Question

9:26 Х Student Portal 1. A satisfactory radiograph is obtained using 10 mAs at an SID of 40". If the technologist were to repeat the exposure at a new SID of 72", what mAs value would be required to maintain radiographic exposure? 2. If a radiographic image is obtained at 40" using 32 mAs, and a repeat exposure would be performed at an ID of 80", what mAs would be required to produce an image demonstrating similar exposure? 3. If a patient receives a dose of 6 mR when radiographed at an SID of 40" what would be the dose if the patient were x-rayed at a distance of 60'? 4. If a patient receives a radiation dose of 2 m when radiographed at an SID of 50" what dose would the patient receive in the SID were decreased to 30"? 5. Convert 100 my rad 6. Convert 10 my- Gy 7. Convert 25 Sievert Rem 8. Convert 150 Rem Sievert 9. At a distance of 72" beam intensity is 10mR. If the distance is decreased to 40" what would the new intensity be? 10. An unknown mAs value was used to produce a satisfactory radiograph at an SID of 40". If a similar radiographic exposure is produced at an ID of 60" @ 100 mAs, what mAs value was used for the original exposure? c

Radiology

Answer 1

Expoaure maintainance formula is :

(SID1)^2 / (SID2)^2 = mAs1 / mAs2 -----(1)

That is it dollows direct square law.

1) SID = source to Image distance

mAs1 = 10 mAs

mAs2 = ?

SID1 = 40"

SID2 = 72"

USing formula (1),

mAs2 = mAs1 * (SID2) ^2 / (SID1) ^2

mAs2 = 10 * (72/40)^2 = 32.4 mAs

2) SID1 = 40"

SID2 = 80"

mAs1 = 32mAs

mAs2 = ?

Using formula (1)

mAs2 = mAs1 * (SID2 / SID1) ^ 2

mAs2 = 32 * (80/40)^2 = 128mAs

Now for Dose = D :

Dose and SID follow inverse square law

D1/D2 = (SID2/SID1)^2 ----(2)

3) D1 = 6mR

D2 = ?

SID1 = 40"

SID2 = 60"

using formula (2)

D2 = D1 * (SID1/SID2)^2 = 6 * (40/60)^2 = 2.67mR

4) D1 = 2mR

SID1 = 50"

SID2 = 30"

using formula (2)

D2 = D1 * (SID1/SID2)^2= 2 * (50/30)^2 = 5.56mR

5) 100 rad = 1Gy = 1000mGy

Thus 100mGy = 10 rad

6) 10mGy = 10*10^-3 = 0.01Gy

7) 1 Sievert = 100 Rem

Thus 25 Sievert = 2500 Rem

8) 150 Rem = 1.5 Sievert

9) Intensity has same unit as Dose, hence use formula (2)

D1 = 100mR

SID1 = 72"

SID2 = 40"

D2 = D1 * (SID1/SID2)^2 = 10 * (72/40)^2 = 324mR

10) using formual (1)

mAs1 = ?

mAs2 = 100mAs

SID1 = 40"

SID2 = 60"

mAs1 = mAs2 * (SID1/SID2)^2 = 100* (40/60)^2 = 44.4mAs