physicis of radiology equipment Flashcards
1
Q
Which part of the imaging system is responsible for keeping incoming voltage adjusted to the proper value?
A
Line Compensator
2
Q
What is the function of the recitier?
A
Convert alternating current to pulsating direct current.
3
Q
When the frequency of the voltage waveform supplied to the x-ray tube is increased, what aspect is reduced?
A
Average wavelength of the produced x-ray photons
Heat loading on the anode disk
Patient exposure
4
Q
Which term refers to the ability of an x-ray imaging system to maintain the same intensity of radiation, from one exposure to another for the same set of technical factors?
A
Reproducibility
5
Q
What causes the build-up of heat at the anode?
A
Electrons colliding with the target.
6
Q
Which condition must be met before diagnostically useful characteristic x-rays can be produced?
A
An inner shell electron must be completely removed
7
Q
Which screen film imaging system characteristics will result in greater recorded detail?
A
Small phosphor crystals.
Small silver halide crystals
Thin phosphor layer
8
Q
Which factors contribute to an increase in the binding energy of an electron within the atomic structure?
A
How close the electron is to the nucleus.
The number of protons in the nucleus
9
Q
Which describes covalent bonding?
A
Valence electrons are shared with another atom
10
Q
Which will increase the amount of x-ray beam attenuation in the patient?
A
Low kVp technique.
Positive contrast agents.
Hypersthenic body habitus
11
Q
What x-ray beam characteristic is reduced by adding aluminum filtration?
A
Quantity of x-rays.
12
Q
Which of the following terms describes stray radiation that is emitted through the x-ray tube housing?
A
Leakage
13
Q
What effects will increasing amounts of filtration have on the x-ray beam?
A
decrease patient exposure
harden the x-ray beam
increase the percentage of beam penetration through the objects of interest
14
Q
What is the reciprocity law?
A
the resultant opacity present on an exposed and processed film is proportional to the intesnity and duration of exposure delivered to the film
15
Q
What effect does scatter radiation have on radiographic contrast?
A
scatter radiaion will decrease radiographic contrast
16
Q
What factors determine the amount of contrast present within a radiographic image?
A
film contrast
developer contrast
subject contrast
17
Q
Shape distortion produced on a finished raiograph will vary directly with what factor?
A
tube angulation
18
Q
A measurement of the resultant opacity present on an x-ray film after exposure and subsequent film processing, describes what?
A
radiographic film contrast will increase
19
Q
What is the radiographic film density measurement that is considered to be the minimum value for diagnostic information?
A
0.25
20
Q
If each system is exposed with the same set of factors, select the imaging system that will yield the greatest radiographic density: par speed film and screens (100), detail speed screens and films (50), high speed film and screens (200), rare earth film and screens (400)
A
rare earth film and screens
21
Q
What is the term used to describe the absorption of the primary beam by the lead strips present within a grid device?
A
cut off
22
Q
What is the ratio of a grid constructed with lead strips that are 72 units tall separated by radiolucent material 6 units wide
A
12:1
23
Q
What formula would you use to get the correct measurement of radiographic contrast ofr an imageyielding density values of 1.57 and 0.87 for two points on the radiograph?
A
mathmatical answer 0.70
24
Q
What are the factors that determine tissue density?
A
thickness
specific gravity
atomic number
25
What is the primary function of setting a back up time when making an exposure with an automatic exposure control or photo timed unit?
to determine the maximum duration of the exposure
26
What effect does an increase in film speed have on distortion of the radiographic image?
film speed has no effect on image distortion
27
What will be the effect on radiographic contrast when the radiation field size is changed from 5x7 to 8x10?
contrast will decrease
28
What is the optimum procedure for storing boxes of unexposed radiographic film?
place boxes of film upright
| store in an enviornment of 50-70 degrees and humidity 40-60 %
29
What factors determine total development time in an automatic film processor?
speed of the transport system
| depth of the developer solution in the developer tank
30
What factors aid in maintaining an optimum level of developer activity in an automatic film processor?
developer temperature and rate of developer replenishment
31
What factors will contribue to films exiting the automatic film processor that are tacky to the touch?
improperly vented automatic film processor
low volume of chemistry in the fixer tank
chronic under replenishment of the fixer sollution
clogged dryer tubes
32
A change from a 1.5 mm focal spot to a 0.5mm focal spot will limit the maximum mA station that may be selected on the control panel. This change in focal spot size will also have what effect on image contrast?
