negron305

It has been suggested that Synchrotron X-ray tomographic microscopy, X-ray tomography be merged into this article or section. (Discuss)

Computed tomography (CT), was originally known as "EMI scan" as it was developed at a research branch of Electric and Musical Industries. It was later known as computed axial tomography (CAT or CT scan) and body section roentgenography. It is a medical imaging method employing tomography where digital geometry processing is used to generate a three-dimensional image of the internals of an object from a large series of two-dimensional X-ray images taken around a single axis of rotation. The word "tomography" is derived from the Greek tomos (slice) and graphein (to write). CT produces a volume of data which can be manipulated, through a process known as windowing, in order to demonstrate various structures based on their ability to block the X-ray beam. Although historically (see below) 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. Image File history File links Mergefrom. ... Synchrotron X-ray tomographic microscopy is a 3-D scanning technique that allows non-invasive high definition scans of fossil embryos to be made. ... X-ray Tomography is a branch of X-ray microscopy. ... CueCat barcode scanner The correct title of this article is :CueCat. ... Medical imaging designates the ensemble of techniques and processes used to create images of the human body (or parts thereof) for clinical purposes (medical procedures seeking to reveal, diagnose or examine disease) or medical science (including the study of normal anatomy and function). ... Tomography is imaging by sections or sectioning. ... Geometry 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. ... 2-dimensional renderings (ie. ... It has been suggested that this article or section be merged into image (disambiguation). ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... negron305 Cat scan redirects here. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...

Although most common in healthcare, CT is also used in other fields, for example nondestructive materials testing. // Nondestructive testing (also called NDT, nondestructive evaluation, NDE, and nondestructive inspection, NDI) is testing that does not destroy the test object. ...

[edit] History

The first commercially viable CT scanner was invented by Sir Godfrey Newbold Hounsfield in Hayes, United Kingdom at Thorn EMI Central Research Laboratories using X-rays. Hounsfield conceived his idea in 1967, and it was publicly announced in 1972. Allan McLeod Cormack of Tufts University, Massachusetts, USA independently invented a similar process, and both Hounsfield and Cormack shared the 1979 Nobel Prize in Medicine. Sir Godfrey Newbold Hounsfield (28 August 1919 - 12 August 2004) 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 computerized axial tomography (CAT). ... , For other places with the same name, see Hayes. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... Year 1967 (MCMLXVII) was a common year starting on Sunday (link will display full calendar) of the 1967 Gregorian calendar. ... Year 1972 (MCMLXXII) was a leap year starting on Saturday (link will display full calendar) of the Gregorian calendar. ... Allan M. Cormack at Tufts University Allan MacLeod Cormack (February 23, 1924 – May 7, 1998) was a South African-born American physicist who shared a part of the 1979 Nobel Prize in Physiology or Medicine for his work on the computerized axial tomography (CAT) scan. ... Tufts University is a private research university in Medford/Somerville, Massachusetts, suburbs of Boston. ... Also: 1979 by Smashing Pumpkins. ... The Nobel Prizes (Swedish: ), as designated in Alfred Nobels will in 1895, are awarded for physics, chemistry, physiology or medicine, literature, and peace. ... For the chemical substances known as medicines, see medication. ...

The prototype CT scanner

The original 1971 prototype took 160 parallel readings through 180 angles, each 1° apart, with each scan taking a little over five minutes. The images from these scans took 2.5 hours to be processed by algebraic reconstruction techniques on a large computer. Image File history File linksMetadata Download high-resolution version (2304x1728, 1554 KB) Summary The very first ct scanner prototype. ... Image File history File linksMetadata Download high-resolution version (2304x1728, 1554 KB) Summary The very first ct scanner prototype. ...

It has been claimed that the CT scanner was "the greatest legacy" of the Beatles, with the massive profits resulting from their record sales enabled EMI to fund scientific research^[1], including into computerised tomography. 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. The first EMI-Scanner was installed in Atkinson Morley's Hospital in Wimbledon, England, and the first patient brain-scan was made with it in 1972. The Beatles appeared on The Ed Sullivan Show in 1964 as part of their first tour of the United States, promoting their first hit single there, I Want To Hold Your Hand. ... Data General SuperNova The Data General Nova was a popular 16-bit minicomputer built by the United States company Data General starting in 1969. ... Perspex could mean several things. ...

a historic EMI-Scanner

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 R. Image File history File links Emi1010. ... Image File history File links Emi1010. ... Main campus in downtown Rochester, Minnesota. ...

The first CT system that could make images of any part of the body, and did not require the "water tank" was the ACTA scanner designed by Robert S. Ledley, DDS at Georgetown University. Georgetown University is an elite private research university located in Georgetown, Washington, D.C., United States. ...

[edit] Previous studies

[edit] Tomography

CT's primary benefit is the ability to separate anatomical structures at different depths within the body. 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. In optics, particularly film and photography, the depth of field (DOF) is the distance in front of and beyond the subject that appears to be in focus. ...

