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17 Cards in this Set
- Front
- Back
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What does an X-ray Tube do? |
Converts Energy from ELECTRICAL ENERGY to HEAT ENERGY (99%) Waste and can destroy tubes. X-rays (1%) Desired |
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What is inside the Glass Insert? |
Filament - Similar to light bulb - Glows when heated Target - Large (usually) tungsten block - Often angled Source of electrons Small coil of tungsten wire |
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What heats the Cathode (Filament) |
It is heated by electrical current - 10 volts - 3-5 amps Filament current is NOT tube current. |
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What are the requirements to Produce X-rays? |
Filament Voltage and High Voltage |
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What is the Tube Current (mA)? |
Rate of electron flow from filament to target Electrons / second Measure in milliamperes (mA) |
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What is meant by Space Charge (electron cloud)? |
When the electrons leave the filament, the filament becomes more POSITIVE. Electron cloud surrounds the filament Cloud repels NEW electrons from filament. Electron stream needs to be accelerated towards the target. |
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Outline the next steps. |
Positive High Voltage is applied to Anode relative to filament > electrons accelerate toward anode target --> gain kinetic energy > electrons strike the target > kinetic energy of electron is converted into heat / xrays |
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How is the X-ray production electrically controlled? |
Measured in kilovoltage (kv / kVp) Voltage given to the x-ray tube controls the speed and power of electron stream. Thus allowing the control of energy / penetrating power of the x-ray beam. high kVp = Dense / larger body parts |
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What is Off Focus Radiation? |
Refers to electrons that interact with the target outside the focal spot (scatter). > This increases patient exposure > increases image fog and blur > increases target Heating |
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List solutions for Off Focus Radiation. |
Lead Collimators near tube window. Housing of x-ray tube |
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What are the benefits of Tube Housing? |
Lead lined Reduces leakage Shields against high voltage issues - electrically grounded - high voltage cable receptacles. Sometimes the housing is filled with oil - cools - electrical insulation --> all air is removed Bellows - allows oil to expand when hot. |
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What is the penetrating power of the x-ray beam measured in? |
kVp mA = number of electrons flowing from filament to target each second msec- length of time the cray are turned on mAs - total quantity of photons produced by an exposure |
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What is meant by Bremsstrahlung Radiation |
X-rays produced when high-speed electrons from the filament are slowed down as they pass close to or strike the nuclei of the target atoms. |
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What is meant by Characteristic Radiation? |
X-rays have energies characteristic of the target material i.e energy = difference between binding energies of target electrons involved "The energy of the high-speed electron from the filament must be higher than the binding energy of the target electron with which it interacts in order to remove the target electrons" |
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How X-ray Spectrum result generated? |
From varying electron/nuclues distances Multiple electron interactions Varying voltage (AC) |
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How is the excess heat controlled? |
Due to high melting point of tungsten and cooling from oil surrounding x-ray tube |
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Distance |
Inverse Square Law - intensity of radiation reduces to 1/4 as distance is doubled. |
