**Saia Unit 5 Flashcards
(169 cards)
1
Q
Battery/DC power
A
Provides electric potential
2
Q
AC power
A
Provides electric potential
3
Q
Capacitor
A
Temporarily stores an electric charge
4
Q
Ammeter
A
Measures current
5
Q
Voltmeter
A
Measures electric potential
6
Q
Switch
A
Controls ON/OFF
7
Q
Transformer
A
Increase or decrease voltage
8
Q
Rheostat
A
Variable resistor
9
Q
Diode/rectifier
A
Electrons flow in only one direction
10
Q
Ground
A
A neutral object ready to receive electrons
11
Q
Rectifier
A
Converts AC to DC
12
Q
Imaging system contains 3 systems
A
Operators console
High voltage-generator/section
X-ray tube
13
Q
Components of the Operators console function on relatively
A
Low voltage and amperage for Personnel safety
14
Q
High voltage generator/section function on relatively
A
High voltage and amperage making them unsafe to be located near humans
15
Q
X-ray tube functions on
A
High voltage and amperage which is Insulated for safety
16
Q
Resistor
A
Inhibits electron flow
17
Q
The operators console allows the radiographer to control
A
The X-ray tube current (mAs), voltage (KVP), and exposure time
18
Q
MAs= quantity
A
Refers to the number of X-rays in the beam
19
Q
KVP= quality
A
Refers to the penetrability of the beam
20
Q
Exposure time =
A
How long voltage is applied
Current will only flow when voltage is applied
21
Q
Operators console also includes
A
AEC selection
Bucky selection
On/off switch
22
Q
Line compensation
A
Adjusts the incoming voltage to the precise value that the system is designed to operate on - most operate on 220V however the power companies voltage can vary by as much as 5% thus the need for a compensator to keep voltage at a constant 220V
23
Q
Auto transformer
A
Variable ratio transformer which supplies a precise voltage to the filament circuit and to the high voltage circuit.
24
Q
Once the voltage has passed through the auto transformer
A
It is no longer susceptible to fluctuations or surges in the line voltage
25
KVP selector
The secondary side of the autotransformer ,the percentage of available voltage is selected by the technologist, usually in 2 control selectors, a major (steps of 10KV) and minor KV (steps of 1-2KV)
26
Selected voltage from secondary of auto transformer is delivered to
The high voltage(step up) transformer
| High voltage transformer has a fixed ratio of 1000:1, every volt becomes a kilovolt
27
The filament circuit
High amperage is required for thermionic emission in the filament, it is necessary to step-down the voltage - as voltage decreases amperage increases.
28
MA selector (part of the filament circuit)
Resistors or a rheostat along the filament circuit which controls the amperage delivered to the filament
29
Most filaments operate at between
3-6 amps,
| As amperage to filament increases thermionic emission increases
30
MA =
The number of electrons thermionically emitted per second
31
Exposure timers (5 different types)
Mechanical (wind up timer)
Synchronous (measures voltage pulses -capable of 1/120 of a second)
MAS (delivers a selected mAs w/o setting the "S")
Electric (modern - capable of 1/1000 of a second)
AEC (automatic exposure control)
32
High voltage generator
Increases voltage to kilovolts, increases amperage for thermionic emission, converts AC to DC
33
A high voltage generator consists of 3 main parts
High voltage transformer - step up
Filament transformer - step down
Rectifier - converts AC to DC
34
The high voltage transformer
Reconfigures wattage from primary to secondary, wattage remains constant between primary and secondary sides of the transformer
35
The more turns on a transformer
The stronger the magnet, the stronger the magnet the higher the voltage
36
Watt
The unit of electrical power
| - volts x amps = watts
37
The primary side of the transformer
Is the side of the transformer that is initially supplied with current
38
The secondary side of the transformer
The side of the transformer in which current is induced to flow
39
Transformers can change voltage and/or amperage between primary and secondary sides of the transformer but...
