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MRAD 251 - Computed Tomography > week 2 lecture 1 > Flashcards

week 2 lecture 1 Flashcards

1
Q

GR is a form of _____ imaging. What does this mean?

A

planar imaging.
it means that it will produce 2d images of 3d objects

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2
Q

what are the limitations to GR?

A
  • all structures are superimposed
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3
Q

why is superimposition bad?

A
  • makes it hard to identify precise location of the abnormalities
  • makes it difficult to distinguish slight change in density
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4
Q

what is blurred in Linear Tomography?

A

structures outside of the area of interest

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5
Q

what purpose is the blurring effect in linear tomography?

A

to improve visualization of the tissue of interest

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6
Q

what is one of the advantages to linear tomography?

A

enhancement of radiographic contrast

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7
Q

how is linear tomography done?

A

the patient is stationary while the x-ray tube and image receptor is following the patient’s longitudinal axis

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8
Q

why is the x-ray tube and detector connected?

A

enables them to move in opposite directions at the same time

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9
Q

focal plane

A

section that images anatomical structures clearly

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10
Q

focal plane is aka?

A

section thickness or object plane

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11
Q

the amount of tube motion is =?

A

size of the section to be imaged clearly

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12
Q

fulcrum

A

imaginary pivot point about which the x-ray tube and detector move

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13
Q

centre of the object plane (aka focal plane aka section thickness) is determined by what?

A

the fulcrum

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14
Q

what causes the objects outside the focal plane to blur in the images?

A

the movement of the x-ray tube and detector during exposure

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15
Q

the objects position on the detector correlates to what?

A

the x-ray tube’s movement; objects are in the opposite direction
*tube movement causes objects to exhibit varying positions on the detector during the exposure

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16
Q

tomographic angle

A

amount of tube motion during an exposure which controls the thickness of the section imaged

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17
Q

decreasing in tube motion = (increase/decrease) tomographic angle

A

decrease tomographic angle

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18
Q

0 degree angle = no tube and detector motion = section thickness to infinity

A
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19
Q

smaller angles = (thinner/thicker) sections

A

smaller angles = thicker sections

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20
Q

image blur increases as object distance from the focal plane (increases/decreases)

A

image blur increases as distance from focal plane increases

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21
Q

what are the advantages of linear tomography over general radiology?

A
  • increase radiographic contrast
  • decrease superimposition
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22
Q

what are the disadvantages of linear tomography over general radiology?

A
  • increases patient dose due to x-ray tube being on for the length of tube travel (longer exposure)
  • multiple exposures may be done
  • requires the use of grids
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23
Q

what are the main advantages of ct?

A
  • low-contrast resolution
  • versatility in data acquisition options
  • image reconstruction capabilities
  • reformatting possibilities
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24
Q

what is the basic principle of computed tomography?

A

production of sharp, clear, cross-sectional images of the human body

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25
Q

how does CT obtain these cross-sectional images?

A

use of a rotating tube, detector array and computer reconstruction algorithms

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26
Q

detector array

A

use of multiple detectors

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27
Q

what are the modifications for ct?

A
  • patient is also moving through the system
  • detector array
  • uses a computer to collect, organize and create axial image
28
Q

what are the main disadvantages to ct?

A
  • produces high radiation doses
  • susceptible to more image artifacts
  • decrease in spatial resolution
29
Q

what are the 5 components of ct?

A
  1. table
  2. gantry
  3. power injector
  4. operating console
  5. workstation
30
Q

what are the four steps to creating a ct image?

A
  1. data acquisition
  2. image reconstruction
  3. image display
  4. image archive
31
Q

data acquisition

A

how we collect information to form an image

32
Q

steps to data acquisition.

A
  1. scouts (planning)
  2. ct slices
33
Q

raw data

A

what is collected by the detectors when the x-ray tube irradiates an area of interest

34
Q

raw data aka?

A

scan data

35
Q

image reconstruction

A

process of manipulating raw data using algorithms

36
Q

how is image reconstruction done?

A
  • radiation flux at the detectors create electrical signals that are converted into digital format (HUs)
  • these will be put onto a matrix
  • data is selected for display
37
Q

DAS - data acquisition system

A

measures radiation collected by detectors
calculates beam attenuation

38
Q

ADC - analog to digital data conversions

A

converts the raw data into digital format

39
Q

how is this conversion of raw data to digital format happening?

A

ADC assigns pixels different HU values

40
Q

algorithms

A

set of rules/directions used to get a specific output from specific input

41
Q

algorithms are required to be:

A
  • simple and well defined
  • terminates after finite number of steps
42
Q

what are common automatic algorithms?

A
  • back projection
  • filtered back projection
  • iterative reconstruction
  • Fourier transform
43
Q

back projection

A

raw data is dragged/smeared onto a matrix in order to view the shape of the scanned object

44
Q

star-pattern artifacts are produced by?

A

back projection

45
Q

filtered back projection

A

uses convolution to remove the blurring caused by back projection = improves image quality

46
Q

iterative reconstruction

A

compares scan data with an assumed image dataset then it projects the calculated difference onto the matrix

47
Q

Fourier transform

A

used in MRI image reconstruction; based on measuring frequencies

48
Q

what are the 3 common “selected” algorithms?

A
  1. standard
  2. smoothing
  3. edge enhancement
49
Q

smoothing

A

improves visualization of soft-tissue structures and can help minimize artifacts

50
Q

when is smoothing usually used?

A

when it is a brain tissue image

51
Q

smoothing = (increase/decrease) noise + (increase/decrease) spatial resolution + (increase/decrease) contrast resolution

A

smoothing = ↓ noise and spatial resolution, ↑ contrast resolution

52
Q

edge enhancement

A

helps demonstrates fine detail (smaller objects)

53
Q

when is edge enhancement usually used?

A

when imaging small bony fragments and pulmonary structures

54
Q

edge enhancement = (increase/decrease) noise + (increase/decrease) spatial resolution + (increase/decrease) contrast resolution

A

edge enhancement = ↑ noise + spatial resolution, ↓contrast resolution

55
Q

standard

A

algorithm that balances noise and detail

56
Q

image display

A

process where the reconstructed data is averaged for display on a monitor

57
Q

image data

A

data of an image that can be viewed on a monitor

58
Q

DAC - digital to analog data conversion

A

assigns the pixels different shades of grey based on the pixel’s HUs

59
Q

why is DAC necessary?

A

it is needed to convert the reconstructed data into image data that can be seen at the workstation/operating console monitors

60
Q

can post-processing functions be used to manipulate image data?

A

yes. as it can improve image viewing

61
Q

image archiving

A

how we store CT image data

62
Q

how are images accessed remotely?

A
  • PACS (picture archival communication system)
  • DICOM (digital imaging and communication in medicine)
63
Q

when does saving images for future viewing occur?

A

after raw data has been reconstructed and image display is acceptable

64
Q

smaller fss is used for?

A

when we want to get finer details (better spatial reso)

65
Q

larger fss is used when?

A

regardless of needing detail but the patient is more hypersthenic

66
Q

the tube and detector needs to be (perpendicular/parallel) to the patient’s longitudinal axis. why?

A

parallel, because it will help with the avoidance of superimposition and too much blur

67
Q

scout image aka?

A

preliminary, pilot, localizer

MRAD 251 - Computed Tomography (13 decks)

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