X-ray machine - National University review (1).pdf · X-ray-department, location and lay out. X-ray...
Transcript of X-ray machine - National University review (1).pdf · X-ray-department, location and lay out. X-ray...
Introduction:
X-ray-department, location and lay out.
X-ray department should be easily accessed from ward
and casual, and in separate building, all protective
methods should be applied.
Types of X-ray machines
1-Portable X-ray machine
2-Mobile X-ray machine—(a) simple-(b) C-arm (c)
mammographic unit.
3-Dental (1) Simple self rectified (2) Othropantomography (OPG)
(3) Cephalostat.
4-Major or static X-ray machine.
Components of X-ray machine
1-Mains switch (Knife switch), manual or Electromagnetic circuit
breaker.
2-Control, disk or panel.
3-Auto-transformer
4-High tension tank (h.t.transformer, filament transformer, h.t
switch, rectifiers and oil).
5- High tension generators
6-X-ray tube assembley (insert, housing, collimator, handle of
brakes).
7-Types of X-ray exposure timers (Clock work, electronic,
automatic, guard, mAs, and synchronous timer).
8-High tension cables.
9-X-ray table (table top, potter Bucky, grid).
10-Stand Bucky.
11-Fluoroscopic attachment (tilting table, under couch tube, serial
changer, image intensifier tube, video camera and monitor).
12-Dark room accessories (safe lights, processing tanks, cassettes,
hungers, dry and wet bench).
X-ray machine
• The x-ray machine is divided into
four major components.
• The Tube
• The Operating Console
• The High Voltage Section
• The Film Holder , Grid Cabinet or
Table
X-ray Room
• Floor mounted x-ray
tube stand.
• Wall grid cabinet or
Bucky
• Mobile Table with
grid cabinet
• Film Holder
X-ray Room
• Control should
contain the operator
console and
technique charts and
space to store
cassettes.
• The wall between
the Control and X-
ray unit is shielded.
Chiropractic X-ray Room
• High Voltage
Section or
Generator used to
change incoming
power to levels
needed to produce
x-rays.
The X-Ray Tube Development
• Dr. Roentgen used a
Crookes-Hittorf tube
to make the first x-
ray image.
• There was no
shielding so x-rays
were emitted in all
directions.
The X-Ray Tube Development
• The Coolidge Hot
cathode tube was
a major
advancement in
tube Design. The
radiator at the
end of the anode
cool the anode.
The X-Ray Tube Development
• This is the variety
of tube designs
available in 1948.
• The Coolidge tube
was still available.
The X-Ray Tube Development
• Two major
hazards plagued
early radiography.
• Excessive
radiation exposure
• Electric Shock
The X-Ray Tube Development
• This is a modern
rotating anode x-
ray tube. It is
encased
completely in a
metal protective
housing.
The X-Ray Modern X-ray Tube
• There are two
principle parts:
• The rotating anode
• The cathode
• Any tube that has
two electrodes is
called a diode.
Protective Housing
• The tube is housed in
a lead lines metal
protective housing.
• The x-ray photons
are generated in all
directions.
• The housing is
designed to limit the
beam to window.
Protective Housing
• The housing also
provide mechanical
support and
protection from
damage.
• On some tubes, the
housing also contains
oil that provides
more insulation and
a thermal cushion.
Protective Housing
• Never hold the
tube during an
exposure.
• Never use the
cables or
terminals as
handles.
The X-Ray Tube Glass Envelope• The glass envelope is
made of Pyrex to withstand the tremendous heat produced during x-ray.
• The window is a 5 cm square with a thin section of glass where the useful beam is emitted.
The Cathode
• The cathode is the
negative side of the
tube and contains
two primary parts:
• The filaments
• The focusing cup
The Filaments
• Most tube have
two filaments
which provide a
choice of quick
exposures or high
resolution.
• The filaments are
made of tungsten.
The Filaments
• Tungsten is used in x-
ray tube because of
it’s high melting
point of 3410°C.
• X-rays are produced
by thermionic
emission when a 4 A
or higher current is
applied.
Focusing Cup
• The focusing
cup has a
negative
charge so that
it can
condense the
electron beam
to a small area
of the anode.
Filament Current
• When the x-ray machine is turned on, a
low current flows through the filament
to warm it and prepare it for the big
thermal necessary for x-ray production.
