CAMRT Review: Apparatus And Image Flashcards
1
Q
Principle components of x-ray equipment?
A
- Operating Console
- X-ray tube assembly
- High voltage generator
2
Q
2 types of tables?
A
- Tilting: fixed height, but tilts
2. Fixed: adjustable height, but no tilt
3
Q
Types of X-ray tubes?
A
- Crookes: no vacuum, gas filled, 1mA station
2. Coolidge: vacuum, glass/metal envelope, various mA stations
4
Q
Function of the tube housing?
A
- hold and protect tube: structure and support
- dissipate heat
- reduce leakage radiation
5
Q
Function of the glass/metal envelope?
A
-maintain a vacuum
6
Q
Which kind of envelope (glass or metal) extends tube life by preventing arcing?
A
Metal
7
Q
Function of the cathode?
A
Provide a source of electrons
8
Q
Parts of the cathode?
A
- Filament
- Focusing cup
9
Q
Purpose of filament? What is it made out of?
A
- Boils off electrons through thermionic emission
- thoriated tungsten
10
Q
Why is the filament made out of thoriated tungsten?
A
- high atomic # (74)
- high melting point (3410)
- thorium increases thermionic emission and extends filament life
11
Q
Function of the anode?
A
- Electrical conductor: some electrons interact, the rest continue as current and flow through the circuit
- Mechanical support for target
- Thermal dissipator: overheating will cause pitting, cracking, melting
12
Q
Types of anodes?
A
- Stationary: doesn’t rotate, electrons hit the same spot and heat builds up faster (only small exposures)
- Rotating: focal track (500x bigger target area)
13
Q
What is the anode target made out of?
A
- molybdenum core with tungsten coating
- would be too heavy if all tungsten
- tungsten adds mechanical strength
14
Q
What is the anode shaft made out of?
A
- molybdenum with a copper coating
- copper is a good thermal and electrical conductor
- molybdenum has a low thermal conductivity and is light weight
15
Q
Parts of an induction motor?
A
- Stator: electromagnets outside of the envelope, energized in opposing pairs to induce a current in the rotor with a magnetic field
- Rotor: iron core surrounded by a copper cuff inside the envelope
16
Q
What happens when the exposure switch is pressed halfway down?
A
- Rotor is accelerating
- filament heats up and begins to boil off electrons
17
Q
What happens when the exposure switch is pressed halfway?
A
- voltage goes to cathode and anode
- created potential difference between the cathode and anode
18
Q
4 ways to extend tube life?
A
- Minimize exposure factors
- Utilize faster image receptors
- Warm up anode (small exposures)
- Use shortest exposure time possible
19
Q
What is the main factor/cause of tube failure?
A
Heat (vaporization)
20
Q
What is the line focus principle?
A
Relationship between the actual and effective focal spot
21
Q
What does the line focus principle allow?
A
Allows for a larger area for heating while maintaining a small focal spot (angling target)
22
Q
Are the actual and effective spot directly or indirectly related?
A
Directly
23
Q
What is the actual focal spot controlled by? (4 things)
A
- Filament length, size, shape
- Target angle
- Charge on focusing cup
- Depth of filament in focusing cup
24
Q
What is a bi-angle target?
A
- 2 focal tracks = 2 target angles
- filaments are stacked
25
Limitations of the line focus principle?
- heat
| - too small of an angle = too small field size
26
What causes the anode heel effect?
Line focus principle
27
What is the anode heel effect?
The intensity of the beam on the anode side is less than on the cathode side
28
Min and max of anode heel effect beam% from anode to cathode?
Anode: as low as 75%
Cathode: as high as 120%
29
The anode heel effect is most apparent with what 2 things?
- Large IR size
| - Shorter SID
30
What is an atom?
The smallest particle that has all of the properties of an element
31
What is contained in the nucleus of an atom?
- Neutrons
| - Protons
32
What is ionization?
When an atom gains or loses an electron, becomes charged, and is now an ion
33
2 forces holding electrons in orbit around an atom?
Centripetal: inward pulling, center seeking
Centrifugal: outward pulling
34
What is the binding energy?
Strength of an attachment of an electron to the nucleus, the closer to the nucleus = higher binding energy
35
What happens to the binding energy with a higher atomic number?
Increased atomic number = increased binding energy because there are more protons in the nucleus and that makes a stronger positive pull
36
What is excitation?
When an electron is infused with energy and jumps to a different shell, it releases energy (non-ionizing)when is returns to its original spot
37
2 types of radiation (interactions) produced at the anode?
1. Characteristic
| 2. Bremsstrahlung
38
What is characteristic radiation?
When an incident electron hits an INNER SHELL electron and removes it (if energy is greater than binding energy). An OUTER SHELL electron drops in to fill the vacancy and gives off characteristic radiation
39
What is Bremsstrahlung radiation?
When an incident electron misses the orbital electrons and gets close to the nucleus. It is influenced by the positive charge of the nucleus. It slows down (releases energy = Brems radiation) and changed direction
-more change in direction = stronger radiation given off
40
What is the emission spectrum?
-a graph of the number of x-ray photons and the range of energies the photons possess at a given exposure setting
41
What is keV?
Killoelectron volt is used to measure binding energies and the energy of the incident photon
42
What is kVp?
-the forced with which incident electrons interact with the tungsten target
43
What controls keV?
kVp
44
A majority of the electrons have what percentage of the peak energy (kVp)?
Majority of electrons are 30-40% of peak energy
45
At what energy level can Brems radiation be produced?
Any level
46
At what energy level can Characteristic radiation be produced?
Only occurs between certain energies (must be higher than binding energies)
47
What does the spike on the characteristic emission spectrum represent?
