Introduction to Radiology

Study Notes

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.

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

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˚.

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.

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.

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.

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.

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.

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.

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

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.

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.