What is the purpose of Protective Housing?
Shield against leakage radiation, reduce mechanical shock to the tube insert, isolate high-voltage exposure, contribute to cooling of the tube insert
Must be <100 mR/hour at a distance of 1m (federal regulation)
What is the Anode Heel Effect?
Variation in X-Ray beam intensity with greater intensity on the cathode side and a decrease on the anode side
Caused by incidental absorption of photons by target material on the anode side
How can the Anode Heel Effect be utilized in practice?
Align thicker body part near cathode end, use larger target bevel to permit wider field of view along the longitudinal axis
Typical angles for target bevel are 5-20 degrees
Define the Line Focus Principle.
The relationship between actual and effective focal spots resulting from the target angle (bevel)
Affects image detail sharpness
What are Actual and Effective Focal Spots?
- Actual Focal Spot: Measured at right angles to the anode
- Effective Focal Spot: Measured at right angle to the long axis of the tube
EFS is always smaller than AFS
What happens when the rotor is depressed in the x-ray tube?
The anode disk rotates, current flows through the filament, heating and thermionic emission vary with mA selection
Depressing the exposure switch applies voltage between cathode and anode
What is the effect of a more efficient generator on the x-ray beam?
Increases beam quantity and quality, with a greater increase in high energy photons compared to low energy photons
What is the Total Filtration requirement for a Diagnostic Tube?
2.5 mm Al equivalent
This includes both inherent and added filtration
What is Half Value Layer (HVL)?
Amount of aluminum needed to reduce beam intensity by half of the original value
Indicator of filtration and beam quality
What is the composition of the anode target disk?
Mo/graphite base with a tungsten-rhenium surface
Tungsten has a Z of 74 and a melting point of 3400°C
Identify the three necessary conditions for x-ray production.
- Source of electrons
- Acceleration of free electrons
- Deceleration of high-speed electrons
What is the function of the cathode in the x-ray tube?
Serves as the negative terminal, containing a filament that emits electrons when heated
The filament is typically made of thoriated tungsten
What are the primary causes of tube failure?
- Filament vaporization
- Vacuum loss
- Focal track vaporization
- Target pitting
- Bearing wear
What is the relationship between mA and beam quantity?
mA and time (mAs) directly affect beam quantity, with proportional changes resulting in changes in the height of the Bremsstrahlung curves
What are the three methods of heat transfer?
- Conduction
- Convection
- Thermal Radiation
What is Off-Focus Radiation?
Result of photons arising from electron or x-ray interactions occurring elsewhere in the tube, not at the target
It reduces image quality and is generally absorbed by housing
What is the maximum heat load for x-ray tubes in heat units?
350,000 heat units
Calculated as mA x time x kV x generator constant
Define Bremsstrahlung interactions.
Interactions where the projectile electron slows down due to the positive field of the nucleus, resulting in the loss of kinetic energy that reappears as x-ray photon energy
What is the emission spectrum?
A visual display (graph) of x-ray emissions from the tube, representing the quantity (mAs) and quality (kV) of the primary beam
How does kV affect the x-ray beam?
Increased kV leads to higher beam quality and quantity, increases the speed of electrons, and shifts the average beam energy upward
Filtration hardens the beam by removing low energy photons
What does KE loss re-appear as?
x-ray photon
This refers to the transformation of kinetic energy into x-ray photons during electron interactions with the nucleus.
What is a Bremstrahlung photon?
A type of photon produced when an electron loses energy due to proximity to a nucleus
Bremstrahlung translates to ‘braking radiation’ in German, indicating the process through which the photon is generated.
What factors determine photon energy?
- Proximity of electron to nucleus
- Amount of energy lost by the electron
- Extent of course change
What type of current is supplied from the street in an x-ray circuit?
Low kilovoltage in AC waveform
This low voltage is essential for the initial stages of the x-ray production process.
