radiography

The technique of producing a photographic image of an opaque specimen by the penetration of radiation such as gamma rays, x-rays, neutrons, or charged particles. When a beam of radiation is transmitted through any heterogeneous object, it is differentially absorbed, depending upon the varying thickness, density, and chemical composition of this object. The image registered by the emergent rays on a photographic film adjacent to the specimen under examination constitutes a shadowgraph or radiograph of its interior. Radiography is the general term applied to this nondestructive film technique of testing the gross internal structure of any object, whether it be of the chest of a patient for evidence of tuberculosis, silicosis, heart pathology, or embedded foreign objects; of bones in case of fractures or of arthritis or other bone diseases; or of a weld in a pipe to observe cracks, inclusions, or voids. Radiography with x-rays is commonly used in both medical and industrial applications. Industrial work also involves gamma and neutron radiography. Radiography with charged particles is under development. Most of this discussion will be concerned with radiography with x-rays and gamma rays. See also Charged particle beams; Gamma rays; Neutron; X-rays.

Industrial radiography enables detection of internal physical imperfections such as voids, cracks, flaws, segregations, porosities, and inclusions. It is frequently used for visualization of inaccessible internal parts in order to check their location or condition. It is extensively applied wherever internally sound metallic components are required such as (1) in the foundry industry to guarantee the soundness of castings; (2) in the welding of pressure vessels, pipelines, ships, and reactor components to guarantee the soundness of welds; (3) in the manufacture of fuel elements for reactors to guarantee their size and soundness; (4) in the solid-propellant and high-explosives industry to guarantee the soundness and physical purity of the material; and (5) in the automotive, aircraft, nuclear, space, oceanic, and guided-missile industries, whenever internal soundness is required.

The general term applied to radiation imaging and inspection is radiology. This includes film and similar photographic image methods, such as radiographic paper, under the term radiography. In medical circles, the term roentgenography, derived from the name of the discoverer of x-rays, W. C. Roentgen, is used. The older technique of registering an image on a fluorescent screen is called fluoroscopy. The fluoroscopic prompt-response imaging of radiation has largely been replaced by electronic detection with image intensifiers or sensitive television cameras. This technique, called radioscopy, is now widely used in both medical and industrial applications. See also Radiology.

Other variations of radiation imaging include xeroradiography, microradiography, flash radiography, and computerized tomography. Xeroradi­ography is a dry-plate, electrostatic image method similar to that used in photocopy machines. Microradiography involves a magnified image to improve spatial resolution and the detection of small detail. Flash radiography is the production of an x-ray image in a very short time, of the order of nanoseconds, in order to stop fast motion. The computerized tomography (CT) method recreates an image that is essentially a slice through the object. Computerized tomography has made a strong impact on medical diagnosis and industrial inspection. See also Computerized tomography; Microradiography.

Neutron beams, obtained from nuclear reactors, accelerators, or radioactive sources, can penetrate matter with relative ease since they are not electrically charged. The attenuation of neutrons by most materials is relatively small because the neutron carries no electric charge and consequently is neither attracted nor repelled by the charged particles in the nucleus, nor by the electron clouds associated with the atoms of the material through which the neutron passes. On the other hand, the neutron absorption coefficients of some elements with low atomic numbers are high; hydrogen, lithium, and boron are particularly attenuating. This reversal of attenuation properties between neutrons and x-rays leads to complementary properties for the two radiographic methods. With neutrons, it is possible to visualize materials such as liquids, adhesives, rubber, plastic, or explosives even when they are in metal assemblies.

Proton radiography employs beams of protons. A rapidly moving, high-energy proton or other charged particle moves through material with little attenuation until it slows sufficiently for the charges on the particle and the material to interact. A monoenergetic charged particle travels a well-defined distance, called the range, in a given material before it is stopped. Since most of the attenuation of the charged particles occurs near the end of the range, a very small change in material thickness will result in a large change in radiation transmission. Therefore, the sensitivity of this method to small changes in object thickness is very great, if the total path for the radiation approximates the range. This is a major advantage of proton radiography. Changes in object thickness as small as 0.05% have been imaged with one-step film.

The making of shadow images on photographic emulsion by the action of ionizing radiation. The image is the result of the differential attenuation of the radiation in its passage through the object being radiographed. Roentgenography refers to production of film by the use of x-rays only.

The making of film records (radiographs) of internal structures of the body by exposure of film specially sensitized to x-rays or gamma rays.

• body-section r. — a special technique to show in detail images and structures lying in a predetermined plane of tissue, while blurring or eliminating detail in images in other planes; various mechanisms and methods for such radiography have been given various names, e.g. laminagraphy, tomography, etc.
• contrast r. — the use of means of exaggerating the differences in density of tissues or organs or intraluminal filling defects, usually by the introduction of contrast agents.
• double contrast r. — see double contrast.
• intraoral r. — small non-screen film is placed in the mouth and x-rays are directed from outside the mouth. Used to assess alveolar bone and roots of teeth.
• mucosal relief r. — a technique for revealing any abnormality of the intestinal mucosa, involving injection and evacuation of a barium enema, followed by inflation of the intestine with air under light pressure. The light coating of barium on the inflated intestine in the radiograph reveals clearly even small abnormalities.
• neutron r. — that in which a narrow beam of neutrons from a nuclear reactor is passed through tissues; especially useful in visualizing bony tissue.
• scout r. — see survey radiograph, straight (2).
• serial r. — the making of several exposures of a particular area at arbitrary intervals.
• spot-film r. — the making of localized instantaneous radiographic exposures during fluoroscopy.
• stress r. — positioning to intentionally place stress on structures being radiographed; most commonly used in the diagnosis of spinal disorders such as atlantoaxial instability, wobbler syndrome and lumbosacral instability.

