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Chapter 6 LMR

Radiographic Tube and Radiation Production

QuestionAnswer
The x-ray tube consists of... A cathode (-) and Anode (+), enclosed within a glass envelope which is then encased in a protective housing.
Cathode (-) Is the electrode or terminal by which current leaves an electrolytic cell (battery)also referred to as the "source".
Anode (+) The electrode or terminal by which current enters an electrolytic cell(battery) also referred to as the "receiver".
Stator A portion of a machine that remains fixed w/ respect to rotating parts.
The Cathode assembly consists of the... filament, focusing cup and associated wiring.
The Anode assebly consists of the... anode, stator and the rotor as the path for the high-voltage flow during exposure.
X-rays are produced when... high speed electrons from the cathode side of the tube hits the anode target surface.
Filament A very fine thread or fiber.
Vaporize Turns into gas.
The purpose of the Filament.... To provide sufficient resistance to the flow of electrons so the heat produced will cause Thermionic Emission.
Filament material used are... Thoriated tungsten, Rhenium and Molybdenium are used because of their high melting point.
The temperature of the filament controls... the quantity of electrons emitted, the higher the temp the more electrons produced.
When kilovoltage is applied between the cathode and the anode the result is... electrical current through the x-ray tube (mA) begins.
Rotor switch is used to heat the filament to start the anode which rotates at 3,000 to 10,000 rpm's
The useful life of a diagnostic x-ray tube filament is estimated to be approximately.. 10,000 to 20,000 exposures.
The Anode has 3 functions... target, conducts the high-voltage from cathode back to circuitry and the primary thermal conductor.
The portion of the anode where the high-voltage electron stream will impact is referred to as... focal point, focal spot or the focal track.
The "line focused principle" is a result from... The electron stream striking an angled target (10-20 degrees to the central ray.
Focal Spot The part of the anode on which the electron stream impacts.
The smaller the focal spot is directed at an angle... the greater the detail in photon.
The difference between the "actual focal spot" and the "effective focal spot" is... The size and angle of the spot.
Heel Effect an unacceptable reduction in x-ray output toward the anode side of the x-ray beam.
Focusing Cup is used to direct the flow of electrons. It has a (-) negative potential as does the filament (cathode)
The filament is heated by a high electrical filament current that is measured in... amperes
kilovoltage (kV) a unit of electromotive force, equal to 1000 volts.
Potential Difference Electrons flowing from (-) Cathode to (+) Anode.
milliamperge (mA) a unit of electric current equal to one thousandth of an ampere.
Tungsten is used due to the high melting point... 3,370 degrees C and atomic number of 74 (z = 74)
The ability of the target material to withstand heat affects both the.... quantity (mA) and the quality (kVp) of the x-ray energy.
By increasing the mA's the number of electrons increase which causes... and increase in the blackness on radiographic films.
Increase in kVp will also increases penetration aka scatter radiation.
2 types of Target interactions 1. Bremsstrahling 2. Characteristic which one occurs depends on kinetic energy and the binding energy of the electron shells of the atom.
Bremsstrahlung The energy that is lost when the electron slows down and is emitted as an x-ray film.
Characteristic Occurs only when the incoming electron interacts with an inner shell electron. aka Seconday Radiation.
The Primary beam consists of... all the x-ray photons emitted through the glass window. The remaining photons are unwanted and the x-ray tube housing is designed to absorb them.
Leakage Radiation any x-ray photons that escape from the housing except at the window or port.
The amount of leakage radiation produced should never exceed... 100 mR/hr at 1 meter
Filtration of the Primary Beam improves this.. image quality & protects the patient from low energy, long wavelength photons.
Inherent filtration consists of the x-ray tube and housing.
Collimator sets of lead shutters mounted at right angles to one another which limits the area being radiated. They are equipped w/ a light source that represents the Primary Radiation Beam.
Body tissue attenuate (change) the radiation based interactions w/ the tissues.
Scatter radiation occurs when... x-rays interact with matter and a change in their direction results.
Remnant Radiation The useful radiation consisting of both primary & secondary radiation.
Never use high kVp on a cold target. Warm with several low exposures of... 50 kVp & 10 mA before making a single high exposure.
X-ray tube heat is measured in... Heat Units (HU)
The mathimatical combo of exposure factors are measure like this... kVp x s x mA = HU (70 kVp x 1.0 s x 100 mA = 7000 HU
Created by: kristiew1