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RT 212 > 4. Flat-Panel Radiography > Flashcards

4. Flat-Panel Radiography Flashcards

1
Q

Limitations of CR

A
  1. X-ray detection of CR is inefficient & this affects
    image quality & dose.
  2. The spatial resolution of CR is less than Film-Screen radiography. CR 3-5 lp/mm, FS 10-15
    lp/mm
  3. CR Imaging plate can easily be damaged,
    susceptible to scratches & cracking.
  4. CR Imaging plate must be transported to a
    separate image processor (reader) for image data
    extraction
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2
Q

Introduced as
early as ____ for
use in radiographic
imaging

A

1995, Flat-panel digital

radiography

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3
Q

A-Si

A

Amorphous Silicon

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4
Q

A-Se

A

Amorphous Selenium

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5
Q 
Digital 
detectors used 
before 1995 
were \_\_\_\_\_
on FPD 
technology
A

not based

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6
Q

(CCD chip) Slot-scan digital detector

A

1990

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7
Q

Selenium drum digital detector

A

1994

  • Chest imaging
  • Thoravision (Philipps Medical Systems)
  • Insert figure 5-2
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8
Q

conducts electrons when struck by

light or X-ray photons

A

Photoconductor

  • Selenium 34
  • Silicon 14
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9
Q

Flat-panel
Digital
Radiography:

S Y S T E M
C O M P O N E N T S

A
  1. Pre-amplifiers
  2. Switching Control
  3. Central Logic Circuits
  4. ADC’s
  5. Internal Memory
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10
Q

It is important to note that X-ray detection &
digitization of the X-ray signal take place
within the _____

A

flat-panel detector

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11
Q

Types of FPD Detectors

A
  • Indirect Detectors

- Direct Detectors

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12
Q

-uses phosphors
-phosphors convert X-ray energy into electrical charge
through an intermediate stage of light photons.

A

Indirect Detectors

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13
Q

-use a photoconductor
-photoconductors convert x-ray energy into electrical
charge without the intermediate stage.

A

Direct Detectors

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14
Q

2 TYPES OF INDIRECT DETECTORS:
technical
components

A
  1. Charged-Coupled Device (CCD) Digital Detector

2. Flat-Panel Thin Film Transistor (TFT) Digital Detector

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15
Q

The most prominent difference between these
two types of detectors is the technical
component used to ____

A

convert light into electrical

signals

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16
Q

based on an indirect conversion process

A

CCD (Charged-coupled Device) digital detectors

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17
Q

uses a CCD chip to convert light to

electrical charge

A

CCD (Charged-coupled Device) digital detectors

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18
Q

not classified as flat-panel digital

detector

A

CCD (Charged-coupled Device) digital detectors

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19
Q 
The main 
technical 
components of 
a CCD-based 
DR detector 
includes:
A
  1. X-ray absorber
  2. Light optics
  3. CCD - sensor (chip) for capturing the
    light electrical charge readout device
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20
Q

A CCD digital detector consists of several CCD’s
in order to _____ the size of the detection
area

A

increase

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21
Q

3 OTHER NOTEWORTHY

COMPONENTS:

A
  1. Scintillation screen – detects X-rays &
    converts them into light
  2. Light collection optics
  3. Array of CCDs – CCD camera
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22
Q

Other
systems
used:

A
  1. Fiberoptic-coupled CCD System
  2. Lens-coupled CCD
  3. Fiberoptic-coupled Scanning Array
    System
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23
Q

based on an indirect conversion process

A

Indirect flat-panel

TFT (Thin Film Transistor) digital detectors

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24
Q

uses several physical components to convert x-rays into light that is subsequently converted
into electrical charges

A

Indirect flat-panel

TFT (Thin Film Transistor) digital detectors

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25
Q 
The main 
technical 
components of a 
TFT digital 
detector 
includes:
A
  1. X-ray scintillator (X-ray conversion layer) CsI,
    Gd2O2S2
  2. Amorphous silicon (a-Si) photodiode flat-panel
    layer with a thin-film transistor (TFT) array for
    readout of the electrical charges by the
    photodiode array.
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26
Q 
DIRECT 
DIGITAL 
DETECTORS:
technical 
components
A
  1. Source of high voltage
  2. Top electrode
  3. Dielectric layer
  4. Photoconductor
  5. Collection electrode
  6. TFT
  7. Storage capacitor
  8. Glass substrate
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27
Q

SOURCE
OF
PHOTOCONDUCTORS:

A

Amorphous Selenium (a-Se)

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28
Q

excellent X-ray detection properties & a very

high spatial resolution

A

Amorphous Selenium (a-Se)

