6. X-ray Production Flashcards
During the 1870s and 1880s, many university physics laboratories were investigating the
conduction of cathode rays through a large, partially evacuated glass tube known as a
Crookes tube
was the forerunner of
modern fluorescent lamps and x-ray tubes
Crookes tube
was experimenting with a type of Crookes tube when he discovered x-rays
Wilhelm Conrad Roentgen
The date x-rays were discovered
November 8, 1895
On November 8, 1895, Roentgen was working in his physics laboratory at
Würzburg University in Germany
He had darkened his laboratory and completely enclosed his Crookes tube with black photographic paper so he could better visualize the effects of the cathode rays in the tube. A plate coated with ________, a
fluorescent material, happened to be lying on a bench
top several meters from the Crookes tube.
Barium Platinocyanide
No visible light escaped from the Crookes tube
because of the black paper that enclosed it, but Roentgen noted that the barium platinocyanide glowed. This glow is called
fluorescence
First Clinical Application of x-rays was conducted at
Dartmouth College in February 1896
X-rays are also called
Roentgen rays
Roentgen was able to capture a radiograph
of the hand of his wife:
Anna Bertha Ludwig
was primarily used to study the nature of electrons
Crookes tube
Crookes tube was primarily used to study
the nature of electrons. In contrast, X-ray
tube now is primarily for _____
Xray production
By making sure that electrons are directed
to one direction only (cathode to anode),
Quality of x-rays is ___ quality and generation of x-rays is _____. Unlike in
Crookes tube.
high,
efficient
is the source of electrons
Cathode
the target, where electrons are bombarded
Anode
is composed of Tungsten
Anode
When electrons hit anode, tungsten is said
to be _____, creating electrons that will used to penetrate patients
ionized
come from the electrons outside nucleus
X-rays
come from the nucleus
Gamma rays
is what encloses the internal components
Pyrex glass
This kind of glass is able to withstand tremendous amount of heat during
the process of x-ray production
Pyrex glass
not all x-rays (1% ) are useful, some are
______ x-rays that only add radiation
dose of patient
low energy
is the area of the glass or metal enclosure, approximately 5 cm^2, that is thin and through which the useful beam
of x-rays is emitted
X-ray tube window
thinnest part of the x-ray tube glass
X-ray tube window
it is thin so that it will not decrease the
energy of the x-rays that will pass through it
X-ray tube window
Other parts of the glass is ____, nonetheless
thick
is not immediately visible
because it is contained within the protective housing which is made up of lead
X-ray tube
has a hole where x-rays
could escape
Protective housing
Inside the x-ray tube is a ______ no air; this
is important so that no molecules/air will
interfere with the flow of electrons from cathode to anode
vacuum
Within the protective housing and x-ray
tube, there is ___ for insulation
Oil
will help to remove away heat during x-ray
production
Oil
One that holds target anode is
rotor
Heat from the target will be conducted
away by the
rotor
Oil will then transfer heat to the protective
housing through
convection
Protective housing will then release heat in
the form of
infrared radiation= environment radiation
X-rays emitted through the window is called the
useful beam
X-rays that escaped through the tube housing are called
Leakage radiation
Leakage radiation should not exceed _____ at 1 m when operated at maximum condition
100 mR/hr
The protective housing around some x-ray tubes contains oil that serves as both an _____ against electric shock and _____ to dissipate heat
insulator,
thermal cushion
Xrays that don’t pass through the x-ray tube
window is called
Leakage radiation
Direction of x-rays is
divergent
X rays goes to all directions from point source. Thus _____
leakage radiation
absorb low energy x-rays. Usually made up of aluminum that has an atomic number of 13
Filters
enables one to see the field of exposure
Collimator
is the negative side of the x-ray tube
Cathode
Cathode has 2 primary parts
filament and focusing cup
must be pressed to start
rotation of rotor
rotor button
while rotor is rotating, ______
(tungsten) will be heated until it boils off
electrons
cathode filament
boiling of electrons
Thermionic emission
accumulation of electrons
after thermionic emission
Space charge
Space charge also called
electron cloud
light indicator will turn
on if it is ready for exposure (if boiling off of
electrons is sufficient already)
Exposure button
Once exposure button is pushed, _____ will be administered that will push electrons to the anode
voltage
If x-ray/exposure button is pushed without pushing the ______ first there will be no exposure that will occur
rotor button
must be pushed first so that electrons will be accumulated at the right
amount
Rotor button
determine amount of electrons.
