X-ray Interaction with Matter
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| Five interactions with Matter: | -Coherent Scattering.
-Compton Effect.
-Photoelectric Effect.
-Pair Production.
-Photodisintegration.
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| Coherent Scattering | -Low energy x-rays (10 keV).
-Also called classical scattering or Thompson scattering.
-Not usually in the diagnostic range but will cause fog on a radiograph.
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| Coherent Scattering: | -Incident x-ray interacts with atom, causing it to become excited and change the original direction of the interaction.
-The x-ray simply changes direction
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| Compton Effect | -Moderate energy x-rays.
-Also called Compton scattering.
-May occur in the diagnostic range.
-The incident x-ray interacts with an outer shell electron causing it to be ejected from the atom (ionization).
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| Compton Effect: | -The ejected electron is the Compton electron or secondary electron.
-The x-ray continues in a different direction with less energy.
-The energy from the incident x-ray is divided by the scattered x-ray and the Compton electron.
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| The __________ electron may be deflected in any direction including back in the direction that the incident electron came from (backscatter). | Compton.
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| Photoelectric Effect | -Usually in the moderate to high energy levels.
-Incident x-ray interacts with and ejects an inner shell electron.
-The incident x-ray must have sufficient energy to eject the inner shell electron.
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| Photoelectric Effect: | -The ejected electron is called the photoelectron.
-After ejected electron is removed the outer shells then drop and fill in the gap in the inner shell electron.
-Creates characteristic or secondary radiation.
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| Pair Production | -Very high energy ranges MeV(out of diagnostic range).
-Incident x-ray passes through all outer shells and comes close enough to interact with the nucleus.
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| Pair Production: | -This interaction causes a two charged particles to appear in place of the incident electron.
-One positive (positron) and one negative.
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| Photodisintegration | -Uses highest energy range (MeV).
-Incident x-ray interacts directly with the nucleus and raises it to an excited state.
-At the same time a nuclear fragment if given off.
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| Radiopaque | Materials which absorb x-ray energy. Appear white on radiographic image.
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| Radiolucent | Materials which allow x-rays to pass through without much interaction. Appear grey or dark on the radiographic image.
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| Differential Absorption | -The difference between the x-rays absorbed photoelectrically in the patient and those transmitted to the image receptor.
-Is a product of the absorption process or attenuation.
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| Atomic Number | The higher the atomic number of the material, the greater the differential absorption.
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| Mass Density | Quantity of matter per unit volume.
(How tightly the atoms of a substance are packed).
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| Contrast Administration | Contrast has a higher atomic number than the surrounding soft tissue there a greater differential absorption.
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| Contrast Administration | Contrast has a higher atomic number than the surrounding soft tissue there a greater differential absorption.
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| Coherent Scattering | Is of little importance to diagnostic radiology.
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| Compton Scattering | Reduces image contrast.
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| Photoelectric Effect | Is total x-ray absorption.
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| The probability of the ___________________ is inversely proportional to the third power of the x-ray energy (1/E)3. | Photoelectric effect.
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| The probability of photoelectric effect is directly proportional to the 3rd power of the atomic number of the absorbing material. | (Z^3).
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| Pair Production | Does not occur during x-ray imaging.
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| Photodisintegration | Does not occur in diagnostic imaging.
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| Differential absorption occurs because of __________, ____________ and ___________ transmitted through the patient. | Compton scattering, photoelectric effect, and x-rays.
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| Differential Absorption | Increases as the kVp is reduced.
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| To image small differences in soft tissue, one must use _______________ to get maximum differential absorption. | Low kVp.
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| The interaction of x-rays with __________ is proportional to the mass density of the ___________ regardless of the type of interaction. | Tissue.
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| Attenuation | Is the product of absorption and scattering.
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| Latent Image | Image on the receptor before it is processed.
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| Which are of particular importance to diagnostic radiology? | Compton Scattering & Photoelectric Effect.
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| Backscatter Radiation | X-rays scattered back in the direction of the incident x-ray beam.
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| Photoelectron | The electron removed from the atom.
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| Annihilation Radiation | The positron unites with a free electron and the mass of both particles is converted to energy.
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| Monoenergetic | A beam containing x-rays that all have the same energy.
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| Polyenergetic | Are emitted over an entire spectrum of energies.
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