Although largely obsolete, conventional tomography is still used in specific situations such as dental imaging (orthopantomography) or in intravenous urography. This x-ray scan illustrates the maxilla and mandible, all the teeth including the wisdom teeth, the frontal, nasal and maxillary sinus air spaces and the temporomandibular joint complex or TMJ. An Orthopantomogram(OPG) also known as an orthopantogram or panorex, is a panoramic scanning dental X-ray of the... Urography (also pyelography, intravenous urogram or IVU) is a medical examination procedure to check the function of the kidneys and its drain tubes (ureters). ...

[edit] 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 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 a extension to mammography, where it may offer better detection rates, with little extra increase in radiation exposure. Mammography. ...

Reconstruction algorithms for tomosynthesis are significantly different from conventional CT, as 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 commercial GPUs to perform the reconstruction. Filtered back projection is a reconstruction algorithm used to invert the Radon transform. ... In statistical computing, an expectation-maximization (EM) algorithm is an algorithm for finding maximum likelihood estimates of parameters in probabilistic models, where the model depends on unobserved latent variables. ... “GPU” redirects here. ...

[edit] Types of Modern CT acquisition

[edit] Scout/Pilot/Topogram

A Scout image is used in planning the exam and to establish where the target organs are located. The beginning and end of the scan are set by the target region and the location of the patient on the table. Once the Scout image is created it is used to determine the extent of the desired Axial/Helical scan. During the Scout scan the gantry is rotated to a fixed position and the table is translated as x-ray is delivered. The image appears similar to a radiograph.

[edit] Axial

In axial "step and shoot" acquisitions each slice/volume is taken and then the table is incremented to the next location. In multislice scanners each location is multiple slices and represents a volume of the patient anatomy. Tomographic reconstruction is used to generate Axial images. The mathematical basis for tomographic imaging was laid down by Johann Radon. ...

[edit] Cine

A cine acquisition is used when the temporal nature is important. This is used in Perfusion applications to evaluate blood flow, blood volume and mean transit time. Cine is a time sequence of axial images. In a Cine acquisition the cradle is stationary and the gantry rotates continuously. Xray is delivered at a specified interval and duration. In physiology, perfusion is the process of nutritive delivery of arterial blood to a capillary bed in the biological tissue. ...

[edit] Helical/Spiral

Helical is a very fast way to examine the target anatomy. The volume is scanned very quickly because the table is in constant motion as the gantry rotates continuously. There is no interscan delay between slices as in a Axial acquisition.

[edit] DRR

A Digitally Reconstructed Radiograph (DRR) is used to help plan the treatment. The DRR is corrected for the fan beam effect. This is the prime difference from the Scout/Pilot image. A Digitally Reconstructed Radiograph (DRR) is created from computed tomography (CT) data. ...

It has been suggested that Digitally Reconstructed Radiograph be merged into this article or section. (Discuss)

Image File history File links Mergefrom. ... A Digitally Reconstructed Radiograph (DRR) is created from computed tomography (CT) data. ...

[edit] Generations

Since the introduction of the first clinical system by Hounsfield, several generations of scanners have been produced, with distinguishing tube-detector configuration and scanning motion (Canadian Association of Medical Radiation Technologists CT Imaging 1-Theory textbook).

Although numbered sequentially, the 3rd and 4th generation designs developed at approximately the same time. The concept of electron beam CT, which some authors have called 5th generation, followed later. Some authors have described up to 7 generations of CT design. However, it is only generations one to four that are widely, and consistently, recognised. A schematic diagram of a Crookes tube apparatus. ...

In the first and second generation designs, the X-ray beam was not wide enough to cover the entire width of the 'slice' of interest. A mechanical arrangement was required to move the X-ray source and detector horizontally across the field of view. After a sweep, the source/detector assembly would be rotated a few degrees, and another sweep performed. This process would be repeated until 360 degrees (or 180 degrees) had been covered. The complex motion placed a limit on the minimum scan time at approximately 20 seconds per image.

In the 3rd and 4th generation designs, the X-ray beam is able to cover the entire field of view of the scanner. This avoids the need for any horizontal motion; an entire 'line' can be captured in an instant. This allowed simplification of the motion to rotation of the X-ray source. Third and fourth generation designs differ in the arrangement of the detectors. In 3rd generation, the detector array is as wide as the beam, and must therefore rotate as the source rotates. In 4th generation, an entire ring of stationary detectors are used.

The third generation design suffers because it is highly sensitive to detector performance. Because of the fixed relationship of a detector to a specific part of the beam, any miscalibration or malfunction of an individual detector will appear as a ring in the final reconstructed image. As the detectors moved and were exposed to physical stress, loss of calibration and subsequent 'ring artifacts' were commonplace. The fourth generation, with its fixed detectors benefited not just from improved reliability of the detectors, but because the detectors could be automatically calibrated as the X-ray beam approached, and because the different reconstruction geometry meant that a malfunction would lead only to subtle loss of image contrast (fogging) rather than a visible ring.

