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Exposures II > Ch.22 Digital Radiography Flat Panel Detector Systems > Flashcards

Ch.22 Digital Radiography Flat Panel Detector Systems Flashcards

1
Q

Referred to as digital radiography (DR)

A

Flat- Panel Detector digital systems

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2
Q

When was DR introduced ?

A

1995

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3
Q

what are the two general classes of DR panels

A

Indirect and Direct

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4
Q

Steps of Indirect Conversion:

A

xrays to light, then to an electrical charge

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5
Q

Steps of Direct conversion

A

xrays directly to electrical charge

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6
Q

Steps of Indirect Conversion: (with more detail)

A

Indirect conversion detectors are used in a two-step process. The first step involves converting incom-ing x-ray photons to light first, which is accomplished through the use of a scintillator. The second step involves a conversion of light photons to an electronic signal using a photodetector. Indirect DR systems include either a charge-coupled device (CCD) or amorphous silicon with a thin film transistor (TFT) array.

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7
Q

Direct Conversion (more detail)

A

Direct DR systems are capable of directly converting incoming x-ray photons to an electronic signal. These systems use amorphous sele-nium and a TFT.

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8
Q

Two types of Indirect DR detectors

A

TFT and CCD

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9
Q

How do scintillators emit light

A

Isotropically

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10
Q

conversion of incoming xray photons to an electronic signal without scintillation

A

Direct Conversion

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11
Q

A two part process involving a scintillator (which converts incoming xray photons to light) and a photodetector (which converts light into an electronic signal)

A

Indirect Conversion

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12
Q

Out of direct and indirect, which has the better image

A

direct. because there is one less step, so less info lost

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13
Q

-uses a scintillator to convert xray energy to light
-light energy converted to eletrical signal in amorphous silicon layer
-2 possible method : Charge couple device (CCD) or Thin Film Transistor (TFT)

A

Indirect detectors

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14
Q

Requires a scintillator because the atomic number is only 14

A

Amorphous silicon

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15
Q

what are two types of scintillators that amorphous silicon would require

A

-Cesium Iodide
-Gadolinium Oxysulfide

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16
Q

what are the three ways the signal is captured by :

A

-charge-coupled device (CCD)
-complimentary metal oxide semiconductor (CMOS)
-Thin Film Transistor (TFT)

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17
Q

Designed to convert light energy into electrical signal

A

Transmission along detector circuit pathways

Analog-to-digital convertor (ADC)

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18
Q

-Used in both indirect and direct detectors
-Electronic readout of signal
-arranged in an array of detector elements (DELs)

A

TFT

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19
Q

how is pixel size related to DEL size

A

directly related

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20
Q

Collects the electric charges produced by either the selenium or silicon as an array or matrix of pixel size detector elements (DEL)

A

TFT

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21
Q

where is the latent image stored

A

TFT

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22
Q

which two use thin film transistors for electronic read out

A

-Amorphous silicon (indirect conversion )

-amorphous selenium (direct conversion)

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23
Q

out of CCD and CMOS which has the high quality, low noise

A

CCD

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24
Q

a photodetector that converts light to electric charge and stores it. The stored charge releases line by line to the ADC. The electrical signal produced is then sent to the computer for image processing

A

CCD

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25
Q

-more susceptible to noise
-light sensitivity tends to be lower

A

CMOS

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26
Q

-uses scintillator
-closely associated with CCD chips
-image sensors, which convert light to electrons

A

CMOS

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27
Q

-storing electric charge
-latent image stored here

A

TFT

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28
Q

Explain steps of TFT:

A

when taking an exposure, flap on TFT closes, capturing signal, when done TFT opens (releases signal), then reading line by line

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29
Q

Each DEL has :

A

-Sensor Surface (picking up that radiation)
-Storage Capactor
-TFT

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30
Q

how is spacial resolution related to DEL dimension?

A

indirectly

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31
Q

-determined by percentage of DEL consisting of sensing material
-how efficient is it picking up the dose of radiation

A

TFT Fill Factor

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32
Q

fill factors relationship with detector dose efficiency

A

Higher fill factor increases x-ray dose efficiency

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33
Q

How does fill factor affect image quality

A

Higher fill factor yields higher spatial and contrast resolution

34
Q

-Use amorphous selenium (a-S e) as photoconductor
-No scintillating layer
-Direct action of x-ray photons converted to electrons in a-Se layer
-Charges collected by T F T for readout

A

Direct Detectors

35
Q

Image processing consists of steps to optimize image quality:

A

-Exposure field recognition
-Histogram creation and analysis
-Rescaling
-L U T application

36
Q

-Latent image with DR is electrical signal values (voltages) created in each DEL

-Readout of signal completed in a logical sequence

-Only D E L s with signal values are read out and make up image

-Image processing similar to CR processing
DR panels capable of pre-processing and post-processing

A

Image Acquisition, Processing, and Display

37
Q

-Image processing consists of steps to optimize image quality

-Brightness and contrast tables applied to image data set

-Processing techniques applied if selected
-Spatial location
-Frequency processing

