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DR and PACS > Ch. 2 Digital Imaging Characteristics > Flashcards

Ch. 2 Digital Imaging Characteristics Flashcards

1
Q

Digital images are recorded as ___ ___ ____ and are divided into an array of____ _____ that can be processed in many different ways.

A

multiple numeric values; small elements

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2
Q

Analog refers to…

A

a device or system that captures or measures a continuously changing signal

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3
Q

An analog signal wave is used in its…

A

original form

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4
Q

In DR analog signals are converted into…

A

numbers that are recorded

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5
Q

Digital images are formed through…

A

multiple samplings of a signal

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6
Q

A digital image begins as a….

A

analog signal

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7
Q

What are the critical characteristics of a digital image?

A

spatial resolution, contrast resolution, noise, and dose efficiency

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8
Q

What is a pixel?

A

a picture element which is the smallest element in a digital image

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9
Q

What is the size of a pixel directly related to?

A

the amount of spatial resolution or detail in the image

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10
Q

smaller pixel =

A

better detail

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11
Q

When can pixel size change?

A

when the size of the matrix or FOV changes

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12
Q

What does FOV stand for?

A

Field of view

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13
Q

What is pixel depth?

A

the number of bits within a pixel

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14
Q

In regards to pixels, what is a factor in determining the image contrast resolution?

A

The gray level

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15
Q

Define matrix

A

a square arrangement of numbers in columns and rows, and in digital imaging, the numbers correspond to discrete pixel values

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16
Q

Each box within the matrix also corresponds to a specific …

A

location in the image and corresponds to a specific area of the patient’s tissue

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17
Q

How is the image digitized/

A

both by position and intensity

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18
Q

What are other terms for position and intensity?

A

position=spatial location; intensity=gray level

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19
Q

What is the typical range in the number of pixels in a matrix?

A

512 x 512 to 1024 x 1024 and can be as large as 2500 x 2500

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20
Q

What does the size of the matrix determine?

A

the size of the pixels

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21
Q

Which has the smaller pixels? a 10x12 or a 14x17 and both have a 512 x 512 matrix

A

the 10x12 will have smaller pixels

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22
Q

The term field of view is synonymous with what?

A

the x-ray field

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23
Q

What does FOV stand for?

A

field of view

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24
Q

What is the field of view?

A

the amount of body part or patient included in the image

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25
Q

What would happen if the field of view changes?

A

it will not affect the size of the matrix, but if the matrix changes, the pixel size will be affected

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26
Q

Why is the pixel size affected if the matrix changes?

A

because as the matrix increases and the FOV remains the same size, the pixel must decrease to fit into the matrix

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27
Q

What is the relationship between the pixel size, matrix size and FOV?

A

The matrix size can be changed without affecting the FOV and the FOV can be changed without affecting the matrix size, but a change in either the matrix size and/or the FOV changes the size of the pixels.

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28
Q

What does the exposure index number refer to?

A

the amount of exposure received by the image receptor (IR), not by the patient.

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29
Q

How is air kerma measured?

A

in J/kg or Gy

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30
Q

What is air kerma?

A

(kinetic energy) the measurement of radiation energy(J) absorbed in a unit of air(kg)

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31
Q

What is the exposure typical of a imaging receptor system?

A

the standardized radiation exposure

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32
Q

The indicated equivalent air kerma is the measurement of…

A

the radiation that was incident on the IR for the particular exposure.

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33
Q

How is the indicated equivalent air kerma derived?

A

from reading the pixel values produced by the exposure on an IR.

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34
Q

What are for-processing pixel values (Q)?

A

pixel values produced by the exposure on an IR

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35
Q

The indicated equivalent air kerma simply stated is…

A

the amount of exposure on the IR

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36
Q

What does the indicated equivalent air kerma help determine?

A

whether the IR has been overexposed or underexposed for that particular body part.

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37
Q

What is the target equivalent air kerma value?

A

a set of values, established by either the system manufacturer or the system user, that represents a optimal exposure for each specific body part and view.

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38
Q

What is the deviation index?

A

the difference between the actual exposure and the target exposure, except it is expressed in logarithmic fashion.

39
Q

What does the DI do?

A

help the tech determine whether the image has been underexposed or overexposed.

40
Q

What number would indicate a perfect image according to DI?

A

0.0

41
Q

What if the DI number is negative?

A

then the image is underexposed

42
Q

What if the DI number is positive?

A

then the image is overexposed

43
Q

If you had to repeat, how would you raise the DI number +1?

A

increase the technique by 20%

44
Q

If you had to repeat, how would you decrease the DI number by -1?

A

decrease technique by 25%

45
Q

What are some of the reasons that could cause the reading of the pixel values to be off?