Solving the issue of detector stability has led 3rd generation designs to the dominant position in contemporary designs. 4th generation designs suffered very high cost (due to the large number of detectors) and had very high susceptibility to 'streak artifacts' (due to compton scattering). All current CT scanners are of the 3rd generation design. In physics, Compton scattering or the Compton effect, is the decrease in energy (increase in wavelength) of an X-ray or gamma ray photon, when it interacts with matter. ...

[edit] Electron Beam CT

Electron beam tomography (EBCT) was introduced in the early 1980s, by medical physicist Andrew Castagnini, as a method of improving the temporal resolution of CT scanners. Because the X-ray source has to rotate by over 180 degrees in order to capture an image the technique is inherently unable to capture dynamic events or movements that are quicker than the rotation time. Patent illustration showing a cutaway view of an electron beam computerized tomography system. ...

Instead of rotating a conventional X-ray tube around the patient, the EBCT machine houses a huge vacuum tube in which an electron beam is electro-magnetically steered towards an array of tungsten X-ray anodes arranged circularly around the patient. Each anode is hit in turn by the electron beam and emits X-rays that are collimated and detected as in conventional CT. The lack of moving parts allows very quick scanning, with single slice acquisition in 50-100 ms, making the technique ideal for capturing images of the heart. EBCT has found particular use for assessment of coronary artery calcium, a means of predicting risk of coronary artery disease.

The very high cost of EBCT equipment, and its poor flexibility (EBCT scanners are essentially single-purpose cardiac scanners), has led to poor uptake; fewer than 150 of these scanners have been installed worldwide. EBCT's role in cardiac imaging is rapidly being supplanted by high-speed multi-detector CT, which can achieve near-equivalent temporal resolution with much faster z-axis coverage.

[edit] Helical or Spiral CT

See main article Helical cone beam computed tomography

Helical, also called spiral, CT was introduced in the early 1990s, with much of the development led by Willi Kalender and Kazuhiro Katada. In older CT scanners, the X-ray source would move in a circular fashion to acquire a single 'slice', once the slice had been completed, the scanner table would move to position the patient for the next slice; meanwhile the X-ray source/detectors would reverse direction to avoid tangling their cables. Helical (or spiral) cone beam computed tomography is a type of three dimensional computed tomography (CT) in which the source (usually of x-rays) describes a helical trajectory relative to the object while a two dimensional array of detectors measures the transmitted radiation on part of a cone of rays... A helix (pl: helices), from the Greek word έλικας/έλιξ, is a twisted shape like a spring, screw or a spiral (correctly termed helical) staircase. ... This article does not cite any references or sources. ... Prof Dr Willi A. Kalender is a medical physicist credited with the invention and development of spiral scan computed tomography. ...

In helical CT the X-ray source (and detectors in 3rd generation designs) are attached to a freely rotating gantry. During a scan, the table moves the patient smoothly through the scanner; the name derives from the helical path traced out by the X-ray beam. It was the development of two technologies that made helical CT practical: slip rings to transfer power and data on and off the rotating gantry, and the switched mode power supply powerful enough to supply the X-ray tube, but small enough to be installed on the gantry. In electrical engineering, a slip ring is a method of making an electrical connection through a rotating assembly. ... A switched-mode power supply, or SMPS, is an electronic power supply unit (PSU) that incorporates a switching regulator - an internal control circuit that switches the load current rapidly on and off in order to stabilise the output voltage. ...

The major advantage of helical scanning compared to the traditional shoot-and-step approach, is speed; a large volume can be covered in 20-60 seconds. This is advantageous for a number or reasons: 1) often the patient can hold their breath for the entire study, reducing motion artifacts, 2) it allows for more optimal use of intravenous contrast enhancement, and 3) the study is quicker than the equivalent conventional CT permitting the use of higher resolution acquisitions in the same study time. The data obtained from spiral CT is often well-suited for 3D imaging because of the lack of motion mis-registration and the increased out of plane resolution. These major advantages led to the rapid rise of helical CT as the most popular type of CT technology.

Despite the advantages of helical scanning, there are a few circumstances where it may not be desirable - there is, of course, no difficulty in configuring a helical capable scanner for scanning in shoot-and-step mode. All other factors being equal, helical CT has slightly lower z-axis resolution than step-and-shoot (due to the continual movement of the patient). Where z-resolution is critical but where it is undesirable to scan at a higher resolution setting (due to the higher radiation exposure required) e.g. brain imaging, step-and-shoot may still be the preferred method.

[edit] Multislice CT

Multislice CT scanners are similar in concept to the helical or spiral CT but there are more than one detector ring. It began with two rings in mid nineties, with a 2 solid state ring model designed and built by Elscint (Haifa) called CT TWIN, with one second rotation (1993): It was followed by other manufacturers. Later, it was presented 4, 8, 16, 32, 40 and 64 detector rings, with increasing rotation speeds. Current models (2007) have up to 3 rotations per second, and isotropic resolution of 0.35mm voxels with z-axis scan speed of up to 18 cm/s.^[2]. This resolution exceeds that of High Resolution CT techniques with single-slice scanners, yet it is practical to scan adjacent, or overlapping, slices - however, image noise and radiation exposure significantly limit the use of such resolutions. High Resolution CT or HRCT of the lung is a medical diagnostic test used for diagnosis and assessment of Interstitial lung disease. ...

