Electron beam tomography

Electron beam tomography
	Patent illustration showing a cutaway view of an electron beam computerized tomography system. Components are 22. electron gun, 23. electron beam, 24. focus coil, 27. beam bending coil, 28-31. target rings, 14. detector array, 11. scan tube. The electron beam creates x-rays at the target rings, which radiates through the patient to the detector on the opposite end of the scan tube.
MeSH	D014057
OPS-301 code	3-26
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Last updated March 29, 2019

Electron beam tomography (EBT) is a specific form of computed tomography (CT) in which the X-ray tube is not mechanically spun in order to rotate the source of X-ray photons. This different design was explicitly developed to better image heart structures which never stop moving, performing a complete cycle of movement with each heart beat.

An X-ray tube is a vacuum tube that converts electrical input power into X-rays. X-ray tubes evolved from experimental Crookes tubes with which X-rays were first discovered on November 8, 1895, by the German physicist Wilhelm Conrad Röntgen. The availability of this controllable source of X-rays created the field of radiography, the imaging of partly opaque objects with penetrating radiation. In contrast to other sources of ionizing radiation, X-rays are only produced as long as the X-ray tube is energized. X-ray tubes are also used in CT scanners, airport luggage scanners, X-ray crystallography, material and structure analysis, and for industrial inspection.

The photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force. The photon has zero rest mass and always moves at the speed of light within a vacuum.

As in conventional CT technology, the X-ray source-point moves along a circle in space around an object to be imaged. In EBT, however, the X-ray tube itself is large and stationary, and partially surrounds the imaging circle. Rather than moving the tube itself, electron-beam focal point (and hence the X-ray source point) is swept electronically along a tungsten anode in the tube, tracing a large circular arc on its inner surface. This motion can be very fast.

Tungsten, or wolfram, is a chemical element with symbol W and atomic number 74. The name tungsten comes from the former Swedish name for the tungstate mineral scheelite, tung sten or "heavy stone". Tungsten is a rare metal found naturally on Earth almost exclusively combined with other elements in chemical compounds rather than alone. It was identified as a new element in 1781 and first isolated as a metal in 1783. Its important ores include wolframite and scheelite.

Advantages and disadvantages

The principal application advantage of EBT machines, and the reason for the invention, is that because the X-ray source-point is swept electronically, not mechanically, it can be swept with far greater speed.

The major medical application for which this design technology was invented in the 1980s was for imaging the human heart, specifically to detect coronary calcium.^[1] The heart never stops moving, and some important structures, such as arteries, move several times their diameter during each heartbeat. Rapid imaging is, thus, important to prevent blurring of moving structures during the scan. EBT detection of calcium deposits is accurate, fast and involves lower exposure to ionising radiation than conventional CT.^[2]^[3] Patients are exposed to radiation for a shorter period as it is faster in creating multiple images of the heart. The most advanced current commercial designs can perform image sweeps in as little as 0.025 seconds. By comparison, the fastest mechanically swept X-ray tube designs require about 0.25 seconds to perform an image sweep.^[4] For reference, current coronary artery angiography imaging is usually performed at 30 frames/second or 0.033 seconds/frame; EBT is far closer to this than mechanically swept CT machines.

The heart is a muscular organ in most animals, which pumps blood through the blood vessels of the circulatory system. Blood provides the body with oxygen and nutrients, as well as assisting in the removal of metabolic wastes. In humans, the heart is located between the lungs, in the middle compartment of the chest.

The second is the base unit of time in the International System of Units (SI), commonly understood and historically defined as ¹⁄₈₆₄₀₀ of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each. Mechanical and electric clocks and watches usually have a face with 60 tickmarks representing seconds and minutes, traversed by a second hand and minute hand. Digital clocks and watches often have a two-digit counter that cycles through seconds. The second is also part of several other units of measurement like meters per second for velocity, meters per second per second for acceleration, and per second for frequency.

