{{Interventions_infobox | Name = X-ray computed tomography | Image = Rosies ct scan.jpg | Caption = A patient is receiving a CT scan for cancer. Outside of the scanning room is an imaging computer that reveals a 3D image of the body's interior. | ICD10 = B?2 | ICD9 = | MeshID = D014057 | OPS301 = | OtherCodes = | }}

X-ray computed tomography (CT) is a medical imaging method employing tomography created by computer processing. Digital geometry processing is used to generate a three-dimensional image of the inside of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation.

CT produces a volume of data that 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. Another example is archaeological uses such as imaging the contents of sarcophagi.

Usage of CT has increased dramatically over the last two decades in many countries. An estimated 72 million scans were performed in the United States in 2007. It is estimated that 0.4% of current cancers in the United States are due to CTs performed in the past and that this may increase to as high as 1.5-2% with 2007 rates of CT usage; however, this estimate is disputed.

Terminology

The word "tomography" is derived from the Greek ''tomos'' (volume) and ''graphein'' (to write). Computed tomography was originally known as the "EMI scan" as it was developed at a research branch of EMI, 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 and single photon emission computed tomography, in practice it usually refers to the computation of tomography from X-ray images, especially in older medical literature and smaller medical facilities.

In MeSH, "computed axial tomography" was used from 1977–79, but the current indexing explicitly includes "X-ray" in the title.

Diagnostic use

Since its introduction in the 1970s, CT has become an important tool in medical imaging to supplement X-rays and medical ultrasonography. It has more recently been used for preventive medicine or screening 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 for the general population.

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 infarction or tumours, hyperdense (bright) structures indicate calcifications and haemorrhage and bone trauma can be seen as disjunction in bone windows. Ambulances equipped with small bore multi-sliced CT scanners respond to cases involving stroke or head trauma.

Lungs

CT can be used for detecting both acute and chronic changes in the lung parenchyma, that is, the internals of the lungs. It is particularly relevant here because normal two-dimensional X-rays do not show such defects. A variety of different techniques are used, depending on the suspected abnormality. For evaluation of chronic interstitial processes (emphysema, fibrosis, and so forth), thin sections with high spatial frequency reconstructions are used; often scans are performed both in inspiration and expiration. This special technique is called high resolution CT. Therefore, it produces a sampling of the lung and not continuous images. diagnose coronary artery disease.

Pulmonary angiogram

CT pulmonary angiogram (CTPA) is a medical diagnostic test used to diagnose pulmonary embolism (PE). It employs computed tomography to obtain an image of the pulmonary arteries.

Cardiac

With the advent of subsecond rotation combined with multi-slice CT (up to 320-slices), high resolution and high speed can be obtained at the same time, allowing excellent imaging of the coronary arteries (cardiac CT angiography).

Abdominal and pelvic

CT is a sensitive method for diagnosis of abdominal diseases. It is used frequently to determine stage of cancer and to follow progress. It is also a useful test to investigate acute abdominal pain.

Extremities

CT is often used to image complex fractures, especially ones around joints, because of its ability to reconstruct the area of interest in multiple planes. Fractures, ligamentous injuries and dislocations can easily be recognised with a 0.2 mm resolution.

Advantages

There are several advantages that CT has over traditional 2D medical radiography. First, CT completely eliminates the superimposition of images of structures outside the area of interest. Second, because of the inherent high-contrast resolution of CT, differences between tissues that differ in physical density by less than 1% can be distinguished. Finally, data from a single CT imaging procedure consisting of either multiple contiguous or one helical scan can be viewed as images in the axial, coronal, or sagittal planes, depending on the diagnostic task. This is referred to as multiplanar reformatted imaging.

CT is regarded as a moderate- to high-radiation diagnostic technique. The improved resolution of CT has permitted the development of new investigations, which may have advantages; compared to conventional radiography, for example, CT angiography avoids the invasive insertion of a catheter. CT Colonography (also known as Virtual Colonoscopy or VC for short) may be as useful as a barium enema for detection of tumors, but may use a lower radiation dose. CT VC is increasingly being used in the UK as a diagnostic test for bowel cancer and can negate the need for a colonoscopy.

The radiation dose for a particular study depends on multiple factors: volume scanned, patient build, number and type of scan sequences, and desired resolution and image quality. In addition, two helical CT scanning parameters that can be adjusted easily and that have a profound effect on radiation dose are tube current and pitch. Computed tomography (CT) scan has been shown to be more accurate than radiographs in evaluating anterior interbody fusion but may still over-read the extent of fusion.

Adverse effects

The increased use of CT scans has been the greatest in two fields: screening of adults (screening CT of the lung in smokers, virtual colonoscopy, CT cardiac screening, and whole-body CT in asymptomatic patients) and CT imaging of children. Shortening of the scanning time to around 1 second, eliminating the strict need for the subject to remain still or be sedated, is one of the main reasons for the large increase in the pediatric population (especially for the diagnosis of appendicitis). CT scans of children have been estimated to produce non-negligible increases in the probability of lifetime cancer mortality, leading to calls for the use of reduced current settings for CT scans of children.