image contrast will remain the same
33
What is the probably cause of evenly spaced scratches on the film emulsion aligned with direction of the film transport through the automatic film processor?
an improperly aligned guide shoe in a turn around assembly
34
What effect would you expect to see on a radiographic fims taken from a box that had been dropped from the loading bench onto floor landing on a corner of the box prior to exposure?
wave like areas of decreased density radiating from the corner of the film where the insult to the film surface occured
35
Measuring the characteristic responses of film to exposure and subsequent fim processing describes what?
sensitometry
36
What is the term given to the area of unsharpened surrounding the image of an object on a radiographic film?
penumbra
37
What is the unit of measurement for calibrating the "resolution" of an imaging system?
line pairs/millimeter
38
safelight fog will have what effect on a finished radiograph?
safelight fog will increase radiographic density and decrease radiographic contrast
39
To avoid absoprtion of the primary x-ray beam by lead strips present within a grid cassette, angulation of the central ray should be limited to what?
angulation along the long axis of the grid
40
An image that demonstrates focal areas of decreased image sharpness, is an image that indiecates the presence of?
poor screen film contact
41
A variation in x-ray beam intensity along the long axis of the x-ray tube, with an increased intensity toward the cathode end of the beam and a decreased intensity toward the anode is called what?
anode heel effect
42
Repeating artifacts that are aligned perpendicular to the direction of travel of the film through the film processor are limited to one surface of the film only, are most likely produced by what?
debris present on a roller in a crossover assembly
43
A safe light test should be always performed with what?
A film that has recieved some level of x-ray exposure
44
In the Compton interaction with mattter the photon enery is _____________ binding engery of the electron in the orbital shell
greater than
45
x-ray radiation is ___________ in terms of frequency and _____________ in wavelength than gamma radiation
lower; longer
46
What will be measured by a meter connected in series in a simple electric circuit?
amperage
47
The acceptable range of variation between consecutive exposures when performing a quality assurance test the consistency of radiation output for a given mAs value is what?
+ or - 5%
48
Where in the x-ray circuit is the prereading kilovolt meter connected?
the primary low voltage circuit
49
What test is performed to determine if you are experiencing rectifier failure of a single phase full wave rectified x-ray unit?
spinning top test
50
What are the four essential things necessary for the production of x-rays?
a source of free elections, a sudden deceleration of high speed electrons, a sudeen acceleration of electrons, and a focusing of electrons
51
Where in the x-ray circuit does the filament circuit draw its electrial energy?
from the low voltage primary circuit
52
What type of motor is required to rotate the anode within a rotating anode x-ray tube?
induction motor
53
As the angle of the face of the anode increases from 14 degrees to 17 degrees the size of the actual focal spot measured for a 1.5 mm filament will do what? increase, decrease, or stay the same?
remain the same
54
According to NCRP requirements an x-ray tube calculated to have 0.75 mm of aluminum equivalent inherent filtration must be fitted with an amount of added filtration equal to what if the tube operates at voltages above 70 kVp?
1.75 mm Al equivalent
55
the thickness of the anatomy seen in best focus on a film taken using linear tomotgraphy is determined by what setting on your euipment?
the amplitude
56
The portion of the image intensifier device that is responsible for converting light photons into free electrons is the what?
the photocathode
57
What is the term used to describe the falling off of sharpnes toward the edges of the image intensified image?
vignetting
58
What form of tramsformer power loss is decreased by utilizing a transformer core made of material with a low magnetic retentivity?
hysteresis losses
59
With increased levels of beam filtration where will the greatest dose savings be realized?
in the initial layers of tissue struck by the beam
60
Radiaition effects that are limited to the exposed population are called?
somatic
61
What exposure factor combinations will result in the least amount of radiaion dose to the patient?
high kVp, low mAs
62
Secondary barriers must contain a minimum thickness of what Pb equivalent?
1/32 inches
63
What is the prescribed distance used when measuring leakage radiation for the housing of a diagnostic x-ray tube?
one meter from the tube housing
64
The filament transformer is also known as the what?
Low voltage or step down transformer
65
The filament transformer operates on the principle of what?
