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Physics - Common Equipment > Chapter 10 > Flashcards

Chapter 10 Flashcards

1
Q

What are the two groups of digital image receptors

A

Direct Radiography
Computer Radiography

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2
Q

Which systems use a capture phosphor to temporarily store the energy that represents image signal?

A

CR

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3
Q

Which systems have detectors that are able to directly capture and read out an electric image signal?

A

DR

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4
Q

Which system does not use a removable imaging plate?

A

DR

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5
Q

Why were CR systems attractive upon introduction?

A

They could be easily integrated with exisiting x-ray setups that were designed for use with film-screen. Minor adjustments to AEC could be done quickly

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6
Q

What are the 4 parts to a CR system?

A

Cassette
Photostimuable phosphor plate
Plate reader
Computer workstation

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7
Q

What are CR cassettes made of and what is their function?

A

Lightweight plastic
To hold the PSP

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8
Q

CR cassettes are lined with felt to help reduce ______

A

Static

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9
Q

What type of backing material is in CR cassettes and what is the function?

A

Aluminum backing that helps reduce back-scatter

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10
Q

What are the layers of PSP?

A

Protective
Phosphor
Reflective
Conductive
Support (color and soft backing)

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11
Q

What is the main purpose of the protective layer?

A

Protect the phosphor layer

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12
Q

What is the phosphor layer made of in CR?

A

Material from the barium fluorohalide family coupled with a europium activator

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13
Q

What are the two types of phosophor layers?

A

Turbid or Structured

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14
Q

What is the difference between turbid and structured phosphor layer?

A

Turbid - phosphor crystals are randomly distributed

Structured - contains columnar phosphor crystals that resemble needles standing on end, packed tightly together

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15
Q

What is the purpose of the reflective layer?

A

Reflects the light released during reading towards the photodetector

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16
Q

What is the purpose of the conductive layer?

A

Helps to reduce and conduct away static electricity

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17
Q

What is the purpose of the color layer?

A

Absorb stimulating light and reflect emitted light

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18
Q

What is the purpose of the soft backing layer?

A

Protect the back of the PSP

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19
Q

When a PSP is exposed to radiation, some ______________ are removed from the atoms of the phosphor?

A

Electrons

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20
Q

What happens to the electrons that are removed from the phosphor atoms?

A

Half become trapped in the conduction band

The other half return immediately to the valence and release excess energy in the form of light

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21
Q

What is the conduction band?

A

Area of an atom just outside it’s outermost valence electron shell

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22
Q

When an electron is trapped in the conduction band, it is still ________ the atom, but is not part of the ____________

A

Orbiting
Structured valence

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23
Q

What allows the phosphor to store xray energy as the latent image?

A

Europium

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24
Q

How long can electrons stay in the conduction band?

A

For hours, but the longer you wait to process the PSP, the more image deterioration there will be

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25
Q

What is used to release the electrons from the conduction band?

A

A laser

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26
Q

When trapped electrons return to the valence, they release an energy known as:

A

Photostimulable luminescence

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27
Q

What is the purpose of the CR reader?

A

Houses the components needed to process the radiated PSP

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28
Q

What happens when the cassette is placed into the CR reader?

A

A drive mechanism moves the plate through the laser-scanning process (slow scan)

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29
Q

How does the fast scanning process work?

A

The optical system protects and guides a controlled laser beam back and forth across the plate (fast scan)

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30
Q

What makes up the optical system?

A

Laser, beam-shaping optics, light-collecting optics, and optical filters

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31
Q

What detects the light that is released from the PSP during scanning?

A

Photodetector

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32
Q

In CR, what does the photodetector do after detecting the light?

A

Amplifies the light in the form of an analog signal

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33
Q

The amplified analog signal is converted to a digital signal by an:

A

ADC (Analog-to-digital converter)

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34
Q

What are the two categories of direct radiography?

A

Direct and indirect

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35
Q

What are the two forms of Indirect capture?

A

CCD/CMOS
TFT

36
Q

What are CCDs?

A

Charge-Coupled Devices; light sensitive devices that are capable of responding to very low levels of light

37
Q

What type of scintillator is used for CCD?

A

Cesium iodide phosphor plate

38
Q

What is a scintillator?

A

Absorbs x-rays and emits visible light in response

39
Q

How is the cesium iodide coupled to the CCD?

A

Fiber-optics or an optical lens system

40
Q

In CCD, how is an image created after a scintillator (cesium iodide) absorbs radiation?

A

The scintillator converts the energy into light

The light energy is captured with the fiber-optics/optical lenses and ends up in the CCD

The energy is convered into electric signal, which is then sent to the computer

41
Q

What is the scintillator in a CMOS system?

A

The CMOS itself

42
Q

What does a CMOS detector consist of?

