Introduction to X-Ray Tube

Overview

X-ray tubes are used in various radiology modalities: radiography, fluoroscopy, mammography, and computed tomography.
They have the same basic function and components across these modalities.

Function: Creates free electrons through thermionic emission.
Charge: Negatively charged.
Structure: Contains a small tungsten filament.
- Process:
  - High amperage current heats the filament.
  - Creates a cloud of free electrons called the space charge.
- Limitations:
  - Space Charge Effect limits the number of free electrons to about 1,000 mA.
  - Dual focus tubes have two cathode filaments for small and large mA.
  - Small filament: 1 cm, used for small exposures.
  - Large filament: 2 cm, used for large exposures.
Focusing Cup: Helps focus the electron beam to enhance spatial resolution.

Function: Absorbs electrons and generates x-rays.
Charge: Positively charged.
Types:
- Stationary Anodes:
  - Simple design with low heat capacity.
  - Used in dental x-ray machines.
- Rotating Anodes:
  - Rotating disk spreads electrons over a larger area.
  - High heat capacity, essential for general radiography.

Function: Creates an air-free vacuum around the cathode and anode.
Material:
- Borosilicate glass (Pyrex) for heat tolerance.
- Alternatives include metal or ceramic.
Importance: Prevents oxidation and corrosion.

Purpose: Prevents leakage of x-rays, absorbs all except directed x-rays towards the patient.
Design Requirement: Limits leakage radiation to a maximum of 0.88 milligray per hour.

Function: Turns the rotating anode without contact.
Components:
- Stators: Electromagnets that induce rotor movement.
- Rotor: Tube shaft attached to the anode disk.
- Bearings: Allow free rotation of the rotor.

Understanding the components and functions of the x-ray tube is essential in radiology.
Each component plays a crucial role in the efficient and safe production of x-rays.