Introduction to Radiology

Introduction to Radiology

• Radiology is the study of the diagnosis, treatment, and research applications of high-energy radiation.
• Dental radiography uses X-ray radiation to create images of the inside and outside of the oral cavity.
• Radiological examinations are crucial for dentists to get information beyond what a clinical examination or patient history can provide.
• This information aids in diagnosis and treatment plan development.

Nature of Radiation

• Radiation transmits energy through space and matter, existing in two forms: electromagnetic and particulate.

X-Ray Radiation

• Discovered by Roentgen in 1895, X-ray radiation travels as pure energy in the form of X-ray photons or quanta.
• X-ray photons travel in sine waves, with the distance between wave crests called wavelength, measured in Angstroms (A˚).
• Diagnostic radiography uses X-ray photons with wavelengths between 0.1-0.5 A˚.

Photon Energy

• The energy contained in each photon is called photon energy, which depends on:
  • Wavelength
  • Frequency of the X-ray
• Higher frequency X-rays have shorter wavelengths and more energy than lower frequency/longer wavelength X-rays.

Comparison between X-rays and Light

• Both belong to the electromagnetic radiation family.
• Both travel in straight lines at the same speed (186,000 miles per second).
• Both affect photographic films and cause them to blacken.
• Both are not affected by magnetic fields.
• Both cast shadows of objects in the same manner.
• X-rays can penetrate objects that light cannot.
• X-rays can ionize atoms.
• X-rays can produce light (blue light) when hitting some objects, a phenomenon called fluorescence.
• X-rays are invisible.

Components of the X-Ray Machine

• The primary components are the X-ray tube and its power supply, contained within the tube head.
• A control panel lets the operator adjust exposure duration, energy, and exposure rate.
• The tube is recessed within the tube head to increase the source-to-object distance and minimize distortion.

X-Ray Tube

• The X-ray tube consists of a cathode and an anode within an evacuated glass envelope or tube.
• The tube's glass is leaded to prevent the generated X-rays from escaping in all directions, while a window of unleaded glass allows X-rays to exit.
• The cathode consists of a filament and a focusing cup.
  • The filament, a coil of tungsten wire, is the source of electrons within the X-ray tube and contains approximately 1% thorium for electron emission.
  • The focusing cup directs emitted electrons in a narrow beam toward the anode's focal spot.
• The anode consists of a tungsten target embedded in a copper stem.
  • The target converts the kinetic energy of colliding electrons into X-ray photons.
  • The copper block functions as a thermal conductor to remove heat from the tungsten, preventing melting.
  • The conversion of electron kinetic energy to X-ray photons is inefficient, with less than 1% converted to X-rays, the rest becoming heat.

Target Material Selection

• Ideal target material characteristics include:
  • High atomic number for efficient X-ray production.
  • High melting point to withstand the heat generated.
  • High thermal conductivity to dissipate heat from the target.
  • Low vapor pressure at operating temperatures to maintain vacuum in the tube.

Collimation

• A process to control the size and shape of the X-ray beam.
• In diagnostic radiography, the X-ray beam diameter at the patient's skin surface should not exceed 2.75 inches for a circular beam or 1.5 × 2 inches for a rectangular beam.

Filtration

• Used to remove the long wavelength (soft) X-rays that are less useful in diagnostic radiology.
• X-rays must be able to penetrate dental hard tissues (teeth and bone).
• Aluminum filters absorb long wavelength X-rays, resulting in a beam mainly consisting of high-energy (hard) photons with higher penetrating power.
• Filter Types:
  • Inherent filtration: built-in to the X-ray machine during manufacturing (glass wall, insulating oil, metal housing).
  • Added filtration: using an extra aluminum sheet filter.
  • Total filtration: inherent filtration + added filtration

Types of Radiation

• Central ray: X-ray photons travelling at the center of the radiation beam, used for positioning and locating the beam.
• Bremsstrahlung radiation: radiation produced when the projectile electron is slowed by the electric field of the target atom nucleus.
• Characteristic radiation: radiation produced when an outer shell electron fills a void (empty orbital) in an inner shell.
• Primary radiation: Radiation emerging from the X-ray machine in the form of a collimated, useful X-ray beam.
• Secondary radiation: Radiation resulting from the interaction of the primary beam with matter.
• Leakage radiation: X-rays escaping through the protective housing, resulting in unnecessary exposure to the patient and radiologic technologist and having no value in diagnostic radiology.

X-Ray Interaction Terms

• Scattering: the change in direction of a photon, with or without a loss of energy.
• Absorption: deposition of energy within matter, removing energy from the beam.