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SEF
secondary exposure factors
| Question | Answer |
|---|---|
| For the best spatial resolution, we would change what factors | increase SID, decrease OID, small FSS, increase mA w low time, decrease pt thickness |
| Spatial resolution | the ability to see detail/image sharpness aka geometric unsharpness |
| spatial resolution is affected by | patient motion also FSS, SID, OID |
| Most important factor in determining resolution | focal spot size |
| penumbra | the blurred borders of the image |
| umbra | the exact center of the image |
| Which is clearer, umbra or penumbra | umbra, the center |
| the focal spot size is controlled by the (3 things) | size of the filament, focusing cup design, and anode angle. |
| which causes more scatter: large or small FSS | large because it increases the QUANTITY of the beam |
| the umbra represents | the true shape of the object |
| Actual focal spot | where the e- interact with the anode (target) |
| Effective focal spot | what exits the tube toward the pt |
| which is larger: actual or effective focal spot | the actual focal spot is always larger |
| Line focus principle | the relationship between the actual and effective focal spot sizes |
| What affects the size of the effective focal spot? | the anode angle |
| Area of the anode where the e- may hit | focal track |
| A steeper anode angle means the angle is | smaller ex: 5-12 degrees |
| A less steep anode angle means the angle is | larger ex: 20 degrees |
| A larger effective focal spot can be created by a ____ anode angle | less steep/larger angle |
| A smaller effective focal spot can be created by a ____ anode angle | steeper/ smaller angle |
| Off focus radiation originates | outside of the anode focal spot, meaning it is from rebounding electrons that did not strike the focal track |
| anodes are made of | tungsten |
| A smaller anode angle results in a smaller effective focal spot (higher resolution) but also a | smaller field of view |
| What factor affects penumbra the most | pt thickness |
| Magnification factor formula | MF = SID/SOD |
| object size formula | object size = image size / MF |
| SOD formula | source-to-to-object-distance= SID-OID |
| an air gap technique will decrease the | intensity of radiation reaching the IR and decrease scatter |
| How will a too high kV or mAs obscure resolution | details not seen due to darkness and scatter |
| How will a too low kV or mAs obscure resolution | could cause quantum mottle from insufficient xrays reaching the IR |
| How can windowing help with resolution | it will not create details but will allow better visualization of what is there |
| Magnification is controlled by ____ | SID and OID |
| Distortion includes which two categories | magnification and shape distortion |
| An improper tube angle will cause what type of distortion | shape distortion |
| An improper OID will cause what type of distortion | magnification (size) |
| inherent filtration is located in the tube while added filtration is located | between the tube and collimator box |
| total filtration | 2.5 mm Al |
| Increasing filtration results in | decrease receptor exposure and decrease pt dose (especially to the skin) |
| what does filtration do | removes low energy photons, makes the beam more homogenous |
| How does filtration affect the quality/quantity of the beam | increases quality while decreasing quantity |
| generators with more efficient output (3 phase units or high frequency) require | less exposure factors to produce a good image. so they lower pt dose |
| while rarely used anymore, what can be added to an exam such as a foot to make a more uniform exposure? | a compensating filter. wedge looking. thicker part goes over thinner part of the body |
Created by:
user-1989152