Wattage remains constant between primary and secondary sides of the transformer
40
Step up transformer
Voltage is increased from primary to secondary sides
41
Step down transformer
Voltage is decreased from primary to secondary
42
Transformer "stepping"
How voltage is affected from primary to secondary sides of a transformer
43
High voltage transformer
Step up transformer
2 iron cores, operates by mutual induction
Fixed ratio - approximately 1000:1
Primary side initially supplied w/volts and amps
Secondary side induced kilovolts and milliamps
44
Filament transformer
Step down transformer
2 iron cores, operates by mutual induction
Fixed ratio - approximately 1:3
Primary side initially supplied with volts and amps
Secondary side induced volts and amps
45
If grid ratio is greater than 1
Step up transformer
46
If grid ratio is less than 1
Step down transformer
47
Voltage rectification
Converting AC to DC
48
Why convert from AC to DC
Transformers only work on AC
| X-ray tube is most efficient on DC
49
Solid state diode/rectifier
Uses material which is semi conductive
| Current is conducted through a diode only in one direction, opposed in the other
50
Cathode is uniquely designed to emit electrons
But not receive
51
Anode is uniquely designed to receive electrons but
But not to emit
52
Filament current
Amperage delivered to filament for thermionic emission
53
Tube current
Electrons traveling from cathode to anode (mAs)
54
The higher the current voltage, the greater the
Amplitude of the wave
55
During the positive cycle of the unrectified waveform
Anode is energized with positive charge
Cathode is energized with negative charge
Electrons flow from cathode to anode
56
During the negative cycle of the unrectified waveform
Anode is energized with negative charge
Cathode is energized with positive charge
Electrons cannot flow from cathode to anode
57
Half wave rectification is accomplished with
2 diodes which only allow the positive cycle of AC waveform to be conducted through the circuit.
1/120 second of dead time between pulses
58
Full wave rectification is accomplished with
4 diodes for each phase of power, two diodes block the negative pulse, two redirect it so that it is traveling the same direction as the positive pulse
59
Cycles per second is measures in
Hertz
60
Each cycle has a positive and negative and positive pulse
(2pulses), 120 pulses per second
61
Have wave rectification
60 pulses per second, only the positive pulse of AC waveform used to make xray, 100% voltage ripple
62
Full wave rectification
120 pulses per second, both the positive and negative pulses used to make xray, 100% voltage ripple
63
3 phase power
3 independent voltage waveforms working together in phase for mor efficient way to use voltage. Each voltage waveform has 120 pulses per second
64
3 phase 6 pulse -
360 pulses per second. 13% ripple
65
3 phase 12 pulse -
720 pulses per second, 4% ripple
66
High frequency generator
Modern system of powering an xray system, more efficient usage of available voltage.
Creates "square" waveforms of extremely high frequency creating high efficient power.
Only 1% ripple - less mAs required, lower patient exposure.
67
Voltage ripple
How far the voltage waveform falls from its peak
68
Main breaker
This is where the alternating current comes from the power circuit
69
Exposure switch
When you push the button to start an exposure this switch closes to the start the exposure
70
Auto transformer
This is where you adjust the KVP for exposure
71
Timer circuit
This part of the circuit stops the exposure
72
High voltage step up transformer
Bumps the voltage up so that the X-ray tube has very high voltage to make the electrons have enough energy to form X-rays
73
Four diode rectification circuit
This makes the current only go in one direction through the X-ray tube
74
Filament circuit variable resistor
Adjusts the current going into the filament
75
Filament step down transformer
Steps the voltage down and therefore the current up.
76
X-ray tube
Where X-rays are created
77
Motor stator
This rotates the anode
78
X-rays are created on demand, the technologist controls
When X-rays are created (exposure switch)
Strength of X-rays created (KVP adjustment)
How many X-rays created (mAs adjustment)
How long X-rays created (exposure timer)
All are controlled at the operators console
79
X-rays are created by a conversion of energy to another
Electrical energy into electromagnetic energy through a series of energy conversions.