The major benefit of multi-slice CT is the increased speed of volume coverage. This allows large volumes to be scanned at the optimal time following intravenous contrast administration; this has particularly benefitted CT angiography techniques - which rely heavily on precise timing to ensure good demonstration of arteries.

Computer power permits increasing the postprocessing capabilities on workstations. Bone suppression, volume rendering in real time, with a natural visualization of internal organs and structures, and automated volume reconstruction really change the way diagnostic is performed on CT studies and this models become true volumetric scanners. The ability of multi-slice scanners to achieve isotropic resolution even on routine studies means that maximum image quality is not restricted to images in the axial plane - and studies can be freely viewed in any desired plane. Isotropic means independent of direction. Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented. ...

[edit] Dual Source CT

Siemens introduced a CT model with dual X-ray tube and dual array of 64 slice detectors, at the 2005 Radiological Society of North America (RSNA) medical meeting. Dual sources increase the temporal resolution by reducing the rotation angle required to acquire a complete image, thus permitting cardiac studies without the use of heart rate lowering medication, as well as permitting imaging of the heart in systole. The use of two x-ray units makes possible the use of dual energy imaging, which allows an estimate of the average atomic number in a voxel, as well as the total attenutaion. This permits automatic differentiation of calcium (e.g. in bone, or diseased arteries) from iodine (in contrast medium) or titanium (in stents) - which might otherwise be impossible to differentiate. It may also improve the characterization of tissues allowing better tumor differentiation. The Radiological Society of North America (RSNA), founded in 1915, has the purpose to promote and develop the highest standards of radiology and related sciences through education and research. The society publishes the journals Radiology and RadioGraphics. ...

[edit] 256 Slice CT

Several companies are developing 256 slice detector systems. The majority of published data with regard to both technical and clinical aspects of the systems have been related to the prototype unit made by Toshiba Medical Systems. The recent 3 month Beta installation at Johns Hopkins Press Release using a Toshiba system tested the clinical capabilities of this technology JHU Gazette. The technology currently remains in a development phase but has demonstrated the potential to significantly reduce radiation exposure by eliminating the requirement for a helical examination in both cardiac CT angiography and whole brain perfusion studies for the evaluation of stroke.

[edit] Inverse geometry CT

Inverse geometry CT (IGCT) is a novel concept which is being investigated as refinement of the classic third generation CT design. Although the technique has been demonstrated on a laboratory proof-of-concept device, it remains to be seen whether IGCT is feasible for a practical scanner. IGCT reverses the shapes of the detector and X-ray sources. The conventional third-generation CT geometry uses a point source of X-rays, which diverge in a fan beam to act on a linear array of detectors. In multidetector computed tomography (MDCT), this is extended in 3 dimensions to a conical beam acting on a 2D array of detectors. The IGCT concept, conversely, uses an array of highly collimated X-ray sources which act on a point detector. By using a principle similar to electron beam tomography (EBCT), the individual sources can be activated in turn by steering an electron beam onto each source target. Patent illustration showing a cutaway view of an electron beam computerized tomography system. ...

The rationale behind IGCT is that it avoids the disadvantages of the cone-beam geometry of third generation MDCT. As the z-axis width of the cone beam increases, the quantity of scattered radiation reaching the detector also increases, and the z-axis resolution is thereby degraded - because of the increasing z-axis distance that each ray must traverse. This reversal of roles has extremely high intrinsic resistance to scatter; and, by reducing the number of detectors required per slice, it makes the use of better performing detectors (e.g. ultra-fast photon counting detectors) more practical. Because a separate detector can be used for each 'slice' of sources, the conical geometry can be replaced with an array of fans, permitting z-axis resolution to be preserved.

[edit] Diagnostic use

Since its introduction in the 1970s, CT has become an important tool in medical imaging to supplement X-rays and medical ultrasonography. Although it is still quite expensive, it is the gold standard in the diagnosis of a large number of different disease entities. It has more recently begun to also be used for preventive medicine or screening for disease, for example CT colonography for patients with a high risk of colon cancer. Although a number of institutions offer full-body scans for the general population, this practice remains controversial due to its lack of proven benefit, cost, radiation exposure, and the risk of finding 'incidental' abnormalities that may trigger additional investigations. The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ... Medical imaging designates the ensemble of techniques and processes used to create images of the human body (or parts thereof) for clinical purposes (medical procedures seeking to reveal, diagnose or examine disease) or medical science (including the study of normal anatomy and function). ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... Medical ultrasonography (sonography) is an ultrasound-based diagnostic imaging technique used to visualize muscles and internal organs, their size, structures and possible pathologies or lesions. ... In medicine, a gold standard test is the diagnostic test that is regarded as definitive in determining whether an individual has a disease process. ... A 1930 Soviet poster propagating breast care. ... Screening, in medicine, is a strategy used to identify disease in an unsuspecting population. ... CT apparatus in a hospital Full-body scan, also known as a full-body CT scan, is a controversial type of preventive medicine. ...