Electromagnetic mutual induction ( two wires)
66
The step up transformer is also known as what?
High voltage or high tension transformer
67
What electron process does bremsstrahlung have?
Slows down
Changes direction
Loses some of its energy
68
What electron process does characteristic radiation have?
High speed
Eject an inner shell electron
Energy is equal to difference in shell
69
What is frequency of the electromagnetic x ray beam?
Rise and fall of photon and is measured in hertz
70
What is the wavelength of the electromagnetic photon?
Is the distance between two successive peaks
71
How are frequency and wave length related?
What type of frequency and wavelength x radiation have?
Inversely
High frequencies and short wavelengths
72
Beam characteristics of kVp?
Quality
| Expresses the penetrating ability
73
What are the beam characteristics of mAs?
Expresses the quantity of amount of X-rays in beam
Measured in Roentgen
Directly proportional to mAs
74
What is attenuation?
Progressive absorption as it passes through matter
75
What is primary radiation?
Useful radiation
| X-ray photons directed through the X-ray tube
76
What is the half value layer?
Thickness of an absorbing material required to reduce X-ray intensity by one half it's original value
77
What are the fundamental properties of X-rays?
```
Travel in wave form.
Highly penetrating
Wide variety of wavelengths and energies
Travel in straight lines
Can ionize matter
Travel at speed of light
Cause fluorescence of certain crystals
Cannot be focused by a lense
Contain no mass or electrical charge
Have high frequencies and short wavelengths
```
78
Photon interactions with matter
| What is the Compton effect?
Partial absorption of incident X-ray photon
Compton interaction is influenced by the energy level of the X-ray beam, the thickness of the tissue irradiated
79
Photon interactions with matter
| What is photoelectric absorption?
Total absorption of X-ray photon
Is influenced by the energy level of X-ray beam, mass density of tissue irradiated, and the atomic number of tissue irradiated.
80
What interaction is the primary source of patient radiation exposure?
Photoelectric
81
Photon interactions with matter
Unmodified scatter, classical, coherent, or Thompson
Change in direction, no energy
| Contribute only to patient skin exposure
82
As tissue thickness increases, attenuation...
| As tissue thickness increases, what interaction increases?
Attenuation increases
Photoelectric and Compton interaction increases
83
As the atomic number of tissue increases attenuation....
As the atomic number of tissue increases,the probability of photoelectric interactions...
Attenuation increases
Increases
84
As photon energy increases...
As photon energy increases the probability of the photoelectric effect....
Attenuation decreases
Decreases
85
Glass envelope is comprised of....
Pyrex glass
Protects internal components of X-ray tube
Maintains a vacuum environment
86
What calculation is used to determine grid ratio?
Height of lead strips divided by the width of the interspace material
87
What are the characteristics of x-rays and gamma rays?
low LET
electromagnetic radiation
damage biologic tissue through indirect action
88
What does the window with control?
contrast
89
How is the image receptor speed demonstrated on an H & D curve?
By the distance of the curve from the y-axis
90
Where would edge enhancement post processing be more helpful in digital radiography?
low contrast situations
91
what is the optimum kVp for an adult AP lumbar spine?
80 kVp
92
Which steps increase contrast in fluoroscopy?
smaller collimated field
| reduce kVp
93
What factors affect radiographic image density?
kVp, film=screen system speed, mAs, SID
94
How does a radiographer maximize signal to digital image receptors?
longer exposure time, compression of the body part, shorter SID
95
What happens to an ima?ge when kVp is increased
number of gray tones will be increased
96
What change in technical factors is most likely to result in decreased film density?
Increased grid ratio
97
Which systems of an automatic film processor are responsible for determining development time?
transport, repenishment
98
Opening the collimators wider than necessary using digital radiography will have what affect on image quality?
spatial resolution of the image will be decreased.
99
What change is needed to compensate for a soft tissue mass in the abdomen?
increased mAs
100
Which is the most likely cause of film fog prior to development?
cracked safelight filter
101
An increase in what will improve recorded detail?
SID
102
How does an increase in noise affect the quality of a digital image?
contrast is decreased
103
What is the formula for bit depth to find the shades of gray
2n
| n = number of bits
104
What is contrast resolution?