Angiography or arteriography is a medical imaging technique used to visualize the inside, or lumen, of blood vessels and organs of the body, with particular interest in the arteries, veins, and the heart chambers. This is traditionally done by injecting a radio-opaque contrast agent into the blood vessel and imaging using X-ray based techniques such as fluoroscopy.

Given the larger size and low production volume of the EBT design, only about 120 exist in the world as of 2004,^{[ citation needed ]} vs. thousands of more conventional design CT machines. Signal to noise ratio and spatial resolution are also worse compared to conventional CT.^[3]

Design specifics

As in standard X-ray tubes, part of the electron current energy when hitting the tungsten target is converted into photons. However, instead of spinning a small target anode in order to dissipate waste heat, the electron current focus spot is swept along a large stationary target anode.^[5]

An anode is an electrode through which the conventional current enters into a polarized electrical device. This contrasts with a cathode, an electrode through which conventional current leaves an electrical device. A common mnemonic is ACID for "anode current into device". The direction of conventional current in a circuit is opposite to the direction of electron flow, so electrons flow out the anode into the outside circuit. In a galvanic cell, the anode is the electrode at which the oxidation reaction occurs.

Waste heat is heat that is produced by a machine, or other process that uses energy, as a byproduct of doing work. All such processes give off some waste heat as a fundamental result of the laws of thermodynamics. Waste heat has lower utility than the original energy source. Sources of waste heat include all manner of human activities, natural systems, and all organisms, for example, a refrigerator warms the room air, an internal combustion engine generates high-temperature exhaust gases, and electronic components get warm when in operation.

The electron current sweep is aimed using wound copper coil magnetic deflection yokes, as in a cathode ray tube (CRT). However, the entire structure of the cathode, deflection yokes, anode and overall vacuum tube size is much larger, therefore made out of steel, not glass, with the main central open midsection of the vacuum tube hollow, leaving room for the scan table and object or person to lie while the scan is performed.

Future

Whether the inherent sweep-speed advantage will maintain commercial viability of the EBT design remains unclear at this time. As of 2002, one major company owns and offers models in both competing designs, with engineering cross-pollination of techniques between the product design teams. As of 2005, it increasingly appears that the spiral CT designs, especially those with (b) 64 detector rows, (b) 3×360°/sec rotation speeds and designed for cardiac imaging, are largely replacing the EBT design from a commercial and medical perspective. However, EBT still offers sweep speeds of effectively 50×360°/sec rotation speeds and lower radiation exposure. The latest version of the EBT eSpeed offers a 33 ms sweep time.

This technology continues to represent the fastest commercial CT temporal resolution.

Since 2008, a single development company has taken the lead on continued development, support and sales of EBT imaging products. The EBT scanner continues to stay in use globally due to the high accuracy, superior repeatability and ultra low dose abilities over high dose mechanical scanners.

Related Research Articles

A CT scan, also known as computed tomography scan, and formerly known as a computerized axial tomography scan or CAT scan, makes use of computer-processed combinations of many X-ray measurements taken from different angles to produce cross-sectional (tomographic) images of specific areas of a scanned object, allowing the user to see inside the object without cutting.

Radiography is an imaging technique using X-rays, gamma rays, or similar radiation to view the internal form of an object. To create the image, a beam of X-rays or other form of electromagnetic radiation is produced by an X-ray generator and is projected toward the object. A certain amount of the X-rays or other radiation is absorbed by the object, dependent on the object's density and structural composition. The X-rays that pass through the object are captured behind the object by a detector. The generation of flat two dimensional images by this technique is called projectional radiography. In computed tomography an X-ray source and its associated detectors rotate around the subject which itself moves through the conical X-ray beam produced. Any given point within the subject is crossed from many directions by many different beams at different times. Information regarding attenuation of these beams is collated and subjected to computation to generate two dimensional images in three planes which can be further processed to produce a three dimensional image.

Radiology is the medical specialty that uses medical imaging to diagnose and treat diseases within the human body.

