Radiography



 Radiography is the use of x-rays to view unseen or hard to image objects. The use of non-ionizing radiations (food irradiation, or radiation processing. [1]

Medical and industrial radiography

Radiography is used for both medical and industrial applications; for further details please see the Industrial radiography pages. If the object being examined is living (human or animal) it is regarded as medical, and all other radiography is regarded as being industrial radiographic work.

History of radiography

 

Radiography started in 1895 with the discovery of ultrasound (1970s), and magnetic resonance imaging (1980s). Although a nonspecialist dictionary might define radiography quite narrowly as "taking X-ray images", this has long been only part of the work of "X-ray departments", radiographers, and radiologists.

Equipment

Below is a very short overview. For more details please see the radiographic equipment page.

Sources

A number of sources of radioactive sources such as 192Ir have been used.

Detectors

A range of detectors including photographic film, semiconductor diode arrays have been used to collect images.

Theory of X-ray attenuation

Medical usage X-ray photons are more likely to be formed by an event involving an electron, while gamma ray photons are more likely to be formed from the nucleus of an atom.[1]. In general, medical radiography is done using X-rays formed in an X-ray tube. Nuclear medicine typically involves gamma rays.

The types of visible light. It is this relatively high energy which makes gamma rays useful in radiography but potentially hazardous to living organisms.

The radiation is produced by X-ray tubes, high energy X-ray equipment or natural commonly used gamma emitting isotopes.

Such a wave is characterised by its wavelength (the distance from a point on one cycle to the corresponding point on the next cycle) or its frequency (the number of oscillations per second). In a vacuum, all electromagnetic waves travel at the same speed, the speed of light (c). The wavelength (λ, lambda) and the frequency (f) are all related by the equation:

f = c / λ

This is true for all electromagnetic radiation.

Electromagnetic radiation is known by various names, depending on its energy. The energy of these waves is related to the frequency and the wavelength by the relationship:

E = hf = h (c / λ)

Where h is a constant known as Planck's Constant.

Gamma rays are indirectly electron. During this interaction, energy is transferred from the gamma ray to the electron, which is a directly ionizing particle. As a result of this energy transfer, the electron is liberated from the atom and proceeds to ionize matter by colliding with other electrons along its path. Other times, the passing gamma ray interferes with the orbit of the electron, and slows it, releasing energy but not becoming dislodged. The atom is not ionised, and the gamma ray continues on, although at a lower energy. This energy released is usually heat or another, weaker photon, and causes biological harm as a radiation burn. The chain reaction caused by the initial dose of radiation can continue after exposure, much like a sunburn continues to damage skin even after one is out of direct sunlight.

For the range of energies commonly used in radiography, the interaction between gamma rays and electrons occurs in two ways. One effect takes place where all the gamma ray's energy is transmitted to an entire atom. The gamma ray no longer exists and an electron emerges from the atom with kinetic (motion in relation to force) energy almost equal to the gamma energy. This effect is predominant at low gamma energies and is known as the Compton effect.

In both of these effects the emergent electrons lose their kinetic energy by ionizing surrounding atoms. The density of ions so generated is a measure of the energy delivered to the material by the gamma rays.

The most common means of measuring the variations in a beam of radiation is by observing its effect on a photographic film. This effect is the same as that of light, and the more intense the radiation is, the more it darkens, or exposes, the film. Other methods are in use, such as the ionizing effect measured electronically, its ability to discharge an electrostatically charged plate or to cause certain chemicals to fluoroscopy.

Obsolete terminology

The term skiagrapher was used until about 1918 to mean radiographer. It was derived from Ancient Greek words for 'shadow' and 'writer'.

See also

References

  • Kodak. (http://www.kodak.com/global/en/health/productsByType/index.jhtml?pq-path=2/521/2970)
  • Agfa. (http://www.piribo.com/publications/medical_devices/mdc/agfa_medical.html)
  • A review on the subject of medical X-ray examinations and metal based contrast agents, by Shi-Bao Yu and Alan D. Watson, Chemical Reviews, 1999, volume 99, pages 2353-2378
  • Composite Materials for Aircraft Structures by Alan Baker, Stuart Dutton (Ed.), AIAA (American Institute of Aeronautics & Ast) ISBN 1-56347-540-5
  1. ^ Radiation Detection and Measurement 3rd Edition, Glenn F. Knoll : Chapter 1, Page 1: John Wiley & Sons; 3rd Edition edition (26 Jan 2000): ISBN-10: 0471073385
 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Radiography". A list of authors is available in Wikipedia.