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MRAD 251 - Computed Tomography > Textbook - Chapter 1 > Flashcards

Textbook - Chapter 1 Flashcards

1
Q

spatial resolution

A

ability of a system define small objects distinctly

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2
Q

low-contrast solution

A

ability of a system to differentiate between objects with similar densities

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3
Q

temporal resolution

A

speed that the data can be acquired

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4
Q

z-axis

A

thickness of a cross-sectional slice

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5
Q

pixel

A

2D picture element consisting of x and y

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6
Q

x-axis

A

width

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7
Q

y-axis

A

height

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8
Q

voxel

A

3D volume element consisting of x, y, & z

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9
Q

what’s the most common matrix size for ct?

A

512x512

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10
Q

what is attenuation?

A

degree which an x-ray beam is reduced

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11
Q

when photons pass through something unimpeded, what colour will it show up on the ct image?

A

black

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12
Q

colour of low attenuation objects

A

black

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13
Q

colour of high attenuation objects

A

white

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14
Q

colour of intermediately attenuating objects

A

differing shades of grey

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15
Q

number of photons that interact with an object is dependent on?

A
  1. thickness
  2. density
  3. atomic number
    *of the object
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16
Q

what is linear attenuation coefficient (µ)?

A

amount of the x-ray beam that is scattered or absorbed per unit thickness of the absorber

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17
Q

____ µ = _____ photon energy

A

↓µ = ↑photon energy

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18
Q

____ µ = _____ atomic number

A

↑ µ = ↑ atomic number

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19
Q

____ µ = _____ density

A

↑ µ = ↑ density

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20
Q

image contrast is determined by?

A

difference in linear attenuation coefficients among tissues

21
Q

soft tissues’ linear attenuation coefficient is ____ (dis/proportional) to physical density

A

proportional

22
Q

what are positive agents?

A

contrast agents that are higher in density than structures they’re introduced to

23
Q

what examples of positive agents?

A

barium sulfate and iodine

24
Q

what is an example of a negative agent?

A

water (low-density)

25
Q

what are Hounsfield units also known as?

A

CT numbers or density values

26
Q

what are HUs?

A
  • indicates the degree that a structure attenuates an x-ray beam in comparison to water
  • average of all the attenuation measurements for the pixel
27
Q

HU of dense bone

A

+1000

28
Q

HU of air

A

-1000

29
Q

HU of distilled water

A

0

30
Q

what are the main advantages of CT over conventional radiography?

A
  • can get the 3d view –> get images of cross sections
  • elimination of superimposed structures
  • differentiation between structures with similar densities
  • good image quality
31
Q

matrix

A

grid that is formed from the rows and columns of pixels

32
Q

what are image artifacts?

A

things that are on the image that isn’t actually there

33
Q

what causes artifacts?

A

polychromatic X-rays and beam hardening

34
Q

what causes beam hardening?

A

when low energy photons are absorbed leaving high energy ones to strike the detector

35
Q

what is the anatomic position?

A

erect with arms to the side and palms facing forward

36
Q

how are x-ray photons produced?

A

when electrons strike the anode

37
Q

1 HU = ___% difference between the linear attenuation coefficient of water

A

0.1%

38
Q

what are cupping artifacts?

A

vague areas of decreased density

39
Q

Raw data

A

Data acquired by the system

40
Q

Scan data

A

Aka raw data

41
Q

Raw data have not been assigned HUs. Why?

A

Haven’t been sectioned to creat pixels

42
Q

Image reconstruction

A

Using raw data to create an image
Done by processing the raw data, assigning HUs to the pixels

43
Q

Image data

A

Data included in the image through image reconstruction

44
Q

Prospective reconstruction

A

Reconstruction automatically produced during scanning

45
Q

Retrospective reconstruction

A

Using the raw data later to generate new images (even after they have undergone perspective reconstruction)

46
Q

Stop and shoot, aka?

A

Axial scanning or conventional scanning or serial scanning

47
Q

2 reasons for changing image plane from axial to coronal?

A
  1. Anatomy of interest lies vertically instead of horizontally
  2. Reduction of artifacts caused by surrounding structures
48
Q

mA

A

quantity of electrons

49
Q

kVp

A

voltage = intensity of x-ray beam

MRAD 251 - Computed Tomography (13 decks)

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