CR/DR Imaging Systems Flashcards
(160 cards)
0
Q
DR
A
Digital radiography
- direct readout detectors
- photodiodes
- charged coupled devices (CCD)
- thin film transistors (TFT)
1
Q
CR
A
Computerized radiography
- Photostimulable phosphor plates
- digitizer/ADC converter
2
Q
Advantages of CR
A
Less expensive
Can be used for portables
Better suited for trauma radiography
Compatible with existing radiographic tables
3
Q
Disadvantages of CR
A
Delayed readout
Cassettes needed
Can’t use for mammo
Plate must be erased after each use
4
Q
DR advantages
A
Immediate readout Cassette free Excellent for high volume radiography FDA approved for mammo Detectors can be reexposed immediately
5
Q
DR disadvantages
A
More expensive
Less flexible, if tethered
6
Q
CR is projection radiography that will use a _________________ in the place of film.
A
PSP - Photostimulable phosphor
7
Q
CR cassettes are similar to film/screen cassettes, and other characteristics are:
A
Made of lightweight aluminum, steel or plastic frame
Need not be light proof as the image plate is not sensitive to normal light
Structurally sound transport method for phosphor plate
Lead foil backing to absorb scatter
Inner surface lined with felt to reduce static and protect from mechanical damage
8
Q
Phosphor plate construction
A
Approximately 1mm thick, flexible containing a protective layer, phosphor layer, anti halo/reflective layer, conductive layer, base layer, and backing layer
9
Q
Protective layer
A
Fluoridated polymer material
10
Q
Phosphor layer
A
Europium barium fluorohalide crystals
11
Q
Anti-halo/reflective layer
A
Prevents laser light from penetrating
Allows reflected light from the phosphor to pass through
12
Q
Conductive layer
A
Removes static electricity
13
Q
Base layer
A
PET - polyethylene terephthalate
14
Q
Backing layer
A
Protects base for handling damage, and contains the barcode label on the IR
15
Q
Phosphor plate function
A
Latent image is formed by remnant radiation striking the plate. X-ray energy is absorbed within the PSP crystal. The absorbed photon energy causes electrons from the crystal to be trapped in “F” centers.
This is the latent image - a chemical code that is invisible to the human eye.
16
Q
Fading
A
The latent image can remain stored on a cassette for up to 24 hrs but gradually weakens. A typical plate loses 25% of its stores energy within 8 hours.
17
Q
CR scanner
A
Reads the IR - the entire cassette is placed in the scanner and opened up internally to remove phosphor plate.
18
Q
The scanner scans the plate with a
A
Helium neon laser light and reads the latent image from the phosphor via a process called readout.
19
Q
The laser reads in a __________ pattern to obtain the image.
A
Transverse raster pattern (side to side)
20
Q
F centers
A
Electrons elevated out of their normal orbital rings and into higher orbitals (further from the nucleus).
21
Q
The latent image is held in a chemical code of rearranged electrons.
A
.
22
Q
“F” in f center stands for
A
Farbe - the German word for color
23
Q
As the laser beam travels over the plate, the latent image (trapped energy in the crystals) is
A
Released as visible light.
24
The electrons elevated to higher orbitals are then
"Slapped back" into their normal orbits by the laser
25
The transfer of electron energy results in the release of visible light energy, this process is called
PSL - Photostimulated luminescence
26
In order for PSL to occur the plate must be exposed to a specific wavelength of light, around 600nm (red light) to release the energy from the
F centers
27
The laser emits a light wavelength of
633nm
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Laser energy bombardment
```
Elevated electrons are "slapped" back into their normal orbits.
Red laser light (helium-neon laser).
Stored energy is released.
Visible light is emitted.
Blue visible light.
```
29
The light emitted by Photostimulated luminescence has a wavelength of
390-400nm (blue-purple light photons)
30
The intensity of the light is directly proportional to the amount of
Radiation absorbed.
31
The PSL is collected by an optical collection system called a light channeling guide (light gate) which
Sends the light to one or more photomultiplier tubes.
32
Photomultiplier tube (PMT) is a
Device that converts light energy to electrical energy called analog signal
33
The analog signal
Is sent to the analog to digital converter (ADC) where it gets digitized so the computer can process the signal.
34
Digitizing
The process of translating an analog image to a binary code that can be read by a computer.
35
The amount of electrical energy received by the ADC is
Measured and assigned a numerical "digital" value
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The digital image is held in the computer and consists of
A series of thousands/millions of numbers, each representing one pixel of the image.
37
Once the imaging plate has been processed the plate is exposed to
A sodium-vapor light or high intensity fluorescent light to release trapped electrons.
38
The exposure to visible light
Erases any residual information and prepares the plate for reuse.
39
PSP plates can be
Reused thousands of times, mechanical damage will occur prior to the phosphor layer degrading.
40
The manifest image will be immediately displayed on the computer screen, if acceptable
The image is delivered to PACS.
