X-ray Tube Part 2 Flashcards
2 principal parts of Induction Motor
Rotor
Stator
Outside part of the enclosure
Stator
Consists of series of electromagnets equally spaced around the neck of the tube
Stator
Stator may either be
Permanent magnet or
Electromagnet
An electromagnetic coil of copper wire that is connected to a power supply
Stator
Sends pulses of energy to the stator which in turn induces motion into the anode assembly
Rotor controller
Wire that transfers rotor controller to the stator
Stator cord
Shaft inside the enclosure
Rotor
Rotor is made of
Bars of copper and soft iron
Works through electromagnetic induction
Induction motor
Production of voltage across a conductor moving through a magnetic field
Electromagnetic induction
Covert electricity into mechanical energy
Electric motor
Current in each stator wirings induces
Magnetic field
Are energized sequentially so that induced magnetic field rotates on the axis of the stator
Stator
Short delay allows
The rotor to accelerate to its designated rpm while filament is heated
Where the high voltage electrons hit the anode
Focal spot
Focal spot is also known as
Target
Focus
Focal point
Area around the anode that is exposed to electrons
Actual focal spot
Area projected onto the patient
Effective focal spot
Impacts the geometric resolution of the X-ray image
Focal spot
Smaller the focal spot
Better spatial resolution
Designed incorporated into the X-ray tube targets allowing large area of heating while maintaining a small focal spot
Line Focus principle
Angling of the target
Line focus principle
Diagnostic tube target angles allows
5 to 20 degrees
Reduce the effective area of the focal spot
Line focus principle
Effective focal spot is controlled by
Size of the actual focal spot
Anode target angle
Electrons can rebound and interact with other areas
Off-Focal Radiation
Control of Off Focal Radiation
Diaphragm (place bet the tube)
Collimator (reduce off focus rays)
Produces two off focal spot sizes because of two diff target angles
Biangular Targets
Radiation intensity on the cathode side is greater than the anode side
Anode-Heel Effect
Heel effect is considered when
Positioning areas with diff thickness or density
Placed over the area if greater density
Cathode side
In full supine X-ray
Anode should be up
Cathode down
Under the control of radiologic technologist
X-ray tube life
Extended by using minimum radio graphic factors
Tube life
Three forms of tube cooling
Radiation
Convection
Conduction
Anode may glow red hot and emit infrared energy
Radiation
Heat is conducted through narrow molybdenum neck to the rotor assembly
Conduction
Glass enclosure raises temperature of the oil bath
Convection
Warming the anode through a series of exposure and increasing the kVp settings, the anode will build up heat
Tube warm-up procedure
Charts that guide radiologic technologist on the use of X-ray tubes
X-ray tube rating charts
Three types of X-ray tube rating charts
Radiographic rating chart
Anode cooling chart
Housing cooling chart
Conveys which radiographic technique is safe or unsafe
Radiographic rating charts
A guide regarding the most common technical factor combinations that can be used without overloading the tube
Radiographic rating charts
There are diff charts for
Filament use
Speed of the anode
Target angle
Voltage rectification
Given mA, any combination of kVP and time that lies below the mA curve
Safe
Lies above the curve
Unsafe
Has limited capacity for storing heat
Anode
Thermal energy is measured in
Heat units (HU)
Anode cooling chart: single-phase formula
HU = kVp x mA x time
Anode cooling chart: three-phase / high frequency formula
HU = 1.4 x kVp x mA x time
Heats in Joules formula
heat (J) = w x kVp x mAs
1 HU =
1.4 J
Used to determine the length of time required for complete cooling after any level of heat input
Anode cooling chart
Maximum of 350,000 HU
15 minutes to cool down
Tube housing have the capacity of ___ HU
1 to 1.5 million
Complete cooling of tube housing
1 to 2 hours
Permits the calculation of the time necessary for the housing to cool enough for additional exposures to be made
Housing Cooling charts
Turn the anode
Induction Motor