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86 Cards in this Set
- Front
- Back
What are the three important ranges of the electromagnetic spectrum? |
Visible light |
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What are the five main parts of the x-ray tube? |
Transformer |
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What does the x-ray transformer do? |
delivers kilivoltage separated into negative and positive charges |
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describe the x-ray cathode |
Cathode is the negative pole it is a tungsten filament in a fucusing cup. |
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Describe the x-ray anode |
anode is the positive tungsten target on a copper base |
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What does the window do? |
Window is where produced x-rays will be directed to foot or ankle region. Alows escape of x-rays |
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Why tungsten in x-ray machines? |
High atomic number so x rays are of good quality (actual rays, not images necessarily) |
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Over-all explanation of how x ray tube works. |
Kilivolts supplied to both cathode and anode |
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How does the x-ray machine protect itself from overload ofheat? |
Anode rotates so electron stream is hitting different areas at each instant. |
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How are the x-rays from the anode directed? |
Angle of infraction- Anode is tilted so the electrons that are knocked off shoot towards the window. |
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What happens to 99% of all x-rays? |
Lost as heat. |
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How is heat dissipated with the x-ray system? |
Tungsten (high specific heat) |
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Of all the Properties of x rays what are some of the most important ones? |
Penetrates matter |
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What are the two inseparable natures of x-rays? |
Wave-like with specific wavelength (non particulate) |
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What is the Energy/Wavelength rule for x-rays? |
The higher the energy of the x-ray the shorter the wavelength. |
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Describe the interaction of Low, Moderate, and High energy x-rays with atoms. |
Low- React with whole atoms (verrrrr bad) |
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What energy x-ray is utilized for radiological imaging? |
Moderate Energy x-rays that interact only with electrons. |
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x-ray percentages |
99% heat |
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What are the three x-ray reactions with matter? |
Non-attenuating- goes through with no interaction (transmission) |
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What are the two important forms of x-ray Interactions (not reactions) important to Diagnostic X-rays |
Compton Effect |
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What is the Compton effect? |
x-rays interacting with electron outer shells in target = reduced energy |
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How does compton effect change with soft tissue/ bone? |
Compton Effect is about the same for soft tissue or bone. |
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What is the Photoelectric effect? |
opposite from Compton, this is an interaction with inner shell electrons of the target atom. This doesn't scatter, either, it is totally absorbed. |
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What is the Photoelectron in the Photoelectric effect? |
- the electron removed from the targe atom. |
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Describe the atomic binding energy of soft tissue vs higher atomic number atoms such as those in "not soft tissue" |
Low "anatomic" number (haha) atoms such as soft tissue have low binding energies (photoelectron E nearly equivalent to incoming x-ray E) |
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When is the photoelectric effect most likely to occur? |
With inner-shell electrons |
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How useful are compton scatter x-rays in Differential Absorption? Why? |
Not at all, because they scatter, mis-represent, and distort. Just like everything out of Compton. |
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What is differential Absorption? |
Absorption of x-rays that make it through the body and contribute to the radiograph, |
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Radiopaque images are shown on the x-ray film because of what interaction? |
Photoelectric interaction with target atom inner shell electrons (blocked) |
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Radiopaque vs Radiolucent |
Opaque- x-rays are absorbed and don't reach the film. They are blocked so the film doesn't turn black. BRIGHT |
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The radiographic image is the result of the difference between WHA? |
xrays absorbed photoelectrically and those not absorbed at all. |
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What is a major reason that radiographs are not as sharp as photographs? |
Except at low kVp most xrays interact via Compton. |
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What % of x rays incident on the pt reach the film? What % of that interact with the film? |
less than 5% |
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What is the caveat of only having 1% of x-rays emitted reaching the film? |
Careful control of the x-ray beam is necessary to produce high quality radiographs |
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Differential Absorption and kVp relationship |
Greater Differential absorption requires lower kVp |
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Is the photoelectric absorption of bone always higher than soft tissue? |
Yes, always about 7x more regardless of energy |
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Effects and Energies |
Low Energy = mainly photoelectric |
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As kVp increses what change needs to happen to mAs? |
Lower output required |
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Tissues/kVp |
Soft tissues need lower kVp for better images (but dangerous) |
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The crossover of photoelectric and compton scattering is at what keV? |
40. |
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What are the degrees of absorption? |
transparent |
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What is the over-all source of attenuation? (x-ray blocking) |
Sum of scattering (compton) and absorption (photoelectric) reactions of radiation. |