Electrical, thermal, potential, kinetic, electromagnetic
80
Voltage
In xray this is the Force/strength of electron propulsion
81
Amperage
In xray this is the number of electrons in motion
82
Voltage
Also known as potential difference or potential or electromotive force (emf)
The force that propels electrons
83
Amperage
Also known as current or impedance.
| The number of electrons in motion
84
1 amp =
6.3 x 10^23 electrons per second
85
Density
The overall blackening of a film/image
86
Density is referred to as ? With digital imaging
Brightness
87
Controlling factors of density are
MA
Time
MAs
88
MAs
The number of X-rays in the polyenergetic beam
89
Contrast
The difference in adjacent shades across a radiographic image
90
Primary function of contrast is to
Make recorded detail visible
91
High contrast
Black and white, few grays
92
Low contrast
Image with many grays
93
Contrast is primarily controlled by
KVP.
94
As KVP increases there is a greater variety of
Xray energies in the primary beam
95
Energy deposited into the IR =
Density
96
More energy values =
More shades of density
| Shades of gray
97
KVP =
Peak xray strength in the polyenergetic primary beam
| - X-rays are created at all energy values up to the peak strength
98
Fluoroscopy was developed
By Thomas Edison in 1896 as a real time dynamic image produced on glass plate covered with a layer of phosphor ,material.
99
Flux gain
Few xray photons converted to many visible light photons
100
Image intensifier for fluoroscopy
```
Glass envelope (maintains vacuum)
Input phosphor (cesium iodide)
Photocathode (antimony)
Focusing lenses (electrostatic - mutual repulsion)
Anode (positive charge attracts electrons)
Output phosphor (zinc cadmium sulfide)
```
101
Image intensifier for fluoro is like am X-ray tube which results in
1 xray photon is amplified to many light photons
| The image is intensified
102
Input phosphor for fluoroscopy
Cesium iodide - efficient at converting xray energy to visible light
Needle like crystals
Xray "Coming in" to the fluoro tube
103
Output phosphor for fluoroscopy
Zinc cadmium sulfide - efficient at converting electron energy to visible light
Last stage of fluoro tube (last letter Z in alphabet - inc)
104
Minification gain
Result of many electrons leaving the relatively large input phosphor/photocathode impacting the relatively small output phosphor
105
As minification gain increases
The visible light image becomes brighter
106
Minification gain formula
Minification gain = input phosphor diameter^2/output phosphor diamter^2
107
Standard input phosphor/photocathode sizes are
6", 9", or 12"
108
Total brightness gain
Minification gain x flux gain
How much has the image been intensified by the image intensifier tube
109
ABC - automatic brightness control
Maintains a preset brightness level by automatically adjusting the exposure factors to compensate for varying subject
110
Fluoro imaging techniques
Very low mA (0.5-5mA)
| Higher KVP utilized
111
SSD for fluoro
Fixed - 15"
Mobile - 12"
112
Quantum mottle can be a problem with fluoroscopy due to
Not enough X-rays (mAs)
| Not enough photons hitting the input phosphor
113
Magnification tubes
Modern tubes can magnify images 1.5-4 times
As voltage increases the electrons are pushed closer to the input phosphor which causes the image to be magnified at the output phosphor
114
The TV camera with fluoro
A camera is placed adjacent to the output phosphor in order to capture and transmit the output intensified image resulting in the radiologist no longer has to view image from phosphor screen and or be in the path of the beam
115
Two basic types of fluoro cameras
Vidicon - general fluoro
Plumbicon - interventional fluoro
116
Fluoro splitter
Able to split the signal from output phosphor to multiple components
- monitor
- video
- digital video
- hard film
117
The smaller the mode, the more magnified the image
Mag mode increases scatter radiation
118
Changes in voltage to the electrostatic focusing lenses causes
The electrons to narrow or widen their stream
119
Common field size for angio
35/25/15 cm
120
Common field sizes for general
25/17cm
121
A conventional fluoro system often has multiple imaging devices
```
TV camera
Spot films
Cine camera
Cassette
All use the image as displayed on the output phosphor
```
122
Fluoro exposure should not exceed
10R/min for general fluoro
123
5 minute timer
Fluoro unit must alarm every 5 minutes to alert radiologist/surgeon of fluoro time
124
Magnification fluoro causes
Increased dose
125
Fluoro is the rad techs #1
Source of exposure
-scatter from patient
Use inverse square law!
