X-ray Tube Components and Function Quiz & Flashcards

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Questions and Answers

What is the primary function of the focusing cup in an x-ray tube?

To focus the electron beam onto the anode, preventing electrostatic repulsion and allowing for a targeted spot on the anode.

What is the purpose of the anode disc in an x-ray tube?

To convert the kinetic energy of the electron beam into x-rays, while also providing thermal dissipation and mechanical support for the target.

What determines the voltage in an x-ray tube?

The kVp, which decides the voltage, and the electrical supply (mA) to the filament.

What is the purpose of the rotor in an x-ray tube?

To rotate the anode at high speeds (3000-10000 rev/minute) to prevent repetitive targeting of electrons on the anode. Signup and view all the answers

What are the three main functions of the anode in an x-ray tube?

Electrical conduction, thermal dissipation, and mechanical support for the target. Signup and view all the answers

What determines the focal spot size in an x-ray tube?

The size, shape, and position of the filaments in the focusing cup. Signup and view all the answers

Describe the process of thermionic emission in the production of X-rays.

Electrons from the cathode filament are accelerated to high speeds by a potential difference between the cathode and anode, resulting in the emission of electrons. Signup and view all the answers

What is the primary difference between Bremsstrahlung and characteristic X-rays?

Bremsstrahlung X-rays are produced when an electron beam travels close to the nucleus, resulting in the loss of energy and re-emission as X-rays, whereas characteristic X-rays are produced when an electron beam hits the tungsten atom and causes an inner electron to be ejected. Signup and view all the answers

What is the relationship between the energy and wavelength of X-rays?

The energy and wavelength of X-rays are inversely proportional, with higher energy corresponding to shorter wavelengths. Signup and view all the answers

How do X-rays interact with matter in medical imaging?

X-rays transfer energy to matter through electrical, electromagnetic, and chemical means, resulting in the creation of a latent image on the imaging receptor. Signup and view all the answers

What is the purpose of the focusing cup in the X-ray production process?

The focusing cup targets the electrons emitted from the cathode filament towards the anode, ensuring that they are all accelerated to high speeds. Signup and view all the answers

What is the typical energy range of diagnostic X-rays?

The typical energy range of diagnostic X-rays is 30-150 kVp. Signup and view all the answers

Study Notes

X-ray Tube Components

2 primary internal components: Cathode and Anode
Secondary external components: Glass enclosure, Cathode assembly, and Anode assembly

Cathode Assembly

Focusing cup:
- Focuses the beam to the anode
- Prevents electron beam from repelling itself
- Targets a spot on the anode
- Effectiveness depends on size, shape, and position of filaments in the cup
Filament:
- Receives electrical supply (mA)
- kVp determines the voltage

Anode Assembly

Anode:
- Tungsten-outer layer (focal track)
- Internal layers: generally graphite, for dissipating heat and lower mass density
- Bevelled edge forms anode angle at the target surface (focal track)
- Angled at 5-20 degrees for x-ray photons to exit the tube
Anode stem:
- Connects rotor and high tension cables
Rotor:
- Rotates at 3000-10000 rev/minute in high capacity x-ray tube
Anode disc:
- Tungsten focal track
- Prevents repetitive targeting of electrons on anode

Focal Spot Size

Fine:
- Used for smaller body parts
- Better spatial resolution
- Used for fine details
Broad:
- Used for large body parts
- More heat is generated

Anode Functions

Electrical conductor
Thermal dissipater
Mechanical support for the target

X-ray Formation

Select voltage, current (mAs to filament), and focus
mA sends current to filament, starting the process of sending electrons to anode
Apply high voltage, creating potential difference between anode and cathode, pulling electrons to anode
Focusing cup targets electrons at the anode

X-ray Spectrum

Beam typically consists of a continuous spectrum of x-ray photon energies
Bremsstrahlung:
- Diagnostic energy range: 30-150kVp
Characteristic (peak):
- 69kVp (for tungsten target)

Factors Affecting X-ray Spectrum

Bremsstrahlung:
- Electron beam travels close to nucleus
- Proton causes electron to change direction and lose speed and energy
- Loss of energy reappears as bremsstrahlung x-rays
Characteristic x-rays:
- Electron beam hits the tungsten atom, causing an inner electron to be ejected (ionisation)
- An outer electron fills the gap, releasing energy as x-ray photons

Properties of X-rays

Short wavelength and high frequency
Higher the energy, shorter the wavelength
Wavelength and energy are heterogeneous
Electromagnetic radiation
Travels through air in straight lines
Divergent beam once emitted from x-ray tube
Energy transfer:
- Electrical: in x-ray machine (control at console)
- Electromagnetic: when x-rays are produced at the anode
- Chemical: conversion to electrical signal at image receptor/detector

Medical Imaging

X-rays pass through patient and are captured on the imaging receptor
Creates a latent image, which is then processed through chemical energy to produce a 2D x-ray image

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Description

This quiz covers the primary internal components and secondary external components of an X-ray tube, including the cathode, anode, and cathode assembly. Learn about the functions of the focusing cup and filament in X-ray production.