Imaging Lab Test 2

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Review of images & concepts from Lab 2 on Prime Factors

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Imaging Lab Test 2

  1. 1. Imaging Test #2 LAB KvP, mAs Reciprocity, SID
  2. 2. kVp- 15% rule • To demonstrate the visible effects of the 15% rule • 1st exposure: 100mA, 10 mAs, 50 kVp • On 2nd exposure, mAs ↓ by ½ & kVp ↑ by 15%
  3. 3. kVp- 15% rule • 2nd exposure: 58 kVp, 5 mAs • 50 kV + 15% • ↑ kV by 15% &↓mAs by ½ to get a similar image • This is the 15% rule • If your goal is to get a similar image and you have to change one of these factors (ex: ↑ kV for a hypersthenic pt) you must change the other accordingly to get a similar image.
  4. 4. Area of Coverage #1 • To demonstrate the result of change in SID • 50 kVP, 2.5 mAs, 40”SID • This is 1st exposure @ 40” SID, all other factors remain constant
  5. 5. Area of Coverage #2 • 2nd Exposure: SID is ↓ to 30”
  6. 6. Area of Coverage-#3 • 3rd exposure: SID ↑ to 50”
  7. 7. kVp #1 • To demonstrate the general response to ↑ kVp • 1st exposure: 100 mA, 5mAs, 40kVp • All other factors constant as kVp is increased for repeat exposures • Note that very few shades of gray are visible on 1st image
  8. 8. kVp #2 • This should be the 3rd image • 60 (maybe 70 kVp) • Note that almost all densities of stepwedge are visible in shades of gray • As kV ↑ penetration ↑ • Scale of shades of gray widens • ↑kV is necessary to penetrate thicker parts
  9. 9. mAs double #1 • To demonstrate the result of change in mAs value • 50kV constant • 1st image 1.25 mAs • All other factors remain constant as mAs is ↑ to 2.5, 5, and 10 on repeat exposures • mAs is therefore doubled on each subsequent exposure
  10. 10. mAs double #2 • Image# 4: 10mAs • As mAs ↑ brightness (density ) ↑ • As mAs doubles, LGM# ↑ by .3 • Once you get to a certain level , doubling mAs only ↑ patient dose; has no effect on image
  11. 11. mAs Reciprocity #1 • To demonstrate mAs reciprocity. • 1st image: 5mAs, 50 kV, 40” SID @ 50mA setting • All other factors remain constant as mA is ↑ to 100 then 200 on repeat exposures
  12. 12. mAs Reciprocity #2 • Image 2: ↑ to 100 mA
  13. 13. mAs Reciprocity #3 • Image #3: ↑ to 200 mA • LGM#’s should be constant • With mAs constant, any combination of mA & s should yield the same results (same image)
  14. 14. mAs visible change #1 • To demonstrate the degree of change in mAs necessary to be visible to the eye • 70kVp 50 mAs • With all other factors constant, make repeat exposures w/10%, 20%, 30% & 50% increase in mAs
  15. 15. mAs visible change #2 • This image represents the 50% increase in mAs. • The only image in the series in which the change can be appreciated. • Either double or ½ your mAs or don’t repeat as there is not enough of a visible difference to warrant the ↑ exposure to patient
  16. 16. Scatter #1 • To demonstrate the relationship between kVp & scatter • 14x17 cassette was placed in holder on table 6” outside of light field • Chest phantom on table collimated • 1st exposure: 100 mA, 10 mAs, 40 kVp
  17. 17. Scatter #2 • Image #2 kVp ↑ to 100 • All other factors remain constant • We can conclude that ↑ kVp = ↑ scatter • This is a direct relationship
  18. 18. SID #1
  19. 19. SID #2 • SID increased to 60” • Collimation unchanged
  20. 20. SID #3 • SID decreased to 20” • Collimation unchanged • RESULT: As distance ↑ magnification of body part ↓ • This is an inverse relationship

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