However, rough estimate only
mAs
are enclosed in a focusing cup
Filaments
focuses electrons so that
electron will not scatter
Focusing cup
is negatively charged to repel electrons, otherwise, it will attract
electrons if it is positive making it difficult to
bombard electrons to the anode
Focusing cup
area in the anode where
electrons will hit. Part of tungsten target
Focal spot
is held by rotor
Target
Filament is usually approximately __ in diameter and ___ long
2 mm,
1 or 2 cm
2 types of filaments
small and large
Filaments are usually made of
thoriated tungsten
Tungsten have high melting point of
3410 degrees Celsius
Does not vaporize easily
Filament (Tungsten)
Addition of 1% to 2% thorium to tungsten increases the efficiency of
thermionic emission
Filaments are not purely tungsten. They are
alloyed with
thorium
Majority of filament is still made of
tungsten
When the current through the filament is sufficiently high, the outer-shell electrons of the filament atoms are
“boiled off” and ejected from the filament
Thermionic emission
Focuses the electrons towards the target
Focusing Cup
a concept in which excess electric charge is treated as a continuum of charge distributed over a
region of space (either a volume or an area) rather than distinct point-like charges
Space charge
is the positive side of the x-ray tube
Anode
Functions of anode assembly
- Electrical conductor
- Mechanical support
- Thermal dissipator
Process of releasing of charged particles through the use of heat.
Thermionic emission
Where the filaments are embedded
Focusing Cup
Negatively charged focusing cup > _____
electrons
repel
it conducts electricity and radiates heat and contains the target
Anode
has a different texture since it has been hit frequently by electrons coming from the cathode and there is pitting
Focal Spot
conduct the electricity that is needed to operate the xray tube
Electrical conductor
rotor holds the target
in place
Mechanical support
rotor (made up of
copper which is a good heat conductor)
conducts the heat away from the target
Thermal dissipator
Area of the anode struck by the electrons from the cathode
Target
Is the actual x-ray source
Focal Spot
Specific area in the target that is struck by electrons
Focal Spot
is used when better spatial resolution is required. Ranges from 0.1 to 1 mm
Small focal spot
is used when large body parts are imaged and when other techniques that produce high are
required
Large focal spot
The _____ the focal spot, the more it is
easier to heat up and increase mas and
produce more electrons. However, more prone to breakage.
smaller
has high heat capacity and less prone to breakage
Large focal spot
Are used in dental x-ray imaging systems, some portable imaging systems, and other purpose units in which high tube current and power are not required
Stationary anode
Capable of producing high intensity x-ray beam
Rotating anode
Rotating anode rotates to
3400 rpm and 10,000 rpm
Heat capacity can be further improved by ______ the speed of anode rotation
increasing
the target is consists of tungsten alloy embedded in a copper anode
Stationary anode tubes
the entire rotating disc is the target
Rotating anode tubes
Stationary anode tubes size
About 4 mm^2
Rotating anode tubes size
About 3159 mm^2
heat is distributed
across different areas
Rotating anode
is powered by an electromagnetic induction motor
Rotating anode
is consist of 2 parts: the stator and the rotor
Induction motor
fixed electromagnet. Become magnetized once they are administered
with electricity
Stator
is surrounded by stator
Rotor
is wrapped around Ferromagnetic material. Will be attracted once stator is given electricity
Copper
Tungsten is the material of choice for the target for general radiography for 3 main reasons:
- Atomic number
- Thermal conductivity
- High melting point
Tungsten atomic number
74
K shell Electron Binding Energy is high about
69.5 keV
Does not store heat for a long term.