The smallest exposure change that can be captured by a detector. Increased contrast resolution is the major advantage of digital receptors
105
A direct conversion is without a scintillator? or with a scintillator?
without
106
An indirect conversion is with a scintillator or without a scintillator?
with
107
indirect flat panel detectors use selenium or silicon?
silicon
108
What are the 4 requirements necessary for the production of x-rays?
source of electrons
acceleration of electrongs
focusing of electrons
deceleration of electrons
109
What is the source of free electrons?
thermonic emissions
110
What is thermonic emmsions?
How many amps of current does it require?
What determines the amount of current that will be sen to the filament?
heating of the filament to the point that electrons boil off its surface
4-6 amps
mA setting
111
What is the cause of accerlation of electrons?
high electrical potential applied to the cathode
kV sent to filament from the step up transformer
x-ray production is produced- high speed electrons bomarding target area of anode
112
Where does the focusing of electrons take place?
| What is it made of?
focusing cup
surrounds the filament
maintains a concentrated stream of electrons from filament to the target area of the anode
made up of molybdenum
113
What happens in deceleration of electrons?
high speed electrons strike the anode target
interaction results primarily in heat production .
heat production 99%
ionzing radiation production 1%
114
What is an atomic number?
```
Z number
# of protons in the nucleus
```
115
What is atomic mass?
of protons and neutrons in the nuecleus
116
What is electron binding energy?
it what holds the electrons in their orbit. The closer the electron is to the nucleus the high binding energy
117
What is iionization?
removing of an electron from and oribal shell.
| uncharged atom will now have a + electrical charge
118
What is an isotope?
An atom of an element with the same atomic number as the elembent but with a different atomic mass. (differeing number of protons and neutrons)
119
What is Bremsstrahlung radiaion?
projectile high speed electron interacts with the electrostatic charge of the target
3 processes:
slows down, changes direction, loses some energy
the greater the direction change the more energy loss and the brem x-ray will possess more energy
120
What is characterisic radiaition?
high speed electron interacts with tungsten target by ejecting the inner shell electron
the K shell vacancy is filled by an outer shell electron
The process of filling the K-shell vacancy results in the emission of a charateristic x-ray photon
Energy of the x-ray photon is euql to the difference between the electron energies
121
T/F
| Are only characteristic x-rays produced from the K-shell diagnostic?
yes
122
Are the characteristic x-rays from shells L, M, N, O, P diagnostic?
no
123
Characteristic x-rays from shells L, M, N, O, P where are they aborbed in the x-ray tube since they are not diagnostic?
they can be abosrbed by the inherent /added filtration of the tube or they contribute to the skin entrance dose to the patient
124
T/F
| x-rays are a form of electromagnetic energy
true
125
What is the frequency of the x-ray beam measured?
Measured in the unit Hertz (Hz)
| x-rays are high frequency and very short wavelengths
126
T/F
| Frequency and wavelength in the x-ray beam ore inversely proprotional?
True
127
explain the QUALITY of the x-ray beam
penetrating ability of the x-ray beam
increase in kVp results in creased x-ray quality and penetration
filtration removes low energy non-diagnotic x-ray photons
increased filtration results in an increase in x-ray quality but not penetrability
128
explain the QUANTITY of the x-ray beam
expresses the intensity or the amount of x-rays
measured in Roentgen (mR)
influenced by mAs
x-ray quantity is directly proportional to mAs
129
explain x-ray beam DISTANCE
x-ray quantity is directly related to distance
| x-ray quantity is inversely proportional to the square of the distance
130
Explain the inverse square law and what is the formula?
used to calculate a change in beam intesity with changes in SID
I1= (D2) 2
_____________
I2 (D1)2
131
Explain the exposure maintenance law
used to maintain radiographic density with changes in SID
mAs1 = (D1)2
_______________
mAs 2 (D2)2
132
T/F
| Quantity is directly related to kVp
True
133
T/F
| x-ray quantity is directly related to filtration
False
| As filtration increases, x-ray quqntity decreases
134
How is filtration measured?
In the half value layer
| Thickness of an absorbing material required to reduce -xray intensity by 1/2 its original value
135
What is primary radiation?
