Refresher Part II Flashcards
When x-yr is centered above the examination table at the standard SID, the x-ray is in a […]
Preferred detent position
Support system equipped in interventional radiology suites
Ceiling mounted and provide for very flexible x-yr tube positioning
C-Arm support system
External components of X-ray tube
Protective housing
Glass or metal enclosure
[protective housing] Special section where where x-rays are emitted
Window
X-rays that are emitted through the window
Useful beam
X-rays that escape through the protective housing
Leakage radiation
Level of reduction of leakage radiation in the protective housing
Less than 1 mGa/hr at 1 m
Guards against excessive radiation exposure and electric shock
Provides mechanical support and protects damage caused by rough handling
Protective housing
Function of oil in X-ray tube
Serves as both an insulator against electric shock and as a thermal cushion
Made of Pyrex and able to withstand the tremendous heat generated
Maintains a vacuum inside the tube which allows for more efficient production and longer tube life
Glass enclosure
Two electrodes in X-ray tube
Cathode ad anode
Maintain constant electric potential between the electrons of the tube current and the enclosure
Metal enclosure
Internal components of an X-ray tube [cathode]
Filament
Focusing cup
The negative side of the X-ray tube
Cathode
It is a coil of wire approx. 2mm in diameter and 1 or 2 cm long
Emits electrons when it is heated
Filament
The phenomenon when the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms are “boiled off” and ejected from the filament
Thermionic emission
Makes up the filament
Provides for higher thermionic emission
Does not vaporize easily
Melting point is 3410 degrees
Thoriated tungsten
1% to 2% added to tungsten filament to enhance efficiency of thermionic emission and prolongs tube life
Thorium
Metal shroud where the filament is embedded
Negatively charged
Focusing cup
Effectiveness of focusing cup is determined by […], […] and […]
Size, shape and position of the filament
Designed to be turned on and off rapidly
Used in portable capacitor discharge imaging systems
Grid-controlled tubes
Cloud of electrons
Space charge
Phenomenon where space charge makes it difficult for subsequent electrons to be emitted bu the filament because of electrostatic repulsion
Space charge effect
Positive side of X-ray tube
Conducts electricity and radiates heat and contains target
Anode
Types of anode
Stationary and rotating anode
Anode tube used in dental and portal imaging systems
Stationary anode
Internal components [anode]
Target
Rotating anode
Three functions of anode
Electrical conductor [receives electrons from emitted by cathode]
Mechanical support
Thermal dissipater
Most common anode materials
Copper, molybdenum and graphite
Material of choice for target
Tungsten
Three main reasons [tungsten material for target]
- Atomic number -74 [high efficiency x-ray production]
- Thermal conductivity
- High melting point - 3400 degrees C
Target material for special X-ray tubes [mammography]
Molybdenum and rhodium - low k characteristic, low atomi number
[atomic number]
Tungsten
Molybdenum
Rhodium
74
42
45
Allows the electron beam to interact with much larger target area; therefore, heating of anode is not confined to one small spot
Rotation anode
Used to turn the anode
Electromagnetic induction motor
Induction motor two principal parts - separated by glass enclosure
Stator and rotor
[induction motor] part outside the glass
Consists of a series of electromagnets equally spaced around the neck of the tube
Stator
[induction motor] part inside enclosure
Shaft made of bars of copper and soft iron fabricated into one mass
Rotor
