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Ct Review Class > Ch 3 Ct Image Quality > Flashcards

Ch 3 Ct Image Quality Flashcards

1
Q

Influences on user parameter selection p 4

A 
Contrast resolution
Spatial resolution 
Temporal imaging 
Image noise
Patient dose
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2
Q

Tissues with difference of _____% in density can be differentiated in ct

A

O.5%

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3
Q

Contrast resolution p 4

A

ability to,differentiate small differences in density on the image

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4
Q

Spatial resolution p 4

A

Measure of size of the smallest on object that can be visualized in an image

In line pairs

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5
Q

Spatial resolution affected by geometric factors of the scanner p 4

A

Focal spot size
Detector Aperture size
Focal spot to patient distance
Patient to detector difference

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6
Q

Spatial resolution factors that control it p 4

A

Slice thickness
Display for
Image matrix
Reconstruction filters

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7
Q

Temporal resolution p 5

A

Precision of measurement with respect to time

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8
Q

2 effects Increases temporal resolution p 5

A

Quicker scans

Increase rows of detectors

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9
Q

Noise p 6

A

Grainy image that makes it difficult to see subtle contrast differences or fine details

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10
Q

Dose p 7

A

Amount of ionizing radiation absorbed by patient per unit of mass

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11
Q

To maximize image quality sometimes there is increase in______ p 8

A

Patient dose

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12
Q

Attenuation p 9

A

Progressive reduction of intensity of the X-ray beam as it passes through patient tissue

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13
Q

Amount attenuation is dependent on p 9

A

Anatomic number
Density of electrons
Thickness
Photon energy

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14
Q

Number photons measure by detectors is reduced as thickness tissue ______ p 9

A

Increases

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15
Q

When X-ray beam passes through patient , number of photons in beam is reduced while mean energy of photons _____ p 10

A

Increase

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16
Q

Ct number p 11

A

Gray scale number assigned to each pixel in Ct image

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17
Q

Hounsfield number p 11

A

Aka Ct number named after inventor of Ct in 1967 aka HU

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18
Q

Water Ct number

A

0

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19
Q

Air Ct number

A

-1000

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20
Q

Fat Ct number

A

-80

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21
Q

Soft tissue Ct number range

A

30-80

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22
Q

Ct number shows calcification

A

Above 100

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23
Q

What calculates ct number p11

A

Filtered back projection

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24
Q

Higher ct numbers assigned to shades of grey?

A

Lighter shades of grey for dense structures

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25
Q

Lower ct numbers assigned to shades of grey? P 11

A

Darker shades for non dense structures

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26
Q

Ma p 13

A

Tube current

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27
Q

Mas p 13

A

Ma x time

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28
Q

Increasing the mas _____ image noise but _____ patient dose

A

Decrease

Increase

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29
Q

What doesn’t affect image contrast or spatial resolution ?

A

Mas

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30
Q

Scan times should be short to minimize _____ and maximize _____

A

Motion

Patient throughput

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31
Q

Kv p 15

A

Tube voltage

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32
Q

Kvp

A

Kilovoltage peak or max energy of photons

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33
Q

_____ kvp increases the energy of photons and _____ ability to penetrate patient

A

Increase

Increase

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34
Q

Kvp controls ? P 15

A

Contrast

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35
Q

Kvp range in ct

A

100-140

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36
Q

Slice thickness p 16

A

Number of millimeters of anatomy intersected by thickness of xray beam which is represented by Ct image

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37
Q

Slice thickness aka (2)

A

Image thickness

Section thickness

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38
Q

Single row detector scanner slic thickness p 16

A

Defined by size focal spot and collimators

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39
Q

Single row detector scanner thinner slice results from collimation?

A

Collimators close together

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40
Q

Single row detector thicker slice results in collimators?

