Editing Tomography (section)

{{Short description|Imaging by sections or sectioning using a penetrative wave}}
{{distinguish|Topography}}
[[File:TomographyPrinciple Illustration.png|200px|thumb|'''Fig.1''': Basic principle of tomography: superposition free tomographic cross sections S<sub>1</sub> and S<sub>2</sub> compared with the (not tomographic) projected image P]]
[[File:Sagittal brain MRI.jpg|thumbnail|[[Median plane]] [[Sagittal plane|sagittal]] tomography of the head by [[magnetic resonance imaging]]]]
'''Tomography''' is [[imaging]] by sections or sectioning that uses any kind of penetrating [[wave]]. The method is used in [[radiology]], [[archaeology]], [[biology]], [[atmospheric science]], [[geophysics]], [[oceanography]], [[plasma physics]], [[materials science]], [[cosmochemistry]], [[astrophysics]], [[quantum information]], and other areas of [[science]]. The word ''tomography'' is derived from [[Ancient Greek]] τόμος ''tomos'', "slice, section" and γράφω ''graphō'', "to write" or, in this context as well, "to describe." A device used in tomography is called a '''tomograph''', while the image produced is a '''tomogram'''.

In many cases, the production of these images is based on the mathematical procedure [[tomographic reconstruction]], such as [[X-ray computed tomography]] technically being produced from multiple [[projectional radiograph]]s. 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.<ref>{{cite book |last=Herman |first=Gabor T. |title=Fundamentals of Computerized Tomography: Image Reconstruction from Projections |date=2009 |publisher=Springer |location=Dordrecht |isbn=978-1-84628-723-7 |edition=2nd}}</ref>

Although MRI ([[magnetic resonance imaging]]), [[optical coherence tomography]] and [[ultrasound]] are transmission methods, they typically do not require movement of the transmitter to acquire data from different directions. In MRI, both projections and higher spatial harmonics are sampled by applying spatially varying magnetic fields; no moving parts are necessary to generate an image. On the other hand, since ultrasound and optical coherence tomography uses time-of-flight to spatially encode the received signal, it is not strictly a tomographic method and does not require multiple image acquisitions.