Computed tomography (CT) is a medical imaging Medical imaging is the technique and process used to create images of the human body for clinical purposes (medical procedures seeking to reveal, diagnose or examine disease) or medical science (including the study of normal anatomy and physiology). Although imaging of removed organs and tissues can be performed for medical reasons, such method employing tomography Tomography is imaging by sections or sectioning, through the use of waves of energy. 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 created by computer processing.[1] Digital geometry processing Geometry processing, or mesh processing, is a fast-growing area of research that uses concepts from applied mathematics, computer science and engineering to design efficient algorithms for the acquisition, reconstruction, analysis, manipulation, simulation and transmission of complex 3D models. Applications of geometry processing algorithms is used to generate a three-dimensional image Stereoscopy is any technique capable of recording three-dimensional visual information or creating the illusion of depth in an image of the inside of an object from a large series of two-dimensional 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 (3 × 1016 Hz to 3 × 1019 Hz) and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma rays. In many images taken around a single axis of rotation A rotation is a movement of an object in a circular motion. A two-dimensional object rotates around a center of rotation. A three-dimensional object rotates around an imaginary line called an axis. If the axis of rotation is within the body, the body is said to rotate upon itself, or spin—which implies relative speed and perhaps free-movement.[2]
CT produces a volume of data which can be manipulated, through a process known as "windowing", in order to demonstrate various bodily structures based on their ability to block the X-ray beam. Although historically the images generated were in the axial or transverse plane, orthogonal to the long axis of the body, modern scanners allow this volume of data to be reformatted in various planes or even as volumetric (3D) representations of structures. Although most common in medicine, CT is also used in other fields, such as nondestructive materials testing Nondestructive testing is a wide group of analysis techniques used in science and industry to evaluate the properties of a material, component or system without causing damage. Because NDT does not permanently alter the article being inspected, it is a highly-valuable technique that can save both money and time in product evaluation,. Another example is the DigiMorph The information core for the DigiMorph library is generated using a high-resolution X-ray computed tomographic scanner at the University of Texas at Austin. This instrument is comparable to a conventional medical diagnostic CAT scanner, but with greater resolution and penetrating power. The device uses X-rays to take images of thin slices through project at the University of Texas at Austin The University of Texas at Austin is a public research university located in Austin, Texas, United States, and is the flagship institution of The University of Texas System. The main campus is located approximately 0.25 miles (0.40 km) from the Texas State Capitol. Founded in 1883, the university has the fifth-largest single-campus enrollment in which uses a CT scanner to study biological and paleontological Paleontology [note 1] is the study of prehistoric life, including organisms' evolution and interactions with each other and their environments (their paleoecology). As a "historical science" it tries to explain causes rather than conduct experiments to observe effects. Paleontological observations have been documented as far back as the 5 specimens.
Usage of CT has increased dramatically over the last two decades[3]. An estimated 72 million scans were performed in the United States in 2007.[4]
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Terminology
The word "tomography" is derived from the Greek Greek , an independent branch of the Indo-European family of languages, is the language of the Greeks. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. In its ancient form, it is the language of classical ancient Greek literature and the New Testament of tomos (slice) and graphein (to write). Computed tomography was originally known as the "EMI scan" as it was developed at a research branch of EMI The EMI Group is a British music company. It is the fourth-largest business group and family of record labels in the recording industry, making it one of the "big four" record companies and a member of the RIAA. EMI Group also has a major publishing arm - EMI Music Publishing - based in New York City. The company was once a constituent, a company best known today for its music and recording business. It was later known as computed axial tomography (CAT or CT scan) and body section röntgenography.
Although the term "computed tomography" could be used to describe positron emission tomography Positron emission tomography is a nuclear medicine imaging technique which 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 (tracer), which is introduced into the body on a biologically active molecule. Images of tracer and single photon emission computed tomography Single photon emission computed tomography is a nuclear medicine tomographic imaging technique using gamma rays. It is very similar to conventional nuclear medicine planar imaging using a gamma camera. However, it is able to provide true 3D information. This information is typically presented as cross-sectional slices through the patient, but can, in practice it usually refers to the computation of tomography from 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 (3 × 1016 Hz to 3 × 1019 Hz) and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma rays. In many images, especially in older medical literature and smaller medical facilities.
