TEST 2 Flashcards
1
Q
What does a line compensator do?
A
modify and adjust incoming voltage to be consistent 220V
2
Q
Kinetic energy in x-ray system
A
kVp setting provides large potential difference to give kinetic energy to filament electrons
mAs provides electrons flow (tube current)
3
Q
KE –> electromagnetic energy
A
electrons flow from cathode to anode
4
Q
potential energy in xray
A
Voltage
5
Q
Potential energy in x-ray
A
Voltage
6
Q
What does an autotransformer do
A
directly determine voltage applied to x-ray tube through kVp selector
7
Q
Is the autotransformer adjustable?
A
YES
8
Q
What is autotransformer made of
A
single coil of insulated wire wound around a large iron core
9
Q
How are X-ray produced
A
1.electrons boiled off the filament –> filament e-
2. interact with the target anode or nucleus that could lead to the release of Characteristic & Brems x-ray photons (1%) AND heat (99%)
10
Q
What do major & minor kVp selector do
A
both to select kVP desired
minor: fine tune the technique
11
Q
3 components of X-ray circuit
A
operating console
high-voltage generator
x-ray tube
12
Q
What does kVp meter do
A
read voltage before exposure
13
Q
What does timing circuit (exposure time) do
A
regulate duration of x-ray exposure
control low voltage
14
Q
4 types of timing circuit
A
Synchronous
Electric
mAs
Automatic Exposure Control (AEC)
15
Q
What is the limitation for Synchronous timers
A
cannot be used for serial exposures because it must be reset after each exposure
16
Q
Synchronous timer
A
use motor that operates at frequency of 60hz @ 60 rotations per second
timer: 1/60s increment
17
Q
Electric timer
A
microprocessor controls it
based on time it takes to charge a capacitor through variable resistor
1ms
18
Q
mAs timer
A
terminate exposure when desired mAs is obtained
located in 2nd circuit
provides safe tube current in shortest time possible
19
Q
AEC
A
measure quantity of radiation that reach IR.
has an ionization chamber
required precise position skills
20
Q
[AEC ] what is the
ionization chamber? what does it do
A
radiolucent device that control exposure when activated
It adjust the amount of necessary radiation to send exposure terminal signal to IR
when there is efficient voltage/ ionization, operational amplifier terminate exposure
21
Q
What does AEC backup timer do
A
terminate exposure in case of malfunction
22
Q
What is good about AEC backup timer
A
protects from tube from overheating and patient from overexposure
23
Q
What is bad about AEC backup timer
A
timer is too short –> underexposed image
24
Q
What does Step-UP transformer do
A
increase voltage from autotransformer by a fixed amount
(V–> kV)
25
Change in voltage & current is an _____ relationship
inverse
26
What does Step-DOWN transformer do
increase current by reducing voltage that applied to the filament
27
What activated step-down transformer
mA adjustment
28
What does mA selector do
control Amperage in filament circuit. In other words, control rate which e- boiled off
29
What does Rectifier do
convert AC--> DC
30
What is the process of Rectification
solid-state rectifier banks are arranged in pairs to route current through xray tube each time
31
What does rectifier make of?