-Final image data set presented for video display

A

Image Acquisition, Processing, and Display

38
Q

two general classes of DR panel

A

Portable (wireless of hard wired with tether cable)

Integral to equipment deign (typically hard wired to radiographic equipment)

39
Q

-DR panels typically require communication with xray generator
-interface is vendor specific
-newer DR panels eliminate the traditional generator interface
-Panels are wireless
-No true generator interface
TFT is charged by on-board capacitor prior to exposure
-Presence of x-radiation hitting panel “triggers” TFT to collect signal
-Exposure terminated by manual timing or automatic exposure control (A E C)
-Data read-out completed and panel recharges for next exposure

A

Auto-Detection Technology

40
Q

Be aware of DR panel Precautions

A

-avoid panel dropping
-clean panels
-fluid invasion (encase protective bags)
-weight load restrictions
-Respect level of sophistication

41
Q

Soft copy

A

what you see on the monitor

42
Q

Hard Copy

A

have actual film

43
Q

Which three components are included in indirect capture flat panel digital image detector systems

A

photodiode
scintillation layer
TFT array

44
Q

Which component of an indirect capture flat panel detector converts incident xray photons into visible light photons

A

Scintillation

45
Q

Which component of an indirect capture flat panel detector converts the visible light into electrons

A

Photodiode

46
Q

Flat panel detector systems typically use a thin film transistor (TFT). This device functions to:

A

collect electrical charge

47
Q

which two of the following flat panel detector components can collect and convert light into an electrical signal

A

photodiode
charge couples device (CCD)

48
Q

which element is used in the construction of a flat panel detector is able to convert xray photons directly into an electrical signal

A

Amorphous Selenium

49
Q

which of the following devices acts as a swicth within a flat panel detector to release the electric charge collected by detector element

A

Thin film transistor (TFT)

50
Q

Cesium Iodide is the preferred material for the scintillation layer because it can be formed into

A

Columns with focus light photons

51
Q

In a charged couples device system, the scintillation layer is connected to the CCD sensor chips by which of the following

A

Lenses and fiber optics

52
Q

the digital image receptor is comprised of small elements called

A

Detector Elements (DELs)

53
Q

Which of the following makes up a single detetctor element

A

capture area
storage capacitor
thin film transistor (TFT) gate

54
Q

Which of the following makes up the capture area of a detector element (DEL)

A

Top electrode
detection layer
bottom electrode

55
Q

What part of the DEL detects radiation

A

Capture Area

56
Q

The storage capacitor of the detetcor element (DEL) stores which of the following

A

A positive charge

57
Q

What is the percentage of the detector element devoted to the detection layer called

A

Fill Factor

58
Q

What is the relationship between fill factor and spacial resolution

A

Directly proportional

59
Q

Which of the following is created on an image receptor by the arrangement of detetcor elements into rows and columns

A

Matrix

60
Q

Which of the following would lead to an increase in patient dose

A

decreased fill factor
(smaller dels have reduced fill factor which reduced efficiency )

61
Q

which of the following will produce the highest spacial resolution

A

large matrix and low pitch
(more dels which means more spacial resolution)

62
Q

A device capable of accumulating and storing an electrical charge

A

Capacitor

63
Q

which is capable of converting light into an electronic signal, used in direct conversion

A

photoconductor

64
Q

converts incoming xray photons to light

A

scintillator

65
Q

used in conversion of light photons to an electric signal, used in indirect conversion

A

photodetector

66
Q

refers to the sensing area compared to the non-sensing area,
and can be expressed as a percentage.

A

fill factor

67
Q

being used to describe both the indirect amorphous silicon and the direct amorphous selenium plates that are being used in some digital systems.

A

flat panel director

68
Q

are positioned in a matrix that allows the charge pattern to be read out on a pixel-by-pixel and column-by-column basis.
Includes sensing area, capacitor , and tft layer

A

Dexel

69
Q

is a photodetector, a device that is capable of converting visible light into an electric charge and storing it in a sequential pattern.

A

CCD

70
Q

designed as image sensors, which convert light to electrons. closely associated with CCD chips

A

CMOS

71
Q

are built into the design of a radiographic table or upright holder.

A

integral detectors

72
Q

An electronic switch on flat-panel detectors commonly made of amorphous silicon.
allows the charge collected at each pixel to be independently transferred to external electronics, where it is amplified and quantized.

A

TFT

73
Q

An electronic element which converts light into charge. With indirect TFT detectors this is accomplished by a light-sensitive amorphous silicon photodiode on top of the TFT array

A

photodiode

74
Q

The scintillator crystal commonly used in indirect capture DR

A

cesium iodide

75
Q

The photoconductor used in direct radiography

A

Selenium

76
Q

Denotes that crystals in the phosphor are randomly distributed

A

Amorphous

77
Q

term for directer element

A

Dexel

78
Q

semiconductors

A

Amorphous silicon, amorphous selenium, CCD

79
Q

when is a photoconductor used

A

In direct conversion

80
Q

is CCD or TFT a photodetector

A

CCD

81
Q

what is the readout scheme

A

read line by line

82
Q

when is a photodetector used

A

indirect

Exposures II (7 decks)

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