Radiology Lecture 1: Physics of Radiation

Study Notes

Introduction to Radiology

Radiology is the science that deals with diagnosis, therapeutic, and research applications of high-energy radiation.
Dental radiography is a process of image production for an object through the use of x-radiation.
Radiologic examination is an integral component of the diagnostic procedure.

Nature of Radiation

Radiation is the transmission of energy through space and matter.
It may occur in two forms: electromagnetic and particulate.
Electromagnetic spectrum: x-ray (blue) have energies of 10 to 120 keV, and Magnetic resonance (MR) imaging uses radio waves (orange).
X-ray was discovered by Roentgen in 1895 and travels in a wave motion called sine-wave.
The basic unit is x-ray photon or quantum, and the distance between the crests of these waves is called wave-length measured in Angstrom units (Å).

Production of Radiation (X-ray Machine)

The x-ray machine consists of a cathode and an anode situated within an evacuated glass envelope or tube.
The glass of the tube is leaded to prevent the generated X-ray from escaping in all directions.
The cathode consists of a filament and a focusing cup, and the filament is the source of electrons within the x-ray tube.
The anode consists of a tungsten target embedded in a copper stem, which converts the kinetic energy of the colliding electrons into x-ray photons.
The tungsten target has a high atomic number, high melting point, and high thermal conductivity, making it an ideal target material.
The x-ray tube is evacuated to prevent collision of the fast-moving electrons with gas molecules, which would significantly reduce their speed.

X-ray Tube Components

Focusing cup: a negatively charged concave molybdenum bowl that directs electrons into a narrow beam.
Filament: a coil of tungsten wire that emits electrons when heated.
Anode: a tungsten target embedded in a copper stem that converts kinetic energy into x-ray photons.

Types of Radiation

X-ray photons can pass through the atom without any change.
Coherent scattering (Thompson scattering): low-energy x-ray photon interaction with an atom, resulting in a change in direction but not energy loss.
Compton effect: moderate-energy x-ray photon interaction with a free or loosely bound outer shell electron, resulting in ionization, energy reduction, and direction change.
Photoelectric effect: high-energy x-ray photon interaction with an inner-shell electron, resulting in the ejection of a high-energy photoelectron.

X-ray Beam Control

Added filtration: using an aluminum sheet as an extra filter to reduce the intensity of the x-ray beam.
Collimation: a process used to control the size and shape of the x-ray beam using diaphragms, metal cylinders, cones, and rectangular tubes.

Collimators

Diaphragms: metal plates or disks with a hole in the center that determines the shape of the x-ray beam.
Collimator shapes: round or rectangular, controlling the diameter of the x-ray beam at the skin surface.

Half-Value Layer

A method of monitoring the penetration quality of the x-ray beam.

Description

This quiz covers the introductory concepts of radiology, including the physics of radiation, types of radiation, production of radiation, and its interaction with matter. It also touches on dental radiography and radiologic examination. Test your understanding of these fundamental principles!