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114 Cards in this Set

  • Front
  • Back
The three main methods of x-ray tube support.
1.) ceiling
2.) floor to ceiling
3.) C-arm
Label Parts of Rotating Anode X-ray tube
When the x-ray tube is centered above the examination table at the standard SID, the tube is in a ___ ___ position.
preferred detent
X-rays are emitted __________ , meaning with equal intensity in all directions.
isotropically
The x-rays emitted through the window of the tube are part of the _____ _____.
useful beam
_______ _______ are x-rays that escape through the protective housing.
leakage radiation
T/F

Even leakage radiation can contribute partly to diagnostic information.
False

leakage radiation contributes nothing but unnecessary exposure of the patient and tech.
properly designed protective housing reduces the level of leakage radiation to less than ______ , when operated at maximum conditions.
100 mR/hr at 1m
What two things does the protective housing guard against?

*penguin
excessive radiation
electric shock
T/F

Death by electrocution was a very real hazard for early techs.
true
Besides guarding against electric shock and excessive radiation exposure, what other purposes does the protective housing serve?
1.) mechanical support
2.) protects against damage from rough handling
Having _____ around the protective housing serves as both an insulator against electric shock and a thermal cushion to dissipate heat.
Oil
A _______ prevents tube use until sufficiently cooled.
microswitch
A thermal cushion helps to _____ ____.
dissipate heat
Which part of the x-ray tube might contain a cooling fan?
protective housing
The glass or metal enclosure of a vacuum provides a ______.
electronic vacuum
The glass enclosure is made of ____ , to enable it to withstand the tremendous heat generated.
pyrex
The ______ tube, is the modern x-ray tube which contains a vacuum.
Coolidge tube
T/F

Early modification of the Crookes tube were vacuums tubes that contained controlled quantities of gas within the enclosure.
False

Early modifications of the Crookes tubes did not contain vacuums but did contain controlled quantities of gas.
What happens if a vacuum tube becomes gassy.
x-ray production falls and the tube can fail.
What vaporizes as a glass enclosure tube ages?
tungsten vaporizes and coats the inside of the glass enclosure.
What is the result of vaporization occurring in a glass enclosure tube.
Arcing and tube failure
_______ enclosure tubes are used in all high capacity x-ray tubes.
metal
This type of tube has a longer life and is less likely to fail.
Metal Enclosure Tubes
Is the x-ray tube window made of glass or metal?
it can be made if either
The x-ray tube window is approx. __ cm^2
5
The cathode is the negative side of the x-ray tube, what are it's two primary parts?

penguin *
filament
focusing cup
How big is the filament inside of the cathode?
approx. 2mm & 1 to 2 cm long
The x-ray filament emits ______
electrons
When the outer-shell electrons of the filament atoms are "boiled off" and ejected from the filament it's known as ______ .
thermionic emission
Filaments are usually made of ____ .
thoriated tungsten
The melting point for tungsten ?
3410 degrees Celsius
If tungsten vaporized easily the tube would become _______ , and the internal parts would become coated with tungsten.
gassy
The addition of ______ to the tungsten filament enhances the efficiency of thermionic emission and prolongs tube life.
1% to 2% of thorium
What is the most common cause of tube failure?

* penguin
tungsten vaporization with deposition on the inside glass enclosure
The filament is embedded in the ______
focusing cup
All electrons accelerated from cathode to anode are electrically ________.
negative
T/F

Some electrons can miss the anode completely
True
The focusing cup is ________ charged? Why does it have this charge?
negatively, so that it electrostatically confines the electron beam to a small area of the anode.
How many filaments do most rotating anode tubes have & how are they situated in the cathode?
they usually have two and they are side by side.
The x-ray tube current is adjusted by controlling the __________.

* penguin
filament current
electrons emitted from the filament stay in the vicinity of the filament before they can be accelerated to the anode, this forms a cloud called a ________.
space charge.
Thermionic emission at ____ kVp and ____ mA can be space charge limited.

*penguin
low kvp and high mA
______ happens when a further increase in kVp cannot provide higher mA because all electrons have been used.
saturation current
When an x-ray tube is operated at the saturation current it is said to be _______.
emission limited
How many focal spots do most diagnostic x-ray tubes have?
2

one small - spatial resolution
one large - large body parts
At approx. ______ mA and up, only the larger focal is allowed because the heat capacity of the anode could be exceeded if the small focal spot were used.
400
What are the two types of anodes?
rotating and stationary
Why do general purpose x-ray tubes use rotating anodes.
because rotating anodes are capable of producing high intensity x-ray beams in short time.
The anode is the _______ side of the tube; it conducts electricity and radiates _________ and contains the ________.