These calculations are based on similar radiation exposures experienced by those present during the atomic bomb explosions in Japan during the second world war and nuclear industry works. Estimated lifetime cancer mortality risks attributable to the radiation exposure from a CT in a 1-year-old are 0.18% (abdominal) and 0.07% (head) — an order of magnitude higher than for adults — although those figures still represent a small increase in cancer mortality over the background rate. In the United States, of approximately 600,000 abdominal and head CT examinations annually performed in children under the age of 15 years, a rough estimate is that 500 of these individuals might ultimately die from cancer attributable to the CT radiation. The additional risk is still low 0.35% compared to the background risk of dying from cancer of 23%. However, if these statistics are extrapolated to the current number of CT scans, the additional rise in cancer mortality could be 1.5 to 2%. Furthermore, certain conditions can require children to be exposed to multiple CT scans.

In 2009, a number of studies that further defined the risk of cancer that may be caused by CT scans appeared. One study indicated that radiation by CT scans is often higher and more variable than cited, and each of the 19,500 CT scans that are daily performed in the US is equivalent to 30 to 442 chest X-rays in radiation. It has been estimated that CT radiation exposure will result in 29,000 new cancer cases just from the CT scans performed in 2007. The most common cancers caused by CT are thought to be lung cancer, colon cancer, and leukemia with younger people, and women more at risk. These conclusions, however, are criticized by the American College of Radiology (ACR), which maintains that the life expectancy of CT scanned patients is not that of the general population and that the model of calculating cancer is based on total-body radiation exposure and thus faulty.

CT scans can be performed with different settings for lower exposure in children, although these techniques are often not employed. Surveys have suggested that, at the current time, many CT scans are performed unnecessarily. Ultrasound scanning or magnetic resonance imaging are alternatives (for example, in appendicitis or brain imaging) without the risk of radiation exposure. Although CT scans come with an additional risk of cancer (it can be estimated that the radiation exposure from a full body scan is the same as standing 2.4 km away from the World War II atomic bomb blasts in Japan), especially in children, the benefits that stem from their use outweigh the risk in many cases. Studies support informing parents of the risks of pediatric CT scanning.

Typical scan dose

!Examination	effective dose (Sievert>mSv)	! (millirem)
X-ray Personnel security screening scan	0.00025	0.025
Chest X-ray	0.1	10
Head CT	1.5	150
Screening mammography	3	300
Abdomen CT	5.3	530
Chest CT	5.8	580
CT colonography (virtual colonoscopy)	3.6–8.8	360–880
Chest, abdomen and pelvis CT	9.9	990
Cardiac CT angiogram	6.7-13	670–1300
Barium enema	15	1500
Neonatal abdominal CT	20	2000

For purposes of comparison, the average background exposure in the UK is 1-3 mSv per year.

Reactions to contrast agents

Because contrast CT scans rely on intravenously administered contrast agents in order to provide superior image quality, there is a low but non-negligible level of risk associated with the contrast agents themselves. Many patients report nausea and discomfort, including warmth in the crotch, which mimics the sensation of wetting oneself. Certain patients may experience severe and potentially life-threatening allergic reactions to the contrast dye.

The contrast agent may also induce kidney damage. The risk of this is increased with patients who have preexisting renal insufficiency, preexisting diabetes, or reduced intravascular volume. In general, if a patient has normal kidney function, then the risks of contrast nephropathy are negligible. Patients with mild kidney impairment are usually advised to ensure full hydration for several hours before and after the injection. For moderate kidney failure, the use of iodinated contrast should be avoided; this may mean using an alternative technique instead of CT, e.g., MRI. However, patients with severe renal failure requiring dialysis do not require special precautions, as their kidneys have so little function remaining that any further damage would not be noticeable and the dialysis will remove the contrast agent.

Low-dose CT scan

An important issue within radiology today is how to reduce the radiation dose during CT examinations without compromising the image quality. In general, higher radiation doses result in higher-resolution images, while lower doses lead to increased image noise and unsharp images. Increased dosage raises the risk of radiation induced cancer — a four-phase abdominal CT gives the same radiation dose as 300 chest x-rays. Several methods that can reduce the exposure to ionizing radiation during a CT scan exist.

# New software technology can significantly reduce the required radiation dose. # Individualize the examination and adjust the radiation dose to the body type and body organ examined. Different body types and organs require different amounts of radiation. # Prior to every CT examination, evaluate the appropriateness of the exam whether it is motivated or if another type of examination is more suitable. Higher resolution is not always suitable for any given scenario, such as detection of small pulmonary masses

Artifacts

Although CT is a relatively accurate test, it is liable to produce artifacts, such as the following:^{, Chapters 3 and 5}

Streak artifact

Streaks are often seen around materials that block most X-rays, such as metal or bone. These streaks can be caused by undersampling, photon starvation, motion, beam hardening, or scatter. This type of artifact commonly occurs in the posterior fossa of the brain, or if there are metal implants. The streaks can be reduced using newer reconstruction techniques.

Partial volume effect

This appears as "blurring" over sharp edges. It is due to the scanner being unable to differentiate between a small amount of high-density material (e.g., bone) and a larger amount of lower density (e.g., cartilage). The processor tries to average out the two densities or structures, and information is lost. This can be partially overcome by scanning using thinner slices.

Ring artifact

Probably the most common mechanical artifact, the image of one or many "rings" appears within an image. This is usually due to a detector fault.

