This glossary is a list of some of the technical terms used on this website.  Please contact us if there are other words or phrases you would like us to add.

[O] - [Z]

 
Oncology: The science dealing with the physical, chemical, and biologic properties and features of tumors including causes, development and treatment.
 
Panoramic Imaging: The first step in the examination of the patient's dental anatomy is to take a panoramic exposure. A panoramic radiograph allows a dentist to see the entire structure of a mouth in a single image.  Within one large film, panoramic X-rays reveal all of the upper and lower teeth and parts of the jaw.  This panoramic exposure is a dental overview that serves as basis for further examinations that will be used to diagnose and treat the patient.
 
Photometer: A photometer is a meter that measures visible Illuminance light levels.  The basic unit of luminance measurement is Candela per square meter (cd/m²).  Both Lux and Candelas measure luminous intensity from a specific direction.
 
Portal Imaging: The aim of radiation oncology is to deliver a high dose of radiation to the tumor while preserving normal surrounding tissues.  Verification of the proper positioning and setup of the patient relative to the beam has traditionally been performed by placing an X-ray film beyond the patient to produce an image with the exit radiation, called a port film. 
Electronic portal imaging devices (EPID) were introduced A few years ago.  They were first used merely as a replacement for port films, but can also be used to exploit the numerous advantages of digital images, in particular the possibility of performing on-line verification.
 
QE - Quantum Efficiency: The ratio of the number of output quanta to the number of input quanta.
 
Radiography: Photography that uses radiation other than visible light.
 
Radiometer: A Radiometer is a meter that measures irradiance of invisible light levels, expressed in Watts per square centimeter (W/cm²).
 
Resolution: This is a measurement of the imaging components ability to reproduce signal/object detail.  AST specifies resolution as the frequency (Line-pairs per mm) at 10% contrast.
 
Therapeutic Radiography: Radiotherapy is another term for therapeutic radiograph.  It is a treatment for patients with cancer and some non-malignant disorders which utilises the biological effects of high energy x-rays and other ionising radiation.  A course of radiotherapy may be given on its own or combined with other treatments such as surgery and chemotherapy.
 
X-ray Imaging: An X-ray image is essentially a shadow image of the object.  Different materials attenuate the x-ray beam differently and thus the number of x-rays passing through the object depends on the materials in the path of the beam. Bone absorbs x-rays well and thus attenuates the beam.  Thus the areas falling in the shadow of the bone appear light or underexposed on an x-ray film image because relatively few x-rays exit the patient and little light is produced in the phosphor screen.  Conversely, areas falling under the shadow of soft tissue (e.g. fat/muscle) appear dark on an x-ray image because large number of x-rays exit the patient and a lot of light is given off from the phosphor screen to overexpose the film.
 
X-ray Radiation: X-rays were discovered accidentally on the 8th of November 1895 when Wilhelm Conrad Roentgen noticed his cathode ray generator was causing a screen across the room to glow.  Roentgen tested the properties of these new `rays' by holding up materials in front of the screen and found the bones of his hand were clearly silhouetted in a faint outline of flesh.  X-ray radiation has a much shorter wavelength than light enabling it to penetrate through objects (approximately .01 nanometers to 200 nanometers).  Higher density materials such as metals have high x-ray absorption coefficients, whereas plastics and water-based substances have lower x-ray attenuation coefficients.  They are commonly produced by bombarding a metal target with high speed electrons.

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