The binding energies of the target material
| Ex. Tungsten = 69.5keV
48
What is mA?
The quantity of electrons
49
How does mA affect the spectrum?
Increase mA = increase amplitude of spectrum because increase in # of xrays
50
What is mAs?
The number of x-rays sent across the tube in 1 second
51
What is kVp in regard to x-rays?
Quality/strength of radiation
52
How does kVp affect the emission spectrum?
-Increased kVp = curve moves up and to the right because the average energy is increased and more x-rays are being produced
53
What do we do to kVp to double the amount of photons?
Increase kVp by 15%
54
What happens to characteristic radiation if we increase the atomic number of the target material?
Increases the efficiency of characteristic radiation because the binding energy for each shell increases
55
What happens to Brems radiation when we increase the atomic number of the target material?
Increases Brems radiation because there is a more positive pull from the nucleus’
56
Image quality factors: photographic properties? (2)
1. Radiographic Density
| 2. Optical Density
57
What is radiographic density? What effects it?
The amount of overall blackness on an image
| -affected by prime exposure factors (kVp, mA, time, SID)
58
What is optical density? How is it measured? What is it affected by?
Degree of blackening on a radiograph
- measured from 0-4 (human vision is 0.25 to 2.5)
- >3 = black
- <0.2 clear
- affected by mAs (direct relationship) and SID
59
What is the reciprocity law?
Any combination of mA and time that results in the same mAs will produce the same density
60
In what situations is the reciprocity law useful?
- motion (trauma/peds)
- focal spot size
- breathing techniques
61
By what % must mAs be changed for us to notice a visible difference on the image?
30%
62
What does kVp control?
Contrast
63
What does mAs control?
Density
64
Decreased kVp = _________ density?
Decrease kVp = decreased density
65
How to double and halve the density by changing kVp
Double: kVp x 1.15
Half: kVp x 0.85
66
The 15% rule for kVp is most effective at (higher or lower) kVps?
Higher kVps
67
What is a latent image?
The image before its processed
68
What is differential absorption?
The process where some of the beam is absorbed and some is transmitted
-different body parts absorb the beam differently depending on what they are made up of
69
Beam attenuation consists of what 3 things?
1. Absorption
2. Scatter
3. Transmission
70
Types of beam absorption?
1. Photoelectric effect
2. Pair Production
3. Photodisintegration
71
Types of scatter?
1. Compton Scatter
| 2. Coherent Scatter
72
What is the photoelectric effect/photoelectric absorption?
- Complete absorption of an x-ray photon by inner shell electron
- INNER SHELL electron ejected (photoelectron) after if absorbs x ray photon
- outer shell electron drop in to fill the spot (characteristic radiation)
- atom is ionized
73
The probability of photoelectric interactions increases when...?
The energy levels of the incoming x-ray photon and the binding energy of the electron are closer together
74
What is Compton Scatter?
- Incoming x-ray photon ejects an OUTER SHELL electron and the electron is scattered (compton electron, secondary electron)
- photon loses energy and changes direction, can leave the body and interact with IR
75
What happens to absorption and scatter with a higher kVp?
Less overall interactions, but more of them are scatter
76
Why are is scatter and issue?
- Degrade image
- Contribute nothing useful to the image
- Also known as image fog
77
Increased kVp = ________ # of interactions?
Increased kVp = DECREASED # of interactions
78
Increased kVp = _____ # of transmitted photons
Increased kVp = INCREASED # of transmitted photons
79
Increased kVp = ________ compton scatter?
increased kVp = INCREASED compton scatter
80
Increase kVp = increased fog = ________ overall density?
Increased kVp = increased fog = INCREASED overall density
81
Increase kVp = _________ contrast?
Increased kVP = DECREASED contrast
82
Increased kVp = ________ patient dose
Increased kVp = DECREASED patient dose (more photons transmitted, but if scatter is absorbed by the body it contributes to patient dose)
83
What is exponential absorption?
For every increment of thickness, x-rays decrease in number by a certain percentage (never reaches 0)
84
What is SID?
The distance between the focal spot and the image receptor
85
Increased SID = _______ density?
Increased SID = DECREASED density because you have the same number of photons, but a larger area to cover (flashlight)
86
Inverse Square Law?
I1/I1 = D2^2/D1^2
87
Density Maintenance Formula?
mAs1/mAs2 = SID1^2/SID2^2
88
In what situations would we use the density maintenance formula?
- portables
- to fit larger parts to a receptor
- patient condition
89
What is OID?
Object to image distance
90
Increased OID = __________ scatter = _______ density?
Increased OID = DECREASED scatter = DECREASED density
91
Types of body habitus?
- Sthenic
- Asthenic
- Hyposthenic
- Hypersthenic
92
2 types of pathologies?
1. Destructive: increases radiolucency
| 2: Constructive: increased radiopacity
93
3 types of filtration?
1. Inherent: can’t be adjusted, built it, glass/metal envelope
2. Added: can be adjusted, aluminum most common, must adjust techniques to compensate
3. Compensating: balance intensity to deliver a uniform exposure across IR
94
How does filtration affect the beam?
- Increased beam quality
- Increased penetrability
- Removes low energy photons
95
Increased filtration = ________ scatter = ______ contrast?
Increased filtration = INCREASED kVp = DECREASED contrast
96
What is a beam restrictor?
A device that attaches to the x-ray tube housing to regulate the size and shape of the beam
Controls and minimizes scatter by limiting the x-ray field soze
97
3 pros of beam restrictors?
1. Limit patient exposure
2. Reduce scatter
3. Increase contrast
98
What is off-focus radiation? What does it cause?
