4. Flat-Panel Radiography Flashcards
1
Q
Limitations of CR
A
- X-ray detection of CR is inefficient & this affects
image quality & dose. - The spatial resolution of CR is less than Film-Screen radiography. CR 3-5 lp/mm, FS 10-15
lp/mm - CR Imaging plate can easily be damaged,
susceptible to scratches & cracking. - CR Imaging plate must be transported to a
separate image processor (reader) for image data
extraction
2
Q
Introduced as
early as ____ for
use in radiographic
imaging
A
1995, Flat-panel digital
radiography
3
Q
A-Si
A
Amorphous Silicon
4
Q
A-Se
A
Amorphous Selenium
5
Q
Digital detectors used before 1995 were \_\_\_\_\_ on FPD technology
A
not based
6
Q
(CCD chip) Slot-scan digital detector
A
1990
7
Q
Selenium drum digital detector
A
1994
- Chest imaging
- Thoravision (Philipps Medical Systems)
- Insert figure 5-2
8
Q
conducts electrons when struck by
light or X-ray photons
A
Photoconductor
- Selenium 34
- Silicon 14
9
Q
Flat-panel
Digital
Radiography:
S Y S T E M
C O M P O N E N T S
A
- Pre-amplifiers
- Switching Control
- Central Logic Circuits
- ADC’s
- Internal Memory
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
11
Q
Types of FPD Detectors
A
- Indirect Detectors
- Direct Detectors
12
Q
-uses phosphors
-phosphors convert X-ray energy into electrical charge
through an intermediate stage of light photons.
A
Indirect Detectors
13
Q
-use a photoconductor
-photoconductors convert x-ray energy into electrical
charge without the intermediate stage.
A
Direct Detectors
14
Q
2 TYPES OF INDIRECT DETECTORS:
technical
components
A
- Charged-Coupled Device (CCD) Digital Detector
2. Flat-Panel Thin Film Transistor (TFT) Digital Detector
15
Q
The most prominent difference between these
two types of detectors is the technical
component used to ____
A
convert light into electrical
signals
16
Q
based on an indirect conversion process
A
CCD (Charged-coupled Device) digital detectors
17
Q
uses a CCD chip to convert light to
electrical charge
A
CCD (Charged-coupled Device) digital detectors
18
Q
not classified as flat-panel digital
detector
A
CCD (Charged-coupled Device) digital detectors
19
Q
The main technical components of a CCD-based DR detector includes:
A
- X-ray absorber
- Light optics
- CCD - sensor (chip) for capturing the
light electrical charge readout device
20
Q
A CCD digital detector consists of several CCD’s
in order to _____ the size of the detection
area
A
increase
21
Q
3 OTHER NOTEWORTHY
COMPONENTS:
A
- Scintillation screen – detects X-rays &
converts them into light - Light collection optics
- Array of CCDs – CCD camera
22
Q
Other
systems
used:
A
- Fiberoptic-coupled CCD System
- Lens-coupled CCD
- Fiberoptic-coupled Scanning Array
System
23
Q
based on an indirect conversion process
A
Indirect flat-panel
TFT (Thin Film Transistor) digital detectors
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
25
```
The main
technical
components of a
TFT digital
detector
includes:
```
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.
26
```
DIRECT
DIGITAL
DETECTORS:
technical
components
```
1. Source of high voltage
2. Top electrode
3. Dielectric layer
4. Photoconductor
5. Collection electrode
6. TFT
7. Storage capacitor
8. Glass substrate
27
SOURCE
OF
PHOTOCONDUCTORS:
Amorphous Selenium (a-Se)
28
excellent X-ray detection properties & a very
| high spatial resolution
Amorphous Selenium (a-Se)
29
detect x-ray photons from the patient &
| converts them directly into electrical charges
Amorphous Selenium (a-Se)
30
Other photoconductors used:
1. Lead Oxide
2. Lead Iodide
3. Thallium Bromide
4. Gadolinium
31
designed as a matrix of detector elements, each of which can be regarded as a pixel & constructed as:
design is called: “______”
Configuration of the Flat-Panel,
| large area integrated circuit
32
also referred to as an active matrix array
Matrix
33
consists of rows & columns that play a role in
addressing & readout of the signal from each
pixel
Matrix
34
Each pixel contains a TFT (switch), a storage
capacitor & a sensing area, referred to as the
_____
sensing/storage element
35
The sensing area will detect the light from the
| ___ scintillator
CsI
36
A concept that examines the response of the image
| receptor to the radiation falling upon it
Exposure Latitude
37
Exposure latitude for CR/DR detectors
0.1-1000 µGy
38
Detectors with wide dynamic range can respond to ____ of exposure (low to high) and still provide an image that appears acceptable to the observer
different levels
39
Typical detector dimensions:
43 cm x 43 cm
30 x 40 cm
18 x 18 cm
40
Typical matrix sizes:
```
1760 x 2140
2000 x 2500
2736 x 2736
2560 x 3072
2688 x 2688
3121 x 3121
```
41
The pixel size & spacing determine the _____ of the image
spatial
| resolution
42
the distance from the
midpoint of one pixel to the midpoint of the
adjacent pixel
Pixel Pitch
43
Pixel sizes in current detectors can be
139 µm,
143 µm, 160 µm, 162 µm, 167 µm, and 200
µm
44
The ratio of sensing area of the pixel to the area
| of the pixel itself
Fill Factor of the Pixel