41
Readers are available as
Single scanner (cheaper/smaller/low volume)
Multi scanner (more expensive/larger/faster/complex)
42
The greatest advantage of DR/CR is
The number of grays available - contrast resolution.
43
CR plates are capable of much wider exposure latitude and contrast range when compared to the latitude of
Film which allows for a reduced number of repeat images/exams due to technique error
44
QDE
Quantum detection efficiency
45
QDE measures
The efficiency of a CR system to convert remnant radiation into useful image signals, closely related to exposure latitude of a plate
46
High QDE systems reduce
Patient dose due to requiring less radiation to produce an acceptable digital signal.
47
There are three inherent factors responsible for image resolution capability:
Image plate crystal size
Laser beam size
Monitor matrix size
48
Currently the resolution in cr digital imaging is approximately
2.5 line pairs per millimeter
49
Conventional radiography an demonstrate
6lp/mm
50
The speed of a digital imaging system is determined by the
Level of exposure received at the image receptor. Varies by manufacturer.
51
Fuji systems
Exposure indicator is the "s" number.
| Calculated by dividing 200 by the exposure amount.
52
The higher the "s" number
The lower the exposure
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The expected range for Fuji systems is
180-220
54
Kodak systems
Uses the EI number.
2000 indicates a perfect exposure
55
The higher the EI number (kodak)
The higher the exposure to the patient
56
A perfect kodak range is
1950-2050.
57
Agfa systems
Use the log mean number
2.2 is a perfect exposure.
58
Agfa has a direct relationship of exposure to
LGM number.
59
The expected range for Agfa systems is
1.9-2.5 LGM
60
The identification terminal (IDT) is used to
Input the patient info and exam details.
- contains bar code reader
- contains RF chip
61
Contrast resolution
The ability to distinguish adjacent structures that have similar densities
62
The higher the contrast resolution, the more...
Distinct structures are with smaller densities
63
Digital imaging systems have significantly higher contrast resolution than film screen, allowing
Ability to visualize more grays and differentiate between shades
64
Direct readout image acquisition technology is
DR - direct radiography - no need for a processor/ADC/digitizer
65
The basic theme to all digital imaging systems is
The conversion of X-ray energy into electrons
66
The steps that occur between X-ray and electrons make
The different types of digital different
67
Why electrons
They can be counted
68
Analog
Refers to a device or system that represents information as continuously variable PHYSICAL QUANTITIES
69
Examples of analog devices
Mechanical watch
X-ray film - information is physical
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Digital
Refers to a device or system that represents information as continuously variable NUMERICAL VALUES
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A common digital device is a
Digital watch
CR and DR - information is numeric
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Digitizing
The process of converting colors, shades, and shapes as analog information into numbers, which is digital information.
73
Computers are capable of processing, storing, and transferring information that is held in the
Numeric form
| - numbers, held in binary code
74
Computers cannot interpret information that is in colors, shades, or shapes (analog)
Such as black, white, and gray of an image
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3 types of flat panel detectors
Tethered
Fixed
Wireless
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Tethered panels
FPD attached by an umbilical cord
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Fixed panels
FPD permanent mounted in Bucky
78
Wireless
Signal sent from FPD to base unit (radio signal about 5.3 gigahertz)
79
Capture element
Remnant X-ray energy is captured
80
Coupling element
Transfers X-ray generated signal to collection element
81
Collection element
Collects photons or electrons to be quantified, assigned a digital value
82
All digital systems start with X-ray and finish with electron energy
Electrons can be counted and assigned a digital value
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Capture elements
CR
Indirect DR
Direct DR
84
CR - Photostimulable phosphor
Converts X-ray to rearranged molecules
85
Indirect DR - amorphous silicon
Converts X-ray to visible light
86
Direct DR - amorphous selenium
Converts X-ray directly to electrons
87
CR - light channel/light gate coupling elements
Light from the IP is sent to the photomultiplier tube
88
Indirect DR - amorphous silicon coupling elements
Light from amorphous silicon is sent to photoconductive material
89
Direct DR - amorphous selenium coupling elements
Electrons from amorphous selenium are sent to TFT
90
CR photomultiplier tube
Collection element light from IP collected by pmt
91
Indirect CR - thin film transistor
Collection element where electrons from photoconductive material collected by TFT
92
Direct DR - thin film transistor
Collection element where electrons from amorphous selenium is collected by TFT
93
Indirect conversion flat panel detectors
Uses thin layers of amorphous silicon with an array of photodiodes
94
The photodiodes are coated with
A Photostimulable phosphor that emits light directly proportional to the amount of radiation received.
95
The visible light is converted to an electrical charge by the
Photodiode array. The electrical signal is sent to the ADC to convert it to a digital signal.