A

Farther apart

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41
Q

Single row scanner , collimated xray beam thickness ____ the acquired slice thickness , which equals final image thickness p 17

A

Equals

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42
Q

On single row detector scanner , the slice thickness is determined by _____ of xray beam

A

Collimation

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43
Q

Acquired slice thickness p 17

A

On mult row detector scanner , indicates which rows of detectors are being used to measure the photons that pass completely throw the patients body

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44
Q

Multi row detector a thinner slice is specified by ____ detectors are used

A

Smaller

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45
Q

Multi row detector thicker acquired slice thickness is specified by ____ detectors or combo of ____ detectors are used

A

Larger

Smaller

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46
Q

On multi row detector scanner , slice thickness is determined by the the data collected from one or several adjacent _____arrays

A

Detector

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47
Q

Reconstructed slice thickness p18

A

Aka effective slice thickness

Thickness of final image

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48
Q

On mdct, final slice thickness must ____ or be ____than acquired slice thickness p 18

A

Equal or greater

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49
Q

Effects of slice thickness p 18

A 
Anatomical coverage 
Number of images
Image noise
Spatial resolution 
Dose
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50
Q

Noise of image is affected by slice thickness by pre patient _____which allows more photons to reach detectors when thick slice selected than a thin one

A

Collimation

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51
Q

Partial voluming or partial volume averaging p 19

A

Mathematical averaging of varying density

52
Q

If we scan a single slice , as slice thickness increases, the volume of irradiated tissue increases and patient dose _____ p 20

A

Increases

53
Q

Multi slice studies, slice thickness increases, the dose of the total volume ____

A

Decreases

54
Q

On conventional or serial , the _________ determines if the slices will be contigious or if there will be a gap or overlap

A

Table increment

55
Q

To get contiguous slices , table increment must equal to ______

A

Slice thickness

56
Q

If table increment is less than slice thickness the slices will _____

A

Overlap

57
Q

If table increment is greater than slice thickness, there will be _____between slices

A

Gaps

58
Q

Using larger table increments , will _____anatomical coverage that you can image with pre determined slice thickness and number slices .

A

Increase

59
Q

Larger table increment , allows use fewer slices thus ______ dose

A

Decreasing

60
Q

Table increment affects visualization of fine detail by larger table increments than slice thickness and gaps occur some anatomy will be skipped

A

P 22

61
Q

Overlapping slices increase number photons passing through patients body thus ___ dose

A

Increasing

62
Q

Pitch p 23

A

AntomicAl coverage of a helical scan

63
Q

Single row detector pitch p 23

A

Pitch equals movement of patient table in one gantry rotation divided by slice thickness

Pitch= movement of patient table in one gantry rotation
——————————————————
Slice thickness

64
Q

Pitch determines ____ p 23

A

How stretched xray path is during helical scan

65
Q

Multi row detector pitch

A

Pitch equals movement of table in on e gantry rotation dived by total slice volume

Or

Pitch equals movement of patient table in one gantry rotation divided by thickness of single slice

66
Q

Effects of pitch on shape of helix p 24

A

Helix is unstretched

Pitch increased the helix stretched

67
Q

Reasons increase pitch p 24

A

Greater anatomical coverage in less time
Faster scan for trauma
Appropriate contrast timing during cta study
Decrease dose to patient

68
Q

Pitch affects p 25

A

Anatomical coverage
Scan time ( temporal resolution)
Spatial resolution
Dose

69
Q

Reconstruction interval p 27

A

When helical scan is compete , mathematical calculation can divide the helical data into planar samples of raw data at the right slice location

70
Q

Reconstruction interval can be modified before the scan is run or as retrospective reconstruction

A

P 27

71
Q

In helical scans , reconstruction interval determines if slice are (2)?

A

Contiguous

Overlap or gap

72
Q

There is no additional dose to patient during reconstruction interval

A

P 27

73
Q

Effect of overlapping slices with reconstruction interval

A

If object falls exactly halfway between two contiguous slices, it may not be visualized well

If slices are overlapped by proper selection of reconstruction interval the object maybe more completely contained in one of the slices

74
Q

Pixel p 29

A

A single picture element in the image

75
Q

Voxel p 29

A

Three dimensional volume element

76
Q

Pixels in ct image reperesent the ________ of a volume of tissue at the position in the slice

A

Ct number

77
Q

One dimension of video?
Other two dimensions ?