Known as useful radiation
Is the x-ray beam prior to interaction with the patient
exits the window part of the tube
known as incident photons
136
What is remnant radiaion? (secondary)
Known as exit radiation
Attenuated from the x-ray beam that emerges from the patient and interacts with the IR
Known as the image forming beam
137
What is attenuation?
progressive absorption of the x-ray beam as it passes through matter
138
What are the fundamental properties of x-rays?
highly penetrating
have a wide variety of wavelengths and energies
travel in straight lines
can ionize matter
can produce chemical and biological changes
produce secondary and scattered radiation
travel at the speed of light
cause fluorescence-intensyfying screens
cannot be focused
contain no mass or electrical charge
very high frequencies, short wavelengths
139
What is the comptom effect?
partial absorption of the incident photon
incident x ray photon interacts with an outer shell electron and removes it
energy from the photon must exceed the energy required to remove the electron from its obrital hsell
some photon energy transferred to the ejected electron
remaining energy of the x-ray photon undergoes a change in direction and given off in the form of a scattered photon
energy of scattered photon and energy of the compton electron determined by the angle of deflection
the greater the energy transferred to the compton, the greater the angle of defection
140
What is the compton interaction influenced by?
the energy level of the the x-ray bweam and the thickness of the tissued irradiated
141
What is Photoelectric absoprtion?
total absorption of the x-ray photon
incdient x-ray photon interacts with an inner electron and removes the electron
the energy of the incident photon must be equal to or greater than the electtron binding energy of the K-shell
Photoelectric interactions are the primary source of patient radiation exposure
142
What are photoelectric interactions influenced by?
the energy level of the x-ray beam, mass density of the irradiated tissue, and the atomic number of the irradiated tissue
143
What is unmodified scatter?
Known as Classical, Coherent or Thompson scattering
No orbital electrons are ejected and no ionization takes place
No energy is exchanged between the incident photon and the target atom
The incident x-ray photon undergoes a change in direction with no energy loss
144
What is differential absorption (rate of attenuation)?
thickness of body part
As thickness increases, attenuation increases
As thickness increases, the photoelectric and Compton interaction increases
As the atomic number increases, attenuation increases
As the photon energy increases,(kVp) attenuation decreases
145
Describe the glass envelope of the x-ray tube
```
leaded pyrex glass
protects the internal components
maintains a vacuum
reduces inherent filtration
x-rays directed throught the window port
```
146
T/F
xrays are produced isotropically
(equal intensity in all directions)
True
147
What is leakage radiation?
radiation emitted through the protective housing
148
What does the insulating oil do in the x-ray tube?
assists in cooling the x-ray tube
| contributes to inherent filtration
149
What are the principles of AEC (automatic exposure control)
designed to produce a desired amount of density/IR exposure on images selected body parts regardless of changes in patient
images will vary due to changes in subject contrast
reduce number of repeated radiographs
dependent on accurate patient postioning and phototimer cell selection
150
What are radiation detectors?
image receptors used in DR
converts remnant radiaion to an electrical signal
the electronic signal forms an electronic latent image
intensity of electrical signal is proportional to the intensity of the remnant radiaiton beam
May be analog, then changed to digital
Displayed image on an image matrix
151
What is the back up timer?
determines the maximum length of exposure time for AEC exposures
provides a level of radiation protection in the event that hte AEC fail to terminate
152
What is the density adjustment?
Will increase or decrease the amount of radiation produced based on the size of the patient
153
What is the manual exposure control?
require the use of a carefully contructed technique chart which determines the exposure factors
154
What are some beam restriction devices?
aperature diaphragm
collimators
cylinders and cones
collimation filtration
155
What is an aperature diaphragm?
simple
lead plate with a hole
Used on x-rays with fixed SID and IR isze
156
What are cylinders and cones?
attached filtration divices, attached to collimator
157
What is Ohms law?
I=V/R
```
V= voltage (electrical potential)
I= current (amps)
R = resistence (ohms)
```
158
What is a Sinusoidal wave? (Sine)
represents the changing electromotive force induced in the armature of an electrical generator
360 degree revolution
For each complete rotaion of the armature, 2 distinct pulses of electromotve force are produced
Each pulse varies in direction
Sine waves contain amplitude, frequency and wavelength
159
What is a series circuit?
components are connected in line
| total voltage is equal to the sum of the individual volt producing devices
160
What is a paralell circuit?
components are connected as branches off a mina circuit
maximum voltage is equal ot the gratest sinale volt
total resistance is inversely proportional to the sum of the individual resistances (1/R1 = 1/R1+1/R2+1/R3)
161
What is AC supply?
