Imaging Test #2 LAB
KvP, mAs Reciprocity, SID

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%

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.

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

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

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

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

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

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

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

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

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

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)

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

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

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

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

SID #1

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

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