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29
Q

detect x-ray photons from the patient &

converts them directly into electrical charges

A

Amorphous Selenium (a-Se)

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30
Q

Other photoconductors used:

A
  1. Lead Oxide
  2. Lead Iodide
  3. Thallium Bromide
  4. Gadolinium
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31
Q

designed as a matrix of detector elements, each of which can be regarded as a pixel & constructed as:
design is called: “______”

A

Configuration of the Flat-Panel,

large area integrated circuit

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32
Q

also referred to as an active matrix array

A

Matrix

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33
Q

consists of rows & columns that play a role in
addressing & readout of the signal from each
pixel

A

Matrix

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34
Q

Each pixel contains a TFT (switch), a storage
capacitor & a sensing area, referred to as the
_____

A

sensing/storage element

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35
Q

The sensing area will detect the light from the

___ scintillator

A

CsI

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36
Q

A concept that examines the response of the image

receptor to the radiation falling upon it

A

Exposure Latitude

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37
Q

Exposure latitude for CR/DR detectors

A

0.1-1000 µGy

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38
Q

Detectors with wide dynamic range can respond to ____ of exposure (low to high) and still provide an image that appears acceptable to the observer

A

different levels

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39
Q

Typical detector dimensions:

A

43 cm x 43 cm
30 x 40 cm
18 x 18 cm

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40
Q

Typical matrix sizes:

A 
1760 x 2140 
2000 x 2500 
2736 x 2736 
2560 x 3072 
2688 x 2688 
3121 x 3121
41
Q

The pixel size & spacing determine the _____ of the image

A

spatial

resolution

42
Q

the distance from the
midpoint of one pixel to the midpoint of the
adjacent pixel

A

Pixel Pitch

43
Q

Pixel sizes in current detectors can be

A

139 µm,
143 µm, 160 µm, 162 µm, 167 µm, and 200
µm

44
Q

The ratio of sensing area of the pixel to the area

of the pixel itself

A

Fill Factor of the Pixel

45
Q

Image Quality Descriptors

A
  1. Spatial Resolution
  2. Density Resolution
  3. Noise
  4. Quantum Detective Efficiency
  5. Artifacts
46
Q

related to the size of the pixels on the image

matrix

A

Spatial Resolution

47
Q

Pixel size of 35 cm x 43 cm (24“ x 17“)

A

0.2 mm

48
Q

Pixel size of 23 cm x 30 cm (10” x 12”)

A

0.14 mm

49
Q

Pixel size of 18 cm x 24 cm (8” x 10”)

A

0.1 mm

50
Q

The smaller the pixel size the ____ the spatial

resolution of the image

A

better

51
Q

The pixel size can be calculated using the

relationship:

A

PS = FOV/ Matrix Size

52
Q

Same FOV, the _____ the matrix size, the _____ the pixels, the better the ____

A

greater,
smaller,
image sharpness

53
Q

A typical CR image matrix size

A

2048 x 2048

54
Q

linked to bit depth

A

Density Resolution

55
Q

range of gray levels per pixel

A

Density Resolution

56
Q

An image with a bit depth of 8 will have _____

shades of gray per pixel

A

256 (2^8)

57
Q

refers to the color

information stored in an image

A

Bit Depth

58
Q

The ___ the bit depth of an image, the

more colors it can store

A

higher

59
Q

1 bit

A

Two values: 0 white, 1 black

60
Q

8 bit

A

256 colors

61
Q

24 bit

A

16 million

62
Q

Noise

A
  1. Electronic Noise (System)

2. Quantum Noise (Quantum Mottle)

63
Q

determined by the number of X-ray photons
(signal) falling upon the detector to create
the image

A

Quantum Noise

64
Q 
Low exposure factors will produce few photons at 
the detector (less signal, more noise)
A

Results in a noisy image, (Grainy/Poor image)

65
Q

Higher exposure factors will generate more

photons at the detector (more signal, less noise)

A

Produce a better image, increase patient dose

66
Q

___ Noise, ___ Detector Exposure

A

More,

Less

67
Q

The detector receives an input exposure &

converts it into a useful output image

A

Detective Quantum Efficiency (DQE)

68
Q

DQE

A

Detective Quantum Efficiency

69
Q

is a measure of the efficiency & fidelity

with which the detector can perform this task

A

Detective Quantum Efficiency (DQE)

70
Q

DQE =

A

SNR^2out / SNR^2in

71
Q

DQE for a perfect digital detector is

A

1 or 100%

This means that there is no loss of information

72
Q

A distortion or error in an image that is

unrelated to the subject being studied

A

Image Artifacts (Morgan, 1983)

