Chapter 1
This German physicist discovered x-rays on November 8, 1895, while experimenting with a Hittorf-Crookes tube.
Who is Wilhelm Conrad Roentgen?
This type of electrical current flows in one direction only and is used in newer dental x-ray machines to produce a constant stream of x-rays.
What is direct current (DC)?
This setting controls the contrast of a dental radiograph, with lower values producing high-contrast, black-and-white images.
What is kilovoltage (kV)?
This component of the dental film packet absorbs unused radiation, reduces backscatter, and helps prevent film fog.
What is the lead-foil backing?
This type of x-ray interaction occurs about 62% of the time in dental radiography and produces a scattered photon and an ejected electron.
What is the Compton effect?
This term describes the process in which an electron is removed from an atom, creating a positively charged atom and a free electron
What is ionization?
This transformer increases ordinary household voltage (110–220 V) to approximately 65,000–100,000 V so electrons can travel from the cathode to the anode.
What is the step-up transformer?
This type of contrast is produced by higher kilovoltage settings and is characterized by many shades of gray, making it useful for detecting subtle changes such as early bone loss or incipient caries.
What is long-scale (low) contrast?
This ANSI-designated film speed is the fastest available and is recommended because it reduces patient radiation exposure.
What is F-speed film?
This term refers to the amount of radiation energy absorbed per unit mass of tissue and is measured in rads or grays (Gy).
What is dose?
Name three properties of x-rays.
What are: they are invisible, travel in straight lines, penetrate opaque tissues, affect film or digital sensors, are produced by electrical energy, and can affect human tissue? (Any three)
This setting controls the penetrating power, or quality, of the x-ray beam.
What is kilovoltage (kV)?
This is the blurred, unsharp border surrounding the edge of a radiographic image that should be kept as small as possible.
What is the penumbra?
This term describes the overall gray appearance of a radiograph caused by exposure to sources other than the primary x-ray beam.
What is film fog?
This radiation protection principle means using the least amount of radiation necessary to obtain a diagnostic image.
What is the ALARA principle (As Low As Reasonably Achievable)?
This heated component at the cathode releases electrons through the thermionic emission effect.
What is the tungsten filament?
This device restricts the size and shape of the x-ray beam, and using its rectangular form can reduce patient radiation exposure by about 60% compared with circular collimation.
What is a rectangular position-indicating device (PID) or rectangular collimation?
List the four conditions that produce the ideal dental radiograph with minimal magnification and distortion.
What are: (1) a small focal spot, (2) a long target-receptor distance (FFD), (3) a short object-receptor distance (OFD), and (4) the receptor parallel to the tooth with the central ray perpendicular to both?
In this type of digital imaging, a sensor sends the radiographic image directly to the computer almost instantly.
What is direct digital imaging?
This type of radiation is always present in the environment and comes from both natural and artificial sources.
What is background radiation?
This type of x-ray radiation is produced when a high-speed electron slows down or is deflected by the nucleus of a tungsten atom.
What is bremsstrahlung (general or braking) radiation?
This term describes the thickness of aluminum required to reduce the intensity of an x-ray beam by 50%, making it a measure of beam quality and penetration.
What is the half-value layer (HVL)?
According to this law, if the target-receptor distance is doubled, the intensity of the x-ray beam decreases to this fraction of its original intensity.
What is one-fourth (1/4)?
These screens emit light when struck by x-rays, reducing the exposure time needed for extraoral radiographs.
What are intensifying screens?
These radiation effects occur by chance, have no threshold dose, and include the risk of radiation-induced cancer.
What are stochastic effects?