Noise artifact

This appears as graining on the image and is caused by a low signal to noise ratio. This occurs more commonly when a thin slice thickness is used. It can also occur when the power supplied to the X-ray tube is insufficient to penetrate the anatomy.

Motion artifact

This is seen as blurring and/or streaking, which is caused by movement of the object being imaged. Motion blurring might be reduced using a new technique called IFT (incompressible flow tomography).

Windmill

Streaking appearances can occur when the detectors intersect the reconstruction plane. This can be reduced with filters or a reduction in pitch.

Beam hardening

This can give a "cupped appearance". It occurs when there is more attenuation in the center of the object than around the edge. This is easily corrected by filtration and software.

Prevalence

Usage of CT has increased dramatically over the last two decades. In the emergency department in the United States, CT or MRI imaging is done in 15% of people who present with injuries as of 2007 (up from 6% in 1998).

Process

X-ray slice data is generated using an X-ray source that rotates around the object; X-ray sensors are positioned on the opposite side of the circle from the X-ray source. The earliest sensors were scintillation detectors, with photomultiplier tubes excited by (typically) cesium iodide crystals. Cesium iodide was replaced during the 1980s by ion chambers containing high-pressure Xenon gas. These systems were in turn replaced by scintillation systems based on photodiodes instead of photomultipliers and modern scintillation materials with more desirable characteristics. Many data scans are progressively taken as the object is gradually passed through the gantry.

Newer machines with faster computer systems and newer software strategies can process not only individual cross sections but continuously changing cross sections as the gantry, with the object to be imaged slowly and smoothly slid through the X-ray circle. These are called ''helical'' or ''spiral CT'' machines. Their computer systems integrate the data of the moving individual slices to generate three dimensional volumetric information (3D-CT scan), in turn viewable from multiple different perspectives on attached CT workstation monitors. This type of data acquisition requires enormous processing power, as the data are arriving in a continuous stream and must be processed in real-time.

In conventional CT machines, an X-ray tube and detector are physically rotated behind a circular shroud (see the image above right); in the electron beam tomography (EBT), the tube is far larger and higher power to support the high temporal resolution. The electron beam is deflected in a hollow funnel-shaped vacuum chamber. X-rays are generated when the beam hits the stationary target. The detector is also stationary. This arrangement can result in very fast scans, but is extremely expensive.

CT is used in medicine as a diagnostic tool and as a guide for interventional procedures. Sometimes contrast materials such as intravenous iodinated contrast are used. This is useful to highlight structures such as blood vessels that otherwise would be difficult to delineate from their surroundings. Using contrast material can also help to obtain functional information about tissues.

Once the scan data has been acquired, the data must be processed using a form of tomographic reconstruction, which produces a series of cross-sectional images. The most common technique in general use is filtered back projection, which is straight-forward to implement and can be computed rapidly. In terms of mathematics, this method is based on the Radon transform. However, this is not the only technique available: the original EMI scanner solved the tomographic reconstruction problem by linear algebra, but this approach was limited by its high computational complexity, especially given the computer technology available at the time. More recently, manufacturers have developed iterative physical model-based expectation-maximization techniques. These techniques are advantageous because they use an internal model of the scanner's physical properties and of the physical laws of X-ray interactions. By contrast, earlier methods have assumed a perfect scanner and highly simplified physics, which leads to a number of artifacts and reduced resolution - the result is images with improved resolution, reduced noise and fewer artifacts, as well as the ability to greatly reduce the radiation dose in certain circumstances. The disadvantage is a very high computational requirement, which is at the limits of practicality for current scan protocols.

Pixels in an image obtained by CT scanning are displayed in terms of relative radiodensity. The pixel itself is displayed according to the mean attenuation of the tissue(s) that it corresponds to on a scale from +3071 (most attenuating) to -1024 (least attenuating) on the Hounsfield scale. Pixel is a two dimensional unit based on the matrix size and the field of view. When the CT slice thickness is also factored in, the unit is known as a Voxel, which is a three-dimensional unit. The phenomenon that one part of the detector cannot differentiate between different tissues is called the ''"Partial Volume Effect"''. That means that a big amount of cartilage and a thin layer of compact bone can cause the same attenuation in a voxel as hyperdense cartilage alone. Water has an attenuation of 0 Hounsfield units (HU), while air is -1000 HU, cancellous bone is typically +400 HU, cranial bone can reach 2000 HU or more (os temporale) and can cause artifacts. The attenuation of metallic implants depends on atomic number of the element used: Titanium usually has an amount of +1000 HU, iron steel can completely extinguish the X-ray and is, therefore, responsible for well-known line-artifacts in computed tomograms. Artifacts are caused by abrupt transitions between low- and high-density materials, which results in data values that exceed the dynamic range of the processing electronics.

Contrast mediums used for X-ray CT, as well as for plain film X-ray, are called radiocontrasts. Radiocontrasts for X-ray CT are, in general, iodine-based. Often, images are taken both with and without radiocontrast. CT images are called ''precontrast'' or ''native-phase'' images before any radiocontrast has been administrated, and ''postcontrast'' after radiocontrast administration.

Three-dimensional reconstruction

Because contemporary CT scanners offer isotropic or near isotropic, resolution, display of images does not need to be restricted to the conventional axial images. Instead, it is possible for a software program to build a volume by "stacking" the individual slices one on top of the other. The program may then display the volume in an alternative manner.