45
Image Quality Descriptors
1. Spatial Resolution
2. Density Resolution
3. Noise
4. Quantum Detective Efficiency
5. Artifacts
46
related to the size of the pixels on the image
| matrix
Spatial Resolution
47
Pixel size of 35 cm x 43 cm (24“ x 17“)
0.2 mm
48
Pixel size of 23 cm x 30 cm (10” x 12”)
0.14 mm
49
Pixel size of 18 cm x 24 cm (8” x 10”)
0.1 mm
50
The smaller the pixel size the ____ the spatial
| resolution of the image
better
51
The pixel size can be calculated using the
| relationship:
PS = FOV/ Matrix Size
52
Same FOV, the _____ the matrix size, the _____ the pixels, the better the ____
greater,
smaller,
image sharpness
53
A typical CR image matrix size
2048 x 2048
54
linked to bit depth
Density Resolution
55
range of gray levels per pixel
Density Resolution
56
An image with a bit depth of 8 will have _____
| shades of gray per pixel
256 (2^8)
57
refers to the color
| information stored in an image
Bit Depth
58
The ___ the bit depth of an image, the
| more colors it can store
higher
59
1 bit
Two values: 0 white, 1 black
60
8 bit
256 colors
61
24 bit
16 million
62
Noise
1. Electronic Noise (System)
| 2. Quantum Noise (Quantum Mottle)
63
determined by the number of X-ray photons
(signal) falling upon the detector to create
the image
Quantum Noise
64
```
Low exposure factors will produce few photons at
the detector (less signal, more noise)
```
Results in a noisy image, (Grainy/Poor image)
65
Higher exposure factors will generate more
| photons at the detector (more signal, less noise)
Produce a better image, increase patient dose
66
___ Noise, ___ Detector Exposure
More,
| Less
67
The detector receives an input exposure &
| converts it into a useful output image
Detective Quantum Efficiency (DQE)
68
DQE
Detective Quantum Efficiency
69
is a measure of the efficiency & fidelity
| with which the detector can perform this task
Detective Quantum Efficiency (DQE)
70
DQE =
SNR^2out / SNR^2in
71
DQE for a perfect digital detector is
1 or 100%
| This means that there is no loss of information
72
A distortion or error in an image that is
| unrelated to the subject being studied
Image Artifacts (Morgan, 1983)
73
An ____ is a feature in an image that masks
| or mimics a clinical feature
artifact, (Willis, 2004)
74
can be disturbing to
radiologists and may even result in an
inaccurate diagnosis
Artifacts
75
Sources of Artifacts
1. Imaging hardware (equipment)
2. Image processing software
3. Objects that are imaged & linked to
the operator errors
76
ensures that every employee plays a
| role in creating a quality product
CQI (Continuous Quality Improvement)
77
CQI
Continuous Quality Improvement
78
are essential not only
for optimizing the assessment and
evaluation of patient care, but also for
monitoring the performance of equipment
QA & QC programs
79
Describe systems & procedures for assuring quality
patient care, quality assessment, continuing
education, the usefulness of quality control
procedures & assessment of outcomes
Quality Assurance
80
deals with the administrative aspects of
| patient care & quality outcomes
QA (Quality Assurance)
81
Component of QA that refers to the monitoring of
important variables that affect image quality &
radiation dose
Quality Control
82
deals with technical aspects of equipment
| performance
QC (Quality Control)
83
Purpose of the procedures & techniques of CQI, QA & QC:
```
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
involves a number of activities that are of
significance to the technologist, particularly if
the technologist is in charge of the QC program
Quality Control
85
Quality Control Activities:
1. Acceptance Testing
2. Routine Performance
3. Analysis of Reject Rates
4. Error Correction
86
Ensures that the equipment meets the
| specifications set by the manufacturer
Acceptance Testing
87
Involves conducting a QC test on the equipment on a regular basis with varying degrees of frequency
Annually, semiannually, monthly, weekly or daily
Routine Performance
88
Ensures that equipment not meeting the performance
criteria or tolerance limit established for specific QC
tests must be replaced or repaired to meet
specifications
Error Correction
89
has recommended a number of
| tools for CR Quality Control
AAPM (American Association of Physicists in Medicine)
90
TOOLS FOR CR QC TESTING
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
Common Beam Filtering Materials
```
Brass,
Copper,
Aluminum,
Lead,
Tin,
Molybdenum,
Tungsten,
Titanium,
Zirconium
```
92
Film-Screen contact test tool
Wire mesh tool/placed on screen & exposed
93
QC TEST 1: Dark Noise
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
QC TEST 2: CR Imaging Plate Test = Uniformity
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
QC TEST 3: Erase Thoroughness
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
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
Memory effect
97
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
Image Lag
98
detects X-rays &
| converts them into light
Scintillation screen