```
Electrons that stray and hit the anode in a different spot
Causes penumbra (fuzzy edge of image)
```
99
Increased beam restrictor distance from tube = _______ off focus radiation and penumbra
DECREASED
100
Types of beam restrictors?
1. Aperture Diaphragm
2. Cones/Cylinders
3. Variable Aperture Collimator
101
What is an aperture diaphragm?
- flat piece of lead of lead lines material that fits onto the tube head
- field size controlled by the size of the opening, shape of opening, and SID
- inexpensive/easy to use
- must have multiple diaphragms
- large penumbra (close to focal spot)
102
What is a cone/cylinder?
- extension cone/cylinder on aperture diaphragm
- field size is determined by the size and position of the distal end
- inexpensive and easy to use, decrease penumbra
- fixed field size, shape is round, doesn’t restrict primary beam
103
What is a variable aperture collimator?
-2 sets of shudders: entrance control off focus radiation and 2nd stage, light and mirror
104
What is Positive Beam Limitation?
Automatic collimators adjust to the size of a cassette put in tray to ensure field size isn’t larger than IR
*does not replace manual collimation*
105
3 factors affecting scatter?
- kVp
- field size (smaller field size = less matter = less scatter)
- patient thickness (more matter more scatter)
106
Decreasing field size = _______ density
Decreasing field size = DECREASED density because there are fewer photons hitting the IR
107
If you increase collimation, you should ________ exposure factors?
INCREASE
108
What is the most effective way to reduce scatter?
Grids
109
What is grid frequency?
The number of lead lines per unit length
110
Will a high frequency show more or less grid lines on an image?
Less because the strips are thinner
111
What is grid ratio?
The height of the strips vs the distance between them
112
Grid ratio formula?
Grid ratio = h/d
113
Increased grid ratio = __________ contrast?
Increased grid ratio = INCREASED contrast
114
3 things about higher ratio grids
- they remove more scatter
- require accurate positioning
- prone to grid errors
115
What is grid cut off?
Absorption of the primary beam by the lead strips
116
How does grid cut off affect density?
Decreases density
117
Grid patterns?
1. Linear (parallel and focused)
| 2. Crossed
118
What is a parallel grid?
- lead strips run parallel
- can’t avoid grid cut off
- decreasing density towards the sides
119
What is a focused grid?
- lead strips are angled to match diverging rays
- less grid cut off
- even density
120
What is a crossed grid?
- lead strips cross
- tube can’t be angled
- precise positioning required
- clean up lots of scatter
121
What is a convergent point?
- where imaginary lines drawn up from the strips on a focused grid would meet
- if the points were connected: “convergent line”
122
What is focal distance/grid radius?
The distance between the grid and convergent point/line
123
What is a focal range regarding grids?
Recommended range of SIDs that can be used with a focused grid
124
Types of moving grids?
1. Reciprocating
| 2. Oscillating
125
Why do we use moving grids?
Prevent grid lines
126
Moving grid disadvantages?
- requires bulky mechanism that can fail
- increased OID
- motion can be transferred from to cassette holding device
127
Moving grid errors?
- incorrect grid installation
| - grid movement with grid lines
128
Stationary grid errors? (4)
1. Off level: grid/tube is angled, loss of density over entire image
2. Off-center: CR is not aligned side to side with center of focused grid, overall loss of density
3. Off-focus: SID out of focal range, increased cut off with increased grid ratio, loss of density along edges
4. Upside down: grid upside down, severe grid cut off on edges
129
Another name for off-center grid error?
Lateral decentering
130
Grid Conversion Formula?
mAs1/mAs2 = GCF1/GCF2
131
When do we use the grid conversion formula?
Used when converting to a grid with a different ratio
132
Grid (Bucky) Factors?
No grid: 1
5: 1:2
8: 1:4
12: 1:5
16: 1:6
133
Contrast Improvement Factor Formula?
K= image contrast with grid/ image contrast without grid
134
If you have a contrast improvement factor of 1, what does that mean?
No improvement seen
135
What is the air gap technique?
Method to reduce scatter, move part 10-15cm away from IR
136
Disadvantages of the air gap technique?
- magnification of part
- image blur
- not effective with high kVps
- increase technique to maintain density
137
What are exposure timers for?
Make or break high voltage across the tube
138
4 types of exposure timers?
1. Synchronous
2. Electronic
3. mAs
4. AEC
139
How does a synchronous timer work?
- electric motor drives a shaft at 60rpm
- exposure time determines the time it takes to move from the on switch to the off switch
- has to be reset in between exposures
140
How does an electronic timer work?
- most sophisticated, expensive, accurate
- complex circuitry based on time it takes to charge a capacitor through a variable resistance (shorter exposure times charge faster)
- capacitor takes a preprogrammed charge, once it is charges the exposure stops
- ex. 1 seconds exposure: the resistance is increased so that it takes 1 second to charge the capacitor
141
How does an mAs timer work?
- monitors current going through tube and will terminate the exposure when the set mAs is achieved
- located in the SECONDARY circuit in order to measure actual tube current
142
How does an AEC timer work?
- only controls time
- measures the quantity of radiation reaching the IR and will terminate exposure when require radiation quantity has been received
143
2 types of AEC?
1. Photodiode/Phototimer
| 2. Ionization Chamber
144
How does a photodiode/phototimer version of AEC work?
- exit type (behind IR)
- converts light to electrical energy
- once certain charge is reached, exposure is terminated
145
How does an ionization chamber type of AEC work?
- entrance type (between patient and IR)
- air inside cell becomes ionized when hit with radiation
- created an electrical charge
- when predetermined charge is reaches, exposure is terminated
146
What happens when more than 1 AEC cell is selected?