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Radiopaque vs |
Bone (white) |
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What is the heel effect? |
Higher concentration of x-rays on cathode side of x-ray window can make for poor images at the heel (area towards the anode) |
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How does the heel effect influence positioning? |
the cathode side (-) becasue has more x-rays, should be over the area of greatest density |
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Anode angle/ heel effect |
Angle decreases/ effect increases |
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What is the key point of a radiological grid? |
Only rays that travel ina relatively straight line (primary radiation) from the source are allowed to reach the film. Scattered or angulated rays (secondary radiation) are absorbed by the lead grid. |
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What are the three important aspects of Grid construction? |
Ratio |
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In considering grid ratio, what are the three important dimensions on a grid? |
Width of grid strip |
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Why are high ratio grids more effective in cleaning up scatter? |
they have smaller holes so only relatively straight rays can get through. Unlike those big loose grids, anything gets into that! |
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what is the major downside of a high ratio grid? |
they clean up the crap so that the Pt has to get higher dose of rays for a decent image. |
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what are the popular grid ratios? |
8:1 on single phase machines |
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What is the grid used in podiatry? |
"podiatry does not need a grid" |
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How does a filter affect the image? |
The filter will block the long low energy un important (quantity) waves, and leave the high quality short waves (quality). Increased quality and decreased number. Fantastic! |
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What is measured in Al equivalence? |
Filter |
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What are the filter Al equivalents needed in podiatry? |
Inherent- 1.5mmAl equivalence |
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Explain X-ray film |
Silver halide crystals in a gel in a + state. |
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So far we have Grid, Filters, Film, what's left? |
Screens |
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What is the major difference in Grid and Screen? |
Grid= better image |
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Explain the 5 steps of film development (basic). |
Developing - developer, accelerator, restrainer, preservative, hardener |
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What is the major control of kVp adjustments? |
kVp controls radiographic contrast. (short to long) |
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Increased kVp= |
Quality change and |
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In a nut shell kVp and contrast |
High kVp= lower contrast (long scale) |
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As kVp increases there are less rays that interact with subject atoms, what does this say about pt exposure? |
kVp increase = pt "exposure" decreased. |
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What is directly correlated with the # of x-rays? |
The number of x-rays are directly proportional to the mA, assuming a fixed exposure time. |
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Increasing MA vs kVp (test q) |
Increasing mA = increasing number of x-rays= more danger. |
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Does podiatry use a Death-Star level of mA? |
No, podiatry uses low mA (15-30) |
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Why is exposure time kept as short as possible? |
NOT to reduce exposure, but to reduce movement |
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mAs affect on x-rays (for the third time) |
mAs control radiation quantity, optical density and pt dose (kvp is qual) |
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What are 2 critical external factors? |
Central ray needs to be on the area b/c of heel effect. |
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What is the kVp/mA change rule? |
15% muthaluva! |
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Increasing kVp enhances what? |
kVp= soft tissue |
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What is the inverse square law? |
That's the reason you can stand 6ft away and be fine. |
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What does distance affect in x-rays? |
Distance affects the intensity of the x-ray beam at the film but has no effet on radiation quality. |
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What is the most common source to image distance? |
40" or 100cm (the major one for us) |
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What does increasing SID do to the image? source to image distance |
Increased distance = decreased magnification distortion and focal spot blur |
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what is the focal spot size used in podiatry? |
1mm |
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What is the collimator? |
robot that destroys the colon. |
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What is the greatest tool in keeping pt exposure as low as possible? |
Collimation |
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Describe why greater SID causes better images |
there is a part in Hook where the son is acting like a zombie in front of a lamp, as he moved closer to the lamp his shadow on the wall got larger and more diffuse, the further from the lamp and closer to the wall the sharper his shadow was. EXACTLY like that instead of in the visible spectrum, it is in x-rays. |
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What is the filter required for podiatry machines/setup? |
Podiatry maxes out about 70kVp which requires 2.5 mm Al equivalent . |
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What is radiographic quality? What are the three main factors? |
Radiographic quality- fidelity at which the anatomic structures being examined are shown on the film. |
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Fog and Scatter= unwanted density from Compton interactions. What causes them to increase? |
Increase with |
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Summary of high kVp: |
Low contrast (long scale) |
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summary of mA: |
quantity change only (no contrast change) |
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x-ray technique summary: |
Moderate to large SID |