問題一覧
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- produced ISOTROPICALLY and has EQUAL INTENSITY to all directions - SIZE is VARIABLE by using X-RAY BEAM COLLIMATORS - Intercepted by MATTER & TISSUE.
X-rays
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- Produced by using a HIGH VOLTAGE and an ELECTRIC CURRENT - Produced when FAST MOVING ELECTRONS coming from the cathode interacts with the target in the anode
X-rays
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this is the x-rays emitted through the window of the x-ray tube The actual x-ray beam that is intercepted by the patient
Primary Beam/Useful Beam
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Transmitted from the x-ray tube to the image receptor. The QUALITY and QUANTITY of this can be determined by the !kVp and mAs! It should never be directed at the radiologic technologist, other personnel, or the control booth.
Primary Beam
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imaginary line in the useful beam centermost part of the x-ray beam should be aligned to the center of the structure being imaged and grid if being used.
Central Ray
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Particularly important in radiographic positioning and reducing image distortion
Central Ray
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If the intensity of the central ray is 100%, what is the x-ray intensity on the cathode and anode side?
Cathode - as high as 120% Anode - as low as 75%
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The part of the x-ray beam that exits the patient after interaction. Interact with the patient and are scattered away.
Exit/Remnant Beam
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any x-rays that escape the protective housing of the X-ray tube Contributes nothing in the way of diagnostic information and results in unnecessary exposure of the patient and radiologic technologist. Must not exceed !!100 mR/hr at !!1m!!
Leakage Radiation
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also known as Extrafocal X-rays
Off-Focus/Stem Radiation
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During off focus radiation creation, this bounce off the focal spot and land on other areas of the target causing x-rays to be produced from outside of the focal spot.
Electrons
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designed so that the projectile electrons from the cathode interacts with the target only at the focal spot. considered to be an ineffective device
X-rays tubes
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x-rays formed outside of the focal spot area undesirable because it extends the focal spot size increasing the skin dose unnecessarily Can reduce the radiographic image contrast.
Off-focus radiation
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Can also be reduced by the use of metal enclosures which extract and conduct the reflected electrons Can be a reason that tissue that was meant to be excluded, appear on the radiograph Reduced by using a fixed diaphragm inside the x-ray tube near its window.
Off-focus radiation
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energy in motion
Kinetic Energy
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Ions with high kinetic energy focused toward a small spot on the anode are necessary for x-ray production. TRUE OR FALSE?
False. Electrons, not ions
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Kinetic Energy Equations
KE = (1/2)(mv^2) M - mass in kg V - velocity in meters per second KE - kinetic energy in joules
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expression of energy of x-rays
Kilo electron volts
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How many joules in 1 keV
1.6 x 10^-16 J
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primary function is to accelerate electrons from cathode to anode
X-ray imaging system
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distance of the filament to the target
1 cm
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most of the projectile electrons' kinetic energy is converted into this
Heat
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99% of projectile electron interaction is converted into this
Thermal Energy
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interact with outer shell electrons which causes excitation then return to the original state.
Projectile electrons
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2 incidents that are responsible for most heat generated in the Anode
constant excitation and return to normal state
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How to increase the anode heat of Tube Current?
Increase mAs
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How to increase anode heat of Tube Voltage?
Increase kVp
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percentage of anode heat used in x-ray production
1%
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Electrons traveling from the cathode to anode These electrons interact with the orbital electrons or the nuclear field of the target atoms interact with an inner shell electron and ionizes it leaving a void to be filled by an outer shell electron
Projectile electrons
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When electrons hit the anode, they transfer their kinetic energy to
Target atoms
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what are 2 results of electrons interacting with orbital electrons or nuclear field. Formation of what?
formation of thermal energy and electromagnetic energy
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produced when an outer shell electron fills an inner shell void Emission of x-ray occurs as the outer shell electron fills the inner shell
Characteristic Radiation
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occurs when radiation is produced by any other outer shell electron filling a K shell vacancy
K X-rays
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only ones useful in x-ray imaging as all other outer shell electron binding energy is lower than of a K-shell electron
K-characteristic x-rays of tungsten
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require an x-ray tube with a potential of 69 kVp and up since the K-shell electron of a tungsten target has an effective energy of 69 KeV
K-shell X-rays
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german word meaning “slowed down”
Bremsstrahlung
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results from the braking of projectile electrons by the nucleus of an atom, where the projectile electrons completely avoids the orbital electrons as it passes through the target atom and may come close enough to the nucleus to interact with its electric field
Bremsstrahlung Radiation
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where projectile electron loses its kinetic energy as it interacts with this then changes direction
Nuclear Force Field
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what lost kinetic energy is converted into
Electromagnetic energy
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causes the "braking" down of electrons occurs between nucleus of atom and projectile electrons
Electrostatic force of attraction
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Charge of a nucleus of an atom
positively charged
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charge of Projectile electrons
negatively charged
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results when the projectile electrons barely interact with the nuclear force field
Low energy bremsstrahlung x-rays
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how much energy can be produced in bremsstrahlung radiation?
1 keV to 70 keV
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In diagnostic range, most x-rays are?
Bremsstrahlung x-rays