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86 Cards in this Set
- Front
- Back
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What are the three important ranges of the electromagnetic spectrum?
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Visible light
Radio frequency X-radiation (others include UV, IR and Microwave) |
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What are the five main parts of the x-ray tube?
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Transformer
Cathode Anode Lead housing unit Window |
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What does the x-ray transformer do?
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delivers kilivoltage separated into negative and positive charges
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describe the x-ray cathode
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Cathode is the negative pole it is a tungsten filament in a fucusing cup.
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Describe the x-ray anode
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anode is the positive tungsten target on a copper base
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What does the window do?
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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?
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High atomic number so x rays are of good quality (actual rays, not images necessarily)
High melting point so heat resistant. |
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Over-all explanation of how x ray tube works.
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Kilivolts supplied to both cathode and anode
Cathode carries flow (miliamps) and starts to boil of electrons (thermionic emission) and forms an electron cloud. Electrons are attracted to anode target at focal spot. The increase of electrons at anode will disturb the electrons of the target tungsten, causing e-s to shoot off in the form of x-rays. |
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How does the x-ray machine protect itself from overload ofheat?
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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?
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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?
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Lost as heat.
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How is heat dissipated with the x-ray system?
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Tungsten (high specific heat)
Copper base (dissipates heat quickly) Radiation system with oil or water or soda pop Fan (self explanatory) Angled tungsten anode that rotates. |
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Of all the Properties of x rays what are some of the most important ones?
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Penetrates matter
electronically neutral travels in straight lines can jack up biological substances Fluoresces materials (screens) Causes Image on film |
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What are the two inseparable natures of x-rays?
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Wave-like with specific wavelength (non particulate)
Bundles of E (particulate characteristic of Photons or Quanta) |
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What is the Energy/Wavelength rule for x-rays?
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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.
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Low- React with whole atoms (verrrrr bad)
Moderate- interact with electrons High- interact with the nuclei of an atom |
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What energy x-ray is utilized for radiological imaging?
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Moderate Energy x-rays that interact only with electrons.
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x-ray percentages
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99% heat
1% = rays of 1%, 10%= radiation 0f 1%, 90%= Bremsstrahlung or "braking" radiation |
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What are the three x-ray reactions with matter?
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Non-attenuating- goes through with no interaction (transmission)
Absorbed Scatter |
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What are the two important forms of x-ray Interactions (not reactions) important to Diagnostic X-rays
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Compton Effect
Photoelectric Effect |
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What is the Compton effect?
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x-rays interacting with electron outer shells in target = reduced energy
= ionized atom )not neutral) = scattered (direction change) is called "compton effect or compton scattering |
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How does compton effect change with soft tissue/ bone?
How does it change with kVp changes? |
Compton Effect is about the same for soft tissue or bone.
Scatter increases with increased kVp (increased x-ray energy) |
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What is the Photoelectric effect?
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opposite from Compton, this is an interaction with inner shell electrons of the target atom. This doesn't scatter, either, it is totally absorbed.
= Photon Absorption Interaction |
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What is the Photoelectron in the Photoelectric effect?
Describe it's collision/energy maintenance reaction |
- the electron removed from the targe atom.
- the photoelectron escapes with kE equal to the difference between the energy of the incoming x-ray and the binding energy of the electron. |
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Describe the atomic binding energy of soft tissue vs higher atomic number atoms such as those in "not soft tissue"
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Low "anatomic" number (haha) atoms such as soft tissue have low binding energies (photoelectron E nearly equivalent to incoming x-ray E)
Higher atomic number target atoms will have higher binding energies. |
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When is the photoelectric effect most likely to occur?
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With inner-shell electrons
With tightly bound electrons when the x-ray energy is higher than the electron binding energy. |
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How useful are compton scatter x-rays in Differential Absorption? Why?
Photoelectrons? Why? |
Not at all, because they scatter, mis-represent, and distort. Just like everything out of Compton.
