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RADT334-Unit 4
Covering x-ray production and interactions
| Question | Answer |
|---|---|
| Electrons emitted by the filament and directed to the target (traveling from the cathode to the anode) | projectile electrons |
| The strength of attachment of electrons to the nucleus | binding energy |
| X-rays produced by transitions of orbital electrons from outer to inner shells | characteristic x-rays |
| X-rays produced by interaction of a projectile electron with the nuclear force field of a target nucleus | bremsstrahlung x-rays |
| X-ray intensity, measured in milliroentgens (mR) or air KERMA (mGy) | x-ray quantity |
| Effective energy of the x-ray beam; penetrating ability | x-ray quality |
| The monoenergetic equivalent of an x-ray beam | effective energy |
| Section of metal added to the x-ray tube housing. Overall result is an increase in the effective energy of the x-ray beam (higher quality) and an accompanying reduction in x-ray quantity. Results in reduced patient radiation dose. | added filtration |
| The measure of x-ray energy of all x-rays, a graphical representation of the relative quantities of photons of each type of energy in the x-ray beam | emission spectrum |
| The x-ray tube target material principally used for mammography | molybdenum |
| calculate the energy of the characteristic x-ray produced when a K-shell electron is replaced by an M-shell electron in tungsten | 66 keV |
| At what fraction of the velocity of light do 90 keV electrons travel? | 60% |
| what does the discrete x-ray spectrum represent? | characteristic x-rays |
| When an x-ray imaging system is operated at 80 kVp, its emission spectrum represents an output intensity of 3.5 mR/mAs. What will be the output intensity if the voltage is increased to 90 kVp? | 4.42 mR/mAs |
| How will the emission spectrum change is going from 80 kVp to 90 kVp? | higher amplitude and shift to right |
| What will happen to the x-ray emission spectrum if you change your imaging system from single phase to three phase? | higher amplitude and shift to right |
| How will the x-ray emission spectrum be changed if you add filtration to the x-ray tube? | lower amplitude and shift to right |
| How is the kinetic energy of the projectile electrons streaming across the x-ray tube increased? | increase kVp |
| Why is the x-ray tube considered an inefficient device? | only 1% of projectile electrons are converted into x-rays |
| What is the importance of K-characteristic x-rays in forming a diagnostic radiograph? | Significantly helpful when the kVp is above 70 kVp (the K shell binding energy for tungsten) |
| What is the range of energies of bremsstrahlung x-rays? | From near zero to an energy in keV equal to the kVp setting |
| Name the factors that affect the shape of the x-ray emission spectrum. | Voltage, rectification, filtration, tube current |
| What is the 15% rule? | A 15% increase in kVp is equivalent to doubling the mAs |
| What is the diagnostic range of x-rays? | 20-150 kVp |
| The filtration provided by the window and oil bath of the x-ray tube | inherent filtration |
| The unit of x-ray quantity | Milliroentgen (mR) or milligray (mGy) |
| Addition of a filter shifts the x-ray emission spectrum to the high-energy side, resulting in an x-ray beam with higher effective energy, greater penetrability, and higher quality, but less intensity. | filtered x-ray spectrum |
| A kVp change equal to twice the mAs | 15% |
| three filter materials used with diagnostic x-ray beams | Aluminum, molybdenum, rhodium |
| The thickness of filter or other absorbing material that will reduce intensity to half its original value | HVL |
| A compensating filter designed to shape the useful x-ray beam to the anatomic structure under examination so that the exposure of the image receptor will be more uniform | wedge filter |
| Identified numerically by half-value layer; also influenced by kVp and the added filtration in the useful beam | unit of x-ray quality |
| The approximate HVL of your x-ray imaging system | Usually totals 2 to 3 mm of aluminum equivalent |
| Another term for x-ray quantity, measured in mR or mGy | x-ray intensity |
| An abdominal radiograph taken at 84 kVp, 150 mAs results in patient radiation exposure of 650 mR. The image is too light and is repeated at 84 kVp, 250 mAs. What is the exposure? | 1083 mR |
| An image of the lateral skull taken at 68 kVp, 20 mAs has sufficient optical density but too much contrast. If the kVp is increased to 78 kVp, what should be the new mAs? | 10 mAs |
| A chest radiograph taken at 180 cm SID results in an expsoure of 12 mR. What would the exposure be if the same radiographic factors were used at 100 cm SID? | 38.9 mR |
