Electron beam tomography
Encyclopedia
Electron beam tomography (EBT), now owned by the General Electric company http://www.gehealthcare.com/usen/ct/products/ebt.html, is a specific form of computed tomography
(CAT or CT) in which the X-ray tube
is not mechanically spun in order to rotate the source of X-ray
photon
s. 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.
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.
The major medical application for which this design technology was invented in the 1980s was for imaging the human heart
. 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. The most advanced current commercial designs can perform image sweeps in as little as 0.025 second
s. By comparison, the fastest mechanically swept X-ray tube designs require about 0.33 seconds to perform an image sweep. 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.
s, part of the electron current energy when hitting the tungsten target is converted into photon
s. 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.
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 mid-section of the vacuum tube hollow, leaving room for the scan table and object or person to lie while the scan is performed.
This CT scanner design has remained more expensive, by over double, than the more widely sold CT design in which a small, more conventional X-ray tube is mechanically spun.
While there are very few of these scanners in use, this technology represents the fastest commercial CT temporal resolution.
Computed tomography
X-ray computed tomography or Computer tomography , is a medical imaging method employing tomography created by computer processing...
(CAT or CT) in which the X-ray tube
X-ray tube
An X-ray tube is a vacuum tube that produces X-rays. They are used in X-ray machines. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light...
is not mechanically spun in order to rotate the source of X-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s. 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.
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
Tungsten , also known as wolfram , is a chemical element with the chemical symbol W and atomic number 74.A hard, rare metal under standard conditions when uncombined, tungsten is found naturally on Earth only in chemical compounds. It was identified as a new element in 1781, and first isolated as...
anode in the tube, tracing a large circular arc on its inner surface. This motion can be very fast.
Design advantage
The principal application advantage of EBT tomographic CT 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
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
. The heart
Heart
The heart is a myogenic muscular organ found in all animals with a circulatory system , that is responsible for pumping blood throughout the blood vessels by repeated, rhythmic contractions...
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. The most advanced current commercial designs can perform image sweeps in as little as 0.025 second
Second
The second is a unit of measurement of time, and is the International System of Units base unit of time. It may be measured using a clock....
s. By comparison, the fastest mechanically swept X-ray tube designs require about 0.33 seconds to perform an image sweep. 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.
Design specifics
As in standard X-ray tubeX-ray tube
An X-ray tube is a vacuum tube that produces X-rays. They are used in X-ray machines. X-rays are part of the electromagnetic spectrum, an ionizing radiation with wavelengths shorter than ultraviolet light...
s, part of the electron current energy when hitting the tungsten target is converted into photon
Photon
In physics, a photon is an elementary particle, the quantum of the electromagnetic interaction and the basic unit of light and all other forms of electromagnetic radiation. It is also the force carrier for the electromagnetic force...
s. However, instead of spinning a small target anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
in order to dissipate waste heat, 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
Cathode ray tube
The cathode ray tube is a vacuum tube containing an electron gun and a fluorescent screen used to view images. It has a means to accelerate and deflect the electron beam onto the fluorescent screen to create the images. The image may represent electrical waveforms , pictures , radar targets and...
(CRT). However, the entire structure of the cathode
Cathode
A cathode is an electrode through which electric current flows out of a polarized electrical device. Mnemonic: CCD .Cathode polarity is not always negative...
, deflection yokes, anode
Anode
An anode is an electrode through which electric current flows into a polarized electrical device. Mnemonic: ACID ....
and overall vacuum tube size is much larger, therefore made out of steel, not glass, with the main central open mid-section of the vacuum tube hollow, leaving room for the scan table and object or person to lie while the scan is performed.
Design disadvantage
Given the vastly larger size and low production volume of the EBT design, only about 120 exist in the world, as of 2004, vs. thousands of more conventional design CT machines.This CT scanner design has remained more expensive, by over double, than the more widely sold CT design in which a small, more conventional X-ray tube is mechanically spun.
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 x 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 x 360°/sec rotation speeds and lower radiation exposure. The latest version of the EBT eSpeed offers a 33ms sweep time.While there are very few of these scanners in use, this technology represents the fastest commercial CT temporal resolution.