RAD 111: X-Ray Tube, Production, and Heat Units

Comprehensive vocabulary flashcards covering x-ray tube components, circuitry, heat unit calculations, and the physical principles of x-ray production based on RAD 111 lecture notes.

Autotransformer

A kVp selector that operates on the principle of self-induction with a variable turns ratio.

Step-Down Transformer

Also called a filament transformer, it operates on mutual induction to supply high current to the cathode filament wire with a fixed turns ratio.

Step-up Transformer

A high-voltage transformer that operates on mutual induction to change volts to kilovolts with a fixed turns ratio.

Copper losses

Transformer efficiency loss caused by resistance in the wires, represented by the formula $I^2R$.

Iron Losses

Transformer efficiency losses categorized as Hysteresis and Eddy Current.

Rectifier

A component located between the secondary side of the step-up transformer and the tube that changes AC to pulsating direct current.

Voltage Ripple

The variation in voltage across the x-ray tube; values include $100\%$ for half-wave/full-wave, $14\%$ for 3-phase 6-pulse, $4\%$ for 3-phase 12-pulse, and $1\%$ for High Frequency.

Cathode assembly

The negative electrode of the x-ray tube containing the focusing cup and filament wires; it serves as the source of electrons and focuses the electron stream.

Thoriated tungsten

Material used for filament wires due to its high melting point and low vaporization.

Thermionic emission

The process of heating the filament wire to release electrons from its surface.

Space charge effect

The tendency of the space charge (electron cloud) to limit the further emission of electrons from the filament.

Focusing Cup

A negatively charged component made of nickel, stainless steel, or molybdenum that focuses electrons into a narrow beam.

Anode assembly

The positive electrode that attracts and stops electrons at the target; it is the site of x-ray production and heat dissipation.

Tungsten (Z=74)

The primary anode target material for general x-ray units, chosen for its high atomic number, high melting point ($3370^{\circ}\text{C}$), and thermal conductivity.

Rhenium (10%)

An alloy added to the tungsten anode target to prevent pitting of the anode disk.

Molybdenum (Z=42)

Material used for anode targets in mammography units and for the anode stem.

Focal Spot Blooming

An increase in focal spot size due to electron repulsion in the tube current, typically occurring with high mA and low kVp settings.

Induction Motor

Device that rotates the anode, consisting of a rotor (inside the glass envelope) and stators (electromagnets outside the glass envelope).

Line Focus Principle

The relationship between the actual focal spot and the effective focal spot; diagnostic tube target angles vary from $7^{\circ}$ to $20^{\circ}$.

Anode Heel Effect

A variation in the intensity of the x-ray beam between the cathode and anode sides, where the cathode side is more intense (up to $120\%$) and the anode side is less intense (as low as $75\%$).

Off-Focus (extrafocal) Radiation

Low-intensity x-ray emission produced when electrons strike areas of the anode other than the focal spot, degrading image quality.

Leakage Radiation Limit

The tube housing must allow no more than $100\,\text{mR/hr}$ of radiation to escape when measured at $1\,\text{meter}$ from the source at maximum output.

Heat Units (HU) Formula

$HU = mA \times \text{sec} \times kVp \times \text{generator factor} \times \text{\# exposures}$.

Generator Factors

Constants used for HU calculation: Single phase ($1$), 3-phase 6-pulse ($1.35$), 3-phase 12-pulse ($1.41$), and High frequency ($1.45$).

Bremsstrahlung (Brems) Radiation

General or 'white' radiation produced by the deceleration of an electron near the nucleus, creating a polyenergetic/heterogenous beam.

Characteristic Radiation

Line radiation produced by the ionization of an inner K-shell electron followed by a characteristic cascade; requires at least $70\,\text{keV}$ for tungsten.

X-Ray Quality

Refers to the energy and penetrating ability of x-ray photons, influenced by kVp, filtration, and circuit waveform.

X-Ray Quantity

Refers to the amount or intensity of x-ray photons, directly affected by mAs, mA, time, kVp, and filtration.

Tube Filtration

The addition of filters (e.g., Al) to the beam which increases beam quality and decreases beam quantity by removing low-energy photons.