Xray Tube, Production & Emission Flashcards
Tube Housing/Protective Housing
Metallic housing usually lead lined which protects tube, absorbs unusable X-ray, protects from unnecessary radiation and electrical shock risk. Contains oil
Primary Beam/Useful Beam
Polyenergetic in nature, exists in a variety of strengths from 1kv to kvp
Tube window
Where the primary beam exists in the tube housing
Leakage Radiation
radiation that leaves the tube housing at a point other than the tube window
glass envelope of the X-ray tube
maintains a vacuum within
cathode
the negative side of the X-ray tube whose function is to emit electrons
filament
thightly wound coil, most xray tubes are dual focus (2 filaments), only one is used at a time
thermionic emission
electron emission from a heated source
filament current
the current supplied to the filament for heating
focusing cup
metallic cup that encases the filaments, composed of nickel or molybdenum; given a negative charge
millamperage
the number of electrons thermionically emitted per second
space charge/electron cloud
the collection of electrons “hovering” off the filament
anode
the positive side of the X-ray tube
rotating anode
anode capable of higher technical factors, anode disk rotates during exposure which spreads out heat over a larger area
stationary anode
lower technical factors, anode stationary as electrons impact to produce xray
target of anode
the point on the anode where the electrons strike
properties of tungsten that make it great for use in xray
high melting point (3422*c)
high atomic number (74)
good conductor of heat
good conductor of electricity
rotor
rotates, located inside the glass envelope, connected to the disk by the shaft of molybdenum.
can be noisy and continue to spin long after exposure
stator/induction motor
turns the anode disk, located on the outside of the glass envelope and tube housing.
no physical contact between the stator and anode, electromagnetism.
true/actual focal spot
the area of electron impact
effective focal spot
the true focal spot projected towards the patient
line focus principle
the effective focal spot will always be smaller than the true/actual focal spot
angle of anode
usually 7-15; 12 is standard
anode heel effect
the construction of the anode results in a disparity of X-ray intensity from cathode to anode. More X-rays on the cathode side versus the anode side
central ray
the portion of the X-ray beam that is directed tower the center of the film or object being imaged
off focus radiation
X-rays produces by stray electrons that interact at positions on the anode at points other than the focal spot
heat units
kvp x mas x rectification factor
methods of heat transfer
conduction, convection, radiation
conduction
the transfer of heat through a material by touching or physical contact of solid objects
convection
the transfer of heat by the mixing of molecules in a liquid or gas
radiation
the transfer of heat by the emission of infrared radiation
dielectric oil in X-ray tube function
absorbs unusable cry energy, electrically insulates, conducts heat away from the X-ray tube
xray tube rating charts
designed for specific manufacturer and tube design,
based upon anode speed, angle, voltage rectification.
used to ensure heat limits not exceeded
anode cooling charts
used to prevent damage to the anode by allowing it to cool sufficiently between exposures, shows how long it takes to cool from its max heat level
3 things for X-ray production
source of free electrons, acceleration of free electrons, abrupt halting of high speed electrons
characteristics of high speed projectile electrons include
have mass (small); negative charge; moving at high speed; possess massive kinetic energy
characteristic of tungsten atoms include
high melting point, good conductor of heat/electricity, high atomic number (74)
electron binding energy
unique characteristic of elements, measurable, no elements have the same binding energy values
electron binding energy varies by
atomic # and distance from nucleus
Tungsten shell levels
K=69.5 L=12.1 M=2.8 N=0.6 O=.008 P=0
kinetic energy
the energy an object in motion possesses
KE=1/2mass x velocity2
kinetic energy equals one half mass times velocity squared
projectile/incident electrons
electrons moving a a high level of speed from cathode to anode by kilovoltage
beam quality/penetrability
the average X-ray strength in the polyenergetic primary beam
beam quality/penetrability is controlled by
KVP (primary) and filtration (as filtration goes up, so does beam quality)
beam quantity
the number of X-rays in the polyenergetic primary beam
beam quantity is controlled by
MAS (primary); KVP; Filtration (as filtration goes up, beam quantity goes down)
beam filtration
anything between the focal spot and the patient, can be gas, oil, plastic, mirror, air, etc
inherent filtration
built into tube and housing
added filtration
between housing and patient
total filtration
inherent + added filtration
minimum total filtration
at least 2.5mm Al/Eq
Filtration is measured in
Aluminum Equivalence
half value layer
the amount of filtration required to reduce beam intensity to half its original value
As filtration increases
beam quality increases
As filtration increases
beam quantity decreases
the 1/3rd rule
the majority of X-rays created in the polyenergetic primary beam will have an energy value that is approximately 1/3 of the set KVP
differential absorption
different materials absorb X-ray energy to differing degrees
Bremsstrahlung Interaction
Braking:
A high speed/high kinetic energy electron enters a tungsten atom.
The (-1) charged electron is magnetically attracted to the (+74) nucleus.
Of a result, the incident electron slows down (brakes)and changes course.
The lost kinetic energy changes form into X-ray energy - unpredictable amount.
How is the strength of Brems X-ray determined
The X-ray created is exactly equal to the amount of kinetic energy lost.
Continuous emission spectrum
A spectrum having no lines or bands
Distributed over an uninterrupted range of wavelengths
Characteristic Interaction
Collision:
High speed/kinetic energy electron enters a tungsten atom.
There is a collision with one of the orbital electrons.
If electron possesses greater energy than the orbitals, the orbital is ejected from its orbit leaving a hole.
An outer shell electron will jump across the space to fill the hole.
The electron she’ll transfer results in the transfer of energy, X-ray.
The strength of the X-ray is exactly equal to the difference in the orbital ring binding energies involved in the interaction. Only k she’ll interactions produce useful X-ray, predictable.
Characteristic cascade
movement of electrons from outer shell to inner shell electrons
how is the strength of a characteristic X-ray determined
The difference in orbital ring binding energies involved in the interaction.
discrete emission spectrum
A spectrum in which the component wavelengths constitute a discrete sequence of values rather than a continuum of values.
xray emission spectrum
A set of X-ray frequencies emitted by a target in an X-ray tube.
Inverse Square Law
Any physical law stating that a specified physical quantity or intensity is inversely proportional to the square of the distance from the source of that physical quantity
Xray intensity
KVP and filtration
Polyenergetic/Heterogenous
X-ray energy exists in a variety of strengths from 1kv to the set KVP
mGya (mR)
?????????
Milliampere-seconds
(mAs)
The number of electrons in motion = the number of X-rays produced
Kilovolt Peak
(KVP)
The strength of electron acceleration = the strength of X-rays produced
compensating filter
A simple or complex system of placing a discretionary metal filter (usually aluminum) in front of the collimator in order to reduce a portion of the primary beam to compensate for varying body part thickness in the same field of view.