P 29

A

One- slice thickness

Two- in plane spatial resolution

78
Q

Scan field of view ( fov) p 29

A

Parameter which is adjusted for the size of the anatomy . The number of detectors collecting data in a scan

79
Q

Two fov

A

Scan fov

Reconstruction fov

80
Q

Out field artifacts characterized by

P 30

A

Image shading
Streaks
Incorrect assignment of ct numbers to image pixels

81
Q

Reconstruction fov p 30

A

Region interest illustrated in resulting image and fov reconstructed from the complete set of raw data

Aka display fov

82
Q

Reconstruction fov ( display fov) is equal to

A

Equal or smaller

83
Q

Two reconstruction fov

A

Small

Large

84
Q

Small/ narrow reconstruction fov p 30

A

Restricting area of interest and displaying image larger like zoom lens

85
Q

Large/ wide reconstruction fov p 30

A

Anatomy appears small

86
Q

Thicker slice means ____ noise p 31

A

Less

87
Q

Wider reconstruction fov mean _______ noise

A

Less noise

88
Q

Reconstruction fov affects p 31

A

Spatial resolution

Image noise

89
Q

In plane spatial resolution p 31

A

Reconstruction fov / number of pixels along direction in image matrix

90
Q

Matrix p 33

A

Grid pixels that form image

91
Q

Resolution of image expressed as reconstruction fov formula

A

Reconstruction fov/ matrix

92
Q

Increase matrix mean ______ pixels and allows ____ detail

A

Smaller

Smaller

93
Q

Small matrix means ____ pixel size

A

Large

94
Q

Large matrix means ______ pixel size

A

Small

95
Q

Larger image matrix means ____ noise

A

More

96
Q

Matrix affects

A

Spatial resolution

Appearance of image noise

97
Q

Common matrix size p 33

A

512x512

98
Q

Magnification p 34

A

Enlarges individual pixels of reconstructed image for display purposes

99
Q

Magnification does not affect (2) p 34

A

Spatial resolution

Image noise

100
Q

Smaller reconstruction fov means _____size of displayed image

A

Increase

101
Q

Decreasing reconstruction fov will _____ spatial resolution and noise level

A

Increase

102
Q

Magnification is post processing technique applied to _____ data

A

Image

103
Q

Magnification is only way to enlarge image data if ____ data no longer available p 35

A

Raw

104
Q

Window width p 36

A

How much contrast appears in image

105
Q

Ct number -1000

A

Air

106
Q

+1000 ct number

A

Dense bone

107
Q

Operator console displays ____ shades grey

P 36

A

256

108
Q

Human eye detects ____ shades of grey

A

20

109
Q

Ct number above range are assigned pixel level ?

A

255 white

110
Q

Any ct number below this range are assigned a pixel value of?

A

0( black)

111
Q

Increase window width ____

A

Higher contrast

112
Q

Lungs studies have ____ contrast

A

High

113
Q

Larger window width mean ____ contrast

A

Less

114
Q

Narrow window width is ____ contrast

A

More

115
Q

Window level p 37

A

Adjusts brightness of the tissues in the image

116
Q

Ct number higher than 250 appears_____

A

White

117
Q

Ct number lower than -250 will appear _____

P 38

A

Black

118
Q

Low window level makes image _____

A

Brighter

119
Q

High window level makes image _____

A

Darker

120
Q

Quality assurance p 39

A

Concept that comprises all the oversight and management practices developed by ct imaging team led by supervising physician, to ensure that every imaging procedure is necessary and approximate, the acquisition parameters are appropriate for clinical situation , image generated are sufficient to solve clinical problem , images are correctly interpreted, and that exam generates lowest risk to patient while meeting clinical objective

121
Q

Quality control p 39

A

Procedure performing specified tests or measurements on periodic basis in order to assure that set level of quality has not been compromised

122
Q

Two daily qa done

A

Ct number calibration test

Ct number standard deviation test

123
Q

Ct number calibration test acceptable limits

A

Ct number water must measure between -3 and + 3 HU

124
Q

Ct number standard deviation test p 40

A

Standard deviation of water must not exceddd a specific level

125
Q

Less frequent tests p 40

A

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Ct Review Class (7 decks)

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