solid-state semiconductor diode (2 electrodes)
current ( + to -)
electron (- to +)
electricity pass through rectifier, created + charge on the anode & - charge on the cathode focusing cup
32
Half-wave rectification
no electric current
no negative swing during half of its cycle
33
Half-wave rec contains how many diodes
0, 1 or 2
34
Half-wave rec produce how many x-ray pulse per second
60
35
Cons of half-wave rect
waste 1/2 of its power--> double exposure time
36
Full-wave rec contain how many diodes
4 in high-voltage circuit
37
What does High-Voltage Generator do
increase V from autotransformer to kVp
38
3 parts of High-Voltage Generator
high voltage (step up transformer)
step down filament transformer
rectifiers
39
What does mA meter do
monitor xray tube current
40
What is single-phase power
resulted from pulsating x-ray beam
41
Characteristics of single-phase power
low in energy, penetrability
little diagnostic value
100% ripple
42
what is the benefit of 100% ripple in single-phase
less energy waste
43
Characteristics of three-phase power
multiple waves at constant high voltage
44
what is the benefit of less ripple in three-phase power
Voltage never drop to 0 during exposure = constant energy
45
What is a ripple
energy fluctuate from 0 to max voltage
46
What do high-frequency generator do
Improve waveforms
smooth V
reduce ripple from three-phase full wave
change incoming-line voltage frequency
47
Benefit of high-frequency generator
produce xray with consistent energy levels
48
3 external components of xray tube
support structure
protective housing
glass or metal enclosure
49
What is an X-ray tube
electronic vacuum, contains 2 electrode inside a glass/metal enclosure
50
purpose of glass or metal enclosure
creates vacuum tube to pack electrons tightly together = more efficiency and longer tube life
51
Why use glass enclosure
high melting point to withstand heat
52
Why use metal enclosure
maintain constant electric potential = longer life tube
53
Purpose of x-ray tube window
emit useful beam
54
For the xray tube, Lead is built in everywhere except
tube window
55
Another name for primary beam
useful beam
56
What is leakage
2nd type of radiation
escape protective housing
57
3 purpose of protective housing
covers tube with lead to reduce leakage
prevents electric shock
mechanical support
58
Some protective housing contains oil which serves as
insulator for electricity
dissipate heat
59
components of cathodes
filament(tungsten-thorium alloy) and focusing cup (nickel)
60
when thermionic emission occur
when filament is heated up and emits electrons
61
What material made up filament
Tungsten
62
What is the charge of focusing cup and its purpose
neg charged
accelerate electrons within a confined space –> focuses electrons to hit focal spot
63
Location of focusing cup
cathode
64
explain how can focusing cup force electrons together into a cloud when both of their charges are negative
the neg charge of focusing cup is greater than the neg of e-. Individual electron-neg charge cause them to repel and scatter as they boiled of the filament
65
Location of focal spot
anode
66
3 Functions of anode
electrical conductor
mechanical support for target
thermal dissipater
67
Types of anode
stationary and rotating
68
pro of rotating anode
spins target = more surface area for electrons to hit ==> high intensity xray beams in short time
69
What drives the anode
electromagnetic induction motor
70
Difference b/w stator & rotor
stator: has electromagnets
rotor: shaft made of bars of copper & soft iron
71
what is the target
area of where electrons hit the anode from cathode
72
Why Tungsten is used as a material for the Target
high atomic # --> high efficiency x-ray production
high thermal conductivity --> efficient at dissipating heat
high melting point --> withstand high tube current w/o bubbling
73
What is a focal spot
area of target from which x-ray are emitted
74
What size of focal spot produce image with better spatial resolution
small effective focal spot
75
The ___ focal spot = the greater heat concentration. Therefore we need a large actual focal spot.
smaller
76
The focal spot size is determined by __
filament size
77
The focal spot size is determined by __
filament size
78
What is line focus principle
Target is angled (5-20 degrees) to allow large area for heating while maintaining small focal spot
79
How do we create small effective focal spot
angle the target (anode) 5-20 degrees to change size of effective focal spot
80
line focus principle is good for what?
greater heat capacity and better radiographic image sharpness
81
what is the effect for
-large actual focal spot
-small effective focal spt
-maintain heat dissipation
- improve image quality
82
What is anode heel effect
radiation intensity on cathode is higher than on the anode
83
Effective compensation for the anode heel effect would involve positioning:
the thinnest portion of the body part under the anode.
