Tomography refers to imaging by sections or sectioning, through the use of any kind of penetrating wave. A device used in tomography is called a tomograph, while the image produced is a tomogram. The method is used in radiology, archaeology, biology, geophysics, oceanography, materials science, astrophysics and other sciences. In most cases it is based on the mathematical procedure called tomographic reconstruction. The word was derived from the Greek word tomos which means "part" or "section", representing the idea of "a section", "a slice" or "a cutting". A tomography of several sections of the body is known as a polytomography.
The word tomography is derived from the Greek tomos ("part") and graphein ("to write").
In conventional medical X-ray tomography, clinical staff make a sectional image through a body by moving an X-ray source and the film in opposite directions during the exposure. Consequently, structures in the focal plane appear sharper, while structures in other planes appear blurred. By modifying the direction and extent of the movement, operators can select different focal planes which contain the structures of interest. Before the advent of more modern computer-assisted techniques, this technique, developed in the 1930s by the radiologist Alessandro Vallebona, proved useful in reducing the problem of superimposition of structures in projectional (shadow) radiography.
More modern variations of tomography involve gathering projection data from multiple directions and feeding the data into a tomographic reconstruction software algorithm processed by a computer. Different types of signal acquisition can be used in similar calculation algorithms in order to create a tomographic image. With current (2005) technology, tomograms are derived using several different physical phenomena listed in the following table.
Physical phenomenon Type of tomogram X-rays CT gamma rays SPECT radio-frequency waves MRI electron-positron annihilation PET electrons Electron tomography or 3D TEM ions atom probe
The term volume imaging might subsume these technologies more accurately than the term tomography. However, in the majority of cases in clinical routine, staff request output from these procedures as 2-D slice images. As more and more clinical decisions come to depend on more advanced volume visualization techniques, the terms tomography/tomogram may go out of fashion.
Many different reconstruction algorithms exist. Most algorithms fall into one of two categories: filtered back projection (FBP) and iterative reconstruction (IR). These procedures give inexact results: they represent a compromise between accuracy and computation time required. FBP demands fewer computational resources, while IR generally produces fewer artifacts (errors in the reconstruction) at a higher computing cost.
Although MRI and ultrasound make cross sectional images they don't acquire data from different directions. In MRI spatial information is obtained by using magnetic fields. In ultrasound, spatial information is obtained simply by focusing and aiming a pulsed ultrasound beam.
Synchrotron X-ray tomographic microscopy
Recently a new technique called synchrotron X-ray tomographic microscopy (SRXTM) allows for detailed three dimensional scanning of fossils.
Types of tomography
Discrete tomography and Geometric tomography, on the other hand, are research areas that deal with the reconstruction of objects that are discrete (such as crystals) or homogeneous. They are concerned with reconstruction methods, and as such they are not restricted to any of the particular (experimental) tomography methods listed above.
- Chemical imaging
- Geophysical imaging
- Medical imaging
- MRI compared with CT
- Network tomography
- Nonogram, a type of puzzle based on a discrete model of tomography
- Radon transform
- Tomographic reconstruction
- Industrial CT scanning
- Discrete tomography
- Geometric tomography
- ^ MeSH Tomography
- ^ Pollak, B. (December 1953). "Experiences with Planography". Chest (American College of Chest Physicians) 24 (6): 663–669. doi:10.1378/chest.24.6.663. ISSN 0012-3692. http://chestjournal.chestpubs.org/content/24/6/663.abstract. Retrieved July 10, 2011.
- ^ Herman, G. T., Fundamentals of computerized tomography: Image reconstruction from projection, 2nd edition, Springer, 2009
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tomography — [tə mäg′rə fē] n. 〚< Gr tomos, a piece cut off (see TOMY) + GRAPHY〛 a process for producing an image of a single plane of an object excluding all other planes, as by using CT SCAN or ULTRASOUND, in … Universalium
tomography — (n.) 1935, from Gk. tomos slice, section (see TOME (Cf. tome)) + GRAPHY (Cf. graphy) … Etymology dictionary
tomography — [tə mäg′rə fē] n. [< Gr tomos, a piece cut off (see TOMY) + GRAPHY] a process for producing an image of a single plane of an object excluding all other planes, as by using CT SCAN or ULTRASOUND, in diagnostic medicine, seismic surveys, etc … English World dictionary
tomography — Making of a radiographic image of a selected plane by means of reciprocal linear or curved motion of the x ray tube and film cassette; images of all other planes are blurred (“out of focus”) by being relatively displaced on the film. SYN:… … Medical dictionary
tomography — n. the technique of rotating a radiation detector around the patient so that the image obtained gives additional three dimensional information. In plain film tomography the source of X rays and the photographic film move round the patient to… … The new mediacal dictionary
tomography — noun Etymology: Greek tomos section + International Scientific Vocabulary graphy more at tome Date: 1935 a method of producing a three dimensional image of the internal structures of a solid object (as the human body or the earth) by the… … New Collegiate Dictionary
tomography — noun Imaging by sections or sectioning. See Also: tomogram, computed tomography … Wiktionary
tomography — tomografija statusas T sritis Standartizacija ir metrologija apibrėžtis Tiriamo erdvinio objekto sluoksnių vaizdų gavimas. atitikmenys: angl. laminography; tomography vok. Körperschichtaufnahmeverfahren, n; Laminographie, f;… … Penkiakalbis aiškinamasis metrologijos terminų žodynas
tomography — tomografija statusas T sritis chemija apibrėžtis Tyrimo metodų, leidžiančių pasluoksniui tyrinėti objekto sandarą, visuma. atitikmenys: angl. body section radiography; laminography; planigraphy; tomography rus. томография … Chemijos terminų aiškinamasis žodynas
tomography — tomografija statusas T sritis fizika atitikmenys: angl. body section roentgenography; laminography; tomography vok. Röntgenschichtaufnahmeverfahren, n; Röntgenschichtverfahren, n; Tomographie, f rus. послойная рентгенография, f; томография, f… … Fizikos terminų žodynas