In MeSH Medical Subject Headings is a comprehensive controlled vocabulary for the purpose of indexing journal articles and books in the life sciences; it can also serve as a thesaurus that facilitates searching. Created and updated by the United States National Library of Medicine (NLM), it is used by the MEDLINE/PubMed article database and by NLM's, "computed axial tomography" was used from 1977–79, but the current indexing explicitly includes "X-ray" in the title.[5]
History
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In the early 1900s, the Italian radiologist Alessandro Vallebona proposed a method to represent a single slice of the body on the radiographic film. This method was known as tomography Tomography is imaging by sections or sectioning, through the use of waves of energy. 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. The idea is based on simple principles of projective geometry In mathematics, projective geometry is the study of geometric properties that are invariant under projective transformations. This means that, compared to elementary geometry, projective geometry has a different setting, projective space, and a selective set of basic geometric concepts. The basic intuitions are that projective space has more: moving synchronously and in opposite directions the X-ray tube and the film, which are connected together by a rod whose pivot point is the focus; the image created by the points on the focal plane appears sharper, while the images of the other points annihilate as noise. This is only marginally effective, as blurring occurs only in the "x" plane. There are also more complex devices which can move in more than one plane and perform more effective blurring.
Tomography had been one of the pillars of radiologic diagnostics until the late 1970s, when the availability of minicomputers and of the transverse axial scanning method, this last due to the work of Godfrey Hounsfield Sir Godfrey Newbold Hounsfield CBE, FRS, was an English electrical engineer who shared the 1979 Nobel Prize for Physiology or Medicine with Allan McLeod Cormack for his part in developing the diagnostic technique of X-ray computed tomography (CT) and South African-born Allan McLeod Cormack Allan MacLeod Cormack was a South African-born American physicist who won the 1979 Nobel Prize in Physiology or Medicine (along with Godfrey Hounsfield) for his work on x-ray computed tomography (CT), gradually supplanted it as the modality of CT.
The first commercially viable CT scanner was invented by Sir Godfrey Hounsfield Sir Godfrey Newbold Hounsfield CBE, FRS, was an English electrical engineer who shared the 1979 Nobel Prize for Physiology or Medicine with Allan McLeod Cormack for his part in developing the diagnostic technique of X-ray computed tomography (CT) in Hayes Hayes is a town in the London Borough of Hillingdon, West London. It is a suburban development situated 13 miles west of Charing Cross. Hayes was developed in the late 19th and 20th centuries as an industrial locality to which residential districts were later added to house factory workers. Its development is typical of the Second Industrial, United Kingdom at EMI The EMI Group is a British music company. It is the fourth-largest business group and family of record labels in the recording industry, making it one of the "big four" record companies and a member of the RIAA. EMI Group also has a major publishing arm - EMI Music Publishing - based in New York City. The company was once a constituent Central Research Laboratories using X-rays. Hounsfield conceived his idea in 1967,[6] and it was publicly announced in 1972. Allan McLeod Cormack Allan MacLeod Cormack was a South African-born American physicist who won the 1979 Nobel Prize in Physiology or Medicine (along with Godfrey Hounsfield) for his work on x-ray computed tomography (CT) of Tufts University Tufts University is a private research university in Medford/Somerville, near Boston, Massachusetts, USA. The university is home to the nation's oldest graduate school of international relations, The Fletcher School of Law and Diplomacy in Massachusetts Massachusetts has been significant throughout American history. Plymouth was the second permanent English settlement in North America. Many of Massachusetts's towns were founded by colonists from England in the 1620s and 1630s. During the eighteenth century, Boston became known as the "Cradle of Liberty" for the agitation there that led independently invented a similar process, and both Hounsfield and Cormack shared the 1979 Nobel Prize in Medicine The Nobel Prize in Physiology or Medicine is awarded once a year by the Swedish Karolinska Institute. It is one of the five Nobel Prizes established by the will of Alfred Nobel in 1895, awarded for outstanding contributions in Physics, Chemistry, Literature, Peace, and Physiology or Medicine since 1901. The first Nobel Prize in Physiology or.[7]
The original 1971 prototype took 160 parallel readings through 180 angles, each 1° apart, with each scan taking a little over 5 minutes. The images from these scans took 2.5 hours to be processed by algebraic reconstruction techniques The Algebraic Reconstruction Technique is an iterative algorithm for the reconstruction of a two-dimensional image from one-dimensional input data (a sinogram), used in Computed Tomography scanning. In numerical linear algebra the method is called Kaczmarz method on a large computer. The scanner had a single photomultiplier detector, and operated on the Translate/Rotate principle.