[edit] Cranial

Normal CT scan of the head; this slice shows the cerebellum, a small portion of each temporal lobe, the orbits, and the ethmoid sinuses.

Diagnosis of cerebrovascular accidents and intracranial hemorrhage is the most frequent reason for a "head CT" or "CT brain". Scanning is done with or without intravenous contrast agents. CT generally does not exclude infarct in the acute stage of a stroke. However, CT is useful to exclude an intra-cranial hemorrhage as a cause, or complication of the stroke. For the detection of acute hemorrhage, especially subarachnoid hemorrhage, CT is the test of choice as it is more sensitive than MRI. Image File history File linksMetadata Head_CT_scan. ... Image File history File linksMetadata Head_CT_scan. ... The cerebellum (Latin: little brain) is a region of the brain that plays an important role in the integration of sensory perception and motor output. ... The temporal lobes are part of the cerebrum. ... In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. ... ethmoidal sinuses can be divided into 3: a) anterior b) middle c) posterior except the posterior ethmoidal sinus, all the ethmoidal sinuses will drain into middle meateus. ... A stroke or cerebrovascular accident (CVA) occurs when the blood supply to a part of the brain is suddenly interrupted by occlusion (an ischemic stroke- approximately 90% of strokes), by hemorrhage (a hemorrhagic stroke - less than 10% of strokes) or other causes. ... This article needs cleanup. ... In medicine, infarction is necrosis of tissue due to upstream obstruction of its arterial blood supply. ... For other uses, see Stroke (disambiguation). ... A subarachnoid hemorrhage (SAH) is bleeding into the subarachnoid space surrounding the brain, i. ...

For detection of tumors, CT scanning with IV contrast is occasionally used but is less sensitive than magnetic resonance imaging (MRI). For malignant tumors specifically, see cancer. ... “MRI” redirects here. ...

CT has an important role in evaluation of the functioning of a ventriculoperitoneal shunt by demonstrating the volume of the ventricular system. Although CT cannot assess intracranial pressure, it can demonstrate several important causes of raised intracranial pressure. Despite the limitation that CT may not detect raised intracranial pressure, it may help in the clinical decision to perform lumbar puncture and is often performed in this context. Intracranial pressure, (ICP), is the pressure exerted by the cranium on the brain tissue, cerebrospinal fluid (CSF), and the brains circulating blood volume. ... A patient undergoes a lumbar puncture at the hands of a neurologist. ...

CT is also useful in the setting of trauma for evaluating facial and skull fractures.

In the head/neck/mouth area, CT scanning is used for surgical planning for craniofacial and dentofacial deformities, evaluation of cysts and some tumors of the jaws/paranasal sinuses/nasal cavity/orbits, diagnosis of the causes of chronic sinusitis, and for planning of dental implant reconstruction. Sinusitis is an inflammation of the paranasal sinuses, which may or may not be as a result of infection, from bacterial, fungal, viral, allergic or autoimmune issues. ...

[edit] Chest

Chest CT: Axial Slice

CT is excellent for detecting both acute and chronic changes in the lung parenchyma. 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 (HRCT). Image File history File links Chest_CT_scan_with_lung_metastatis_2. ... Image File history File links Chest_CT_scan_with_lung_metastatis_2. ... Human respiratory system The lungs flank the heart and great vessels in the chest cavity. ... Fibrosis is the formation or development of excess fibrous connective tissue in an organ or tissue as a reparative or reactive process, as opposed to a formation of fibrous tissue as a normal constituent of an organ or tissue. ...

For detection of airspace disease (such as pneumonia) or cancer, relatively thick sections and general purpose image reconstruction techniques may be adequate. IV contrast may also be used as it clarifies the anatomy and boundaries of the great vessels and improves assessment of the mediastinum and hilar regions for lymphadenopathy; this is particularly important for accurate assessment of cancer. This article is about human pneumonia. ... Lung cancer is the malignant transformation and expansion of lung tissue, and is the most lethal of all cancers worldwide, responsible for 1. ... Great vessels is a term used to refer collectively to the primary blood vessels, which include: Vena cavae Superior vena cava Inferior vena cava Pulmonary artery Pulmonary trunk Right pulmonary artery Left pulmonary artery Pulmonary veins Right superior Right inferior Left superior Left inferior Aorta Category: ... FIG. 967– Transverse section through the upper margin of the second thoracic vertebra The mediastinum is a non-delineated group of structures in the thorax (chest), surrounded by loose connective tissue. ... Lymphadenopathy is a term meaning disease of the lymph nodes. ...

CT angiography of the chest is also becoming the primary method for detecting pulmonary embolism (PE) and aortic dissection, and requires accurately timed rapid injections of contrast (Bolus Tracking) and high-speed helical scanners. CT is the standard method of evaluating abnormalities seen on chest X-ray and of following findings of uncertain acute significance. Aortic dissection is a tear in the wall of the aorta (the largest artery of the body). ... A Sagital MPR of an AAA Volume Rendered Carotid Angiogram Bolus tracking is a technique used in CT imaging, to visualise vessels more clearly. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz...

