Tomography
Encyclopedia
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.
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 projection
al (shadow) radiography
.
In a 1953 article in the medical journal Chest
, B. Pollak of the Fort William Sanatorium
described the use of planography, another term for tomography.
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.
Some recent advances rely on using simultaneously integrated physical phenomena, e.g. X-rays for both CT
and angiography, combined CT
/MRI and combined CT
/PET
.
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 algorithm
s 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.
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.
Wave
In physics, a wave is a disturbance that travels through space and time, accompanied by the transfer of energy.Waves travel and the wave motion transfers energy from one point to another, often with no permanent displacement of the particles of the medium—that is, with little or no associated mass...
. A device used in tomography is called a tomograph, while the image produced is a tomogram. The method is used in radiology
Radiology
Radiology is a medical specialty that employs the use of imaging to both diagnose and treat disease visualized within the human body. Radiologists use an array of imaging technologies to diagnose or treat diseases...
, archaeology
Archaeology
Archaeology, or archeology , is the study of human society, primarily through the recovery and analysis of the material culture and environmental data that they have left behind, which includes artifacts, architecture, biofacts and cultural landscapes...
, biology
Biology
Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...
, geophysics
Geophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
, oceanography
Oceanography
Oceanography , also called oceanology or marine science, is the branch of Earth science that studies the ocean...
, materials science
Materials science
Materials science is an interdisciplinary field applying the properties of matter to various areas of science and engineering. This scientific field investigates the relationship between the structure of materials at atomic or molecular scales and their macroscopic properties. It incorporates...
, astrophysics
Astrophysics
Astrophysics is the branch of astronomy that deals with the physics of the universe, including the physical properties of celestial objects, as well as their interactions and behavior...
and other sciences. In most cases it is based on the mathematical procedure called tomographic reconstruction
Tomographic reconstruction
The mathematical basis for tomographic imaging was laid down by Johann Radon. It is applied in computed tomography to obtain cross-sectional images of patients...
. The word was derived from the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
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.
Etymology
The word tomography is derived from the Greek tomos ("part") and graphein ("to write").Description
In conventional medical X-rayX-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
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 projection
Projection
Projection, projector, or projective may refer to:* The display of an image by devices such as:** Movie projector** Video projector** Overhead projector** Slide projector** Camera obscura** Projection screen...
al (shadow) radiography
Radiography
Radiography is the use of X-rays to view a non-uniformly composed material such as the human body. By using the physical properties of the ray an image can be developed which displays areas of different density and composition....
.
In a 1953 article in the medical journal Chest
Chest (journal)
Chest is a scientific medical journal published by the American College of Chest Physicians on the subject of chest diseases and related issues . The 2008impact factor is 5.154. The journal has a circulation of some 21,000 copies. Editor in chief is Richard S. Irwin....
, B. Pollak of the Fort William Sanatorium
Fort William Sanatorium
Fort William Sanatorium was a tuberculosis hospital or sanatorium in Fort William, Ontario, today part of the city of Thunder Bay. It opened in 1935.It later provided treatment for people with other disorders, including physical and mental handicaps....
described the use of planography, another term for tomography.
Modern tomography
More modern variations of tomography involve gathering projection data from multiple directions and feeding the data into a tomographic reconstructionTomographic reconstruction
The mathematical basis for tomographic imaging was laid down by Johann Radon. It is applied in computed tomography to obtain cross-sectional images of patients...
software algorithm
Algorithm
In mathematics and computer science, an algorithm is an effective method expressed as a finite list of well-defined instructions for calculating a function. Algorithms are used for calculation, data processing, and automated reasoning...
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-ray X-ray X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma... s |
CT Computed tomography X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing... |
| gamma ray Gamma ray Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei... s |
SPECT |
| radio-frequency waves Radio waves Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves,... |
MRI |
| electron-positron annihilation Electron-positron annihilation Electron–positron annihilation occurs when an electron and a positron collide. The result of the collision is the annihilation of the electron and positron, and the creation of gamma ray photons or, at higher energies, other particles:... |
PET Positron emission tomography Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a... |
| electron Electron The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton... s |
Electron tomography Electron tomography Electron Tomography is a tomography technique for obtaining detailed 3D structures of subcellular macromolecular objects. Electron tomography is an extension of traditional transmission electron microscopy and uses a transmission electron microscope to collect the data... or 3D TEM Transmission electron microscopy Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through... |
| ions | atom probe Atom probe The atom probe is a microscope used in material science that was invented in 1967 by Erwin Wilhelm Müller, J. A. Panitz, and S. Brooks McLane. The atom probe is closely related to the method of Field Ion Microscopy, which is the first microscopic method to achieve atomic resolution, occurring in... |
Some recent advances rely on using simultaneously integrated physical phenomena, e.g. X-rays for both CT
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
and angiography, combined CT
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
/MRI and combined CT
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
/PET
Positron emission tomography
Positron emission tomography is nuclear medicine imaging technique that produces a three-dimensional image or picture of functional processes in the body. The system detects pairs of gamma rays emitted indirectly by a positron-emitting radionuclide , which is introduced into the body on a...
.
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 algorithm
Reconstruction algorithm
In tomography, a variety of practical reconstruction algorithms have been developed to implement the process of reconstruction of a 3-dimensional object from its projections...
s exist. Most algorithms fall into one of two categories: filtered back projection (FBP) and iterative reconstruction
Iterative reconstruction
Iterative reconstruction refers to iterative algorithms used to reconstruct 2D and 3D images in certain imaging techniques.For example, in computed tomography an image must be reconstructed from projections of an object...
(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
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
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
Discrete tomography
Discrete Tomography focuses on the problem of reconstruction of binary images from a small number of their projections....
and Geometric tomography
Geometric tomography
Geometric tomography is a mathematical field that focuses on problems of reconstructing homogeneous objects from tomographic data . More precisely, according to R.J...
, 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.
See also
- Chemical imagingChemical imagingChemical imaging is the analytical capability to create a visual image of components distribution from simultaneous measurement of spectra and spatial, time informations....
- Geophysical imagingGeophysical imagingGeophysical imaging is geophysical technique that investigates the subsurface. There are many different kinds of imaging techniques, all which are based on applied physics.Types of geophysical imaging include:...
- Medical imagingMedical imagingMedical imaging is the technique and process used to create images of the human body for clinical purposes or medical science...
- MRI compared with CT
- Network tomographyNetwork tomographyNetwork tomography is the study of a network's internal characteristics using information derived from end point data. The word tomography is used to link the field, in concept, to other processes that infer the internal characteristics of an object from external observation, as is done in magnetic...
- Nonogram, a type of puzzle based on a discrete model of tomography
- Radon transformRadon transformthumb|right|Radon transform of the [[indicator function]] of two squares shown in the image below. Lighter regions indicate larger function values. Black indicates zero.thumb|right|Original function is equal to one on the white region and zero on the dark region....
- Tomographic reconstructionTomographic reconstructionThe mathematical basis for tomographic imaging was laid down by Johann Radon. It is applied in computed tomography to obtain cross-sectional images of patients...
- Industrial CT scanningIndustrial CT ScanningIndustrial CT scanning is a process which uses X-ray equipment to produce three-dimensional representations of components both externally and internally. Industrial CT scanning has been used in many areas of industry for internal inspection of components...
- Discrete tomographyDiscrete tomographyDiscrete Tomography focuses on the problem of reconstruction of binary images from a small number of their projections....
- Geometric tomographyGeometric tomographyGeometric tomography is a mathematical field that focuses on problems of reconstructing homogeneous objects from tomographic data . More precisely, according to R.J...