Photoelectrons provide diagnostic information to the receptor since they don't reach the film they are seen as anatomic structures (underlined) = Radioopaque |
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What is differential Absorption?
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Absorption of x-rays that make it through the body and contribute to the radiograph,
The ones that paint the picture. |
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Radiopaque images are shown on the x-ray film because of what interaction?
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Photoelectric interaction with target atom inner shell electrons (blocked)
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Radiopaque vs Radiolucent
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Opaque- x-rays are absorbed and don't reach the film. They are blocked so the film doesn't turn black. BRIGHT
Lucent- fools get through develop white silver to BLACK. |
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The radiographic image is the result of the difference between WHA?
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xrays absorbed photoelectrically and those not absorbed at all.
CALLED DIFFERENTIAL ABSORPTION |
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What is a major reason that radiographs are not as sharp as photographs?
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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?
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less than 5%
less than 1/2 |
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What is the caveat of only having 1% of x-rays emitted reaching the film?
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Careful control of the x-ray beam is necessary to produce high quality radiographs
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Differential Absorption and kVp relationship
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Greater Differential absorption requires lower kVp
-lower kVp = more damaging exposure compromise compromise |
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Is the photoelectric absorption of bone always higher than soft tissue?
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Yes, always about 7x more regardless of energy
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Effects and Energies
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Low Energy = mainly photoelectric
Higher Energy= mainly compton photoelectric |
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As kVp increses what change needs to happen to mAs?
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Lower output required
Lower mAs |
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Tissues/kVp
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Soft tissues need lower kVp for better images (but dangerous)
Bony structures use high kVp, this lowers pt exposure |
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The crossover of photoelectric and compton scattering is at what keV?
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40.
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What are the degrees of absorption?
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transparent
Translucent opaque |
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What is the over-all source of attenuation? (x-ray blocking)
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Sum of scattering (compton) and absorption (photoelectric) reactions of radiation.
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Radiopaque vs
Radiolucent vs Tansparent |
Bone (white)
Soft tissues (shades of grey) Air (black as satan's heart) |
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What is the heel effect?
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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?
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the cathode side (-) becasue has more x-rays, should be over the area of greatest density
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Anode angle/ heel effect
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Angle decreases/ effect increases
(too high an angle and rays won't cover entire film) |
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What is the key point of a radiological grid?
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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?
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Ratio
Frequency Material |
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In considering grid ratio, what are the three important dimensions on a grid?
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Width of grid strip
Width of interspace material Height of the grid. |
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Why are high ratio grids more effective in cleaning up scatter?
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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?
What is the caveat to the downside? |
they clean up the crap so that the Pt has to get higher dose of rays for a decent image.
Increased dose, but higher kVp which decreases apsorption. |
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what are the popular grid ratios?
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8:1 on single phase machines
10:1 on high frequency machines |
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What is the grid used in podiatry?
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"podiatry does not need a grid"
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How does a filter affect the image?
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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 or grid? What are the two types? |
Filter
Inherent- built in filter Added |
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What are the filter Al equivalents needed in podiatry?
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Inherent- 1.5mmAl equivalence
Added- 1.0 mm Al equivalence Thus 2.5mm total Al equivalence needed in podiatry |
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Explain X-ray film
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Silver halide crystals in a gel in a + state.
x-rays turn crystal silver into neutral state (metallic silver) which is very black. More x-rays = blacker less = white. But, once it goes black it never goes back. |
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So far we have Grid, Filters, Film, what's left?
What is their purpose in life? |
Screens
One is used in podiatry. Screen of rare earth metals that fluoresce when hit by x-ray. Fluorescence reduces silver halide better than x-rays. = less rays for better image. |
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What is the major difference in Grid and Screen?
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Grid= better image
Screen= safer for patient |
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Explain the 5 steps of film development (basic).
What is the temperature relationshp? |
Developing - developer, accelerator, restrainer, preservative, hardener
Rinse Fixer (acetic acid stops developing) Wash Dry Temperature and time are inverse relationship |
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What is the major control of kVp adjustments?