[edit] Cardiac

With the advent of subsecond rotation combined with multi-slice CT (up to 64-slice), high resolution and high speed can be obtained at the same time, allowing excellent imaging of the coronary arteries (cardiac CT angiography). Images with an even higher temporal resolution can be formed using retrospective ECG gating. In this technique, each portion of the heart is imaged more than once while an ECG trace is recorded. The ECG is then used to correlate the CT data with their corresponding phases of cardiac contraction. Once this correlation is complete, all data that were recorded while the heart was in motion (systole) can be ignored and images can be made from the remaining data that happened to be acquired while the heart was at rest (diastole). In this way, individual frames in a cardiac CT investigation have a better temporal resolution than the shortest tube rotation time.

Because the heart is effectively imaged more than once (as described above), cardiac CT angiography results in a relatively high radiation exposure around 12 mSv. For the sake of comparison, a chest X-ray carries a dose of approximately 0.02^[3] to 0.2 mSv and natural background radiation exposure is around 0.01 mSv/day. Thus, cardiac CTA is equivalent to approximately 100-600 chest X-rays or over 3 years worth of natural background radiation. Methods are available to decrease this exposure, however, such as prospectively decreasing radiation output based on the concurrently acquired ECG (aka tube current modulation.) This can result in a significant decrease in radiation exposure, at the risk of compromising image quality if there is any arrhythmia during the acquisition. The significance of radiation doses in the diagnostic imaging range has not been proven, although the possibility of inducing an increased cancer risk across a population is a source of significant concern. This potential risk must be weighed against the competing risk of not performing a test and potentially not diagnosing a significant health problem such as coronary artery disease.

It is uncertain whether this modality will replace invasive coronary catheterization. Currently, it appears that the greatest utility of cardiac CT lies in ruling out coronary artery disease rather than ruling it in. This is because the test has a high sensitivity (greater than 90%) and thus a negative test result means that a patient is very unlikely to have coronary artery disease and can be worked up for other causes of their chest symptoms. A positive result is less conclusive and often will be confirmed (and possibly treated) with subsequent invasive angiography. For the record, the positive predictive value of cardiac CTA is estimated at approximately 82% and the negative predictive value is around 93%. Coronary angiogram A coronary catheterization is a minimally invasive procedure to access the coronary circulation and blood filled chambers of the heart using a catheter. ...

Dual Source CT scanners, introduced in 2005, allow higher temporal resolution by acquiring a full CT slice in only half a rotation, thus reducing motion blurring at high heart rates and potentially allowing for shorter breath-hold time. This is particularly useful for ill patients who have difficulty holding their breath or who are unable to take heart-rate lowering medication. Year 2005 (MMV) was a common year starting on Saturday (link displays full calendar) of the Gregorian calendar. ... This article does not cite any references or sources. ...

The speed advantages of 64-slice MSCT have rapidly established it as the minimum standard for newly installed CT scanners intended for cardiac scanning. Manufacturers are now actively developing 256-slice and true 'volumetric' scanners, primarily for their improved cardiac scanning performance.

The latest MSCT scanners acquire images only at 70-80% of the R-R interval (late diastole). This prospective gating can reduce effective dose from 10-15mSv to as little as 1.2mSv in follow-up patients acquiring at 75% of the R-R interval. Effective doses at a centre with well trained staff doing coronary imaging can average less than the doses for conventional coronary angiography.

[edit] 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. Renal/urinary stones, appendicitis, pancreatitis, diverticulitis, abdominal aortic aneurysm, and bowel obstruction are conditions that are readily diagnosed and assessed with CT. CT is also the first line for detecting solid organ injury after trauma. The human abdomen (from the Latin word meaning belly) is the part of the body between the pelvis and the thorax. ... “Bladder stone” redirects here. ... Appendicitis (or epityphlitis) is a condition characterized by inflammation of the appendix[1]. While mild cases may resolve without treatment, most require removal of the inflamed appendix, either by laparotomy or laparoscopy. ... Pancreatitis is inflammation of the pancreas. ... Diverticulitis is a common digestive disorder particularly found in the large intestine. ... An aortic aneurysm is a general term for any swelling (dilatation or aneurysm) of the aorta, usually representing an underlying weakness in the wall of the aorta at that location. ... Bowel obstruction is a mechanical blockage of the intestines, preventing the normal transit of the products of digestion. ...

Oral and/or rectal contrast may be used depending on the indications for the scan. A dilute (2% w/v) suspension of barium sulfate is most commonly used. The concentrated barium sulfate preparations used for fluoroscopy e.g. barium enema are too dense and cause severe artifacts on CT. Iodinated contrast agents may be used if barium is contraindicated (e.g. suspicion of bowel injury). Other agents may be required to optimize the imaging of specific organs: e.g. rectally administered gas (air or carbon dioxide) for a colon study, or oral water for a stomach study. Granulated Barium Sulfate Barium sulfate (or barium sulphate) is the white crystalline solid with the formula BaSO4. ... A modern fluoroscope. ... A barium enema, also called a lower gastrointestinal series, is a medical procedure used to examine and dignose problems with the human large intestines. ... iodinated contrast is an intervenous radiographic die containing iodine, which enhances vascular structures and organs. ... Carbon dioxide is a chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom. ...