The average signal is used
147
What does a backup timer do?
Protects the patient from overexposure
1.5 times the expected length of exposure
Max 6 seconds (may need to override for larger body parts)
148
What does density control do?
Regulates radiographic density of image
149
Steps of density control? How much change is there between steps?
-3, -2, -1, 0, 1, 2, 3
| Increase/decrease 0.1, about a 25% change from step to step
150
What is APR?
Anatomically Programmed Radiography
151
What is the most common cause of repeats with AEC?
Improper centering
152
What happens if collimation is too big when using AEC?
Too much scatter will reach the cell and AEC will shut off prematurely
153
What happens if the field size is too small when using AEC?
Cell will take longer to receive enough radiation to end exposure
154
Optimal use of AEC?
- appropriate kVp
- precise centering
- appropriate collimation
- appropriate selection of cell
155
What is the min kVp for grids?
70kVp
156
What is electrodynamics?
The study of electric charges in motion
157
What is the flow of electric current in relation to the flow of electrons?
Opposite
158
2 types of electric current?
1. AC
| 2. DC
159
2 parts of the general x-ray circuit
1. Main x-ray circuit
| 2. Filament circuit
160
Components of the main x-ray circuit? (Primary side)
- Main power switch
- Line compensator
- Circuit breakers
- Autotransformer
- Step up transformer
- Timer circuit
161
Components of the main x-ray circuit? (Secondary Circuit)
- mA meter to monitor tube current
| - Rectifiers
162
What does the line compensator do?
Automatically adjusts the power supply to 200V
163
What do the circuit breakers do?
-protect against short circuits and electrical shock
164
What does the autotransformer do?
- controlled by kVp selector
- provides voltage
- depending on what kV is set, different combinations of the secondary connections allow for increasing or decreasing voltage
- step up: increase number of coils used
- step down: decrease number of coils used
165
What does the step up transformer do?
- dividing line between primary and secondary circuits
- increases voltage from the autotransformer to the kV needed for x-ray production (not adjustable, increases by fixed amount)
166
What does the timer circuit do?
- “makes or breaks” voltage across the tube, breaks the circuit when its time to end the exposure
- located in the primary circuit because its easier to control a low voltage
167
What do rectifiers do?
- converts AC to DC because anode is not constructed to emit electrons
- diode will not conduct when AC cycle reverses
168
4 types of rectification?
1. Unrectified: x-rays not made during negative 1/2 of cycle
2. Half Wave: inverse voltage removed, gaps when current not being conducted, wastes half of power supply
3. Full Wave: inverts negative half so that it is always positive, 0-100% ripple
4. Three Phase Power: uses 3 AC waveforms at the same time, but out of sync, 3phase, 6 pulse (4-12% ripple). 3phase, 12 pulse (4% ripple)
169
Components of the filament circuit?
- Rheostat
| - Step down transformer
170
What does the rheostat do?
Controls filament temperature and rate at which electrons are boiled off and the time determines the duration of the process
-the higher the mA number, the lower the resistance
171
What does a step down transformer do?
Reduces voltage and increases current going to the filament so that it doesn’t break
172
2 types of generators?
1. High frequency
| 2. Falling Load
173
High frequency generators?
- less then 1% ripple
- smaller, lightweight
- less costly
- better exposure reproducibility
174
Falling load generators?
- initial tube load is higher and drops during exposure
| - achieves mAs in a shorter exposure (good for interventional)
175
Advantages of less ripple?
- greater radiation quality and quantity
- quantity of photons is higher because of efficiency of x-ray production is higher and higher energy photons are produced
- increased energy of x-rays
- increased efficiency of x-rays
176
More high energy photons = ________ # of interactions
More high energy photons = INCREASED number of reactions because photons can break electrons free of binding energy
177
Path of the circuit?
1. Line compensator
2. Circuit breaker
3. Autotransformer
4. Step up transformer
5. Rectifier
(Meanwhile filament circuit also going)
1. Line compensator
2. Autotransformer
3. Rheostat
4. Step down transformer
5. Filament
178
3 types of tube rating charts?
1. Radiographic Rating Chart
2. Anode Cooling Chart
3. Housing Cooling Chart
179
Which is considered the most important x-ray tube rating chart?-
Radiographic rating chart
180
Radiographic rating chart
- provides info about which radiographic techniques are safe for the x-ray tube
- for any given mA, any combination of kVp and time that lies below the curve is safe
181
Anode cooling chart
- chart shows thermal capacity and heat dissipation characteristics of the anode: how much time is required for the anode to be completely cooled and the max heat capacity of the anode
- does not depends on filament size of speed of rotation
- the rate of cooling is rapid at first and then slows down
182
More heat is generated with what type of units?
- 3phase
| - high frequency
183
How to calculate heat units?
HU= kVp x mA x time x modification factor
184
Modification factors?
Single phase: 1.0
3 Phase: 1.4
High Frequency: 1.4
185
Which will reach its heat limit first- the anode or the housing?
Anode
186
What is radiographic contrast?
The difference in optical density between adjacent structures, or the variation in optical density on an image
187
Radiographic contrast is a result of what?
Differential absorption
188
High contrast
- aka short scale
- few densities, great difference between them
- sharp image
189
Low contrast
- aka long scale
- large number of densities, but small differences between them
- lots of grey
190
Radiographic contrast is the PRODUCT of what 2 things?
- image receptor contrast
| - subject contrast
191
The only time radiographic density affects contrast is when the image is _______ or ______?
Overexposed
| Underexposed
192
Increased OID = _______ density
Increased OID = DECREASED density because less scatter, less photons hitting IR
193
3 subject factors to consider when selecting radiographic techniques?
