The CAT scanner is made up of three primary
systems, including the gantry, the computer, and the operating console. Each of
these is composed of various subcomponents. The gantry assembly is the largest
of these systems. It is made up of all the equipment related to the patient,
including the patient support, the positioning couch, the mechanical supports,
and the scanner housing. It also contains the heart of the CAT scanner, tungstenalloy x-ray tube, as well as detectors that generate and detect x- rays.
William Roentgen, who discovered x rays in
1895. Around this time, various scientists were investigating the movement of
electrons through a glass apparatus known as a Crookes tube. Roentgen wanted to
visually capture the action of the electrons, so he wrapped his Crookes tube in
black photographic paper. When he ran his experiment, he noticed that a plate
coated with a fluorescent material, which just happened to be lying nearby the
tube, fluoresced or glowed. This was unexpected because no visible light was
being emitted from the wrapped tube. Upon further investigation, he found that
indeed there was some kind of invisible light produced by this tungsten alloy tube, and it
could penetrate materials such as wood, aluminum, or human skin.
The electron beam gun is a triode system
operated with a small-size tungsten bolt cathode that is indirectly heated by
electron bombardment. The Wehnelt electrode and the anode are shaped as a Rogowski
transducer with a bell-shaped through-hole anode. This configuration has been
chosen since it greatly reduces the dependence of focal spot size on electron beam
current. The electron beam gun is operated at about 10−6 mbar gas pressure
which is provided by a vacuum pump system, consisting of a scroll pre-pump and
a turbo molecular main pump operated in series. The gas pressure in the beam column
and the scanner head is somewhat higher in the range of 10−5 mbar.
There are a few other notable approaches to
fast tomography using x-rays or gamma rays. Since all of the above-mentioned
approaches have numerous drawbacks and limitations regarding multiphase flow
tomography, it was decided to design and build up a dedicated electron beam
x-ray CT scanner for this application. The decision for an electron beam type
CT and against a CT with stationary gated sources was due to several reasons.
First, electron beam technology provides excellent versatility since the
electron beam can be almost arbitrarily steered and shaped as needed. In the
simplest case the electron beam will be swept along a semicircular target as in
medical electron beam CT to generate projection data from a single plane.
Moreover, subsequent sweeping on different circular paths on the target enables
multi-slice CT as well as velocity measurement for two-phase flows. Additional
beam optics can be provided to shape the focal spot as required and to adjust
the beam focus when scanning at different axial positions (planes). Only one
beam power supply is required. Another strong argument is the straightforward
upgrade capability towards higher x-ray energy by introduction of high-energy
electron beam generators or superconducting accelerators. Therefore, tungsten
alloy material will have advantage in this case.
Made
from Tungsten, this Hamilton Vial Heating Shield holds vials the size of 2.65cm
in width. Fits within standard aluminum heat blocks. Easy button top and vial
cut to lift vials
Scanned electron beam x-ray tomography is
therefore a promising technology. Instead of mechanical rotation of scanner
components, an electron beam is rapidly swept across an x-ray target using
deflection coils. This technology was introduced in medicine more than two
decades ago where it is mainly being used for cardiovascular diagnostics.
Tungsten Alloy material is a good choice for medical CT and X-ray radiation
protection.
Tungsten alloy X-ray CT target as an imaging modality is highly
advantage due to its non-intrusiveness and its ability to penetrate opaque wall
materials. One essential disadvantage of existing CT system is the requirement
for rotating components. To measure multiphase flows in a velocity range of one
meter per second or more, frame rates of at least 1000 frames per second are
required to produce sharp phase distribution images with a spatial resolution
of about one millimeter. To achieve this, mechanically rotating parts are to be
avoided.