CT has limited application in the evaluation of the pelvis. For the female pelvis in particular, ultrasound and MRI are the imaging modalities of choice. Nevertheless, it may be part of abdominal scanning (e.g. for tumors), and has uses in assessing fractures. The pelvis (pl. ... Medical ultrasonography (sonography) is an ultrasound-based diagnostic imaging technique used to visualize muscles and internal organs, their size, structures and possible pathologies or lesions. ... “MRI” redirects here. ...

CT is also used in osteoporosis studies and research along side DXA scanning. Both CT and DXA can be used to assess bone mineral density (BMD) which is used to indicate bone strength, however CT results do not correlate exactly with DXA (the gold standard of BMD measurement). CT is far more expensive, and subjects patients to much higher levels of ionizing radiation, so it is used infrequently. Osteoporosis is a disease of bone in which the bone mineral density (BMD) is reduced, bone microarchitecture is disrupted, and the amount and variety of non-collagenous proteins in bone is altered. ... Dual energy X-ray absorptiometry (DXA, previously DEXA) is a means of measuring bone mineral density (BMD). ...

[edit] 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. A fractured bone in a living person is typically treated by restoring the fractured pieces of bone to their natural positions (if necessary), and maintaining those positions while the bone heals. ...

[edit] Advantages and hazards

[edit] Advantages over projection 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. Third, 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. A radiograph of a right elbow-joint Radiography is the use of certain types of electromagnetic radiation—usually ionizing—to view objects. ...

[edit] Radiation exposure

CT is regarded as a moderate to high radiation diagnostic technique. While technical advances have improved radiation efficiency, there has been simultaneous pressure to obtain higher-resolution imaging and use more complex scan techniques, both of which require higher doses of radiation. The improved resolution of CT has permitted the development of new investigations, which may have advantages; e.g. Compared to conventional angiography, CT angiography avoids the invasive insertion of an arterial catheter and guidewire; CT colonography may be as useful as a barium enema for detection of tumors, but may use a lower radiation dose. Radiation as used in physics, is energy in the form of waves or moving subatomic particles. ... Angiography or arteriography is a medical imaging technique in which an X-ray picture is taken to visualize the inner opening of blood filled structures, including arteries, veins and the heart chambers. ... Cardiac catheterization (heart cath) is the insertion of a catheter into a chamber or vessel of the heart. ... A barium enema, also called a lower gastrointestinal series, is a medical procedure used to examine and dignose problems with the human large intestines. ...

The greatly increased availability of CT, together with its value for an increasing number of conditions, has been responsible for a large rise in popularity. So large has been this rise that, in the most recent comprehensive survey in the UK, CT scans constituted 7% of all radiologic examinations, but contributed 47% of the total collective dose from medical X-ray examinations in 2000/2001.^[4] Increased CT usage has led to an overall rise in the total amount of medical radiation used, despite reductions in other areas.

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. Additionally, two helical CT scanning parameters that can be adjusted easily and that have a profound effect on radiation dose are tube current and pitch.^[5] 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.^[6]

[edit] Typical scan doses

In pharmacology an effective dose is the amount of drug that produces a therapeutic response in 50% of the people taking it. ... The sievert (symbol: Sv) is the SI derived unit of dose equivalent. ...

[edit] Adverse reactions to contrast agents

Because 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. Certain patients may experience severe and potentially life-threatening allergic reactions to the contrast dye. Intravenous therapy or IV therapy is the giving of liquid substances directly into a vein. ... Radiocontrast agents (or simply contrast agents) are compounds used to improve the visibility of internal bodily structures in an X-ray image. ... Anaphylaxis is an acute systemic (multi-system) and severe Type I Hypersensitivity allergic reaction in humans and other mammals. ...

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. Perhaps paradoxically, 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. Nephropathy refers to damage to or disease of the kidney. ... Renal failure is the condition in which the kidneys fail to function properly. ... For the disease characterized by excretion of large amounts of very dilute urine, see diabetes insipidus. ... iodinated contrast is an intervenous radiographic die containing iodine, which enhances vascular structures and organs. ... The mri are a fictional alien species in the Faded Sun Trilogy of C.J. Cherryh. ...

[edit] Process

CT scan illustration

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. Many data scans are progressively taken as the object is gradually passed through the gantry. They are combined together by the mathematical procedure known as tomographic reconstruction. Image File history File links Size of this preview: 268 × 277 pixelsFull resolution (268 × 277 pixel, file size: 11 KB, MIME type: image/jpeg) en:Computed tomography scan File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Computed tomography... Image File history File links Size of this preview: 268 × 277 pixelsFull resolution (268 × 277 pixel, file size: 11 KB, MIME type: image/jpeg) en:Computed tomography scan File links The following pages on the English Wikipedia link to this file (pages on other projects are not listed): Computed tomography... The mathematical basis for tomographic imaging was laid down by Johann Radon. ...