Multiplanar reconstruction

Multiplanar reconstruction (MPR) is the simplest method of reconstruction. A volume is built by stacking the axial slices. The software then cuts slices through the volume in a different plane (usually orthogonal). As an option, a special projection method, such as maximum-intensity projection (MIP) or minimum-intensity projection (mIP), can be used to build the reconstructed slices.

MPR is frequently used for examining the spine. Axial images through the spine will only show one vertebral body at a time and cannot reliably show the intervertebral discs. By reformatting the volume, it becomes much easier to visualise the position of one vertebral body in relation to the others.

Modern software allows reconstruction in non-orthogonal (oblique) planes so that the optimal plane can be chosen to display an anatomical structure. This may be particularly useful for visualising the structure of the bronchi as these do not lie orthogonal to the direction of the scan.

For vascular imaging, curved-plane reconstruction can be performed. This allows bends in a vessel to be "straightened" so that the entire length can be visualised on one image, or a short series of images. Once a vessel has been "straightened" in this way, quantitative measurements of length and cross sectional area can be made, so that surgery or interventional treatment can be planned.

MIP reconstructions enhance areas of high radiodensity, and so are useful for angiographic studies. MIP reconstructions tend to enhance air spaces so are useful for assessing lung structure.

3D rendering techniques

;Surface rendering: A threshold value of radiodensity is set by the operator (e.g., a level that corresponds to bone). From this, a three-dimensional model can be constructed using edge detection image processing algorithms and displayed on screen. Multiple models can be constructed from various different thresholds, allowing different colors to represent each anatomical component such as bone, muscle, and cartilage. However, the interior structure of each element is not visible in this mode of operation.

;Volume rendering: Surface rendering is limited in that it will display only surfaces that meet a threshold density, and will display only the surface that is closest to the imaginary viewer. In volume rendering, transparency and colors are used to allow a better representation of the volume to be shown in a single image. For example, the bones of the pelvis could be displayed as semi-transparent, so that, even at an oblique angle, one part of the image does not conceal another.

Image segmentation

Where different structures have similar radiodensity, it can become impossible to separate them simply by adjusting volume rendering parameters. The solution is called segmentation, a manual or automatic procedure that can remove the unwanted structures from the image.

Industrial use

Industrial CT Scanning (Industrial Computed Tomography) is a process which utilizes x-ray equipment to produce 3D representations of components both externally and internally. Industrial CT scanning has been utilized in many areas of industry for internal inspection of components. Some of the key uses for CT scanning have been flaw detection, failure analysis, metrology, assembly analysis and reverse engineering applications

History

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. The idea is based on simple principles of projective geometry: 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 in only the "x" plane. There are also more complex devices that can move in more than one plane and perform more effective blurring.

Tomography has 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 and South African-born Allan McLeod Cormack – gradually supplanted it as the modality of CT. In terms of mathematics, the method is based upon the use of the Radon Transform invented by Johann Radon in 1917. But as Cormack remembered later, he had to find the solution himself since it was only in 1972 that he learned of the work of Radon, by chance.

The first commercially viable CT scanner was invented by Sir Godfrey Hounsfield in Hayes, United Kingdom, at EMI Central Research Laboratories using X-rays. Hounsfield conceived his idea in 1967. The first EMI-Scanner was installed in Atkinson Morley Hospital in Wimbledon, England, and the first patient brain-scan was done on 1 October 1971. It was publicly announced in 1972.

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 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, EMI could fund research and build early models for medical use. 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 minicomputer) was about 7 minutes per picture. This scanner required the use of a water-filled Perspex 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.

In the U.S., the first installation was at the Mayo Clinic. 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. Allan McLeod Cormack of Tufts University in Massachusetts independently invented a similar process, and both Hounsfield and Cormack shared the 1979 Nobel Prize in Medicine.

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. 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 minicomputer both to operate the servo-mechanisms and to acquire and process the images. The Pfizer 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.

Since the first CT scanner, CT technology has vastly improved. Improvements in speed, slice count, and image quality have been the major focus primarily for cardiac imaging. Scanners now produce images much faster and with higher resolution enabling doctors to diagnose patients more accurately and perform medical procedures with greater precision. In the late 90's CT scanners have broke into two major groups, "Fixed CT" and "Portable CT". "Fixed CT Scanners" are large, require a dedicated power supply, electrical closet, HVAC cooling system, a separate workstation room, and a large lead lined room. "Fixed CT Scanners" can also be mounted inside large tractor trailers and driven from site to site and are known as "Mobile CT Scanners". "Portable CT Scanners" are light weight, small, and mounted on wheels. These scanners often have built-in lead shielding and run off of batteries or standard wall power.

Previous studies

Pneumoencephalography Study for brain was quickly replaced by CT. 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 and different degrees of blurring of "out of plane" structures. Although largely obsolete, conventional tomography is still used in specific situations such as dental imaging (orthopantomography) or in intravenous urography.

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. 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 are 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, where it may offer better detection rates with little extra increase in radiation exposure.

Reconstruction algorithms for tomosynthesis are significantly different from those of conventional CT because the conventional filtered back projection algorithm requires a complete set of data. Iterative algorithms based upon expectation maximization are most commonly used, but are extremely computationally intensive. Some manufacturers have produced practical systems using off-the-shelf GPUs to perform the reconstruction.

