X-Ray Tube Components and Principles

Polarities and Primary Components of the X-ray Tube

  • X-ray Tube Polarities

    • Positive side: The positive side of the x-ray tube is the Anode.

    • Negative side: The negative side of the x-ray tube is the Cathode.

  • The Glass Envelope

    • Role: Its primary functions are containment and the maintenance of a vacuum environment.

  • The Tube Housing

    • Role: It acts as an insulator and prevents radiation leakage.

The Cathode Assembly

  • Components of the Cathode: The cathode end of the tube contains the filament and the focusing cup.

The Anode Assembly and Material Composition

  • Types of Anodes: There are two primary types of anodes:

    • Rotating

    • Stationary

  • Anode Material Composition:

    • Material: Tungsten.

    • Rationale for use: Tungsten is the chosen material because it has a high atomic number, which means it possesses a high melting point suitable for high-heat environments.

The Induction Motor

  • Design and Position:

    • Stator: Located on the outside of the tube.

    • Rotor: Located on the inside of the tube.

  • The Stator:

    • Defined as an electric motor that turns the rotor at high speeds.

    • It creates a rotating magnetic field when energized.

  • The Rotor:

    • Spins the anode to allow for heat to be spread out across a larger area.

  • Motor Bearings:

    • These provide support and enable the rotation of the motor components.

The Anode Heel Effect

  • Definition: The Anode Heel Effect is the variation in x-ray intensity between the anode and cathode sides of the tube.

  • Intensity Distribution:

    • The Cathode side of the x-ray tube possesses the more intense beam.

  • Physics of the Anode Heel Effect:

    • X-rays produced deeper within the anode material must pass through more of that material to exit.

    • This material absorbs some of the beam, and this absorption reduces the overall intensity on the anode side.

  • Impact of Anode Angle:

    • If the degree of the anode angle decreases, the anode heel effect increases.

    • Reason: A smaller angle means that x-rays are required to travel through more anode material to exit the tube.

The Line Focus Principle

  • Definition: This principle involves using a large Actual focal spot to spread heat while maintaining a small Effective focal spot, which is necessary for better image detail.

  • Size Comparison: The Actual focal spot is larger than the Effective focal spot.

  • Spatial Orientation:

    • Actual focal spot: Located on the surface of the anode target.

    • Effective focal spot: The focal spot that is projected towards the patient (ptpt).