84
Explain why the intensity at cathode side is stronger than anode side
x-ray constitute to the useful beam emitted tw the cathode traverse a lesser thickness of target material than anode
85
Why anode heel effect important
imaging anatomic structure that varies in thickness or mass density
86
A ____ angle tube will give greater anode heel effect
SMALL
87
What are 3 causes of x-ray tube failure
Heat
maintaining anode at elevated temperature for prolonged period
filament (high temp cause filament to vaporize)
88
What effect does temperature have on filament
high temp cause them to vaporize
89
The X-ray tube is very thermal. What are the 3 ways to dissipate heat for tube
1. radiation
2. conduction
3. convection
90
Explain radiation as a way to dissipate heat
transfer heat by emission of infrared radiation (light)
91
Explain conduction as a way to dissipate heat
transfer energy from one objec to another
92
Explain convection as a way to dissipate heat
transfer heat by movement of heated substance from one place to another
93
3 things needed to produce X-ray
1. kVp provide large potential difference to give energy for filament e-
2. mAs giving quantity of e-
3. the target anode for e- to interact
94
Example of conduction
heat-tolerant materials
95
Example of radiation
heat energy from anode to oil bath
96
Example of convection
rotating anode
cooling fans
97
What do you do to extend tube life
1. warm up the tube before normal operations
2. maintain filament in an energized state --> shortens its useful life.
3.no use of extreme exposure factors
98
Radiographic rating chart conveys ___
which radiographic techniques are safe & unsafe for x-ray tube operation
99
Anode cooling chart conveys _____
thermal capacity of anode & its heat dissipation
100
Housing cooling chart conveys___
thermal capacity of housing & its heat dissipation
101
Rotating anode is made of ____
copper
102
Why copper for rotating anode
good at thermal and electricity
103
Why molybdenum is used
low thermal conductivity
tensile strength
104
How does rotating anode turn
use induction motor to operate through electromagnetic mutual induction
105
How does angling the target affect the intensity of beam on anode side
the heel of target is partially in the path of xray beam produced --> cause absorption and reduce intensity of beam on anode side
106
what reduces leakage radiation to required standards
protective housing
107
Primary function of x-ray imaging system
speed up electrons from cathode to anode
108
Speed of electrons determine _____
if excitation or ionization happened
109
Heat is ____ rather than ___
excitation - ionization
110
what is ionization
transfer sufficient energy to overcome BE of orbital electrons eject them from atom
111
Heat is ___ proportional to the tube current and kVp
directly
112
increase kVp will ____ efficiency of x-ray production
increase ==> better quality x-ray w/o overheating tube
113
What is responsible for most of the heat in the xray tube
cycle of outer-shell electron excitation and neutralization
114
How is heat produced?
filament e- enters anode target and interact with outer-shell electrons. They transfer sufficient energy to excite. This excess energy is given of as infrared radiation (light)
115
when does Brems radiation occur
when incident electron interacts with force field of nucleus
116
What is required for incident electron to interact with the force field of nucleus to produce Brems
incident electrons must have enough energy to pass by orbital electrons without interacting
117
How are Brems photons produced?
incident electrons interacts with force field of nucleus creates a force of attraction between the 2. This attraction slows down electrons and make them change direction which causes loss of kinetic energy. This energy is released as Brems photons
118
What is the energy of Brems photons
difference between the entering - exiting KE of electron
119
More loss of KE when e- pass close to the nucleus results in ____
more Brems photon
120
Why 1 e- can cause many x-ray
after the first interaction, the e- can go on to interact with different atoms before losing all of its energy
121
When does Characteristics radiation occur
when e- interacts with inner-shell electron
122
What is required for incident electrons to produce Characteristics photons
enough energy to knock inner-shell electron from orbit
123
At what kVp levels Characteristic X-rays are produced
above 70
124
How are Characteristics photons are produced
If energy of incident photon is greater than the BE of orbital electron, the electron is removed from the orbit => Unstable => e- from outer shell drop expend its PE to fill in the vacancy. This energy is given off as Characteristic photons
*expending of energy during cascade that produce characteristic xray*
125
Electrons drop into ___ -shell produce ____ within diagnostic xray range
K
characteristics
126
The effective energy of characteristic xrays increase with _____
increase atomic number of target element
127
What is ionization
adding or removing electron from an atom
128
What happened to X-ray when they interact with matter
1. can be absorbed (attenuation)
2. can partially transfer energy and scatter
3. pass through matter unaffected (direct transmission)
129
Can we predict what happen to a single photon
NO - the interaction is random
Can only predict what happened on the average
130
what does moderate energy xray interact with?
