chapter 7 ( The X ray tube) Flashcards
Which of the following will not damage the X-Ray tube?
Exceeding the ideal field size for an exposure
The main method of heat transfer from the focal spot/target to the rest of the anode is
conduction
An exposure rate of 100 mR/hr is the maximum allowed
leakage rate
The effective focal spot size is
the actual filament size.
smaller than
____________enclosures allow for more support and a constant potential between the tube current and enclosure.
Metal
A loud grinding sound from a tube is most likely due to
damaged ball bearings
Thermionic emission is the emission of
electrons from a heated cathode
In a fixed anode, there are_____
allowable heat loads and a_______
overall target area.
low, small
The space charge effect______.
occurs in the vicinity of the cathode
Localized pitting on the anode can occur from_______.
a single excessive exposure
The external structure of the X-Ray tube includes
support structure, protective housing, and tube enclosure
The filament is made of_____.
tungsten
Oil is added to the tube housing, creating a layer between the housing and tube enclosure to do what of the following?
remove heat from the X-Ray tube enclosure
When saturation is achieved at a fixed filament current, tube current
remains the same with increasing kVp
Which of the following could allow for an increase in heat capacity of an anode?
a. An increased anode diameter
b. A faster rotation speed
c. A larger focal spot X
d. All of the above
Because of the line focus principle, the effective focal spot size decreases with decreasing
target angle
Which of the following is not done by the protective housing?
Protection from scatter
The impact of the heel effect on the image is reduced by positioning the cathode
over the thickest part of the patient
What is the most common cause of abrupt tube failure?
open filament
The heel effect is more pronounced
with a small target angle
What does the focusing cup do?
help emitted electrons to a small region on the target
The main method of heat transfer from the anode to the tube enclosure is
Radiation
Extrafocal or off-focus radiation is produced from
rebounding electrons
The negative side of the X-Ray tube holds the
filament
Thermotropic emission allows______
to leave the filament.
electrons
The target of the rotating anode is usually made of
tungsten
Thorium is added to the filament to increase
thermionic efficiency
The______
is the source of X-Rays in the tube
focal spot
The filaments lay inside the focusing cup which has _____ with respect to the filaments in order to ______ electrons to the beam.
negative potential, repel
The term “isotropic” means
X-Rays are emitted in all directions
The typical target angle in general radiography is_____
degrees.
15
The effective focal spot is determined by the target angle and the_____.
filament size
The only way to increase saturation tube current is to increase
filament current
The part that actually turns the anode is the
rotor
The______
current is always less than the______
current.
tube, filament
The rotating anode is turned by the induction motor, which uses a
changing magnetic field
The X-Ray intensity is lower on the anode side of the tube because of the
heel effect
The X-Ray tube current____.
is controlled by the filament current
Each tube has its own radiographic rating chart to show
maximum exposure techniques
The best way to avoid cracking a cold anode is to
warm it with several low-technique exposures
Dual focus tubes usually have two
filaments
What are the main functions of the anode?
a.
Support the actual target region
b.
Acts as electrical conductor
c.Remove the heat generated
D.
(All of the above )
The main method of heat transfer from the tube housing to the room is
convection
If excessive heat is conducted through the rotor, it could
damage ball bearings in the rotor
Generally, for the same total mAs, the small focal spot results in exposure times that are ____ a large focal spot
greater than
The
is/are outside the tube enclosure.
stators
As an X-Ray tube ages, the inside can become coated with tungsten, which can cause
in the tube.
arcing
For the same kVp and mAs setting, what waveform would technically generate the most heat units?
high frequency
A molybdenum shaft is used to connect the anode to the rotor because it
is a poor heat conductor
X-Ray tube failure may be due to
a. a broken filament
Flag question
b. overheating of the anode
c.
damage to the ball bearings
d. lack of anode rotation
(All of the above)
The filament of an X-Ray tube is about_____
in length.
1-2 cm
The most important property to consider when choosing an anode material is
high melting point
What is the most probable result of a single exposure made on a tube if the factors slightly exceed those permitted by the radiographic rating chart?
The useful life of the tube would be reduced
The most widely used support structure for the X-Ray tube is the
ceiling support system
The effective focal spot size is largest
on the cathode side of the tube