1. Anatomy
2. Thickness
3. Composition
194
What can help when a part is super thick rather than increasing kVp?
Compression devices and positioning (PA)
195
For anatomy with lower subject contrast, we want ______ (high/low) contrast?
Higher contrast
196
Will tissues with high atomic numbers absorb more or less?
Absorb more
197
Are digital IRs more sensitive to scatter than film screen receptors?
Yes
198
What is the primary purpose of radiographic imaging?
To transfer the information from the x-ray beam to the eye
199
Layers of Film? (4)
1. Film Base/Base layer
2. Adhesive Layer/Substratum layer
3. Emulsion
4. Supercoat/Overcoat
200
What is the purpose of the base layer? What is it made out of?
- polyester to plastic
- allows us the handle the film
- lucent, but has a blue dye/tint to reduce strain
201
What is the purpose of the adhesive layer?
-holds the emulsion and base layer together
202
What is the purpose of the emulsions layer? What is it made out of?
- radiation and light sensitive
- silver halide crystals suspended in gelatin
- x-ray film double emulsion
- mammo single emulsion
203
What is the purpose of the supercoat? What is it made out of?
- protective layer
- made of hard gelatin
- to protect emulsion
204
How is the latent image formed?
- invisible change in the halide crystals
| - film processing changes the latent image into a manifest image
205
Where are intensifying screens found?
In cassettes
206
What does an intensifying screen do?
- contain phosphors that convert x-rays into light which then exposes film
- only 1-10% of energy reaching film is film is from x-rays when using a screen
- purpose is to lower patient dose
207
Layers of an intensifying screen? (4)
1. Protective coating
2. Phosphor layer
3. Reflective layer
4. Base layer
208
Purpose of the phosphor layer? What is it made out of?
- converts x-rays to light
- used to be calcium tungstate, now rare earth metals
- faster screen = lower patient dose, less load on tube (shorter exposures)
209
Purpose of reflective layer?
- between phosphor and base
| - redirects light towards film to enhance efficiency
210
What is spectral matching?
-film sensitivity must be properly matched to the spectrum of light emitted by the screen
211
What happens if there is no spectral matching between the film and intensifying screen?
- IR speed is greatly reduced
- increased patient dose
- higher exposure time needed to get image
212
What is a cassette?
-container for intensifying screens and film
213
Limitations of film (6)?
1. Limited dynamic range
2. Cost
3. Time
4. Film processors -equipment/maintenance costs
5. Processed film is permanent
6. Storage
214
Purpose of a cassette in a CR system? Why is it lined with felt? What is the backing made up of?
- to contain the PSP plate (photostimuable phosphor)
- lined with felt to prevent static buildup
- back made of aluminum
215
Layers of the PSP plate? (5)
1. Protective layer
2. Phosphor layer
3. Reflective layer
4. Conductive layer
5. Support layer
216
What is the purpose of the phosphor layer of a PSP plate? What is it made up of? How does it work?
- image forming layer
- barium fluorohalide and europium activated
- traps electrons during exposure
217
2 types of phosphor layers
1. Turbid: random distribution of phosphor crystals
| 2. Structured: columnar phosphor crystals resembling needles stacked on ends
218
Purpose of reflective layer of a PSP?
-redirect light released during “reading phase” towards the photodetector
219
Purpose of conductive layer of a PSP?
-reduces and conducts away static electricity
220
How do CR cassettes acquire an image?
- PSP plate is exposed and phosphor atoms are ionized
- electrons are excited to a metastable state (50% return to ground state immediately and emit visible light)
- remaining metastable electrons are what create latent image
- light released during “reading phase” proportional to radiation received
221
What is the purpose of europium in the active layer of a PSP?
- used as an activator for the phosphor
- traps electrons and keeps them in the excited stage
- no europium = no latent image
222
When the energy of the trapped electrons is released by exposure to a laser, it is called?
Photostimulable luminescence
223
3 stages of photostimuble luminescence
1. Stimulation
2. Reading: light released detected by photodetector
3. Erasing
224
2 ways the image plate can be removed from the cassette? How do they work?
1. Horizontal: IP fits into drive that moved it along at a constant pace along the long axis (slow scan), mirror is used to deflect the laser beam across the IR (fast scan)
2. Vertical: IP barely leaves cassette and is less likely to be damaged
225
CR reader optical components? (5)
1. Laser
2. Beam shaping optics
3. Light collecting optics
4. Optical filters
5. Photodetector
226
Why are beam shaping optics needed in a CR reader?
-they keep the size, shape, and intensity of the laser correct across the plate
227
What are the light collecting optics for?
-they filter the light before it reaches the photodetector so that none of the stimulation light goes through and swamps the emitted light signal
228
2 types of technique charts?
1. Fixed mAs/variable kVp
| 2. Fixed kVp/variable mAs (most common)
229
Advantages of the fixed kVp/variable mAs chart?
- lower dose (high kVp settings)
- adequate penetration of all anatomic parts
- consistent image contrast for exams
- greater latitude with exposures
- measurement of part is not critical
230
How does a variable kVp/fixed mAs chart work?
+2 kVp for every additional 1cm thickness
* measurement for this is critical
* only effective for peds and small extremities
231
What does an outcomes assessment include?
- repeat analysis: to avoid future repeats
- artifact analysis: to identify the cause of the repeat
- accuracy, sensitivity, and specificity analysis: analysis of the combination of image quality and correct diagnosis
232
3 advantages of repeat/reject analysis?
1. Improved department efficiency
2. Lower costs
3. Lower patient dose
233
Causal repeat rate formula?