electrons
131
what does high energy xray interact with?
nuclei
132
what does low energy xray interact with?
whole atoms
133
2 factors determine types of interaction between photons and atoms
1. atomic number of atom
2. energy of photons
134
5 types of patient interactions
1. classical (coherent scattering)
2. photoelectric interaction
3. compton interaction
4. pair production
5. photodisintegration
135
does the photons always interact with atoms?
no --> atoms = empty space --> passes through without interactions
136
What is produced for coherent scattering and how?
Scatter x-rays are produced as extra energy with a wavelength equals to incident x-rays when it interacts with atom and became excited
137
What is the energy level for incident xray for coherent scattering?
low enegry (< 10keV)
138
What does it mean to say no ionization happened ?
incident photons are unable to remove orbital electrons from their shell due to its low-energy level
139
Effect of coherent scattering?
slightly contribute to pt DOSE
create image noise
140
What are produced in Compton scattering interaction? and How
1. ejected electrons
2. scatter photons
incident photon interacts with the electrons in the outer-shell causing ionization. As a result, an electron is ejected with the energy equals to its BE and KE that leaves the atom. This is the secondary electron. Scattered photon is also ejected and changed direction which get absorbed photoelectrically
141
compton scattering energy level
30-40
142
Compton scattering is the greatest hazard to whom ?
radiation workers
143
who discovered photoelectric effect
albert einstein
144
when does photoelectric occur
energy of incident photon is equal to or slightly higher than binding energy of inner shell
145
What happened to incident photon in Photoelectric
totally absorbed by the atom when trying to remove an electron
146
What is produced in photoelectric interaction
photoelectron
147
What is the equation represent the energy transfer of incident photon for Photoelectric & Compton
Ei = Eb + Eke
Ei = Es + (Eb + Eke)
148
how to decrease photoelectric effect
pro?
high kVp --> by hardening beam
lower radiation dose
149
compton scattering ____ proportional to kVp
photoelectric effect ____ proportional to kVp
directly
inversely
150
What happened to incident photon in Pair Production
disappear after interact with nucleus of atom
151
What happened to the energy of incident photon in Pair production
transformed into negatron & positron
152
What does negatron do
What does position do
lose KE by exciting & ionizing atoms in its path
annihilate electron to result in 2 photons (0.511 meV each)
153
Which modality do we use annihilation
PET
154
Which types of interaction are used for radiation therapy
PP
photodisintegration
155
how does energy transfer in photodisintegration
high energy photon collides with nucleus of atom which directly absorbs all the energy of photon
156
What are produced when incident photon interact with nucleus in photodisintegration
neutron
nuclear fragment by nucleus
157
what is heterogeneous
xray beams with various energies
158
xray emission spectrum
the collective of all different energies of xrays
aka the different potential energy in single beam
159
90% of primary beams is from____
Brems interactions because it can be created at any energy level
160
Discrete xray spectrum produced by_____
characteristics X-ray
161
Why does the energy of characteristic xray produced is different
due to the difference in BE of electrons for every element
162
what cause fluctuation when xray output is above K shell peak
characteristic peak
163
Discrete xray spectrum produced by _____
Continuous xray spectrum produced by ____
Emission xray spectrum produced by _____
characteristic
brems
both
164
What 6 factors affect the spectrum
mA, time
kVp
target
generator
distance
filtration
165
How does mA -tube current affect spectrum
change amplitude of emission graph
166
How does kVp -tube potential affect spectrum
change in # of higher-energy photon + amplitude
167
How does TARGET affect spectrum
