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Coherent Scattering
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Imaging Ch.10
X-ray Interaction with Matter
| Question | Answer |
|---|---|
| Five interactions with Matter: | -Coherent Scattering. -Compton Effect. -Photoelectric Effect. -Pair Production. -Photodisintegration. |
| 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. |
| 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 |
| 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). |
| 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. |
| The __________ electron may be deflected in any direction including back in the direction that the incident electron came from (backscatter). | Compton. |
| 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. |
| 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. |
| 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. |
| Pair Production: | -This interaction causes a two charged particles to appear in place of the incident electron. -One positive (positron) and one negative. |
| 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. |
| Radiopaque | Materials which absorb x-ray energy. Appear white on radiographic image. |
| Radiolucent | Materials which allow x-rays to pass through without much interaction. Appear grey or dark on the radiographic image. |
| 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. |
| Atomic Number | The higher the atomic number of the material, the greater the differential absorption. |
| Mass Density | Quantity of matter per unit volume. (How tightly the atoms of a substance are packed). |
| Contrast Administration | Contrast has a higher atomic number than the surrounding soft tissue there a greater differential absorption. |
| Contrast Administration | Contrast has a higher atomic number than the surrounding soft tissue there a greater differential absorption. |
| Coherent Scattering | Is of little importance to diagnostic radiology. |
| Compton Scattering | Reduces image contrast. |
| Photoelectric Effect | Is total x-ray absorption. |
| The probability of the ___________________ is inversely proportional to the third power of the x-ray energy (1/E)3. | Photoelectric effect. |
| The probability of photoelectric effect is directly proportional to the 3rd power of the atomic number of the absorbing material. | (Z^3). |
| Pair Production | Does not occur during x-ray imaging. |
| Photodisintegration | Does not occur in diagnostic imaging. |
| Differential absorption occurs because of __________, ____________ and ___________ transmitted through the patient. | Compton scattering, photoelectric effect, and x-rays. |
| Differential Absorption | Increases as the kVp is reduced. |
| To image small differences in soft tissue, one must use _______________ to get maximum differential absorption. | Low kVp. |
| The interaction of x-rays with __________ is proportional to the mass density of the ___________ regardless of the type of interaction. | Tissue. |
| Attenuation | Is the product of absorption and scattering. |
| Latent Image | Image on the receptor before it is processed. |
| Which are of particular importance to diagnostic radiology? | Compton Scattering & Photoelectric Effect. |
| Backscatter Radiation | X-rays scattered back in the direction of the incident x-ray beam. |
| Photoelectron | The electron removed from the atom. |
| Annihilation Radiation | The positron unites with a free electron and the mass of both particles is converted to energy. |
| Monoenergetic | A beam containing x-rays that all have the same energy. |
| Polyenergetic | Are emitted over an entire spectrum of energies. |
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