Medical imaging technique and process of creating visual representations of the interior of a body

Medical imaging is the technique and process of creating visual representations of the interior of a body for clinical analysis and medical intervention, as well as visual representation of the function of some organs or tissues (physiology). Medical imaging seeks to reveal internal structures hidden by the skin and bones, as well as to diagnose and treat disease. Medical imaging also establishes a database of normal anatomy and physiology to make it possible to identify abnormalities. Although imaging of removed organs and tissues can be performed for medical reasons, such procedures are usually considered part of pathology instead of medical imaging.

An X-ray generator is a device that produces X-rays. Together with an X-ray detector, it is commonly used in a variety of applications including medicine, fluorescence, electronic assembly inspection, and measurement of material thickness in manufacturing operations. In medical applications, X-ray generators are used by radiographers to acquire x-ray images of the internal structures of living organisms, and also in sterilization.

Tomography is imaging by sections or sectioning, through the use of any kind of penetrating wave. The method is used in radiology, archaeology, biology, atmospheric science, geophysics, oceanography, plasma physics, materials science, astrophysics, quantum information, and other areas of science. The word tomography is derived from Ancient Greek τόμος tomos, "slice, section" and γράφω graphō, "to write". A device used in tomography is called a tomograph, while the image produced is a tomogram.

Technicare, formerly known as Ohio Nuclear, made CT, DR and MRI scanners and other medical imaging equipment. Its headquarters was in Solon, Ohio. Originally an independent company, it was later purchased by Johnson & Johnson. At the time, Invacare was also owned by Technicare. The company did not do well under Johnson & Johnson and in 1986, under economic pressure following unrelated losses from two Tylenol product tampering cases, J&J folded the company, selling the intellectual property and profitable service business to General Electric, a competitor.

High-resolution computed tomography (HRCT) is a type of computed tomography (CT) with specific techniques to enhance image resolution. It is used in the diagnosis of various health problems, though most commonly for lung disease, by assessing the lung parenchyma.

A coronary CT calcium scan is a computed tomography (CT) scan of the heart for the assessment of severity of coronary artery disease. Specifically, it looks for calcium deposits in the coronary arteries that can narrow arteries and increase the risk of heart attack. This severity can be presented as Agatston score or coronary artery calcium (CAC) score. The CAC score is an independent marker of risk for cardiac events, cardiac mortality, and all-cause mortality. In addition, it provides additional prognostic information to other cardiovascular risk markers. A typical coronary CT calcium scan is done without the use of radiocontrast, but it can possibly be done from contrast-enhanced images as well, such as in coronary CT angiography.

Flat-panel Volume CT is a technique under development to make computed tomography images with improved performance. The key difference between volume CT and traditional CT is that volume CT uses a two-dimensional x-ray detector orientation, to take multiple two-dimensional images. On the other hand, the conventional CT uses a one-dimensional x-ray detector orientation to take one-dimensional x-ray images.

Cardiac PET is a form of diagnostic imaging in which the presence of heart disease is evaluated using a PET scanner. Intravenous injection of a radiotracer is performed as part of the scan. Commonly used radiotracers are Rubidium-82, Nitrogen-13 ammonia and Oxygen-15 water.

Industrial computed tomography (CT) scanning is any computer-aided tomographic process, usually X-ray computed tomography, that uses irradiation to produce three-dimensional internal and external representations of a scanned object. Industrial CT scanning has been used in many areas of industry for internal inspection of components. Some of the key uses for industrial CT scanning have been flaw detection, failure analysis, metrology, assembly analysis and reverse engineering applications. Just as in medical imaging, industrial imaging includes both nontomographic radiography and computed tomographic radiography.

Cone beam computed tomography is a medical imaging technique consisting of X-ray computed tomography where the X-rays are divergent, forming a cone.

Coronary CT angiography procedure used to assess the extent of occlusion in the coronary arteries, usually in order to diagnose coronary artery disease.