It has been claimed that thanks to the success of The Beatles The Beatles were an English rock band, formed in Liverpool in 1960, and one of the most commercially successful and critically acclaimed acts in the history of popular music. From 1962 the group consisted of John Lennon , Paul McCartney (bass guitar, vocals), George Harrison (lead guitar, vocals) and Ringo Starr (drums, vocals). Rooted in skiffle, EMI The EMI Group is a British music company. It is the fourth-largest business group and family of record labels in the recording industry, making it one of the "big four" record companies and a member of the RIAA. EMI Group also has a major publishing arm - EMI Music Publishing - based in New York City. The company was once a constituent could fund research and build early models for medical use.[8] The first production X-ray CT machine (in fact called the "EMI-Scanner") was limited to making tomographic sections of the brain, but acquired the image data in about 4 minutes (scanning two adjacent slices), and the computation time (using a Data General Nova The Data General Nova was a popular 16-bit minicomputer built by the American company Data General starting in 1969. The Nova was packaged into a single rack mount case and had enough power to do most simple computing tasks. The Nova became popular in science laboratories around the world, and eventually 50,000 units were sold. It was followed by minicomputer) was about 7 minutes per picture. This scanner required the use of a water-filled Perspex Poly (PMMA) is a transparent thermoplastic, often used as a light or shatter-resistant alternative to glass. Chemically, it is the synthetic polymer of methyl methacrylate. The material was developed in 1928 in various laboratories, and was first brought to market in 1933 by Rohm and Haas Company, under the trademark Plexiglas. It has since been tank with a pre-shaped rubber "head-cap" at the front, which enclosed the patient's head. The water-tank was used to reduce the dynamic range of the radiation reaching the detectors (between scanning outside the head compared with scanning through the bone of the skull). The images were relatively low resolution, being composed of a matrix of only 80 x 80 pixels. The first EMI-Scanner was installed in Atkinson Morley Hospital in Wimbledon Wimbledon is a district of South London, England, located in the London Borough of Merton. It is situated 7 miles south-west of Charing Cross. The area is identified in the London Plan as one of 35 major centres in Greater London. For most of the past one hundred years, Wimbledon has been internationally known as the home of the Wimbledon Tennis, England, and the first patient brain-scan was made with it in 1972. In the U.S., the first installation was at the Mayo Clinic Mayo Clinic is a not-for-profit organization and a medical practice and medical research group located in 3 metropolis areas: Rochester, Minnesota, Scottsdale/ Phoenix, Arizona, and Jacksonville, Florida, along with Mayo Clinic Hospitals and some satellite healthcare and research facilities in and near those cities . It is an integral part of the. As a tribute to the impact of this system on medical imaging the Mayo Clinic has an EMI scanner on display in the Radiology Department.
The first CT system that could make images of any part of the body and did not require the "water tank" was the ACTA (Automatic Computerized Transverse Axial) scanner designed by Robert S. Ledley, DDS, at Georgetown University Georgetown University is a Jesuit private university located in Georgetown, Washington, DC. Father John Carroll founded the school in 1789, though its roots extend back to 1634. While the school struggled financially in its early years, Georgetown expanded into a branched university after the American Civil War under the leadership of university. This machine had 30 photomultiplier tubes as detectors and completed a scan in only 9 translate/rotate cycles, much faster than the EMI-scanner. It used a DEC PDP11/34 The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corp. from 1970 into the 1990s. Though not explicitly conceived as a successor to DEC's PDP-8 computer in the PDP series of computers (both product lines lived in parallel for more than 10 years), the PDP-11 replaced the PDP-8 in many real-time applications. It had several minicomputer both to operate the servo-mechanisms and to acquire and process the images. The Pfizer Pfizer Incorporated is a pharmaceutical company, ranking number one in sales in the world. The company is based in New York City, with its research headquarters in Groton, Connecticut. It produces Lipitor (atorvastatin, used to lower blood cholesterol); the neuropathic pain/fibromyalgia drug Lyrica (pregabalin); the oral antifungal medication drug company acquired the prototype from the university, along with rights to manufacture it. Pfizer then began making copies of the prototype, calling it the "200FS" (FS meaning Fast Scan), which were selling as fast as they could make them. This unit produced images in a 256×256 matrix, with much better definition than the EMI-Scanner's 80×80.
Previous studies
Tomography
A form of tomography can be performed by moving the X-ray source and detector during an exposure. Anatomy at the target level remains sharp, while structures at different levels are blurred. By varying the extent and path of motion, a variety of effects can be obtained, with variable depth of field In optics, particularly as it relates to film and photography, the depth of field is the portion of a scene that appears acceptably sharp in the image. Although a lens can precisely focus at only one distance, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under and different degrees of blurring of "out of plane" structures.[9]:25
Although largely obsolete, conventional tomography is still used in specific situations such as dental imaging (orthopantomography) or in intravenous urography An intravenous pyelogram is a radiological procedure used to visualize abnormalities of the urinary system, including the kidneys, ureters, and bladder.
