X-Ray Beam Flashcards
The size of the area on the anode target that is exposed to electrons from the tube current
actual focal spot
Filtration that is added to the port of the x-ray tube. Aluminum is the material primarily used for this purpose because it absorbs more low-energy photons while the useful higher-energy photons can exit
Added filtration
positively charged electrode
Anode
What materials is the anode made of?
Tungsten Z #74
Molybdenum Z#42
Copper Z#24
Graphite
Target is made of Tungsten & Rhenium Z#75
Anode Heel Effect
How the x-ray beam has greater intensity (number of x-rays) on the cathode side of the tube but a lower intensity toward the anode side
projectile electron completely avoids the orbital electrons of a tungsten atom and travels very close to its nucleus
Bremsstrahlung interactions
negatively charged electrode
Cathode
projectile electron interacts with an electron from the inner shell (K-shell) of a tungsten atom
Characteristic interactions
added to the primary beam to alter its intensity
Compensating filter
Examples of compensating filters
trough, wedge, boomerang, Ferlic
focal spot size as measured directly under the anode target
effective focal spot
coiled tungsten wire, which is the source of electrons during x-ray production
filament
Describe the function and purpose of the focusing cup
Made of nickel
surrounds the filament
open at one end to allow electrons to flow freely across the tube from cathode to anode.
negative charge – keeps the cloud of electrons emitted from the filament from spreading apart.
Its purpose is to focus the stream of electrons.
amount of filtration that reduces the intensity of the x-ray beam to one-half of its original value
Half-value layer (HVL)
amount of heat produced from any given exposure is expressed
Heat Units HU
An exposure is made with a three-phase x-ray unit at 800 mA and 80 kVp over 0.5 s. How many heat units are produced from this exposure?
43,200 HU
An exposure is made with a high frequency x-ray unit at 400 mA and 75 kVp over 0.05 s. How many heat units are produced from this exposure?
2,100 HU
An exposure is made with a single-phase x-ray unit at 300 mA and 73 kVp over 0.03 s. How many heat units are produced from this exposure?
657 HU
Describe inherent filtration
filtration that is permanently in the path of the x-ray beam
(1) the envelope of the tube
(2) the oil that surrounds the tube
(3) the window in the tube housing
any x-rays, other than the primary beam, that escape the tube housing
Leakage radiation
100 mR/hr to escape when measured at a distance of 1 m from the source while the tube operates at maximum output
Maximum allowance of leakage radiation
relationship between the actual and the effective focal spots in an x-ray tube
Line focus principle
Tube current is the number of electrons flowing per unit time between the cathode and the anode
mA
when projectile electrons are reflected and x-rays are produced from outside the focal spot
off focus radiation
connected to the target through the anode stem
rotor
causes the target to rapidly rotate during x-ray production
electrons liberated from the filament during thermionic emission form a cloud around the filament
space charge
tendency of the space charge to prevent more electrons to be boiled off of the filament
space charge effect
electric motor that turns the rotor at very high speed
stator
part of the anode that is struck by the focused stream of electrons coming from the cathode
Target
When a third-grade student was asked to define the term “vacuum” in class she answered…
“A vacuum is an empty region of space where the Pope lives.”
hahahaha!
Are we having fun yet!
Absolutely
When the tungsten filament gains enough heat (therm), the outer-shell electrons (ions) of the filament atoms are boiled off, or emitted, from the filament.
Thermionic Emission
The speed of the electrons traveling from the cathode to the anode increases as the kilovoltage applied across the x-ray tube increases.
Relationship between kVp and speed of e-
voltage waveforms in terms of how much the voltage varies during x-ray production
voltage ripple
x-ray beam is polyenergetic (has many energies) and consists of a wide range of energies
x-ray emission spectrum