(# of repeats from a specific cause / total # of repeats) x 100
234
With a QC program in place, most repeats are due to what?
Positioning errors
235
Total repeat rate formula
(# of repeats / total # of views) x 100
236
Repeat rate is affected by? (6)
- quality of equipment
- staff skill level
- patient type
- data collection method
- shift
- radiologist
237
Acceptable repeat rates?
General: less than 4-6%
Mammo: less than 5%
If repeat is greater than 10-12%, needs to be investigated
Any repeat rate less than 2% should be skeptical
238
What is a reject film?
Anything film that did not require a repeat exposure on a patient
- test images
- scout films
- QC
- green
- clean-up films
239
2 types of detectors?
1. Direct Conversion
| 2. Indirect Conversion
240
What is a direct conversion detector made out of?
Amorphous selenium
- a semi-conductor with excellent ability to detect x-rays
- sandwiched between 2 charged electrodes
241
How does a direct conversion detector work?
- just before the exposure is taken, a charge is applied to the top surface of the selenium layer
- x-ray photons are absorbed by the amorphous selenium and immediately converted to an electric signal (Photoconductor)
- selenium atoms release electrons when they become ionized
- free electrons are collected bu the electrode at the bottom of the selenium layer
- charge is collected by a storage capacitor and read out line by line by the TFT to the computer for processing
242
How does an indirect conversion detector work?
-x-rays converted to light by a scintillator
-light converted to electric signal by a photodetector
-TFT isolates each pixel and acts as a switch to send the electrical charges to the image processor
OR
-CCD converts light to electric charge and stores it in a sequential pattern, stored charge is released to ACD, electric signal is sent to computer for image processing
243
2 materials that an indirect conversion detector can be made out?
1. Cesium Iodide (CsI)
| 2. Gadolinium Oxysulfide (Gd2O2)
244
Characteristics of Cesium Iodide?
- x-ray interactions are high
- thin, structured crystals perpendicular to detector surface = high spatial resolution, directs light to detector = less light spread
- can be used portably, although delicate, because of advanced in technology
245
Characteristics of Gadolinium Oxysulfide?
- x-ray interactions are high
- turbid phosphor, unstructured = light can escape laterally before reaching TFT = decreased efficiency and spatial resolution, more scattered light
- good for rugged applications, not delicate
246
What is a CCD?
Charged couple device
| -photodetector and electronics embedded in a silicon chip
247
What is fill factor?
- the % of pixel face that is sensitive to x-rays
- detector electronics aren’t x-ray sensitive and take up a certain amount of space
- approx. 80% 20%
248
Direct conversion summary (components)
Directly converts x-rays to electrical signal
1. Photoconductor (amorphous selenium)
2. TFT
249
Indirect conversion summary (components)
Converts x-rays to light to electrical signal
1. Scintillator (cesium iodide, gadolinium oxysulfide)
2. Photodetector (amorphous selenium)
3. TFT or CCD
250
Advantages of direct conversion (2)?
- no light spread from phosphor material
| - no loss of spacial resolution
251
Advantage of indirect conversion (1)?
-high quantum detection efficiency (can absorb more x-rays and lower the patient dose) (you are using not just the x-rays, but the light as well to produce the image)
252
Advantages of film?
- CR equipment compatible with existing x-ray equipment
- excellent image quality
- improved diagnostic range
- wide dynamic range
253
Advantages/disadvantages of digital?
- wide exposure latitude
- reduction in repeats
- can compensate for over/underexposure
- environmentally friendly
- initial capital costs high, but can be recovered quickly
- DOSE CREEP
254
Main reason for intensifying screens? Pros/cons?
Reduce patient dose
- Pro: decreases patient dose
- Con: decreases resolution
255
What is DQE?
Detective quantum efficiency
- % of x-rays absorbed by screen
- high atomic # is important
256
What is CE?
Conversion efficiency
| -amount of light emitted for each x-ray absorbed
257
2 types of luminescence? How do they work?
1. Fluorescence: light emitted only while being stimulated
| 2. Phosphorescence: light continues to be emitted after stimulation
258
4 phosphor composition characteristics that affect the image?
1. Material composition: efficiency (calcium tungstate vs rare earth)
2. Thickness of layer
3. Concentration
4. Size of phosphor
259
Thicker phosphor layer = ___________ DQE?
Thicker phosphor layer = INCREASED DQE
260
________ concentration of phosphor layer = higher screen speed?
INCREASED concentration = higher screen speed
261
The large the phosphor, the _______ light produced per x-ray interaction?
More: larger crystals “catch” x-rays better
262
Intensification factor formula
IF = exposure without screen / exposure with screen
263
Increased intensification factor = _______ dose
Increased IF = DECREASED dose
264
What does screen speed describe?
The efficiency of x-ray conversion (x-rays to light)
265
What is used as a basis of comparison for screen speed?
Calcium tungstate (assigned value is 100)
266
Increased speed = ________ detail of image
Increased speed = DECREASED detail of image
267
Uncontrolled factors that affect speed? (6)
1. Phosphor composition
2. Phosphor thickness
3. Reflective layer
4. Dye in phosphor layer
5. Crystal size
6. Crystal concentration
268
Controllable factors that affect speed? (3)
1. Radiation quality: high kVP = high IF due to atomic # of screen
2. Processing: film processing/development
3. Temperature: high IF at low temperature
269
The relationship between optical density and radiation exposure?
Sensitometry
- characteristic curve
- H & D curve
- sensitometric curve
270
What is the toe and shoulder of the characteristic curve?
Toe: bottom
Shoulder: top
271
Where is the ideal density range on a characteristic curve?