alternating current
| primary side or low voltage circuit
162
What is the master wall switch?
priimary side or low voltage circuit
| series connection
163
What are fuses?
interrup in circuit in the event of an electrical hazard
| primary side or low voltage side
164
What is the line voltage meter?
primary side or low voltage circuit
measures incoming line voltage
voltmeter-paralell circuit
ammeter-series circuit
165
What is a transformer?
operate on the pirnciple of electromagnetic induction and require Ac current to opperate
creates an electromagnetic force (EMF)
166
What are the factors that determine the strength of an electromagnetic force?
speed at which it cuts through the lines of force, as speed increases, greater EMF
the strength of the magnetic field, MF increases, EMF increases
The angle between the conductor and the direction of the magnet. As the angle approaches 90 degrees, greater EMF
The number of turns of the conductor material, turns increase EMF
167
What is Air Core?
simplest
2 highly insulated coils of wire side by side
primary coild supplied with AC, secondary coil develops AC by mustual induction
168
What is Open Core?
iron core inserted into each of the solenoids
significant increase in magnetic force
has leakage flux from open core
169
What is Closed Core?
Winding wrapped around eachend of a square or cicular core
| much less loss of power due to closed core
170
What is Shell Core?
Two closed cores
Primary and secondary coils wrapped around a central portion of the core
most efficient
171
What is the transformer formula?
Vs =ts
________
Vp Tp
172
What is the autotransformer?
Located within the primary or low voltage circuit between incoming line voltage andprimary side of the step up transformer
Determines the amount of line voltage that will be sent to the step-up transformer
Operates on electromagnetic self induction (1 wire)
the number of turns on the secondary side of the autotransformer is altered to correspond to the kVp selected
Secondary voltage on the autotransformer can equal primary voltage but will never eceed primary voltage
173
What ist he line voltage compensator?
Located within the primary or low voltage circuit connected to the primary side of the autotransformer
Designed to maintain constant volt/turns ratio within the autotransformer
174
What is the step up transformer?
known as the high voltage transformer
separates the x-ray circuitry into primary or low voltage and secondary or high voltage sections
operates on electromagnetic mutual induction (2 wires)
Converts incoming low voltage from secondary side of autotransformer into high voltage or kilovoltage required to produce x-rays
Voltage is stepped up and current reduced
175
What is the step down transformer (filament transformer?
Known as the low voltage or step down transformer
Located in the low voltage filament circuit
Operates on electromagnetic mutual induction (2wires)
Adjusts the amount of current and voltage supplied to the filament
mA selected determines the amount of current and voltage 8-12 volts
Amount of current sent from the filament transformers to the secondary side is at least 3 -6 amps
voltage causes thermonic emmsions
176
What is the kVp meter?
Located within the primary or low voltage ciruit between the secondary side of the autotransformer and the primary side of the step up trnasformer
Provides a readying of th evoltage that will induced in the secondary side of the step up transformer
177
What is the exposure switch?
Located within the primary or low voltage circuit between the secondary side of autotransformer and the primary side of the step up transformer
Closes the circuit between autotransformer and the step up transformer which allows electromagnetic induction
Deadman type
178
What is the exposure timer?
Located within the priamry or low voltage circuit between secondary side of autotransformer adn the primary side of the step up transformer
Controls the duration of a radiographic exposure
Types:
Mechanical
Synchronous
Electronic
179
What is the mA selector?
Connected in series within the low voltage filament between the auto transformer and the step down transformer
Regulates the amps which regulates thermionic emission
3-6 amps
180
What is the focal spor selector?
```
Located within the filament, low voltage circuit
Selects the size of the filament
Lower mA stations
Small focal spots (0.1mm to 1.0mm)
Large focal spots (0.3mm to 2.0mm)
```
181
Where is the mA meter located?
In series to the midpoint of the secondary side of the step up transformer
182
What is the energy supplied 60 cycle AC current?
```
Each cycle 2 pulses of electric current
1 sec ...60 cycles & 120 pulses of energy
Single phase ...-70.7 percent
3phase, 6 pulse...-87
3phase, 12 pulse ... 97
High frequency...99
```
183
What is half wave rectification?
The negative pulse of each cycle of alternating current is prevented from going across the tube
184
What is full wave rectification?
