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Radiography is the use of X-rays to view unseen or hard-to-image objects. The main diagnostic purposes of X-rays are to see inside ones' body, especially of the brain and fetus, where the bones can be viewed at an optimum resolution (128 shades of grey). The impact on society of this technique has also been immense. Physicists and researchers have developed numerous types of medicines to assist in the function and development of organs such as the brain and heart, and radiography has improved the economy of most countries in the western world due to the employment of physicists and doctors. [http://www.johnstonsarchive.net/nuclear/radevents/1993RUS1.html]

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

Equipment

Sources

A number of sources of X-ray photons have been used; these include sealed X-ray tubes, betatrons, and linear accelerators (linacs). For gamma rays, radioactive sources such as 192Ir have been used.

Detectors

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

Theory of X-ray attenuation

X-ray photons used for medical purposes are formed by an event involving an electron, while gamma ray photons are formed from an interaction with the nucleus of an atom. [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 ] . In general, medical radiography is done using X-rays formed in an X-ray tube. Nuclear medicine typically involves gamma rays.

The types of electromagnetic radiation of most interest to radiography are X-ray and gamma radiation. This radiation is much more energetic than the more familiar types such as radio waves and visible light. It is this relatively high energy which makes gamma rays useful in radiography but potentially hazardous to living organisms.

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:

:$f = frac\left\{c\right\}\left\{lambda\right\}$

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:

:$E = hf = h \left(frac\left\{c\right\}\left\{lambda\right\}\right)$

where "h" is a constant known as the Planck constant.

Gamma rays are indirectly ionizing radiation. A gamma ray passes through matter until it undergoes an interaction with an atomic particle, usually an 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 photoelectric effect. The other major effect occurs when a gamma ray interacts with an atomic electron, freeing it from the atom and imparting to it only a fraction of the gamma ray's kinetic energy. A secondary gamma ray with less energy (hence lower frequency) also emerges from the interaction. This effect predominates at higher 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 fluoresce as in 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'.

ee also

* CAD Systems (Computer Aided Diagnosis)
* List of civilian radiation accidents

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&ndash;2378
*"Composite Materials for Aircraft Structures" by Alan Baker, Stuart Dutton (Ed.), AIAA (American Institute of Aeronautics & Ast) ISBN 1-56347-540-5

[http://www.mdct.com.au Online Radiologic Website Free For RAdiographers and Radiologists:] Free Online Text Books, more than 5000 cases online with CT and MRI correlation. Its Free to become a member.
* [http://rad.usuhs.edu/medpix/index.html MedPix] Medical Image Database
* [http://physics.nist.gov/PhysRefData/XrayMassCoef/cover.html NIST's XAAMDI: X-Ray Attenuation and Absorption for Materials of Dosimetric Interest Database]
* [http://physics.nist.gov/PhysRefData/Xcom/Text/XCOM.html NIST's XCOM: Photon Cross Sections Database]
* [http://physics.nist.gov/PhysRefData/FFast/Text/cover.html NIST's FAST: Attenuation and Scattering Tables]
* [http://www.acr.org/s_acr/index.asp American College of Radiology]
* [http://www.birmingham.gov.uk/x Major John Hall-Edwards, British radiography pioneer]
* [http://www.iaea.org/Publications/Booklets/SealedRadioactiveSources/industry_lessons.html UN information on the security of industrial sources]
* [http://www.sor.org/ The Society of Radiographers] Definitive information on the practice of Radiography Professionals
* [http://www.xray2000.co.uk/ Nick Oldnall's radiography site]
* [http://www.esr-online.org EUROPEAN SOCIETY OF RADIOLOGY]
* [http://www.nyssrs.org] New York State Society of Radiologic Technologists web site
* [http://www.biospacemed.com] New technology with low-dose 2D/3D x-ray imaging

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### Look at other dictionaries:

• radiography — a di*og ra*phy (r[=a] d[i^]*[o^]g r[.a]*f[y^]), n. Art or process of making radiographs, radiograms, or autoradiograms. {ra di*o*graph ic} (r[=a] d[i^]*[ o]*gr[a^]f [i^]k), {ra di*o*graph ic*al} (r[=a] d[i^]*[ o]*gr[a^]f [i^]*kal), a. {Ra… …   The Collaborative International Dictionary of English

• Radiography — Radiography. См. Радиография. (Источник: «Металлы и сплавы. Справочник.» Под редакцией Ю.П. Солнцева; НПО Профессионал , НПО Мир и семья ; Санкт Петербург, 2003 г.) …   Словарь металлургических терминов

• Radiography — Film records (radiographs) of internal structures of the body. Radiography is made possible by X rays (or gamma rays) passing through the body to act on a specially sensitized film. * * * Examination of any part of the body for diagnostic… …   Medical dictionary

• radiography — [[t]re͟ɪdiɒ̱grəfi[/t]] N UNCOUNT Radiography is the process of taking X rays …   English dictionary

• radiography — n. diagnostic radiology: traditionally, the technique of examining the body by directing X rays through it to produce images (radiographs) on photographic film or a fluoroscope. Increasingly radiography includes the production of images by… …   The new mediacal dictionary

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• radiography — radiografija statusas T sritis chemija apibrėžtis Jonizuojančiosios spinduliuotės fotografinis registravimas. atitikmenys: angl. radiography rus. радиография …   Chemijos terminų aiškinamasis žodynas