See also

Virtopsy

Xenon-enhanced CT scanning

X-ray microtomography

MRI versus CT

References

External links

CTisus: Information on body CT (Computed tomography) including a 3D vascular atlas with volume rendering, spiral CT protocols, and teaching files

Open-source computed tomography simulator with educational tracing displays

idoimaging.com: Free software for viewing CT and other medical imaging files

CT Artefacts by David Platten

DigiMorph A library of 3D imagery based on CT scans of the internal and external structure of living and extinct plants and animals.

MicroCT and calcified tissues A website dedicated to microCT in the microscopic analysis of calcified tissues.

Radiation Risk Calculator Calculate cancer risk from CT scans and xrays.

CT scanner video - gantry

CT in your clinical practice by Gregory J. Kohs and Joel Legunn.

Coronary CT angiography by Eugene Lin

CT physics lecture excellent video lectures about physics in computed tomography

Video documentary of patient getting a CT Scan

Atlas of Radiological Images on atlas.mudr.org. Hundreds of imaging cases and thousands of radiological images sorted by method, topography, organs, with short description.

Category:X-ray computed tomography Category:1972 introductions Category:British inventions

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birth name	James Eugene Carrey
birth date	January 17, 1962
birth place	Newmarket, Ontario, Canada
occupation	Actor, comedian
years active	1979–present
spouse	(divorced) (divorced)
website	JimCarrey.com
signature	Firma de Jim Carrey.svg }}

James Eugene "Jim" Carrey (born January 17, 1962) is a Canadian American actor and comedian. He has received two Golden Globe Awards and has also been nominated on four occasions. Carrey began comedy in 1979, performing at Yuk Yuk's in Toronto, Ontario. After gaining prominence in 1981, he began working at The Comedy Store in Los Angeles where he was soon noticed by comedian Rodney Dangerfield, who immediately signed him to open his tour performances. Carrey, long interested in film and television, developed a close friendship with comedian Damon Wayans, which landed him a role in the sketch comedy hit ''In Living Color'', in which he portrayed various characters during the show's 1990 season.

Having had little success in television movies and several low-budget films, Carrey was cast as the title character in ''Ace Ventura: Pet Detective'' which premiered in February, 1994, making more than $72 million domestically despite receiving mixed critical reception. The film spawned a sequel, ''Ace Ventura: When Nature Calls'' (1995), in which he reprised the role of Ventura. High profile roles followed when he was cast as Stanley Ipkiss in ''The Mask'' (1994) for which he gained a Golden Globe Award nomination for Best Actor in a Musical or Comedy, and as Lloyd Christmas in the comedy film ''Dumb and Dumber'' (1994).

Between 1996 and 1999, Carrey continued his success after earning lead roles in several highly popular films including ''The Cable Guy'' (1996), ''Liar Liar'' (1997), in which he was nominated for another Golden Globe Award and in the critically acclaimed films ''The Truman Show'' and ''Man on the Moon'', in 1998 and 1999, respectively. Both films earned Carrey Golden Globe awards. Since earning both awards, Carrey continued to star in comedy films, including ''How the Grinch Stole Christmas'' (2000) where he played the title character, ''Bruce Almighty'' (2003) where he portrayed the role of unlucky TV reporter Bruce Nolan, ''Lemony Snicket's A Series of Unfortunate Events'' (2004), ''Fun with Dick and Jane'' (2005), ''Yes Man'' (2008), and ''A Christmas Carol'' (2009). Carrey has also taken on more serious roles including Joel Barish in ''Eternal Sunshine of the Spotless Mind'' (2004) alongside Kate Winslet and Kirsten Dunst, which earned him another Golden Globe nomination, and Steven Jay Russell in ''I Love You Phillip Morris'' (2009) alongside Ewan McGregor.

Early life

Carrey was born in Newmarket, Ontario, the son of Kathleen (née Oram), a homemaker, and Percy Carrey, a musician and accountant. He has three older siblings, John, Patricia, and Rita. He was raised Roman Catholic. His mother was of French, Irish, and Scottish descent and his father was of French Canadian ancestry (the family's original surname was ''Carré''). After his family moved to Scarborough, Ontario, when Carrey was 14 years old, he attended Blessed Trinity Catholic School, in North York, for two years, enrolled at Agincourt Collegiate Institute for another year, then briefly attended Northview Heights Secondary School for the remainder of his high school career (all together, he spent three years in Grade 10).

Carrey lived in Burlington, Ontario, for eight years and attended Aldershot High School, where he once opened for 1980s new wave band Spoons. In a ''Hamilton Spectator'' interview (February 2007), Carrey remarked, "If my career in show business hadn't panned out I would probably be working today in Hamilton, Ontario at the Dofasco steel mill." When looking across the Burlington Bay toward Hamilton, he could see the mills and thought, "Those were where the great jobs were." At this point, he already had experience working in a science testing facility in Richmond Hill, Ontario.

Career

Comedy

In 1979, under the management of Leatrice Spevack, Carrey started doing stand-up comedy at Yuk Yuk's in Toronto, where he rose to become a headliner in February 1981, shortly after his 19th birthday. One reviewer in the ''Toronto Star'' raved that Carrey was "a genuine star coming to life." In the early 1980s, Carrey moved to Los Angeles and started working at The Comedy Store, where he was noticed by comedian Rodney Dangerfield, who signed the young comedian to open Dangerfield's tour performances.