Between the toe and shoulder
272
On a characteristic curve, what are the X and Y axis?
X axis: LRE: log relative exposure
| Y axis: optical density
273
Does unexposed film have an optical density? Why/Why not?
Yes
- because of base + fog
- base: colour added to the film base
- fog: any exposure during storage, contamination, or processing
274
How do we find degree of contrast from a characteristic curve?
Slope (rise/run)
| -steeper angle = high contrast
275
How do you find the average gradient on a characteristic curve?
-line drawn between the points corresponding to 0.25 and 2 above base and fog densities
276
Increased latitude = _______ contrast?
Increased latitude = DECREASED contrast
277
Speed formula?
RS2/RS1 = mAs1/mAs2 (indirect)
278
Image receptor speeds affect what 3 things?
1. Radiation sensitivity
2. Density
3. Dose
279
Increased speed = _______ density?
Increased speed = INCREASED density
280
4 factors that affect radiographic image quality? (2 main, 2 other)
1. Photographic: optical density and contrast
| 2. Geometric: detail and distortion
281
Define recorded detail
-degree of sharpness or distinctness of structural lines on a radiograph
282
Synonyms of detail?
- recorded detail
- definition
- sharpness
- blur
- resolution
283
Define resolution. How is it measured?
- the ability of the imaging system to differentiate between two adjacent structures
- measure in line pairs per millimeter
284
Increased line pairs = _______ resolution?
Increased line pairs = INCREASED resolution
285
What 3 factors control detail?
1. Geometric unsharpness
2. Motion unsharpness
3. Image receptor unsharpness
286
Factors that affect geometric unsharpness?
1. Focal spot
| 2. SID and OID (distance)
287
Normal range of a focal spot?
0.1 to 3.0mm
288
Is focal spot blur smaller or larger on the anode side?
Smaller
289
How can we decrease focal spot blur?
- small focal spot
- large SID
- small OID
290
What has the greatest effect on the amount of geometric unsharpness?
OID
291
What is the most detrimental effect on recorded detail of the radiographic image?
Motion unsharpness
292
Smaller pixel = ______ resolution?
Smaller pixel = INCREASED resolution
293
High fill factor = ________ resolution?
High fill factor = HIGHER resolution
| -high active area
294
2 types of distortion?
1. Size: magnification
| 2. Shape: elongation/foreshortening
295
Distortion is directly related to ?
Positioning
296
Longer SID = _____distortion?
Longer SID = DECREASED distortion because of straighter rays hitting the part
297
Magnification formula?
```
MF = SID/SOD
MF = Image size/object size
```
298
SOD formula?
SOD = SID-OID
299
Inaccurate alignment of the part = ?
Foreshortening
300
Inaccurate alignment of the IR = ?
Elongation
301
More irregular shape of object = ________ distortion?
INCREASED distortion due to beam divergence
302
What is a bit?
A single unit of data
303
What is a byte?
Made up of 8 bits
304
What does a data recognition program do?
Works by finding the collimation edges and eliminating the scatter outside of the collimation
305
What is a histogram?
Graph representing the optimal densities within the collimated area
306
Values at the left on a histogram represent (black or white)?
Black
| White = right
307
What is the nyquist theorum?
When sampling a signal, the sampling frequency must be greater than twice the frequency of the input signal so that the reconstruction of the original image will be as accurate as possible
308
Too few sampled pixels = ______ resolution?
DECREASED
309
What is aliasing?
Produces an image that looks like 2 superimposed images just slightly misaligned
-moire effect
310
What is responsible for dose creep?
Automatic rescaling
311
Does a look up table change the raw data?
No
312
Why do we need LUTs?
- due to the wide dynamic range and response of the digital receptors, the image recorded is usually very low contrast because every density is displayed
- increase contrast and make it look like film
313
What is an EI?
The amount of exposure received by the IR
314
A computer basically consists of what 3 things?
1. Input devices
2. Output devices
3. Processing devices
315
2 main types of monitors?
1. CRT
| 2. LCD
316
What is the refresh rate of a CRT monitor?
- how fast the monitor rewrites the screen or the number of times the image is redrawn on the display/second
- higher refresh rate = less flicker
317
What is the response rate of an LCD monitor?
- the amount of time for crystal to go from off state to on and vice versa
- slower response rate will cause blurring during viewing of dynamic images
318
What is the aspect ratio?
Ratio of the width to the height of the monitor
319
How does a CRT monitor work?
- consists of a cathode and anode in a vacuum tube
- electrons sent to the anode which is a sheet of glass coated with phosphors
- electrons beam starts in the upper left corner and scans across the glass from side to side top to bottom
320
How does an LCD monitor work?
- images are produced by shining or reflecting light through a layer of liquid crystal and a series of coloured filters
- two pieces of polarized glass with a liquid crystal layer in between
- light passes through the first layer and when a current is applied to the crystal layer, it aligns and allows light in varying intensities through to the next layer
321
What is an array processor?
Uses its own memory to perform simultaneous mathematical operations at extremely high speeds (puts all the info together into image)
322
Critical characteristics of a digital image (4)?
1. Spatial resolution
2. Contrast resolution
3. Noise
4. Dose efficiency (of the IR)
323
Smaller pixel = ________ detail
Smaller pixel = INCREASED detail
324
How to calculate the number a greys a pixel can display?
Bit depth: a 5 bit pixel = 2^5 = how many greys
325
Increase matrix = _________ resolution?
Increase matrix = INCREASE resolution
326
Larger matrix = ________ pixels (when the IR size stays the same)
Larger matrix = SMALLER pixels
327
What is dynamic range?