Coronary CT angiography (CTA) is the use of computed tomography (CT) angiography to assess the coronary arteries of the heart. The subject receives an intravenous injection of radiocontrast and then the heart is scanned using a high speed CT scanner, allowing physicians to assess the extent of occlusion in the coronary arteries, usually in order to diagnose coronary artery disease.

Cardiac imaging techniques include coronary catheterization, echocardiogram, Intravascular ultrasound, Cardiac PET scan, Cardiac CT scan and Cardiac MRI.

X-ray computed tomography operates by using an X-ray generator that rotates around the object; X-ray detectors are positioned on the opposite side of the circle from the X-ray source.

In a medical facility, such as a hospital or clinic, a gantry holds radiation detectors and/or a radiation source used to diagnose or treat a patient's illness. Radiation sources may produce gamma radiation, x-rays, electromagnetic radiation, or magnetic fields depending on the purpose of the device.

The history of X-ray computed tomography goes back to at least 1917 with the mathematical theory of the Radon transform In October 1963, William H. Oldendorf received a U.S. patent for a "radiant energy apparatus for investigating selected areas of interior objects obscured by dense material". The first commercially viable CT scanner was invented by Sir Godfrey Hounsfield in 1967.

References

↑ Mittal, Tarun K.; Rubens, Michael B. (2006). "Computed Tomography Techniques and Principles. Part a. Electron Beam Computed Tomography". In Anagnostopoulos, Constantinos D.; Bax, Jeroen J.; Nihoyannopoulos, Petros; van der Wall, Ernst. Noninvasive Imaging of Myocardial Ischemia. New York: Springer-Verlag. p. 93. doi:10.1007/1-84628-156-3_6. ISBN 978-1-84628-027-6.
↑ Raggi, Paolo (January 2001). "Imaging of cardiovascular calcifications with electron beam tomography in hemodialysis patients". American Journal of Kidney Diseases. 37 (1): S62–S65. doi:10.1053/ajkd.2001.20745.
1 2 Peebles, C R (1 June 2003). "Non-invasive coronary imaging: computed tomography or magnetic resonance imaging?". Heart. 89 (6): 591–594. doi:10.1136/heart.89.6.591. PMC 1767702  . PMID 12748207.
↑ "SOMATOM Force". Siemens. Retrieved 29 June 2017.
↑ Hill, David G. (2005). "Electron Beam CT of the Heart". In Schoepf, U. Joseph. CT of the Heart. Totowa, N.J.: Humana Press. p. 15. doi:10.1385/1-59259-818-8:015. ISBN 978-1-58829-303-9.

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[NoninvBook-1] Mittal, Tarun K.; Rubens, Michael B. (2006). "Computed Tomography Techniques and Principles. Part a. Electron Beam Computed Tomography". In Anagnostopoulos, Constantinos D.; Bax, Jeroen J.; Nihoyannopoulos, Petros; van der Wall, Ernst. Noninvasive Imaging of Myocardial Ischemia. New York: Springer-Verlag. p. 93. doi:10.1007/1-84628-156-3_6. ISBN 978-1-84628-027-6.

[2] Raggi, Paolo (January 2001). "Imaging of cardiovascular calcifications with electron beam tomography in hemodialysis patients". American Journal of Kidney Diseases. 37 (1): S62–S65. doi:10.1053/ajkd.2001.20745.

[Peebles-3] 1 2 Peebles, C R (1 June 2003). "Non-invasive coronary imaging: computed tomography or magnetic resonance imaging?". Heart. 89 (6): 591–594. doi:10.1136/heart.89.6.591. PMC 1767702  . PMID 12748207.

[4] "SOMATOM Force". Siemens. Retrieved 29 June 2017.

[5] Hill, David G. (2005). "Electron Beam CT of the Heart". In Schoepf, U. Joseph. CT of the Heart. Totowa, N.J.: Humana Press. p. 15. doi:10.1385/1-59259-818-8:015. ISBN 978-1-58829-303-9.