The negative pulse of current is redirected through the series of rectifiers in order to be applied to the cathode side do the X-ray tube
4 rectifiers are required
Both pulses of each AC cycle are successful
Ability to double the production of radiation for each cycle
185
What is three phase power?
```
3 separate sine waves
connections can be delta or star
capacitator discharge unit
require 3 autotransformers, 3 primary and secondary windings
provides a direct current to the tube
used in portable radiographic units
```
186
What is in the image intensifier with fluoroscopy?
Glass envelope, input phosphor, photocathode, anode, electrostatic lenses, output phosphor
187
What does the glass envelope do?
vacuum
188
What does the input phosphor do?
converts incoming x-ray to light photons
| intensity of light is proportional to intensity of x-ray
189
What does the photocathode do?
converts light photons to electrons (thermonic emissions
190
What does the electrostatic lenses do?
located along the full length of the image intensification tube
directs and focuses electrons from photocathode to output screen
191
What does the output phosphor do?
converts electrons to light photons, intensity of light greater at input
192
What is brightness gain?
increase in the light intensity
| minification gain X flux gain
193
What is minification gain?
input screen diameter (2)/outputscreen diameter (2)
194
What is flux gain?
increase in the number of photons exiting the tube for every light photon produced at the input end of the tube
195
What is the physiology of vision?
bright light vision - cones
low light vision - rods
refresh rate 1/20 to 1/30 before responding to light changes
196
What is the purpose of fluoroscopic viewing?
real time or dynamic motion
| is the single greatest source of acute radiation exposure in diagnotic radiology
197
What is the visualization of the fluoroscopic image?
1 to 3 lpm
198
What are the resolution test tools in fluoro?
star and line pair phantoms
199
What is vignetting?
loss of detain and brightness along edges
200
What are the recording systems in fluoro?
photospot film device -exposed by light
cine fluoroscopic device - exposed by light
spot films- exposed by radiation
digital storage device - electronic signal
magnetic tape recorder - electronic signal
201
What is the automatic brightness control in fluoro?
fluoro mA is directly related to the brightness of the fluoro image
light intensity is measured by the photocell at the output phosphor end
If light intensity and video signal fall below established values, automatic adjustments in the fluoro mA will help maintain brightness and video signal
202
Magnification of the fluoro image is a function of what>
input phosphor size
203
Does magnifiying the image increase or decrease patient dose?
increase
204
How do you calculate the patient dose with magnification?
input phosphor 1 (2) / input phosphor 2 (2)
205
What do imaging plates with CR contain?
```
backing layer
support layer
color layer
conductive layer
reflective layer
phosphor or active layer
protective layer
```
206
T/F
| energy stored in the CR imaging plate dissipates over time?
True
207
How is the latent image formed with CR?
electronic image of valence electrons stored in high energy traps, Made manifest by exposure to a very small beam from a high energy laser
208
How does the imaging plate reader work?
employs the laser that caused stored electrons to return to their valence bonds with the emission of violet light that is amplified by a photomultiplier, electronic signal is digitized and stored for display
209
How is a CR plate erased?
by exposing to bright light
210
What film/speed is CR
sensitivity 200 speed film/screen
211
Does CR have a greater exposure latitude than conventional film? greater contrast?
yes
212
How is the digtial spatial resolution determined with CR?
Determined by the thickness of the phosphor layer and the number of pixels.
Greater the number of pixels per mm the greater the resolution
Greater the number ofo pixels sampled, the greater the recoreded detail
CR has a wide dynamic range
213
What are the 2 types of image receptors in digital?
Flat panel detector and Charged Couple device
214
Describe the flat panel detector used in DR
Use TFT
3 step process:
scintillator based (indirect)
cesium idodide
scintillator converts x-ray photons into light photons
Light photons interact with a photo conductive(silicon) matieral which converts light into electrons
electrons migrate to the TFT and produce a electronic signal
2 step process: (non scintallator- direct)
Uses amorphous selenium which converts the x-ray photons into electrons that are collected by the TFT
Provides improved spatial resolution compared to Csi phosphor
215
How does a charged coupled devices work?
require a scintillaotr material top produce light
light from the scintialltor strikes CCd converts into electronic signal
signal sent to an analog to digital converter to form digtial image