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, is 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. Helical (or spiral) cone beam computed tomography is a type of three dimensional computed tomography (CT) in which the source (usually of x-rays) describes a helical trajectory relative to the object while a two dimensional array of detectors measures the transmitted radiation on part of a cone of rays...

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. An X-Ray tube is a vacuum tube designed to produce man made X-Ray photons on demand. ... Patent illustration showing a cutaway view of an electron beam computerized tomography system. ...

The data stream representing the varying radiographic intensity sensed reaching the detectors on the opposite side of the circle during each sweep is then computer processed to calculate cross-sectional estimations of the radiographic density, expressed in Hounsfield units. Sweeps cover 360 or just over 180 degrees in conventional machines, 220 degrees in EBT. The Hounsfield scale is a quantitative scale for describing radiodensity. ...

CT scanner with cover removed to show the principle of operation

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. Image File history File linksMetadata Download high resolution version (681x674, 102 KB)A modern (2006) CT scanner with the cover removed, demonstrating the principle of operation. ... Image File history File linksMetadata Download high resolution version (681x674, 102 KB)A modern (2006) CT scanner with the cover removed, demonstrating the principle of operation. ... For the chemical substances known as medicines, see medication. ... An intravenous drip in a hospital Intravenous therapy or IV therapy is the administration of liquid substances directly into a vein. ... For the record label, see Iodine Recordings. ...

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 -1024 to +3071 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 differ 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. This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen. ... Radiodensity is the property of relative transparency to the passage of X-rays through a material. ... The Hounsfield scale is a quantitative scale for describing radiodensity. ... This example shows an image with a portion greatly enlarged, in which the individual pixels are rendered as little squares and can easily be seen. ... A voxel (a portmanteau of the words volumetric and pixel) is a volume element, representing a value on a regular grid in three dimensional space. ... The Hounsfield scale is a quantitative scale for describing radiodensity. ...

[edit] Windowing

Windowing is the process of using the calculated Hounsfield units to make an image. The various radiodensity amplitudes are mapped to 256 shades of gray. These shades of gray can be distributed over a wide range of HU values to get an overview of structures that attenuate the beam to widely varying degrees. Alternatively, these shades of gray can be distributed over a narrow range of HU values (called a "narrow window") centered over the average HU value of a particular structure to be evaluated. In this way, subtle variations in the internal makeup of the structure can be discerned. This is a commonly used image processing technique known as contrast compression. For example, to evaluate the abdomen in order to find subtle masses in the liver, one might use liver windows. Choosing 70 HU as an average HU value for liver, the shades of gray can be distributed over a narrow window or range. One could use 170 HU as the narrow window, with 85 HU above the 70 HU average value; 85 HU below it. Therefore the liver window would extend from -15 HU to +155 HU. All the shades of gray for the image would be distributed in this range of Hounsfield values. Any HU value below -15 would be pure black, and any HU value above 155 HU would be pure white in this example. Using this same logic, bone windows would use a "wide window" (to evaluate everything from fat-containing medullary bone that contains the marrow, to the dense cortical bone), and the center or level would be a value in the hundreds of Hounsfield units. Processing will most likely take between five minutes and one hour. The Hounsfield scale is a quantitative scale for describing radiodensity. ... UPIICSA IPN - Binary image Image processing is any form of information processing for which the input is an image, such as photographs or frames of video; the output is not necessarily an image, but can be for instance a set of features of the image. ... For the human abdomen, see human abdomen. ... For the bird, see Liver bird. ... Hounsfield is a town located in Jefferson County, New York. ... This article is about the skeletal organs. ... This article is about the skeletal organs. ... This article does not cite any references or sources. ... This article is about the skeletal organs. ... The Hounsfield scale is a quantitative scale for describing radiodensity. ...

[edit] Artifacts

Although CT is a relatively accurate test, it is liable to produce artifacts, such as the following.

Example of Beam Hardening

• Aliasing Artifact or Streaks

These appear as dark lines which radiate away from sharp corners. It occurs because it is impossible for the scanner to 'sample' or take enough projections of the object, which is usually metallic. It can also occur when an insufficient mA is selected, and insufficient penetration of the x-ray occurs. These artifacts are also closely tied to motion during a scan. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ...

• Partial Volume Effect

This appears as 'blurring' over sharp edges. It is due to the scanner being unable to differentiate between overlying structures and respective HU's. The processor tries to average out the two densities or structures. 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 due to a detector fault.

• Noise Artifact

This appears as gaining 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 kV or mA is too low.

• Motion Artifact

This is seen as blurring which is caused by patient movement. This is not so much a problem these days with faster scanning times in the use of MDCT.

• 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. Attenuation is the decrease in intensity of electromagnetic radiation due to absorption or scattering of photons. ...

[edit] Three dimensional (3D) Image Reconstruction

Some statements in this article may be misleading. Please help clarify this article. Suggestions may be on the talk page.

Image File history File links Emblem-important. ...

[edit] The principle

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. Isotropy (the opposite of anisotropy) is the property of being independent of direction. ...

[edit] Multiplanar reconstruction