Filament Current
• Once the current is high enough for
thermionic emission a small rise in
filament current will result in a
large rise in tube current.
Filament Current & Tube Current
• The x-ray tube
current is adjusted
by controlling the
filament current.
• The relationship
between tube and
filament current is
dependent upon the
tube voltage.
Space Charge
• When emitted by the
filament, the
electrons form a
cloud near the
filament
momentarily before
being accelerated to
the anode. This is
called a space
charge.
Saturation Current• When very high mA and
very low kVp, the
thermionic emission
can be space charge
limited.
• With high mA the cloud
makes it difficult for
subsequent electrons to
be emitted.
• Above 1000 mA space
charge limited exposure
can be a major problem.
The Anode• The anode is the
positive side of the
tube.
• X-ray tubes are
classified by the type
of anode:
–Stationary ( top)
–Rotating (bottom)
The Stationary Anode
• Stationary anodes
are used in dental
x-ray and some
portable x-ray
machine where
high tube current
and power are not
required.
The Rotating Anode
• The rotating anode
allows the electron
beam to interact with
a much larger target
area.
• The heat is not
confined to a small
area.
The Rotating Anode
• The anode serves three
functions:
– Receives the
electrons emitted
from the cathode.
– It is a electrical
conductor.
– Mechanical support
for the target.
The Rotating Anode
• The Anode must also
be a good thermal
conductor.
• When the electron
beam strikes the
anode more than
99% of the kinetic
energy is converted
to heat.
Tungsten is used as a target material, for the
following reasons:
(1) It has a high atomic number (74) and
efficiency of X-ray production increases with the
atomic number of the target.
( 2 ) It has a high melting point (3400°C) and is
thus able to withstand the high temperatures
reached by the target during an exposure.
(3) The characteristic radiation of tungsten
makes a useful contribution to the beam of X-rays.
Tungsten is used as a target material,
for the following reasons:
(4) It has reasonably good thermal
conductivity. This is important as heat must
be transferred from the focal areas to the
mass of the anode.
(5) It has reasonable thermal capacity.
(6) It has low vapor pressure at high
temperature which helps to preserve the
vacuum within the insert.
The Rotating Anode
• When the
exposure button is
depressed, current
is applied to the
tube that produces
a magnetic field
that starts the
rotation of the
anode.
The production of x-ray
• The heart of an X-ray machine is an
electrode pair ion a cathode and an anode
ions that sits inside a glass vacuum tube.
• Cathode is a heated filament, like you
might find in an older fluorescent lamp.
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The production of x-ray
• The machine passes current through the
filament, heating it up. The heat sputters
electrons off of the filament surface.
• The positively-charged anode, a flat disc
made of tungsten, draws the electrons
across the tube
The production of x-ray
• The voltage difference between the cathodeand anode is extremely high, so theelectrons fly through the tube with a greatdeal of force.
• When a speeding electron collides with atungsten atom, it knocks loose an electron inone of the atom's lower orbital. An electronin a higher orbital immediately falls to thelower energy level, releasing its extraenergy in the form of a photon.
The production of x-ray
• Free electrons can also generate photonswithout hitting an atom.
• An atom's nucleus may attract a speedingelectron just enough to alter its course. theelectron slows down and changes directionas it speeds past the atom.
The production of x-ray
• This "braking" action causes the electron to
emit excess energy in the form of an X-ray
photon.
• In conventional x-ray only about 1% of the
electron energy converted to x-ray, the
remaining 99% appears as heat (that why
we use oil in tube housing)
The production of x-ray
• The high-impact collisions involved in X-
ray production generate a lot of heat.
• A motor rotates the anode to keep it from
melting (the electron beam isn't always
focused on the same area). A cool oil bath
surrounding the envelope also absorbs
heat.
The production of x-ray
• The entire mechanism is surrounded by a
thick lead shield. This keeps the X-rays
from escaping in all directions.
• A small window in the shield lets some of
the X-ray photons escape in a narrow
beam. The beam passes through a series of
filters on its way to the patient.2/4/201953
Bremsstrahlung x-ray
• produced the X-ray by the acceleration of
fast moving electron resulting in
conversion of some of its kinetic energy
into x-ray.