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kVp controls radiographic contrast. (short to long)
Affects Quality!!! |
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Increased kVp=
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Quality change and
quantity change Increased kVp= more penetration with higher energy= more compton scatter= noisier image= reduced contrast. |
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In a nut shell kVp and contrast
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High kVp= lower contrast (long scale)
Low kVp= high contrast (short scale) but increased dose. |
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As kVp increases there are less rays that interact with subject atoms, what does this say about pt exposure?
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kVp increase = pt "exposure" decreased.
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What is directly correlated with the # of x-rays?
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The number of x-rays are directly proportional to the mA, assuming a fixed exposure time.
QUANTITY Quality is kVp |
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Increasing MA vs kVp (test q)
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Increasing mA = increasing number of x-rays= more danger.
Increasing kVp= less subject atom interaction = less pt exposure= less dangerous. |
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Does podiatry use a Death-Star level of mA?
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No, podiatry uses low mA (15-30)
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Why is exposure time kept as short as possible?
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NOT to reduce exposure, but to reduce movement
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mAs affect on x-rays (for the third time)
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mAs control radiation quantity, optical density and pt dose (kvp is qual)
mAs determine the number of x-rays in the beam and therefore radiation quantity (kvp is quality) mAs does NOT influence radiation quality, kvp does. |
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What are 2 critical external factors?
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Central ray needs to be on the area b/c of heel effect.
object to film distance needs to be close for sharpness. |
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What is the kVp/mA change rule?
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15% muthaluva!
15% change in kVp is equivalent to 2x change in mA. As an example: normal kVp in pod is 60. If you increase to 65 you decrease the mA to 1/2x, decrease to 55 then increase mA by 2. |
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Increasing kVp enhances what?
mAs? |
kVp= soft tissue
mAs= optical density (blackness) |
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What is the inverse square law?
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That's the reason you can stand 6ft away and be fine.
Radiation intensity is inversely proportional to the square fo the distance from the source - decrease in radiation b/c of increased area. (like using a 1 LED old school flashlight, great upclose, but then 3 foot away sucks something terrible, can't see anything) |
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What does distance affect in x-rays?
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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?
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40" or 100cm (the major one for us)
and 72" or 182cm |
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What does increasing SID do to the image? source to image distance
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Increased distance = decreased magnification distortion and focal spot blur
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what is the focal spot size used in podiatry?
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1mm
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What is the collimator?
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robot that destroys the colon.
Lead shutters used to restrict beam, attached to the x-ray tube below the glass where the useful beam is emitted. Shapes the beam. |
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What is the greatest tool in keeping pt exposure as low as possible?
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Collimation
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Describe why greater SID causes better images
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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?
Where are the filters? |
Podiatry maxes out about 70kVp which requires 2.5 mm Al equivalent .
.5 mmAl in tube housing Additional added at collimator to meet the 2.5mm Al needed by law. |
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What is radiographic quality? What are the three main factors?
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Radiographic quality- fidelity at which the anatomic structures being examined are shown on the film.
Film factors Geometric factors Subject factors |
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Fog and Scatter= unwanted density from Compton interactions. What causes them to increase?
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Increase with
kVp Part thickness Field Size (collimation reduces scatter) |
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Summary of high kVp:
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Low contrast (long scale)
Decreased dose Decreased photoelectric effect Increased compton Changes quality primarily, quantity secondarily 62kVp for podiatry change in 5-10 increments. |
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summary of mA:
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quantity change only (no contrast change)
Allows you to see the image controls Optical Density (blackness) increases dose need to change by 2 or halves |
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x-ray technique summary:
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Moderate to large SID
Low OID Collimate to smallest field Heel effect (cathode at thicker part) Grids= decreased scatter (increased quality)/ increased dose (not safer) Screens= less xrays needed (safer) Filters protect pt. |