Tomosynthesis
Digital tomosynthesis combines digital image capture and processing with simple tube/detector motion as used in conventional radiographic tomography. Although there are some similarities to CT, it is a separate technique. In CT, the source/detector makes a complete 360-degree rotation about the subject obtaining a complete set of data from which images may be reconstructed. In digital tomosynthesis, only a small rotation angle (e.g., 40 degrees) with a small number of discrete exposures (e.g., 10) are used. This incomplete set of data can be digitally processed to yield images similar to conventional tomography with a limited depth of field In optics, particularly as it relates to film and photography, the depth of field is the portion of a scene that appears acceptably sharp in the image. Although a lens can precisely focus at only one distance, the decrease in sharpness is gradual on each side of the focused distance, so that within the DOF, the unsharpness is imperceptible under. However, because the image processing is digital, a series of slices at different depths and with different thicknesses can be reconstructed from the same acquisition, saving both time and radiation exposure.
Because the data acquired is incomplete, tomosynthesis is unable to offer the extremely narrow slice widths that CT offers. However, higher resolution detectors can be used, allowing very-high in-plane resolution, even if the Z-axis resolution is poor. The primary interest in tomosynthesis is in breast imaging, as an extension to mammography Mammography is the process of using low-dose amplitude-X-rays to examine the human breast and is used as a diagnostic and a screening tool. The goal of mammography is the early detection of breast cancer, typically through detection of characteristic masses and/or microcalcifications. Mammography is believed to reduce mortality from breast cancer, where it may offer better detection rates with little extra increase in radiation exposure.
Reconstruction algorithms for tomosynthesis are significantly different from conventional CT, because the conventional filtered back projection In mathematics, the Radon transform in two dimensions, named after the Austrian mathematician Johann Radon, is the integral transform consisting of the integral of a function over straight lines. The transform was introduced by Johann Radon , who also provided a formula for the inverse transform. Radon further included formulas for the transform algorithm requires a complete set of data. Iterative algorithms based upon expectation maximization An expectation-maximization algorithm is used in statistics for finding maximum likelihood estimates of parameters in probabilistic models, where the model depends on unobserved latent variables. EM is an iterative method which alternates between performing an expectation (E) step, which computes an expectation of the log likelihood with respect are most commonly used, but are extremely computationally intensive. Some manufacturers have produced practical systems using off-the-shelf GPUs A graphics processing unit or GPU is a specialized processor that offloads 3D graphics rendering from the microprocessor. It is used in embedded systems, mobile phones, personal computers, workstations, and game consoles. Modern GPUs are very efficient at manipulating computer graphics, and their highly parallel structure makes them more effective to perform the reconstruction.
Diagnostic use
Since its introduction in the 1970s, CT has become an important tool in medical imaging Medical imaging is the technique and process used to create images of the human body for clinical purposes (medical procedures seeking to reveal, diagnose or examine disease) or medical science (including the study of normal anatomy and physiology). Although imaging of removed organs and tissues can be performed for medical reasons, such to supplement X-rays 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 (3 × 1016 Hz to 3 × 1019 Hz) and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma rays. In many and medical ultrasonography Diagnostic sonography is an ultrasound-based diagnostic imaging technique used to visualize subcutaneous body structures including tendons, muscles, joints, vessels and internal organs for possible pathology or lesions. Obstetric sonography is commonly used during pregnancy and is widely recognized by the public. There is a plethora of diagnostic. It has more recently begun to also be used for preventive medicine Preventive medicine or preventive care refers to measures taken to prevent diseases, rather than curing them or treating their symptoms. The term contrasts in method with curative and palliative medicine, and in scope with public health methods (which work at the level of population health rather than individual health) or screening Screening, in medicine, is a strategy used in a population to detect a disease in individuals without signs or symptoms of that disease. Unlike what generally happens in medicine, in screening tests are performed on persons without any clinical sign of disease for disease, for example CT colonography for patients with a high risk of colon cancer, or full-motion heart scans for patients with high risk of heart disease. A number of institutions offer full-body scans Full-body scan is a scan of the patient's entire body to support the diagnosis and treatment of illnesses. It may also be known as a full-body CT scan if computed tomography technology is used, though there are many types of medical imaging technology which can perform full-body scans (see box on bottom of page) for the general population. However, this is a controversial practice, given its lack of proven benefit, cost, radiation exposure, and the risk of finding 'incidental' abnormalities that may trigger additional investigations.
Head
CT scanning of the head is typically used to detect infarction, tumours, calcifications, haemorrhage and bone trauma. Of the above, hypodense (dark) structures indicate infraction or tumours, hyperdense (bright) structures indicate calcifications and haemorrhage and bone trauma can be seen as disjunction in bone windows.
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Objectives: This study sought to describe a protocol for myocardial perfusion imaging using dipyridamole stress, with 128-slice dual-source . computed tomography. (CT), and to assess the ability of CT myocardial perfusion imaging (MPI) to ...
Q. computed tomography
Asked by lyssa - Mon Mar 24 19:35:25 2008 - - 1 Answers - 0 Comments
A. It determines whether the machine is focused.
Answered by Susan S - Mon Mar 24 20:23:13 2008