atomic number of target affect both QUALITY & QUANTITY of xrays
168
How does GENERATOR affect spectrum
generator efficiency increases = increases Xray beam intensity
Voltage ripple = decrease ma & kVp
169
How does DISTANCE affect spectrum
farther = xray photons decreases in each square cm of beam = decrease exposure
170
How does FILTRATION affect spectrum
thicker filter = higher atomic # = decrease ma & kVp
171
What is HVL is used for
measure quality (kVp) of Xray
172
typical HVL
3-5 mm Al
173
how does kvp relate to HVL
more kvp = more intensity = more HVL
174
Attennuation
reduction in xray intensity occurring from absorption and scattering
175
4 effects of filtration
decreases mAs (intensity) of beam
increases kVp (average photon energy)
lower pt dose
image brightness
176
Purpose of filtration
harden xray beam to remove low-energy photons
produce highest quality (penetrating) xray possible
177
Why do we need to harden the beams
lower pt dose
178
What is the standard material for filtering material
Aluminum
179
3 types of filtration
inherent
added
compensating
180
Difference in 3 types of filtration
inherent: glass/metal enclosure
added: thin sheet of Al between protective xray tube housing (window) and beam collimator
compensating: additional filter added to compensate differences in subject radiopacity
between collimator and patient
181
Purpose of collimator
decrease pt dose
increase image resolution
182
total filteration
inherent + added filtration
at least 2.5mm Al equivalent
183
Differential absorption and attenuation of xray beam depend on 3 factors
1. atomic #
2. mass density
3. xray energy
184
what are 2 interactions have significant impact on xray image
PE & Compton
185
___ atomic number = ____ attenuation
why
increase
increase
higher atomic number = more atoms to interact with
186
___ mass density = ____ attenuation
why
decrease
decrease
less atoms to interact with
187
___ xray energy = ____ attenuation
why
increase
decrease
more push power = less interactions
188
to see grayscale effect
more photoelectric affect + less scatter & noise
189
types of cell dysfunctions
repaired
altered
dead
190
For a certain body part, why should we have a good technique
too much kVp = push hard = less interaction w atom= nothing reach IR = black/w image
increase kVp =
190
For a certain body part, why should we have a good technique
too high kVp = push hard = less interaction w atom= nothing reach IR = black/w image
increase kVp = decrease PE = good for pt dose = increase scatter
==> just right kVp
191
what is the most dangerous cellular dysfunction
why?
altered
given long exposures --> less immunity = less likely to repair --> risk of cancer
192
what can occur with dead cellular dysfunction
risk of organ failure because of apoptosis
193
what does EXPOSURE measure? unit?
radiation intensity in the air.
roentgen
194
what does DOSE measure? UNIT?
radiation absorbed from radiation exposure
rad
195
what is exposure used for
calculates entrance skin exposure
196
what is dose used for
estimates irradiation of patients
197
What is ESE? what does it measure?
entrance skin exposure
skin dose of radiation exposure as beam enters
198
where is ESE calculated at
minimum SOD
CR where the beam is most intense = most radiation will hit pt
199
When we dealing with patient protection, what should we assume?
maximum effect at entrance exposure to minimize exposure rather than internal exposure.
200
3 areas of high ESE? why?
L-spine
pelvis & hip
abdomen
thicker body parts = more exposure = more pt dose
201
7 ways to reduce patient dose
communication
positioning
kVp
mAs
distance
collimation
shielding
202
REDUCE PT DOSE BY
reduce technique
collimate
no repeat
203
relationship bw SID/SOD & ESE
inverse
204
SOD
source to object distance
ex: anode target to patient
205
SSD
source skin distance
ex. CR
206
What are 2 target production
brems & characteristic
207
What are produced in each types of interaction?
1. coherent (excitation only, no ionization)
2. comp scatter (secondary characteristics) - leakage & scatter
3. PE ( cascade)
4. PP (2 photons
5. Photodisintegration (absorption only)
