Electron beam computed tomography (EBCT) is a specific form of computed tomography (CT) in which the

X-ray tube An X-ray tube is a vacuum tube that converts electrical input power into X-rays. 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 ...

is not mechanically spun in order to rotate the source of

X-ray An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...

photon A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they a ...

s. This different design was explicitly developed to better image heart structures that never stop moving, performing a complete cycle of movement with each heartbeat. 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 Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...

anode in the tube, tracing a large circular arc on its inner surface. This motion can be very fast. Electron beam CT was unable to compete with more rapid advancement in multidetector CT imager technology and had become completely obsolete by the 2020s.

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 The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide to t ...

, specifically to detect coronary calcium. The

never stops moving, and some important structures, such as

arteries An artery (plural arteries) () is a blood vessel in humans and most animals that takes blood away from the heart to one or more parts of the body (tissues, lungs, brain etc.). Most arteries carry oxygenated blood; the two exceptions are the pu ...

, move several times their diameter during each heartbeat. Rapid imaging is therefore 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 Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...

than conventional CT. 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. For reference, current

coronary artery The coronary arteries are the arterial blood vessels of coronary circulation, which transport oxygenated blood to the heart muscle. The heart requires a continuous supply of oxygen to function and survive, much like any other tissue or organ ...

angiography 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. Modern angiography is perfor ...

imaging is usually performed at 30 frames/second or 0.033 seconds/frame; EBT is far closer to this than mechanically swept CT machines. Given the larger size and low production volume of the EBT design, only about 120 existed in the world as of 2004, vs. thousands of more conventional design CT machines. signal-to-noise ratio and spatial resolution are also worse compared to conventional CT.

Design specifics

As in standard

s, part of the electron current energy when hitting the tungsten target is converted into photons. However, instead of spinning a small target

anode An anode is an electrode of a polarized electrical device through which conventional current enters the device. This contrasts with a cathode, an electrode of the device through which conventional current leaves the device. A common mnemonic ...

in order to dissipate

waste heat 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 ...

, the electron current focus spot is swept along a large stationary target anode. 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 A cathode is the electrode from which a conventional current leaves a polarized electrical device. This definition can be recalled by using the mnemonic ''CCD'' for ''Cathode Current Departs''. A conventional current describes the direction in wh ...

, 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 64 detector rows, 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. As of the early 2020s EBT imaging had become completely obsolete and had been replaced by multidetector CT imaging everywhere.

References

{{DEFAULTSORT:Electron Beam Tomography Electron beam X-ray computed tomography