A
  1. a prostheses within the image
  2. gonadal shielding within the image
  3. failure of the system to recognize the collimated border
  4. an unexpected body part in the image
46
Q

What does brightness in the digital terms refer to?

A

its appearance on the display monitor of the computer

47
Q

How can brightness be controlled?

A

there are controls on the monitor

48
Q

What is window leveling?

A

when you adjust the brightness on the computer monitor

49
Q

Contrast resolution is…

A

it refers to the ability of the digital system to display subtle changes in the shade of gray

50
Q

What does higher contrast resolution mean?

A

the differences between adjacent densities are enhanced–more shades of gray

51
Q

contrast resolution in digital imaging is directly related to what?

A

the bit depth of the pixels in the image

52
Q

How is contrast resolution adjusted in digital imaging?

A

higher kVp values and lower mAs values

53
Q

What happens to the patient if you raise kVp and lower mAs?

A

patient dose goes down

54
Q

What contrast resolution in digital imaging DOES depend on is…

A

the amount of scatter

55
Q

How are we able to use higher kVp values without compromising contrast resolution in digital imaging?

A

With the use of tight collimation and the correct grid

56
Q

How is screen resolution controlled?

A

by a technique called window width

57
Q

what is spatial resolution?

A

the ability of the imaging system to demonstrate small details of an object

58
Q

What determines resolution in film/screen?

A

the crystal size and thickness of the phosphor layer

59
Q

What determines resolution in photostimulable phosphor systems?

A

phosphor layer thickness and pixel size

60
Q

As far as resolution goes, the thinner the layer of phosphor, the….

A

higher the resolution

61
Q

In film/screen resolution at its best is limited to..

A

about 10 line pairs per millimeter

62
Q

In digital receptors, resolution is about…

A

2.55 lp/mm up to 10 lp/mmin PSP systems–giving less detail

63
Q

what is dynamic range?

A

the ability to respond to varying levels of exposure

64
Q

In digital, what would cause more tissue densities on the digital image to be seen, giving the appearance of more detail?

A

dynamic range

65
Q

Why are we able to see more soft tissue (like in a knee radiograph) in digital than we are able to see in film/screen?

A

because there is a wider dynamic recording range but does not mean there is additional detail

66
Q

Spacial resolution: the smaller the pixels…

A

the higher the spacial resolution

67
Q

What is modulation transfer function?

A

the ability of a system to record available spatial frequencies

68
Q

What does MTF stand for?

A

modulation transfer function

69
Q

MTF is a …

A

ratio

70
Q

The sum of the components in a recording system cannot be…

A

greater than the system as a whole

71
Q

What does MTF quantify?

A

the contribution of each system component to the overall efficiency of the entire system

72
Q

A perfect system would have a MTF of…

A

1 or 100%

73
Q

Anything that interferes with the formation of the image is considered..

A

noise

74
Q

What is anatomic noise?

A

if superimposition of body parts occurs

75
Q

What does radiographic noise consist of?

A

equipment noise and quantum noise

76
Q

Where does equipment noise come from?

A

noise in the detector elements and non-uniform detector responses

77
Q

Can the tech control equipment noise?

A

no

78
Q

How do we put a value on noise?

A

with the noise power spectrum

79
Q

What is NPS?

A

noise power spectrum

80
Q

What is the NPS?

A

it describes the spatial frequency content of the noise as well as spatial characteristics

81
Q

What does SNR stand for?

A

signal-to-noise ratio

82
Q

define SNR

A

how much noise can be tolerated in the image

83
Q

As SNR increases, the noise…

A

decreases

84
Q

What does the term exposure latitude refer to?

A

the range of exposure diagnostic image values the image detector is able to produce.

85
Q

exposure latitude is dependant on…

A

the image detector

86
Q

detective quantum efficiency:

A

how efficiently a system converts the x-ray input signal into a useful output image

87
Q

What does DQE stand for?

A

detective quantum efficiency

88
Q

What is DQE a measurement of?

A

the percentage of x-rays that is absorbed when they hit the detector

89
Q

Systems with higher quantum efficiency can produce…

A

higher quality images at lower doses

90
Q

What have increased DQE over PSP?

A

amorphous selenium, amorphous silicon thin film transistor (TFT), charge couple device (CCD), and complementary metal oxide semiconductor detector technology

91
Q

What has the highest DQE? Why?

A

amorphous selenium detectors because they do not have the light conversion step and consequently not light spread.

92
Q

Why would the newer complementary metal oxide semiconductor capture system be equal to direct image acquisition?

A

because of the crystal light tubes, which also prevent light spread

93
Q

The DQE of detectors changes with…

A

kVp

94
Q

The greater the area of the TFT array, the…

A

higher the DQE

DR and PACS (5 decks)

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