Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
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
|