96
Advantage of indirect conversion flat panel detectors
High QDE allowing lower patient dose
97
Disadvantage of indirect conversion flat panel detectors
Loss of resolution due to divergence of the light emitted
98
Steps in indirect image formation
Amorphous silicon
Remnant X-ray enters amorphous silicon crystal
X-ray energy converted to visible light energy
Light carried along amorphous silicon crystals
Photoconductive material receives light
Electron energy captured by TFT device
99
Indirect DR energy conversions
X-ray - as remnant radiation
Visible light - product of Photostimulable luminescence, X-ray converted to light by scintillating phosphor
Electrons - product of photodiode material, visible light energy converted to electron energy
100
Thin film transistors
```
Both a-Si and a-Se use TFT's
Collect electrical charges
Positioned in a matrix
Direct charges on a pixel by pixel basis
Active matrix array
Capable of very high spatial resolution - greater than 20 lp/mm
```
101
Dead zones
TFT's have dead zones, the species between individual DELs
102
Larger dead zones
Decreased resolution
103
Smaller dead zones
Increased resolution
104
Measuring pixels by pixel pitch takes into consideration the
Dead zones - more accurate assessment
105
Direct conversion flat panel detectors
Use an amorphorous selenium coated thin film transistor array that directly converts X-ray energy into an electrical signal.
No light conversion therefore no light divergence.
106
Direct digital image formation with amorphous selenium
Remnant X-ray beam ->
Amorphous selenium ->
Thin film transistors
107
Direct DR energy conversions
X-ray - as remnant radiation
Electrons - product of a-Se ionization
X-ray energy is directly converted to electrons by amorphorous selenium crystals
No visible light in the image formation proces
108
No visible light
No loss of detail due to the divergence of light
109
Algorithms
A finite sequence of instructions for solving a problem often used for calculation and data processing. Not one size fits all.
110
Histograms
The exposure is converted to a histogram, initial is compared to stored, computer makes changes as necessary.
111
Histograms are specific to
The anatomy.
Aka frequency distribution charts.
112
Look up table
Contains predetermined luminescence values, anatomy dependent. Mapping function in which every pixel is changed to a new shade of gray simultaneously. Results in the image having the appropriate brightness and contrast.
113
Automatic rescaling
Regardless of appropriate exposure, the computer is able to display the image with a diagnostically correct gray scale (within limits).
114
Way too little exposure
Quantum mottle
115
Way too much exposure
Loss of contrast
116
Tools a tech should use to get a good image
Exposure indicator
"Tech eye"
117
Spatial resolution
Ability to see small objects lp/mm
| Controlled by crystal size in CR, del size in DR, pixel size on display monitor - all digital.
118
Contrast resolution
Ability to differentiate between shades controlled by bit depth/bit range/pixel depth
119
Film screen is capable of
5-7 lp/mm
120
Cr digital imaging is capable of
2-5 lp/mm
121
Modern state of the art DR are capable of spatial resolution up to
20 lp/mm
122
Spatial resolution controls
Detail or sharpness of the image
123
Small pixels
Better spatial resolution
124
More pixels
Better spatial resolution
125
Pixel
The smallest component of a picture. One dot of image info.
Each picture is made up of many thousands/millions of pixels
126
Pixel density
The number of pixels per given area.
127
Image matrix
Layout of cells in rows and columns
- pixels
- vowels
- Hounsfield units
128
Hounsfield units aka
CT numbers
129
Pixel
2 dimensional
| -length x width
130
Voxel
3 dimensional
| -length x width x height
131
Pixel
Picture element
- 2 dimensional
- each pixel corresponds to a shade of gray
132
A pixel or voxel can only report
One shade at a time
133
Contrast resolution
The ability to distinguish adjacent structures that have similar densities.
134
The higher the contrast resolution
The more distinct adjacent structures are with similar densities
135
Contrast resolution aka
Pixel depth
Bit range
Dynamic range
136
Contrast resolution is rated in
Bit depth
137
Film screen contrast resolution
A few dozen shades of gray
138
CR digital imaging contrast resolution
Thousands of shades of gray
139
The human eye is capable of only differentiating
30-32 shades of gray
140
Dynamic range - bit range
Scale showing how many shades of gray per given bit
141
1 bit
1+1=2
2 shades of gray
142
2 bit
2+2=4
4 shades of gray
143
3 bit
4+4=8
8 shades of gray
144
4 bit
8+8=16
16 shades of gray
145
5 bit
32 shades of gray
146
6 bit
64 shades of gray
147
7 bit
128 shades of gray
148
8 bit
256 shades of gray
149
9 bit
512 shades of gray
150
10 bit
1024 shades of gray
151
11 bit
2048 shades of gray
152
12 bit
4096 shades of gray
153
13 bit
8192 shades of gray
154
14 bit
16384 shades of gray
155
15 bit
32768 shades of gray
156
16 bit
65536 shades of gray
157
Latitude
Margin for technique error
158
With digital, just getting an image
Does not mean its a good image.
159
With digital, the almost unlimited range of grays means
That exposure latitude is almost unlimited as well.
