This document discusses various imaging test parameters and their effects: 1) It demonstrates the 15% rule - if kVp is increased by 15%, mAs must be decreased by half to maintain similar image quality. 2) Increasing source-to-image distance (SID) decreases the area of coverage, while decreasing SID increases magnification. 3) Increasing kVp improves penetration and widens the scale of shades of gray visible, while increasing mAs increases brightness up to a certain point with diminishing returns. Maintaining the mAs product yields the same image regardless of mA and time combination.

1. Imaging Test #2 LAB
KvP, mAs Reciprocity, SID

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. 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. 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. Area of Coverage #2
• 2nd Exposure: SID is ↓
to 30”

6. Area of Coverage-#3
• 3rd exposure: SID ↑ to
50”

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. 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. 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. 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. 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. mAs Reciprocity #2
• Image 2: ↑ to 100 mA

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. 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. 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. 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. Scatter #2
• Image #2 kVp ↑ to 100
• All other factors remain
constant
• We can conclude that ↑
kVp = ↑ scatter
• This is a direct relationship

18. SID #1

19. SID #2
• SID increased to 60”
• Collimation unchanged

20. SID #3
• SID decreased to 20”
• Collimation unchanged
• RESULT: As distance ↑
magnification of body
part ↓
• This is an inverse
relationship