73
Q

An ____ is a feature in an image that masks

or mimics a clinical feature

A

artifact, (Willis, 2004)

74
Q

can be disturbing to
radiologists and may even result in an
inaccurate diagnosis

A

Artifacts

75
Q

Sources of Artifacts

A
  1. Imaging hardware (equipment)
  2. Image processing software
  3. Objects that are imaged & linked to
    the operator errors
76
Q

ensures that every employee plays a

role in creating a quality product

A

CQI (Continuous Quality Improvement)

77
Q

CQI

A

Continuous Quality Improvement

78
Q

are essential not only
for optimizing the assessment and
evaluation of patient care, but also for
monitoring the performance of equipment

A

QA & QC programs

79
Q

Describe systems & procedures for assuring quality
patient care, quality assessment, continuing
education, the usefulness of quality control
procedures & assessment of outcomes

A

Quality Assurance

80
Q

deals with the administrative aspects of

patient care & quality outcomes

A

QA (Quality Assurance)

81
Q

Component of QA that refers to the monitoring of
important variables that affect image quality &
radiation dose

A

Quality Control

82
Q

deals with technical aspects of equipment

performance

A

QC (Quality Control)

83
Q

Purpose of the procedures & techniques of CQI, QA & QC:

A 
1. To ensure optimum image quality for the 
purpose of enhancing diagnosis
2. To reduce the radiation dose to both 
patients and personnel 
3. To reduce costs to the institution
84
Q

involves a number of activities that are of
significance to the technologist, particularly if
the technologist is in charge of the QC program

A

Quality Control

85
Q

Quality Control Activities:

A
  1. Acceptance Testing
  2. Routine Performance
  3. Analysis of Reject Rates
  4. Error Correction
86
Q

Ensures that the equipment meets the

specifications set by the manufacturer

A

Acceptance Testing

87
Q

Involves conducting a QC test on the equipment on a regular basis with varying degrees of frequency

Annually, semiannually, monthly, weekly or daily

A

Routine Performance

88
Q

Ensures that equipment not meeting the performance
criteria or tolerance limit established for specific QC
tests must be replaced or repaired to meet
specifications

A

Error Correction

89
Q

has recommended a number of

tools for CR Quality Control

A

AAPM (American Association of Physicists in Medicine)

90
Q

TOOLS FOR CR QC TESTING

A
  1. Densitometer
  2. Copper & aluminum filters
  3. Calibrated ion chambers
  4. Screen contact wire mesh patterns
  5. Anti-scatter grid
  6. High contrast resolution line pair phantoms
  7. Low contrast phantoms
  8. Anthropomorphic phantoms
91
Q

Common Beam Filtering Materials

A 
Brass,
Copper,
Aluminum,
Lead,
Tin,
Molybdenum,
Tungsten,
Titanium,
Zirconium
92
Q

Film-Screen contact test tool

A

Wire mesh tool/placed on screen & exposed

93
Q

QC TEST 1: Dark Noise

A

Purpose: To assess the level of noise present in
the system

Exposure condition: No exposure. Erase a single screen and read it without exposing it

Process in the image
reader: Use the appropriate QC image
processing tool.

Qualitative criterion
for acceptance: Uniform image without artifacts.

94
Q

QC TEST 2: CR Imaging Plate Test = Uniformity

A

Purpose: To assess the uniformity of the
recorded signal from a uniformly exposed imaging plate

Exposure condition: Expose imaging plate using appropriate
exposure factors

Process in the image
reader: Use the appropriate QC image
processing tool

Qualitative criterion
for acceptance: Uniform image without artifacts

95
Q

QC TEST 3: Erase Thoroughness

A

Purpose: To test the minimal residual signal (ghosting)
on a CR imaging plate after readout &
exposure
Exposure condition: Place a step-wedge at the center of a 14X17
CR IP and expose using appropriate exposure
technique & process the in the image reader.
:Re-expose the same IP a second time without
the step-wedge using the appropriate exposure technique. Collimate in by about 5 cm on each side of the CR IP

Process in the image reader: Use the appropriate QC image processing tool

Qualitative criterion for
acceptance: Absence of a ghost image of the step-wedge from the first exposure in the re-exposed image

96
Q

refers to the persistence of the image, that is, charge is still being produced after
the radiation beam from the X-ray tube has been
turned off

A

Memory effect

97
Q

Charge has been trapped in the metastable band-gap
states in the a-Si and a-Se material during exposure &
is only released slowly over time

A

Image Lag

98
Q

detects X-rays &

converts them into light

A

Scintillation screen

RT 212 (10 decks)

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