Conduct heat easily. We don’t want heat to
accumulate in the target so that it won’t
crack
Tungsten
Specialty x-ray tubes for mammography have ___________ targets principally because of their low atomic number and low K characteristics x-ray energy
Molybdenum or Rhodium
Alloying ________ gives it added mechanical strength to withstand the stresses of high
speed rotation
Tungsten (usually with rhenium )
have lower mass density than tungsten, thus allowing the target easier to rotate
Molybedum and graphite
Molybdenum atomic number
42
Rhodium atomic number
45
Molybdenum k-shell electron binding energy:
19 keV
Rhodium k-shell electron binding energy:
23 keV
____ energy is required for breasts because
the breast is a soft tissue. If ____ energy will
be used, all will penetrate through the
breast resulting to a dark radiograph
Low,
high
is needed
to visualize the soft tissues.
Differential absorption of x-rays
Results in an effective focal spot size much less than the actual focal spot size
Line-Focus Principle
Line-Focus Principle is also known as
Goetze Principle
Diagnostic x-ray tubes have target angles that vary from approximately ______ degrees
5 to 20
allows high anode heating with small effective focal spots. As the target decreases, so does the focal spot size
Line-Focus Principle
Radiation intensity is greater on the cathode side of the x-ray field than that on the anode side.
Anode Heel Effect
is made possible with
the angulation of the target
Line-Focus Principle
The bigger the anode angulation the ____ the
effective focal spot size
larger
Intensity of xrays is greater on the _____
side (Anode Heel Effect)
cathode (Fat Cat)
In greater anode angulations, changes in
intensity from cathode to anode is _____
and not abrupt, unlike in smaller anode angle that has abrupt changes
gradual
To correct heel effect, ______ are used
wedge filters
If wedge filters are not available, thicker
parts must be placed near the _____ side
and less thicker parts on the ____ side.
cathode (thicker),
anode (thinner)
Electrons bounce off the focal spot and then land on other areas of the target, causing x-rays to be produced
from outside of the focal spot
Off Focus Radiation
is the energy of motion
Kinetic Energy
Electrons travelling from cathode to anode
Projectile Electrons
interacts with orbital electron of the target atom
Projectile Electrons
Projectile electron interacts with orbital electron of the target atom. This interaction results in the conversion of electron kinetic energy into ______ and electromagnetic energy in the form of ______
KE- thermal energy (heat),
EME- infrared radiation (also heat) and x-ray
Approximately ____ of kinetic energy of projectile electrons is converted to heat
99%
Only approximately ___ of projectile electrons is converted to x-ray
1%
X-rays produced
outside of the focal spot
Off Focus Radiation
electrons ejected from
the outer shell
Compton electron
In 1% , ___ is characteristic radiation but
only those with 69 kev where k shell electron vacancy is filled is useful
15%
characteristic radiation
from them usually do not penetrate patient
and reach IR
LMNOP shells
The slowing of nucleus and loss of kinetic energy produces
X-rays
The efficiency of x-ray production is independent of the tube current.
o At 60 kVp, ___ conversion
o At 100 kVp, ___ conversion
o At 20 MV, ___ conversion
0.5%,
1%,
70%
are emitted when an outer-shell electron fills an inner-shell void
Characteristic x-rays
At 100 kVp, approximately ____ of the x-ray beam is characteristic
15%
Are produced when a projectile electron is slowed by the electric field of a target atom nucleus
Bremsstrahlung Radiation
“Slowed down radiation”
Bremsstrahlung Radiation
German word which means “braking radiation” or “deceleration radiation”
Bremsstrahlung Radiation
to brake
bremsen
radiation
Strahlung
In characteristic radiation, About _____ are Bremsstrahlung. But
large portion of bremsstrahlung radiation
produced is not useful
75- 85%
