Unit 2 Exam Flashcards
What is applied to the cathode side of the tube during an exposure?
A large negative potential.
What is the process of producing an electron cloud referred to as?
Thermionic emission
Two reasons why Tungsten is an ideal target material
High Melting Point
High Z number (74)
Why are the tungsten filaments coated in thorium?
Thoriated tungsten burns off 2% more electrons.
More efficient thermionic emission process.
What does the acronym mAs stand for?
Milliampere Seconds
How do you convert seconds into milliseconds?
Move the decimal 3 places to the right
How do you convert milliseconds into seconds?
Move the decimal 3 places to the left
What happens to the patient’s dose if you cut the mA in half?
Patient dose is cut in half
What happens to the patient dose if you double the exposure time?
Patient does is doubled.
What is the definition of exposure time?
The amount of time potential difference (voltage) is applied to the tube.
Amount of time the patient is exposed to x-rays.
One reason why a shorter exposure time would be desired?
Motion Artifacts (image blur)
Moving children
List one reason why a longer exposure time would be desired.
Lateral T Spine
Reciprocity Law
Exposure to the IR will remain constant with adjustments to exposure time or mA if mAs remains constant.
AFS
Actual Focal Spot
Actual area of the target where incoming electrons hit.
What is the location of x-ray production?
AFS
EFS
Effective Focal Spot
Spot on patient where x-rays hit
99.8% of the energy created at the anode target is converted into?
Heat
What is the term that describes the way the beam travels after being created at the Anode?
Isotropic
Inherent Filtration
Filtration within the tube housing.
0.5mm Al equivalent
Glass
Added Filtration
Filtration outside the tube housing.
2.0mm Al equivalent
Mirror - 1.0mm Al
Al Filter - 1.0mm
Beam-Limiting Device
Variable-Aperture Collimator
Most common device
Beam - Restrictor Examples
Aperture Diaphragm
Cones/Cylinders
Off Focus Radiation
X-rays produced outside of the focal track
Leakage Radiation
X-ray photons escape the lead housing when the housing is compromised.
3 requirements for the production of x-rays
- Source of electrons
- Way to accelerate electrons
- Target
4 requirements for efficient x-ray production
- Source of electrons
- Way to accelerate electrons
- Vacuum
- Target
What is the controlling factor for beam quality?
kVp
What is the controlling factor for beam quantity?
mA
What material is the focusing cup made out of?
Nickel
Which electrode has a negative charge?
Cathode
Which electrode has a positive charge?
Anode
The cathode has a ____ negative potential during exposure.
The cathode has a large negative potential during exposure.
The focusing cup has a ____ negative charge in order to keep the electrons tightly bound.
The focusing cup has a low negative charge in order to keep the electrons tightly bound.
Thermionic Emission
Burning off of electrons due to the heating of a small coil of thoriated tungsten wire.
Why is the X-ray tube made of Pyrex?
To withstand high temperatures.
What is the x-ray tube surrounded by?
Oil Bath
What is the purpose of the oil bath?
To dissipate heat that is generated during x-ray production.
Most common type of x-ray tube failure?
Tungsten Filament Vaporization
What does the Cathode house?
The two filaments and the focusing cup.
What is the small filament (focal spot) used for?
Smaller body parts.
Greater spatial resolution
What is the large filament (focal spot) used for?
Larger body parts.
Needs more electrons that can be turned into x-ray photons.
What term describes when the filament is heated up to be “white hot”?
Incandescent
Why are the filaments coated in thoriated tungsten?
Thorium makes for a more efficient thermionic emission process by burning off 2% more electrons.
Why is the focusing cup made of Nickel?
Nickel has a high heat capacity
What type of charge does the focusing cup have?
Negative
What does the focusing cup house?
The filaments
What is the role of the focusing cup?
Focuses electrons that are produced by thermionic emission.
The focusing cup and the electrons both have a negative charge. Because of this, they _____ each other.
Repel
What do electrons form after thermionic emission?
Thermionic Cloud or Space Charge
What focuses the thermionic cloud/space charge?
Focusing cup
Electrons travel from the cathode to the anode by ____ _____
Kinetic energy
What is kinetic energy converted into once the electrons hit the anode?
X-rays
What percentage of kinetic energy from the electrons is turned into heat?
99.8%