Ch 3 Ct Image Quality Flashcards Preview

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Flashcards in Ch 3 Ct Image Quality Deck (125):
1

Influences on user parameter selection p 4

Contrast resolution
Spatial resolution
Temporal imaging
Image noise
Patient dose

2

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

O.5%

3

Contrast resolution p 4

ability to,differentiate small differences in density on the image

4

Spatial resolution p 4

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

In line pairs

5

Spatial resolution affected by geometric factors of the scanner p 4

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

6

Spatial resolution factors that control it p 4

Slice thickness
Display for
Image matrix
Reconstruction filters

7

Temporal resolution p 5

Precision of measurement with respect to time

8

2 effects Increases temporal resolution p 5

Quicker scans
Increase rows of detectors

9

Noise p 6

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

10

Dose p 7

Amount of ionizing radiation absorbed by patient per unit of mass

11

To maximize image quality sometimes there is increase in______ p 8

Patient dose

12

Attenuation p 9

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

13

Amount attenuation is dependent on p 9

Anatomic number
Density of electrons
Thickness
Photon energy

14

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

Increases

15

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

Increase

16

Ct number p 11

Gray scale number assigned to each pixel in Ct image

17

Hounsfield number p 11

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

18

Water Ct number

0

19

Air Ct number

-1000

20

Fat Ct number

-80

21

Soft tissue Ct number range

30-80

22

Ct number shows calcification

Above 100

23

What calculates ct number p11

Filtered back projection

24

Higher ct numbers assigned to shades of grey?

Lighter shades of grey for dense structures

25

Lower ct numbers assigned to shades of grey? P 11

Darker shades for non dense structures

26

Ma p 13

Tube current

27

Mas p 13

Ma x time

28

Increasing the mas _____ image noise but _____ patient dose

Decrease
Increase

29

What doesn't affect image contrast or spatial resolution ?

Mas

30

Scan times should be short to minimize _____ and maximize _____

Motion
Patient throughput

31

Kv p 15

Tube voltage

32

Kvp

Kilovoltage peak or max energy of photons

33

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

Increase

Increase

34

Kvp controls ? P 15

Contrast

35

Kvp range in ct

100-140

36

Slice thickness p 16

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

37

Slice thickness aka (2)

Image thickness
Section thickness

38

Single row detector scanner slic thickness p 16

Defined by size focal spot and collimators

39

Single row detector scanner thinner slice results from collimation?

Collimators close together

40

Single row detector thicker slice results in collimators?

Farther apart

41

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

Equals

42

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

Collimation

43

Acquired slice thickness p 17

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

44

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

Smaller

45

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

Larger

Smaller

46

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

Detector

47

Reconstructed slice thickness p18

Aka effective slice thickness

Thickness of final image

48

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

Equal or greater

49

Effects of slice thickness p 18

Anatomical coverage
Number of images
Image noise
Spatial resolution
Dose

50

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

Collimation

51

Partial voluming or partial volume averaging p 19

Mathematical averaging of varying density

52

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

Increases

53

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

Decreases

54

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

Table increment

55

To get contiguous slices , table increment must equal to ______

Slice thickness

56

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

Overlap

57

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

Gaps

58

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

Increase

59

Larger table increment , allows use fewer slices thus ______ dose

Decreasing

60

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

P 22

61

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

Increasing

62

Pitch p 23

AntomicAl coverage of a helical scan

63

Single row detector pitch p 23

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

Pitch determines ____ p 23

How stretched xray path is during helical scan

65

Multi row detector pitch

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

Effects of pitch on shape of helix p 24

Helix is unstretched
Pitch increased the helix stretched

67

Reasons increase pitch p 24

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

68

Pitch affects p 25

Anatomical coverage
Scan time ( temporal resolution)
Spatial resolution
Dose

69

Reconstruction interval p 27

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

70

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

P 27

71

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

Contiguous

Overlap or gap

72

There is no additional dose to patient during reconstruction interval

P 27

73

Effect of overlapping slices with reconstruction interval

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

Pixel p 29

A single picture element in the image

75

Voxel p 29

Three dimensional volume element

76

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

Ct number

77

One dimension of video?
Other two dimensions ?

P 29

One- slice thickness

Two- in plane spatial resolution

78

Scan field of view ( fov) p 29

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

79

Two fov

Scan fov
Reconstruction fov

80

Out field artifacts characterized by
P 30

Image shading
Streaks
Incorrect assignment of ct numbers to image pixels

81

Reconstruction fov p 30

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

Aka display fov

82

Reconstruction fov ( display fov) is equal to

Equal or smaller

83

Two reconstruction fov

Small
Large

84

Small/ narrow reconstruction fov p 30

Restricting area of interest and displaying image larger like zoom lens

85

Large/ wide reconstruction fov p 30

Anatomy appears small

86

Thicker slice means ____ noise p 31

Less

87

Wider reconstruction fov mean _______ noise

Less noise

88

Reconstruction fov affects p 31

Spatial resolution
Image noise

89

In plane spatial resolution p 31

Reconstruction fov / number of pixels along direction in image matrix

90

Matrix p 33

Grid pixels that form image

91

Resolution of image expressed as reconstruction fov formula

Reconstruction fov/ matrix

92

Increase matrix mean ______ pixels and allows ____ detail

Smaller

Smaller

93

Small matrix means ____ pixel size

Large

94

Large matrix means ______ pixel size

Small

95

Larger image matrix means ____ noise

More

96

Matrix affects

Spatial resolution
Appearance of image noise

97

Common matrix size p 33

512x512

98

Magnification p 34

Enlarges individual pixels of reconstructed image for display purposes

99

Magnification does not affect (2) p 34

Spatial resolution
Image noise

100

Smaller reconstruction fov means _____size of displayed image

Increase

101

Decreasing reconstruction fov will _____ spatial resolution and noise level

Increase

102

Magnification is post processing technique applied to _____ data

Image

103

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

Raw

104

Window width p 36

How much contrast appears in image

105

Ct number -1000

Air

106

+1000 ct number

Dense bone

107

Operator console displays ____ shades grey

P 36

256

108

Human eye detects ____ shades of grey

20

109

Ct number above range are assigned pixel level ?

255 white

110

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

0( black)

111

Increase window width ____

Higher contrast

112

Lungs studies have ____ contrast

High

113

Larger window width mean ____ contrast

Less

114

Narrow window width is ____ contrast

More

115

Window level p 37

Adjusts brightness of the tissues in the image

116

Ct number higher than 250 appears_____

White

117

Ct number lower than -250 will appear _____

P 38

Black

118

Low window level makes image _____

Brighter

119

High window level makes image _____

Darker

120

Quality assurance p 39

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

Quality control p 39

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

122

Two daily qa done

Ct number calibration test

Ct number standard deviation test

123

Ct number calibration test acceptable limits

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

124

Ct number standard deviation test p 40

Standard deviation of water must not exceddd a specific level

125

Less frequent tests p 40

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