry during scan

43
Q

advantages of multi-row detectors against single row detectors

A
  • reduced scan time (more coverage + faster scans)
  • shorter breath holds
  • fewer motion artifacts
  • allows for multiphase contrast enhanced scanning
  • reduced dose
  • more efficient use of x-rays with increasing slices
44
Q

how many images are created per rotation when using single slice detectors

A

1 per rotation

45
Q

how many images are created per rotation when using multi slice detectors

A

hundred per rotation

46
Q

what controls slice thickness along z-axis for single slice detectors

A

collimation

47
Q

what controls slice thickness along z-axis for multi slice detectors

A

activating diff combo of detector rows along z-axis; by detector size

48
Q

detector pitch definition

A

distance table travels in 1 360 degrees gantry rotation divided by beam collimation / x-ray beam width

49
Q

pitch detector ranges from

A

0.75 to 1.5

50
Q

choice of pitch influences __

A

image quality + dose

51
Q

the higher the pitch, the ___ the dose & image quality

A

lower

52
Q

the lower the pitch, the ___ the dose & image quality

A

higher

53
Q

what does pitch fundamentally influence

A
  1. dose
  2. image quality
  3. scan time
54
Q
A

CT & MRI (12 decks)

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