Exam 3 Review (s1) Flashcards
Review exam 3
What is the Typical incoming line voltage to the high voltage circuit?
220 volts
Autotransformer:
makes adjustments to voltage before it is stepped-up
on low-voltage side of the high voltage circuit for safety
3 ways the exposure switch and exposure time initiates/terminates
manual timer
mAs timer
Automatic exposure control (AEC)
What is part A in the xray machine?
Main power switch
&
circuit breaker
What is part B in the xray machine?
Autotransformer
What is part C in the xray machine?
Exposure switch
&
exposure timer
What is part D in the xray machine?
Kvp Meter
(parallel circuit)
What is part E in the xray machine?
Step-up transformer
turn ratio 500:1 to 1000:1
What is part F in the xray machine?
mA meter
(series circuit)
What is part G in the xray machine?
Rectification bridge
(changes alternate to direct current)
What is part H in the xray machine?
x-ray tube
thermionic emission- cathode (-)
x-ray production- anode (+)
What is part I in the xray machine?
Rotor switch
anode spin at 3400 RPM
heats up the filament
boils off electrons from filament due to high amps and high resistance
What is part J in the xray machine?
mA selection
(resistors)
What is part K in the xray machine?
Step Down Transformer
ratio 1:44
Main power switch and circuit breaker (step?):
A
typical incoming line voltage to the high voltage circuit is 220V
Autotransformer (step?):
B
adjusts voltage before stepping up
Exposure switch and time (step?):
C
initiates exposure and terminates 1 of 3 ways:
Manual timer
mAs Timer
Automatic exposure control (AEC)
Kvp Meter (step?):
D
measures the Kvp
(parallel)
Step-up transformer (step?):
E
turns ratio 500:1- 1000:1
mA meter (step?):
F
Measures the amount of mA
(series)
Rectification bridge (step?):
G
Diode changes alternate to direct current
electrons approach “n” side, electrons are repelled towards bridge
p is positive side that repels holes toward the bridge
x-ray tube (step?):
H
thermionic emission (cathode)
x-ray production (anode)
rotor switch (step?):
I
spins anode 3400 rpm
heats up filament in the x-ray tube
thermionic emission due to high amperage and high resistance
mA selection (step?):
J
Resistors
more resistors less amperage (vice versa)
Step down transformer (step?):
mA increased by:
K
ratio of 1:44
mA is increased by a factor of 44, up to 5 AMPS
Thermionic emission:
“BOILING OFF” electrons from filament due to high amperage and high resistance
Half wave/self-rectified circuits
60 pulses a second
100% voltage ripple
30% average Kvp
single-phase/ full wave rectified
120 pulses a second
100% voltage ripple
30% average Kvp
3 phase/ 6-pulse generators
360 pulses per second
14% voltage ripple
91% average Kvp
3-phase/ 12-pulse generators
720 pulses per second
4% voltage ripple
97% average Kvp
high frequency generators
greater than 500 pulses
per second 500<
1% voltage ripple
100% average kvp
hz is altered from 60 to 500-25,000 HZ
Ch 9: xray tube
Cathode:
negative side of the x-ray tube
Thermionic emission
Ch 9: xray tube
How many filaments in x-ray tube?
2 filaments
small= 1 cm
large: 1.5-2 cm
What does focal spot do?
Small?
Large?
smaller focal spot creates sharper images
large focal spot better for high heat x-rays (L-spine)
Filaments are made up of:
thorium-impregnated tungsten
thorium z=90 helps with heat tolerance
Thermionic emission occurs in the:
What is thermionic emission?
Cathode
“boils off” electrons from the filament due to high current flow and high resistance
What is space charge?
electron cloud forms around the filament when the rotor button is pushed
focal spot (in anode) is _% of filament?
5%
(0.5mm-1mm)
Focusing cup:
What is its charge?
Negative charge
prevents electrons from rushing away by surrounding the filament (negative focusing cup narrows the electrons due to the law of attraction)
Focal spot for hands/feet x-rays:
Small focal spot
1cm
focal spot for lateral lumbar:
large focal spot
1.5cm to 2cm
Anode:
positive side of the x-rays tube
Xray production
Rotor:
A part of what?