For medical radiography, see Radiology.

A plain radiograph of the elbow.

An X-ray from the Vietnam war shows an unexploded grenade embedded in a patient's skull. (As demonstrated by the intubation, the patient is lying down, not standing up. The circumstances behind the image are otherwise unknown.)

Radiography is the use of the property of X-rays to cross materials to view inside objects. The impact on society of this technique has also been immense : application fields are medical, non-destructive testing, food inspection, security and archeology.

A homogeneous beam of X-rays is produced by an X-ray generator and is sent to an object. According to the density and composition of the different areas of the objects, X-rays are more or less absorbed. They are then captured behind the object by a detector (film sensitive to X-ray, digital detector) which give a 2D image of this as if it was transparent. In tomography, images are captured under different angles to get a 3D picture of the object analysed.

Contents 1 Medical and industrial radiography 2 History of radiography 3 Equipment 3.1 Sources 3.2 Detectors 4 Theory of X-ray attenuation 5 Obsolete terminology 6 See also 7 References 8 External links

Medical and industrial radiography

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.

History of radiography

Taking an X-ray image with early Crookes tube apparatus, late 1800s.

Radiography started in 1895 with the discovery of X-rays, also referred to as Röntgen rays after Wilhelm Conrad Röntgen who first described their properties in rigorous detail. These previously unknown rays (hence the X) were found to be a type of electromagnetic radiation. It wasn't long before X-rays were used in various applications, from helping to fit shoes, to the medical uses that have persisted. X-rays were put to diagnostic use very early, before the dangers of ionizing radiation were discovered. Indeed, Marie Curie pushed for radiography to be used to treat wounded soldiers in World War I. Initially, many kinds of staff conducted radiography in hospitals, including physicists, photographers, doctors, nurses, and engineers. The medical specialty of radiology grew up over many years around the new technology. When new diagnostic tests were developed, it was natural for the radiographers to be trained in and to adopt this new technology. Radiographers now often do fluoroscopy, computed tomography, mammography, ultrasound, nuclear medicine and magnetic resonance imaging as well. 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. Initially, radiographs were known as roentgenograms.^[1]

Equipment

For more details on this topic, see radiographic equipment.

Sources

A number of sources of X-ray photons have been used; these include X-ray generators, betatrons, and linear accelerators (linacs). For gamma rays, radioactive sources such as ¹⁹²Ir, ⁶⁰Co or ¹³⁷Cs are 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

Radiographs of the Darwinius fossil Ida.

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.^[2]. 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.

The radiation is produced by X-ray tubes, high energy X-ray equipment or natural radioactive elements, such as radium and radon, and artificially produced radioactive isotopes of elements, such as cobalt-60 and iridium-192. Electromagnetic radiation consists of oscillating electric and magnetic fields, but is generally depicted as a single sinusoidal wave. While in the past radium and radon have both been used for radiography, they have fallen out of use as they are radiotoxic alpha radiation emitters which are expensive; iridium-192 and cobalt-60 are far better photon sources. For further details see commonly used gamma emitting isotopes.

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'.

See also

• CAD Systems (Computer Aided Diagnosis)
• Radiation
• Radiation contamination
• List of civilian radiation accidents
• Radiographer
• Projectional radiography

References

1. ^ Ritchey, B; Orban, B: "The Crests of the Interdental Alveolar Septa," J Perio April 1953
2. ^ Radiation Detection and Measurement 3rd Edition, Glenn F. Knoll : Chapter 1, Page 1: John Wiley & Sons; 3rd Edition edition (26 Jan 2000): ISBN 0471073385

• Carestream. (http://www.kodak.com/global/en/health/productsByType/index.jhtml?pq-path=2/521/2970)
• Agfa. (http://www.piribo.com/publications/medical_devices/companies_medical/agfa_medical_device_company_intelligence_report.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

External links

• 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.
• Online Radiographic Positions and Procedures Guide: Have access to positioning information anywhere with this quick and easy procedure manual.
• MedPixMedical Image Database
• NIST's XAAMDI: X-Ray Attenuation and Absorption for Materials of Dosimetric Interest Database
• NIST's XCOM: Photon Cross Sections Database
• NIST's FAST: Attenuation and Scattering Tables
• American College of Radiology
• Australian Institute of Radiography
• UN information on the security of industrial sources
• RadiologyInfo - The radiology information resource for patients: Radiography (X-rays)
• The Society of Radiographers Definitive information on the practice of Radiography Professionals
• Sumer's Radiology Site Radiology Blog working as an Online Radiology Magazine
• Nick Oldnall's radiography site
• EUROPEAN SOCIETY OF RADIOLOGY
• What is Radiology?
• New York State Society of Radiologic Technologists web site

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