14/10/2025
An X-ray tube is a key component in generating X-rays for imaging and therapeutic purposes. It consists of several key components, each with a specific role in the X-ray production process. Here’s an overview of the main components of an X-ray tube and the effects of their operation:
1. Cathode (Negative Electrode)
Components:
Filament (Heater): The filament is a thin wire, usually made of tungsten, which when heated by an electric current, emits electrons via thermionic emission.
Focusing Cup: A metal cup, often made of molybdenum or nickel, that focuses the emitted electrons into a narrow beam toward the anode.
Effects:
The cathode's primary role is to generate and direct the electrons toward the anode. As the filament heats up, it emits electrons which are accelerated across the tube towards the positively charged anode.
2. Anode (Positive Electrode)
Components:
Rotating Anode (in high-powered systems): A disc made of tungsten, sometimes alloyed with rhenium, that rotates to dissipate the heat generated by electron impact. In some systems, a stationary anode is used, but rotating anodes are more common in higher-power systems.
Target (Focal Spot): The area on the anode where the electron beam is focused. When electrons hit the target, they produce X-rays. The efficiency of X-ray production is closely related to the material of the anode and the angle of the target surface.
Effects:
When electrons from the cathode collide with the target of the anode, their kinetic energy is converted into X-rays and heat. About 99% of the energy goes into heat, while only about 1% is converted into X-rays. The rotating anode helps spread out the heat generated during the process, preventing damage to the tube.
3. Glass or Metal Envelope
Components:
The X-ray tube is enclosed in a vacuum-sealed glass or metal envelope (often made of borosilicate glass or metal alloys).
The envelope maintains the vacuum environment inside the tube, which is necessary for the free movement of electrons without interference from air molecules.
Effects:
The vacuum ensures that the electrons can travel without scattering or losing energy due to air resistance. The envelope also contains the insulating oil that helps dissipate heat and protect the components.
4. High Voltage Supply
Components:
The high-voltage generator creates a potential difference between the cathode and anode (typically 30 kV to 150 kV, depending on the X-ray system).
This voltage accelerates the electrons toward the anode.
Effects:
The higher the voltage, the greater the energy of the electrons when they strike the anode, which results in higher-energy X-rays. This is crucial for imaging dense tissues, like bone, or for therapeutic X-ray treatments.
5. X-ray Tube Housing and Shielding
Components:
The tube is housed in a protective metal casing, often filled with oil that serves to absorb heat and act as an electrical insulator.
Lead shielding is used to block unwanted radiation (leakage radiation), ensuring that X-rays only exit through a window (the port).
Effects:
This shielding protects the operator and patient from unnecessary exposure to radiation. Only the X-rays directed at the imaging receptor (e.g., film, detector) or the area to be treated are allowed to pass through.
6. X-ray Window
Components:
This is a thin section of the tube housing that allows X-rays to exit while keeping the vacuum sealed inside the tube.
Effects:
The window is typically made of a material (like beryllium or glass) that is transparent to X-rays but resistant to the heat generated by the tube. The X-rays that exit the tube pass through this window and are directed to the patient or imaging system.
7. Filtration
Components:
Filtration Materials: Typically, a layer of metal (such as aluminum) is placed in the path of the X-rays to remove low-energy (soft) X-rays that contribute to patient dose but do not improve image quality.
Effects:
Filtration ensures that only higher-energy X-rays (which are more penetrating and useful for imaging) reach the patient, reducing unnecessary radiation exposure. It helps to optimize the image quality while minimizing radiation risk.
X-ray Production Process and Effects
Electron Acceleration:
When the filament in the cathode is heated, it releases electrons (thermionic emission). These electrons are accelerated across the tube by the high voltage to the anode.
Interaction with Anode Target:
As the high-speed