| Old technique: 60 kVp, 10 mAs = 28 mR New technique: 55 kVp, 10 mAs = what new intensity? | 23.5 mR |
| The kVp is reduced from 78 to 68 kVp. What should be done to the mAs to maintain the same exposure of the image receptor? | double the mAs |
| what is the relationship between x-ray quantity and mAs? | directly proportional |
| List two ways x-ray beam can be shifted to a higher average energy? | Increase kVp or added filtration. |
| Why is aluminium used for x-ray beam filtration? | Because it is efficient at removing low-energy x-rays, and because it is readily available, inexpensive, and easily shaped into filters |
| Describe the use of a wedge filter during a foot x-ray | The thicker part of the wedge should be positioned toward the toes in order to equalize optical density. |
| Does adding filtration to the x-ray beam affect the quantity of x-rays reaching the image receptor? | Yes |
| Effect of increasing mAs on x-ray quality | none |
| Effect of increasing mAs on x-ray quantity | increase |
| effect of increasing kVp on x-ray quality | increase |
| effect of increasing kVp on x-ray quantity | increase |
| effect of increasing distance on x-ray quality | none |
| effect of increasing distance on x-ray quantity | decrease |
| effect of increasing filtration on x-ray quality | increase |
| effect of increasing filtration on x-ray quantity | decrease |
| The relationship among transmitted x-rays, photoelectrically absorbed x-rays, and Compton scattered x-rays resulting in the x-ray image | differential absorption |
| Scattering of very-low-energy x-rays with no loss of energy; also called coherent or Thompson scattering | classical scattering |
| The quantity of matter per unit volume, usually specified in kilograms per cubic meter (kg/m3). Sometimes reported in grams per cubic centimeter (gm/cm3). | mass density |
| The threshold energy required by a photon to undergo pair production | 1.02 MeV |
| A high-atomic number material (for example, iodine and barium), or a low density, low-atomic number material (air) administered in liquid or gas form to improve the contrast resolution of an x-ray examination | contrast agent |
| X-ray ionization resulting in x-ray scattering | Compton effect |
| The reduction in x-ray beam intensity as a result of photoelectric absorption and Compton scattering | attenuation |
| Having a single energy. Characteristic x-rays are monoenergetic, and the effective x-ray energy of an x-ray beam is the monoenergetic equivalent of the actual beam. | monoenergetic |
| Electrons released in ionization as the result of photoelectric interaction and Compton scattering | secondary electron |
| An x-ray absorption interaction in which the x-ray is not scattered but totally absorbed. A photoelectron is then released from the atom. | photoelectric effect |
| what are the two factors of importance to differential absorption? | keV and atomic number of absorber |
| 1000 x-rays with energy of 140 keV are incident on bone and soft tissue of equal thickness. If 87 are scattered in soft tissue, approximately how many are scattered in bone? | 87 |
| Why are iodinated compounds such excellent agents for vascular contrast examinations? | high atomic number and high mass density |
| Compton-scattered x-rays leave the scattering object in the approximate direction of the incident x-ray beam. | backscatter radiation |
| Which 3 of the 5 basic mechanisms of x-ray interaction with matter are not important in diagnostic radiology? | Classical, photodisintegration, pair production |
| Why are there 3 mechanisms of x-ray interaction with matter that are not important in diagnostic radiology? | The x-ray energies involved are outside of the diagnostic energy range |
| Does the probability of the Compton effect depend on the atomic number of the target atom? | No |
| when kVp is increased, is Compton scattering increased or reduced? | decreased |
| how much more likely is it that an x-ray will interact with bone than with muscle? | (13.8/7.4)3 = 6.5 |
| What is the relationship between atomic number and differential absorption? | Differential absorption resulting from photoelectric effect is proportional to the third power of the atomic number. Compton effect is unrelated to atomic number. |
| What is the relationship between mass density and differential absorption? | The probability of interaction is proportional to mass density, and therefore, so is differential absorption. |
| What kVp is used to penetrate barium in a contrast examination? | 90 kVp |
Created by:
hschmuck1
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