Carrey then turned his attention to the film and television industries, auditioning to be a cast member for the 1980–1981 season of NBC's ''Saturday Night Live.'' Carrey was not selected for the position (although he did host the show in May 1996, and again in January 2011). Joel Schumacher had him audition for a role in ''D.C. Cab,'' though in the end, nothing ever came of it. His first lead role on television was Skip Tarkenton, a young animation producer on NBC's short-lived ''The Duck Factory,'' airing from April 12, 1984, to July 11, 1984, and offering a behind-the-scenes look at the crew that produced a children's cartoon. Carrey continued working in smaller film and television roles, which led to a friendship with fellow comedian Damon Wayans, who co-starred with Carrey as an extraterrestrial in 1989's ''Earth Girls Are Easy.'' When Wayans' brother Keenen began developing a sketch comedy show for Fox called ''In Living Color,'' Carrey was hired as a cast member, whose unusual characters included masochistic, accident-prone safety inspector Fire Marshall Bill, and masculine female bodybuilder Vera de Milo.

Film

Carrey made his film debut in ''Rubberface'' (1981), which was released as ''Introducing...Janet.'' Later that year, he won the leading role in Damian Lee's Canadian skiing comedy ''Copper Mountain,'' which included his impersonation of Sammy Davis Jr. Since the film had a less than one hour runtime consisting largely of musical performances by Rita Coolidge and Rompin' Ronnie Hawkins, it was not considered a genuine feature film. Two years later, in 1985, Carrey saw his first major starring role in the dark comedy ''Once Bitten,'' in the role of Mark Kendall, a teen virgin pursued by a 400-year-old female vampire, played by Lauren Hutton. After supporting roles in films such as ''Peggy Sue Got Married'' (1986), ''Earth Girls Are Easy'' (1988), and ''The Dead Pool'' (1988), Carrey did not experience true stardom until starring in the 1994 comedy ''Ace Ventura: Pet Detective,'' which premiered only months before ''In Living Color'' ended. ''Ace Ventura'' was panned by critics, and earned Carrey a 1995 Golden Raspberry Award nomination as Worst New Star. But the film was as embraced by fans as it was derided by critics. The Ventura character became a pop icon, and the film made Carrey a superstar. It was a commercial success, as were his two other starring roles from that year: ''The Mask'' and ''Dumb and Dumber''. In 1995, Carrey appeared as the Riddler in ''Batman Forever'' and reprised his role as Ace Ventura in ''Ace Ventura: When Nature Calls.'' Both films were successful at the box office and earned Carrey multi-million-dollar paychecks. Carrey earned $20 million for his next film, ''The Cable Guy'' (directed by Ben Stiller), a record sum for a comedy actor. The film did not do well with critics, but Carrey quickly rebounded with the successful ''Liar Liar,'' a return to his trademark comedy style.

Carrey took a slight pay cut to play a more serious role to star in the critically praised science-fiction film ''The Truman Show'' (1998), a change of pace that led to forecasts of Academy Award nominations. Although the movie was nominated for three other awards, Carrey did not personally receive a nomination, leading him to joke that "it's an honor just to be nominated...oh no," during his appearance on the Oscar telecast. However, Carrey did win a Golden Globe for Best Actor in a Drama and an MTV Movie Award for Best Male Performance. That same year, Carrey appeared as a fictionalized version of himself on the final episode of Garry Shandling's ''The Larry Sanders Show'', in which he deliberately ripped into Shandling's character. In 1999, Carrey won the role of comedian Andy Kaufman in ''Man on the Moon.'' Despite critical acclaim, he was not nominated for an Academy Award, but again won a Best Actor Golden Globe award for the second consecutive year. In 2000, Carrey reteamed with the Farrelly Brothers, who had directed him in ''Dumb and Dumber,'' in their comedy, ''Me, Myself & Irene,'' about a state trooper with multiple personalities who romances a woman played by Renée Zellweger. The film grossed $24 million on its opening weekend and $90 million by the end of its domestic run.

In 2003, Carrey reteamed with Tom Shadyac for the financially successful comedy ''Bruce Almighty''. Earning over $242 million in the U.S. and over $484 million worldwide, this film became the second highest grossing live-action comedy of all time. His performance in ''Eternal Sunshine of the Spotless Mind'' in 2004 earned high praise from critics, who again predicted that Carrey would receive an Oscar nomination; the film did win for Best Original Screenplay, and co-star Kate Winslet received an Oscar nomination for her performance. (Carrey was also nominated for a sixth Golden Globe for his performance).

In 2004, he played the villainous Count Olaf in ''Lemony Snicket's A Series of Unfortunate Events'', which was based on the popular children's novels of the same name. He was also inducted into the Canadian Walk of Fame that year. In 2005, Carrey starred in a remake of ''Fun with Dick and Jane'', playing Dick, a husband who becomes a bank robber after he loses his job. In 2007, Carrey reunited with Joel Schumacher, director of ''Batman Forever'', for ''The Number 23'', a psychological thriller co-starring Virginia Madsen and Danny Huston. In the film, Carrey plays a man who becomes obsessed with the number 23, after finding a book about a man with the same obsession. Carrey has stated that he finds the prospect of reprising a character to be considerably less enticing than taking on a new role. The only time he has reprised a role was with Ace Ventura. (Sequels to ''Bruce Almighty'', ''Dumb and Dumber'', and ''The Mask'' have all been released without Carrey's involvement.) As of December 2010, Carrey's films grossed over $2.3 billion in total.