The ability to respond to varying levels of exposure
- the range of grey values that can be displayed
- human eye can only differentiate about 30 shade of grey
328
X-Ray: window width and level: 1 shows up as (white or black)?
White
329
Window level controls what?
Brightness
330
Decrease window level = ________ brightness
Decrease window level = INCREASED brightness
331
Window width controls what?
Contrast
332
Large window width = ________ contrast?
Large window width = DECREASED contrast because more shades of grey
333
Is shuttering/masking meant to replace manual collimation?
No
334
Two types of post processing magnification?
1. Magnifying glass: enlarges portion of an image like a magnifying glass
2. Zoom: enlarges entire image
335
2 types of spatial frequency filtering? What do they do?
1. High pass filtering: frequencies amplified, increased contrast, edge enhancement
2. Low pass filtering: frequencies are suppressed, decreased contrast, smoothing, reduce noise
336
4 main types of artifacts?
1. Imaging plate artifacts
2. Plate reader artifacts
3. Image processing artifacts
4. Printer artifacts
337
What is an imaging plate artifact?
- usually due to aging or wear
- plate can become prone to cracks due to the constant removal and replacement within the reader
- cracks show up radiolucent
- static
- backscatter (dark line)
338
What are image processing artifacts?
Can occur because of incorrect part selection or incorrect sampling
-poor technique and positioning can cause misrepresentation of the image
339
What are plate reader artifacts?
- line patters than appear randomly (not regularly) can be issue with electronics
- white lines parallel to the direction of plate travel caused by debris on the light guide
- multiple IPs loaded into a single cassette
- insufficient erasure can result in residual info being on the IP before the next exposure
340
What are printer artifacts?
-fine white lines may appear on the image die to debris in the laser printer
341
Human error that leads to artifacts?
1. Collimation
2. Cassette use/orientation
3. Technical factors
342
Flat panel artifacts? (4)
1. Dead pixels
2. Incorrect gain calibration
3. Image lag
4. Offset correction
343
What is gain calibration? How does it work?
Used for the correction of flaws in the detector
- if there is any area with many dead pixels or poor connections between the layer and the array, the gain calibration will correct this
- creates a mask of the defects so that when the image is taken, the software uses the mask to removed unwanted densities (fills in white spots with grey)
344
What is image lag?
If there is an image taken before the detector has finished releasing all of the signal for the previous image, there may be a faint image of the previous image still visible
345
What is image lag caused by? (3)
- taking images in rapid succession
- over exposure
- areas with little beam attenuation (marker)
346
What is offset correction?
Determines the amount of signal inherent in the detector, creates a mask of the residual signal
-if this is done before the residual signal has left the pixels, the info can be stored as inherent and cause a negative image of the signal: inverse image
347
What is a network?
A group of 2 or more computers linked together
348
2 network classifications?
1. LAN: local area network: linked computer close together
| 2. WAN: wide area network: computer further apart connected by telephone lines, cables, or radiowaves
349
2 types of network connections?
1. Wired
| 2. Wireless
350
What is a client-server based network?
Client: used to request information
Server: facilitates communication between and delivers info to other computers, passive (does not request, waits for request)
351
3 types of computers found on a network?
1. Server
2. Thin client: requires server for tasks
3. Thick client: can work independently
352
Geometric arrangements of computer systems? (4) (network topologies)
1. Star (most common)
2. Bus
3. Ring
4. Mesh (most commonly used to connect network to other networks)
353
What is DICOM?
A set of standards for medical imaging interchange
- allows medical images to be exchanged among networked devices
- base standard of images so that they can be viewed
354
What is HL-7?
Health level 7
| -universal standards used for most clinical and administrative data
355
3 fundamentals of PACS?
1. Image acquisition
2. Display workstations
3. Archiving
356
Types of workstations?
- Review workstations (most interactive part of PACS)
- Radiologist workstation
- Technologist workstation
- Image management workstation
357
Common functions of workstations? (4)
- Navigation
- Image manipulation/enhancement
- Image management
- Advanced
358
Advance workstation functions? (4)
- Multiplanar reconstruction
- Max and Min intensity projection
- Volume rendering
- Shaded surface display
359
What is a mirrored database?
-two identical databases are running at the same time, so if one fails, the system can call on the mirror and continue to run as normal
360
What does the database contain?
- only image header info not the image data
| - pt name, ID, exam date, etc.
361
3 tiers of storage?
1. Short term
2. Mid term
3. Long term
362
What type of storage is RAID? What level of RAID does PACS use?
Short term
| -level 5 commonly used by PACS
363
3 types of optical disks?
- Magneto-optical disk (MOD)
- Digital Versatile Disk (DVD)
- Ultra Density Optical
364
What is the least expensive method of optical disk?
DVD
365
Why are tape libraries good?
Because they provide the greatest ability to expand: can continually grow and expand storage limits
366
Disadvantages of Tape?
- can become unreliable over multiple uses
- can wear out with heavy use
- longer access time
367
Types of magnetic disks?
- DAS
- NAS
- SAN
368
2 types of image compression?
1. Lossy: reduces storage by eliminating some information: not diagnostic quality
2. Lossless: exact replica of the original
369
2 types of film digitizers?
1. Laser film digitizer
| 2. CCD film digitizer
370
What is considered the gold standard for film digitizers?
Laser
371
Why are digitizers needed?
- Teleradiology
- comparison
- duplication
- computer aided diagnosis
372
2 types of printers (imagers)
1. Wet imager: uses chemicals, needs darkroom
| 2. Dry laser imager: uses heat, exposed with laser, slightly lower quality
373
Why are printers needed?
- Backup if PACS is unavailable
- outside physicians
- legal cases
- teaching purposes