* Penguin
The anode is the positive side of the tube; it conducts electricity and radiates heat and contains the target.
What are the three functions that the anode serves?
electrical conductor
mechanical support
thermal dissipator
The anode provides _______ _______ for the target.
mechanical support
When the electrons from the cathode interact with the anode, more than 99 % of their ________ energy is converted into heat.
kinetic
Three most common materials the anode is made of?
copper
molybdenum
graphite
in rotating anode tubes, the entire rotating disc is the _______ .
target
________ & __________ have lower mass density than tungsten, making the anode lighter and easier to rotate.
molybdenum; graphite
What are the three main reasons tungsten is the material of choice for the target?
1. High Atomic Number
- 74
2. Thermal conductivity
- heat dissipation
3. High Melting Point
- 3400 degrees Celsius
The rotating anode tube provides nearly _____ times more area to interact with the electron beam than the stationary anode tube.
500
_______ tube currents and ______ exposure times are possible with the rotating anode.
higher ; shorter
Most anodes revolve at _________ rpm (revolutions per minute)
3600 rpm
The anodes of high capacity tubes rotate at up to _______ rpm (revolutions per minute)
10,000 rpm
The stem of the anode is the shaft located between the ______ and the _____.
anode and the rotor
The rotating anode is powered by an _______ _______ _______.

* Penguin
electromagnetic induction motor
In a new x-ray tube, the coast time is approx. _____ sec.
60

* with age the coast time is reduced because of wear of the rotor bearings.
The focal spot is the actual _____ _____.


*Penguin
x-ray source
The ______ is the area of the target from which x-rays are emitted
focal spot
What is the limiting factor of the focal spot size?
Heat

As the size of the focal spot decreases, the heating of the target is concentrated onto a smaller area.
Diagnostic tube target angles vary from __ to __ degrees
5 to 20 degrees
When the target angle is made smaller, the effective focal spot size is made ______.
smaller
The _______ results in an effective focal spot size much less than the actual focal spot size.

*Penguin
line focus principle
What is the advantage of the line focus principle.
It improves spatial resolution and heat capacity
What is the difference between actual focal spot and effective focal spot?
Actual focal spot - the area of the target material being bombarded by electrons from the filament.

Effective focal spot- area projected onto the patient.
The smaller the anode angle, the larger is the _______.

* Penguin
heel effect
What does NEMA stand for?
national electrical manufacturers association
A ________ effective focal spot is preferred for high resolution.
circular
A circular effective focal spot has a shape characterized by a ________.
double banana
The ________ has established standards and variances for focal spot sizes.
NEMA
When a manufacturer states a focal spot size, that is its _______ size.
nominal
A consequence of the line-focus principle is that the radiation intensity is greatest on the ______ side
cathode side.
Its best to place the thicker body part over the ______ side to provide a more uniform exposure.
cathode
where should the cathode be placed for a chest x-ray
inferior, to the thicker lower thorax
The ________ results in smaller focal spot and less radiation intensity on the anode side of the x-ray beam
heel effect
x-rays produced from outside the focal spot.
off focus radiation
Off focus radiation is undesirable because it extends the size of the _______.
focal spot.
________ images patient tissue that should have been excluded by collimation (shapes).
off focus radiation
T/F

The use of a grid does not reduce off focus radiation.
True
open filament means _______ filament.
broken filament

(burned through)
One HU (heat unit) is equal to the product of 1 ___, 1 ____, & 1 ____.
One HU is equal to the product of 1 kVp, 1mA, and 1 s
Thermal energy is measured in ____
HU's
Used to determine the length of time required for complete cooling or cooling to a certain point so that another exposure can be made.
Anode cooling chart
1 HU = ____ J (HF)
1.4
When referring to the radiographic rating chart, any combination of kVp and time that lies below the mA curve is _____.
safe.
The thermal capacity of an anode and it's heat dissipation characteristics are contained in a rating chart called an _________.
anode cooling chart
What two determinations can be made using the anode cooling chart?
1.) Length of time required for complete cooling
2.) cooling to a certain point so that another exposure can be made.
Three phase / High Frequency Equation?
HU=1.4 x kVp x mA x s
how many heat units are generated by an exposure of 110kVp, 200 mA , and .15 second on a 3 phase 6 pulse unit? must set up the formula to receive full credit for this question.
110 x 200 x .15 x 1.35 = 4455

6 pulse = 1.35
12 pulse = 1.41
High Freq = 1.45
What items are necessary for the production of x rays?
Vaccum
target
source for electrons (filament)
means to move electrons (kVp)
the diagnostic range of x ray energy is _____.
30 to 150 kVp
x rays are usually Identified by their
energy
the target of the rotating anode is usually coated with a ____ alloy
Tungsten
The ___ is the source of radiation in the x ray tube.
focal spot
Because of the line focus principal the effective focal spot size decreases with decreasing ____.
rotor speed
target angle
window thickness
space charge
target angle
tube failure can occur from ___
long exposure times
dual focus tube has two _____
filaments
Each tube has its own tube rating chart to show.

housing cooling times
anode cooling times
max exposure times
max patient doses
max exposure times
extrafocal or off focus radiation is produced from _____.
rebounding electrons.

not x rays yet.
localized pitting can occur from ___
a Single excessive exposure
the Gray is equivalent to ____.
rads
0.01 rads
what size is a small focal spot in mm?
0.3 -0.7
small focal spot results from the selection of the small ____
filament
Target angle is from ____ to ___
7 to 15
Most common type of timer used is ..
synchronous timer
Leakage radiation must not exceed ___ at one meter
100 mR / hour
What part of Cat or An assemblies is located outside the vacuum of the glass envelope
stator