In 2010, Carrey was the narrator of the documentary film, ''Under the Sea 3D''.

Personal life

Family and relationships

Carrey has been married twice, first to former actress and Comedy Store waitress Melissa Womer on March 28, 1987; the two were divorced in late 1995. Their only child, a daughter named Jane Erin Carrey, was born on September 6, 1987, in Los Angeles County. After his separation from Womer in 1994, Carrey began dating his ''Dumb and Dumber'' co-star Lauren Holly. They were married on September 23, 1996; the marriage lasted less than a year.

In December 2005, Carrey began dating actress and model Jenny McCarthy. They made their relationship public in June 2006. She announced on ''The Ellen DeGeneres Show'' on April 2, 2008, that the two were then living together, but had no plans to marry; as they do not need a "piece of paper." In April 2010, Carrey and McCarthy ended their near five-year relationship.

In Los Angeles on February 27, 2010, Carrey announced via his Twitter account that he had become a grandfather when his daughter Jane gave birth to her first child with musician husband Alex Santana, who performs in the band Blood Money under the stage name Nitro. He announced that his grandson's name was Jackson Riley Santana.

On the 11th season of the reality show singing competition ''American Idol'', Carrey's daughter Jane auditioned during the January 22, 2012 episode. Jane was put through to the Hollywood round.

Citizenship

Carrey received U.S. citizenship in October 2004 and remains a dual citizen of both the United States and his native Canada.

Depression

Carrey discussed his bouts of depression in a November 2004 interview on ''60 Minutes''.

Friendship with Eckhart Tolle

Carrey is a great admirer and friend of author Eckhart Tolle, and in June 2009, Carrey gave an introduction for Tolle when together they headlined the first conference of the Global Alliance for Transformational Entertainment.

Beliefs

Carrey has been a critic of the scientific consensus that no evidence links the childhood MMR vaccination to the development of autism, and wrote an article questioning the merits of vaccination and vaccine research for the ''Huffington Post''. With former partner Jenny McCarthy, Carrey led a "Green Our Vaccines" march in Washington, D.C., to advocate for the removal of toxins from children's vaccines, out of a belief that children had received "too many vaccines, too soon, many of which are toxic".