Anode
Connects the shaft and spins when influenced by the stator (induction)
Target:
A part of what?
area of the anode disk that is struck by the electrons
made of tungsten and rhenium z=75
What is struck by electrons in the xray tube?
the target in the anode (anode disk)
very durable to high amounts of heat
Main cause of x-ray tube failure?
arcing
What is arcing?
vaporized tungsten coats the inside of the tube
type of short circuit:
1. cracks the glass
2. eliminates vacuum
3. burns out the filament
What is a way we can protect the x-ray tube?
warm up procedures to prevent thermal shock (hot water on cold glass=crack)
avoid excessive rotoring
calculate the heat units to prevent overheating of the anode
what is heat units for?
to measure how much heat the anode can withstand
(a unit of measurement for anode heat capacity)
HU (heat units) formula:
1.4 (constant/ don’t forget)
x
kVp
x
mA
x
s (seconds)
What is the purpose for a tube rating chart?
to ensure that a technique will not exceed the heat capacity of an x-ray tube
What is the anode cooling chart purpose?
how long will it take for the anode to cool before making another exposure.
stream of electrons:
How fast?
using the voltages in x-ray electrons can accelerate at 1/2 the speed of light in just one inch
heat interactions:
99.5% of interactions at 60 Kv
99% of interactions at 100 kv
Bremsstrahlung:
“braking radiation”
interactions with the nucleus
bremsstrahlung is responsible for the:
vast majority of x-rays
how does Bremsstrahlung work?
closer an electron passes to the nucleus, the more it will be declerated and more energy is lost in the form of an x-ray
In Bremsstrahlung was is the average kv exiting?
(The avg kv after filtration is 1/3 of kvp setting)
the average KV exiting the xray tube after filtration is about 1/3 of the kVp setting
Characteristic:
projectile electron from CATHODE interacts with INNER shell electron
it can be ejected
What are the steps of characteristic?
- electron interacts with inner shell electron
- outer shell electron will drop down to fill the vacancy (L to K)
- The strength of the x-ray is equal to the difference between the two shell electrons
Any _____ can fill the vacancy in an inner shell electron, including ____ _______ outside the atom in characteristic
Electrons
Free electrons
Characteristic cascade:
Inner shell electrons are replaced in sequence (k by L,L by M, M by N,N by O).
MULTIPLE x-rays are created
The result of characteristic cascade is x-rays at _____ _________
Specific energies
K shell- 57, 66, 68, 69 KV
L shell- 9,11,12 KV
(T/F) when the Bremsstrahlung spectrum and characteristic spectrum are combined we have a complete graph of all the x-rays leaving the x-ray tube
True
What are factors that affect the x-ray emission spectrum?
- Target material (mammography)
- Milliampere-seconds (mAs)
- added filtration
- Kilovoltage-peak (kVp)
- generator type
(3 are of these are most common)
mAs directly controls the number:
of x-rays that exit the tube
Doubling mAs will:
double the amount of x-rays created
Filtration removes what kind of xrays?
adding more filtration will:
Filtration removes weak x-rays and adding more filtration will remove even more weak ones
Increasing the average kvp
When we filtrate more x-rays what happens to the average KV?
What is this known as?
the average KV will go up
this is known as “hardening” the x-ray beam
Increasing the kVp will move:
the x-ray emission spectrum to the right due to the increase energy from x-rays
How do generator type play a role in x-ray emission spectrum?
single phase
high frequency
etc
(Changes the pulses, voltage ripple, average kvp)
Things to concentrate on:
The xray machine and circuits
The x-ray tube
read and do math on anode cooling chart
read the max exposure time graph
How does target material play a role in the x-ray emission spectrum?
(won’t be tested much on)
(Certain material will lower the average kvp)
like in mammography the material of the target will affect the average KV
(ex: in mammography avg is 17 KV)
Focusing cup
Surrounds filaments
Prevents electrons from rushing away from each other
Resulting focal spot in anode is 5% size of filament – 0.5 - 1 mm
Thermionic emission in the CATHODE:
a “boiling off” of electrons from the filament due to high current flow and high resistance
Average KV after exiting the x-ray tube after:
filtration is about 1/3 of the kVp setting
At the bridge current:
can flow
(T/F) free electrons outside of the atom can fill the vacancy of the inner shell?
True
ANY electron
Hardening the x-ray beam:
adding more filtration for weak x-rays
thus increasing the average kVp