A

Amplifier, photodiode, and storage capacitor and is surrounded by transistors

43
Q

Is CCD or CMOS more light sensitive?

A

CCD

44
Q

Which provides better resolution - CCD or CMOS?

A

CCD

45
Q

Which is more efficient - CCD or CMOS?

A

CMOS

46
Q

CMOS is currently available in what type of areas?

A

Mammography and dental

47
Q

What is TFT?

A

A form of indirect capture - thin-film transistor

48
Q

What is TFT coupled with?

A

Amorphous silicon

49
Q

What is the function of amorphous silicon in TFT?

A

Acts as the photodetector - allows the capture element to absorb light emitted by the phosphor layer

50
Q

How is an image created using TFT?

A

Thin-film transistors are laid out on a glass substrate

The capture element is painted with amorphous silcon, which allows it to absorb light emitted by the phosphor layer

The emitted light is converted to electric signal

51
Q

In indirect systems, what is a scintillator used for?

A

A scintillator is used to convert radiation into light

52
Q

In indirect capture systems, what is light coverted into?

A

Electric signal

53
Q

What is the difference between direct capture and indirect capture?

A

Direct - turns radiation into electronic signal

Indirect - needs visible light for electronic signal

54
Q

What is CMOS?

A

Complementary Metal Oxide Semiconductors

55
Q

Direct capture systems use a photoconductor made of:

A

Amorphous selenium

56
Q

What is the function of amorphous selenium?

A

Absorb radiation as input and create an electric charge as output

57
Q

During image acquisition, the computer creates a:

A

Histogram

58
Q

What is the x-axis and y-axis of a histogram?

A

X-axis: Amount of exposure
Y-axis: How many pixels were radiated for each exposure level

59
Q

What is histogram analysis?

A

The computer analyzes the created histogram and compares it with a default histogram

60
Q

During the recognition proess of histogram analysis, how many edges must be identified?

A

Minimum of 3, but ideally 4

61
Q

When does sampling occur?

A

During transmission from the photodetector to the ADC

62
Q

What is sampling?

A

Taking a peice of the original analog signal and using that sample piece to create the digital signal

63
Q

The closer individual sample sections are to each other, the greater the:

A

Sampling frequency

64
Q

Sampling frequency must be at least ______ times the original bandwidth of the analog signal in order to accurately digitize the signal (Nyquist Theorem)

A

2 times

65
Q

What is the key difference between CR and DR when it comes to processing the histogram?

A

DR - only the detector pixels that were radiated contribute to image formation; you can center the part over any part of the cassette

CR - region of interest, must be in the center of the cassette

66
Q

What is defined as the range of exposure values that a receptor can receive and still produce a diagnostic image

A

Exposure latitude

67
Q

Numerical values that represent how much radiation exposure a receptor received

A

Exposure indicators

68
Q

S numbers are ___________ proportional to the amount of radiation received

A

Inversely

69
Q

EI numbers are _________ proportional to the amount of radiation received

A

Directly

70
Q

What is DAP?

A

Dose Area Product - a measure of exposure in air

71
Q

What are the three values when measuring DAP as an exposure indicator?

A

EI - Exposure index
EI-T - Exposure index target
DI - Deviation index

72
Q

What is exposure index?

A

Exposure detected at the time of exposure

73
Q

What is exposure index target?

A

The predetermined ideal exposure index

74
Q

What is the deviation index?

A

The measure of difference between EI and EI-T

75
Q

What is DQE?

A

Detective Quantum Efficiency - a meausrement of the efficiency of the receptor converting x-ray exposure into a diagnostic quality image

76
Q

Spatial frequency is:

A

The amount of line pairs per millimeter within the matrix

77
Q

Spatial frequency is ______ of the Nyquist frequency

A

1/2

78
Q

Nyquist frequency is the ___________ spatial frequency that a digital detector can record

A

Highest

79
Q

Monthly and quarterly quality checks should be done to evaluate:

A

Distortion
Ambient light reflection
Resolution

80
Q

How often should imaging plates be cleaned?

A

Every 3 months or as needed

81
Q

CR imaging plates need to be erased before use after ___ hours

A

48

82
Q

What is PACS?

A

Picture Archiving and Communication Systems - integral part of digital imaging

83
Q

What are the 3 parts of PACS?

A

Acquisition
Network
Storage

84
Q

What is DICOM?

A

Digital Imaging and Communication in Medicine - file format that allows for exams from all modalities to be able to be stored and used at any PACS terminal across the network

85
Q

One major limitation of PACS is:

A

Storage

86
Q

3 main classifications of PACS storage

A

Online - data is stored on hard drives that provides near instant access

Nearline - data is stored on removable drives that are able to be loaded by a robatic arm on demand

Offline - data is stored on removable drives that must be manually retrieved

Physics - Common Equipment (7 decks)

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