Filmography

Title	Year	Role	Notes
''The Sex and Violence Family Hour''	1980	Various roles
''All in Good Taste''	1981	Ralph Parker
! scope="row"	1983	Bobby Todd
! scope="row"	1984	Lane Bidlekoff
! scope="row"	1985	Mark Kendall
''Peggy Sue Got Married''	1986	Walter Getz
''The Dead Pool''	1988	Johnny Squares
! scope="row"	1989	Comedian
''Earth Girls Are Easy''	1989	Wiploc
''High Strung''	1991	Death
''Doing Time on Maple Drive''	1992	Tim Carter
! scope="row"	1992	The Exterminator	Voice role
''Ace Ventura: Pet Detective''	1994	Ace Ventura
! scope="row"	1994		London Critics Circle Film Award for Newcomer of the Year (also for ''Ace Ventura: Pet Detective'')Nominated - Golden Globe Award for Best Actor - Motion Picture Musical or ComedyNominated - MTV Movie Award for Best Comedic PerformanceNominated - MTV Movie Award for Best Dance Sequence (shared with Cameron Diaz)
''Dumb and Dumber''	1994	Lloyd Christmas	MTV Movie Award for Best Comedic PerformanceMTV Movie Award for Best Kiss (shared with Lauren Holly)Nominated - MTV Movie Award for Best On-Screen Duo (shared with Jeff Daniels)
''Batman Forever''	1995		Nominated - MTV Movie Award for Best Villain
''Ace Ventura: When Nature Calls''	1995	Ace Ventura
''The Cable Guy''	1996	Ernie "Chip" Douglas	Kids' Choice Award for Favorite Movie ActorMTV Movie Award for Best Comedic PerformanceMTV Movie Award for Best VillainNominated - MTV Movie Award for Best Fight (shared with Matthew Broderick)
''Liar Liar''	1997	Fletcher Reede	Blockbuster Entertainment Award for Favorite Actor - ComedyMTV Movie Award for Best Comedic PerformanceNominated - Golden Globe Award for Best Actor - Motion Picture Musical or ComedyNominated - Kids' Choice Award for Favorite Movie Actor
''The Truman Show''	1998	Truman Burbank
''Simon Birch''	1998	Adult Joe Wenteworth
! scope="row"	1999	Andy Kaufman / Tony Clifton	Boston Society of Film Critics Award for Best ActorGolden Globe Award for Best Actor - Motion Picture Musical or ComedyNominated - American Comedy Award for Funniest Actor (Leading Role)Nominated - Canadian Comedy Award for Film - Male PerformanceNominated - London Critics Circle Film Award for Actor of the Year (also for '' ''[[Me, Myself & Irene">How the Grinch Stole Christmas (film)
''[[Me, Myself & Irene''	2000	Officer Charlie Baileygates/Hank	Teen Choice Award for Wipeout Scene of the SummerNominated - MTV Movie Award for Best Comedic PerformanceNominated - Blockbuster Entertainment Award for Favorite Actor - Comedy/Romance
! scope="row"	2000	The Grinch
! scope="row"	2001	Peter Appleton
! scope="row"	2003	The driver	2-minute short film
''Bruce Almighty''	2003	Bruce Nolan	Kids' Choice Award for Favorite Movie ActorMTV Movie Award, Mexico, for Most Divine Miracle in a MovieTeen Choice Award for Choice Movie Actor - ComedyNominated - MTV Movie Award for Best Comedic PerformanceNominated - MTV Movie Award for Best Kiss (shared with Jennifer Aniston)Nominated - Teen Choice Award for Choice Movie Chemistry (shared with Morgan Freeman)
''Eternal Sunshine of the Spotless Mind''	2004	Joel Barish	San Diego Film Critics Society Award for Best ActorWashington D.C. Area Film Critics Association Award for Best EnsembleNominated - BAFTA Award for Best Performance by an Actor in a Leading RoleNominated - Empire Award for Best ActorNominated - Golden Globe Award for Best Actor - Motion Picture Musical or ComedyNominated - Online Film Critics Society Award for Best ActorNominated - People's Choice Award for Favorite Leading ManNominated - People's Choice Award for Favorite On-Screen Chemistry (shared with Kate Winslet)Nominated - Satellite Award for Best Actor, Musical or Comedy FilmNominated - Saturn Award for Best Actor
''Lemony Snicket's A Series of Unfortunate Events''	2004	Count Olaf	People's Choice Award for Favorite Funny Male StarTeen Choice Award for Choice Movie Bad GuyNominated - MTV Movie Award for Best VillainNominated - Kids' Choice Award for Favorite Movie ActorNominated - Teen Choice Award for Choice Movie Actor: Action/Adventure/ThrillerNominated - Teen Choice Award for Choice Movie Liar
! scope="row"	2005	Dick Harper	Nominated - Kids' Choice Award for Favorite Movie ActorNominated - Teen Choice Award for Choice Actor: Comedy
''The Number 23''	2007	Walter Sparrow / Fingerling
! scope="row"	2008		Voice roleNominated - Kids' Choice Award for Favorite Voice from an Animated Movie
! scope="row"	2008	Carl Allen	MTV Movie Award for Best Comedic PerformancePeople's Choice Award for Favorite Funny Male StarNominated - Kids' Choice Award for Favorite Movie ActorNominated - Teen Choice Award for Choice Movie Actor: ComedyNominated - Teen Choice Award for Choice Movie Hissy FitNominated - Teen Choice Award for Choice Movie Rockstar Moment
''I Love You Phillip Morris''	2009	Steven Jay Russell
! scope="row"	2009	Ebenezer ScroogeGhost of Christmas PastGhost of Christmas PresentGhost of Christmas Yet to Come
''Under the Sea 3D	2009	Narrator
! scope="row"	2011	Tom Popper
	2013	Steve Haines	''pre-production''

Television

! Year	! Title	! Role	Notes
1980	''The All-Night Show''	Various voices	(voice only)
1981	''Rubberface''	Tony Moroni	Television movie
		Jerry Lewis Impersonator	Television series (uncredited)
''The Duck Factory''	Skip Tarkenton	Television series
1989	''Mike Hammer: Murder Takes All''	Brad Peters	Television movie
1990	''In Living Color''	Various roles	Television series
1992	''Doing Time on Maple Drive''	Tim Carter	Television movie
1994	''Space Ghost Coast to Coast''	Himself	Television series (two episodes)
2011		Finger Lakes guy	Episode: "Search Committee"Nominated - People's Choice Award for Favorite TV Guest Star

Other appearances

! Year	! Song	! Album
1998	"I Am the Walrus"

Other accolades

|- |2001 | People's Choice Awards | Favorite Motion Picture Star in a Comedy | |- |2003 | rowspan="2"| Teen Choice Awards | rowspan="2"| Choice Comedian | |- |2004 | |- |rowspan=2| 2005 | People's Choice Awards | Favorite Funny Male Star | |- | Teen Choice Awards | Choice Comedian | |- |2006 | MTV Movie Awards | MTV Generation Award | |- |2009 | People's Choice Awards | Favorite Funny Male Star | |- |2012 | People's Choice Awards | Favorite TV Guest Star | |}

References

Further reading

External links

Category:1962 births Category:Living people Category:20th-century actors Category:20th-century writers Category:21st-century actors Category:Actors from Ontario Category:Comedians from Ontario Category:Best Drama Actor Golden Globe (film) winners Category:Best Musical or Comedy Actor Golden Globe (film) winners Category:Canadian comedians Category:Canadian expatriate actors in the United States Category:Canadian film actors Category:Canadian film producers Category:Canadian emigrants to the United States Category:Canadian impressionists (entertainers) Category:Canadian people of Scottish descent Category:Canadian stand-up comedians Category:Canadian television actors Category:Canadian television writers Category:Canadian voice actors Category:Franco-Ontarian people Category:Naturalized citizens of the United States Category:People from Burlington, Ontario Category:People from Newmarket, Ontario Category:People from Scarborough, Ontario Category:Anti-vaccination activists

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