126
Lead aprons must be worn in fluoroscopy that have at least
0.5mm Pb equivalent
127
Fluoro Bucky slot covers and lead drapes =
At least 0.25mm Pb
128
High contrast
Few shades of gray, increased contrast, lower KVP, "short scale" contrast
129
Low contrast
Many shades of gray, decreased contrast, high KVP, "long scale" contrast
130
Grid conversion factors
No grid = 1
5: 1 = 2
6: 1 = 3
8: 1 = 4
12: 1 = 5
16: 1 = 6
131
Filtration a minimum of
2.5mm Al/eq
132
The purpose of filtration
To remove weaker xray from the primary beam
133
Half value layer
The amount of filtration required to lower xray intensity to 1/2 of its original value
134
Collimator illuminance
Brightness of collimator bulb and field,
| At least 15 foot candles (160 lux) at 40"
135
Xray to light field
Collimator to xray beam alignment
+/- 2%
Semiannual
136
Nine penny test
Test done for xray to light field (diameter of penny is .8 inches)
137
Positive beam limitation
Auto collimation of light field to IR size. Can be smaller, can NEVER be larger!
+/- 2%
Semiannual
138
Focal spot size is tested by
Pinhole camera, star pattern, slit camera
+/- 50%
Annual
139
KVP accuracy is measured with
Voltmeter and radiation meter
+/- 10%
Annual
140
Exposure timer accuracy
+/- 5% greater than 10ms
| +/- 20% less than 10ms
141
Exposure linearity
Using the same mAs but differing combinations of mA and S
| i.e. 100mA @ 1/2S same as 200mA @ 1/4S
142
AEC backup timer is set to self terminate if...
600 mAs reached
143
If the AEC backup timer is manually set, it should be set to
150% of expected mAs
144
AEC optical density versus change
+/- .30D
145
Film illuminator standard is
15 Watt daylight bulb
146
Fluoro rate ESE shall not exceed
10R/min
147
IR exposure rate ESE shall not exceed
20R/min
148
Repeat analysis goal
To minimize patient exposure
149
Wire mesh test is used to evaluate
Contact between intensifying screen and film
| Annually
150
Speed uniformity is tested to assure
That all like speed intensifying screens respond to the same xray stimulation by releasing the same amount of visible light
+/- 10%
Annual
151
Darkroom fog can be no greater than
.08 (xray) or .05 (mammo)
| Semiannual
152
Sensitometry
Measuring the response of film to exposure and processing
| Daily
153
Developer is sensitive to changes in
Temperature, oxidation, concentration, contamination
154
Sensitometer
Device that emits varying intensities of light in a star pattern on a film
155
Pemetrometer
Aluminum step wedge that is exposed to radiographic film and developed to measure xray penetration
156
21 step sensitometer is
```
Most common (41% difference between steps)
Also a 11 step (100% difference between steps)
```
157
Densitometer
Reads/measures image density, measures how much light is emitted to film and how much is transmitted
158
Optical density
Incident light striking the film to the intensity of light transmitters through film
159
The higher the optical density, the less light transmitted
Therefore the greater density
160
Density difference of contrast indicator
Found by subtracting the Dmin from Dmax
| +/-.15OD
161
Hyporetention (fixer=hypo)
Must be less than .05Gr/m^2
Emulsion turns brown in storage due to inadequate washing of film in processor
Quarterly
162
+/-2%
Collimator dial accuracy (2% of SID)
SID accuracy (2% of SID)
Xray to light field
Positive beam limitation
163
+/-5%
REPRO
Exposure reproducibility
AEC reproducibility
164
+/-10%
```
KVP accuracy
mR/mAs (from installation)
Exposure linearity
AEC density steps
Film illuminators (speed uniformity)
```
165
+/- 50%
Focal spot size
166
Daily
Sensitometry
167
Quarterly
Hyporetention
168
Semiannual
Collimator dial accuracy
Xray to light field
Positive beam limitation
Darkroom fog
169
Annual
```
Filtration
Half value layer
Collimator illuminance
SID accuracy
Focal spot size
KVP accuracy
mR/mAs
Exposure timer accuracy
Exposure linearity
Exposure reproducibility
Protective apparel
Film illuminators
Film screen contact
Speed uniformity
```
