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