Reproducibility

Normally, when x-ray technologists input a given radiographic technique, the radiation intensity produced by the x-ray generator should be same from one exposure to another when using the same technique. In order to check the reproducibility of the x-ray unit and mammo unit, we need to take 10 consecutive exposures and record each reading from Rad Check. For each exposure, we need to change the factor settings to provide different combinations of mAs.


Before each exposure, we need to put an apron on table then put Rad Check on it. It is showed in the picture below:

Reproducibility for mammo unit:

Because the mammo unit in our department does not allow us to change exposure time or mA, the combination of mAs cannot be changed. In this lab, we keep mAs same for each exposure.

5 mAs @ 25 kVp, 100 cm SID:

	Exposure #1	#2	#3	#4	#5	#6	#7	#8	#9	#10	Average
Rad Check Reading	0.096	0.097	0.097	0.096	0.097	0.097	0.096	0.097	0.096	0.097	0.0966

X_i = ith exposure measurement

 = mean value of exposure measurements

n = number of exposure measurements

C= 1/0.0966 * {[(0.096-0.0966)² + (0.097-0.0966)² + (0.097-0.0966)² + (0.096-0.0966)² + (0.097-0.0966)² + (0.097-0.0966)² + (0.096-0.0966)² + (0.097-0.0966)² + (0.096-0.0966)2 + (0.097-0.0966)2] / 9}1/2 = 0.0053457

For two extreme values 0.096 and 0.097:
(0.096-0.0966)/0.0966=-0.62%
(0.097-0.0966)/0.0966=0.41%

According to SC33, Coefficient of radiation for any 10 consecutive radiation should not be greater than 0.05. Mean value of 10 measurements should be within 15%. Therefore, the reproducibility of mammo unit in our department is within acceptable limits.

Reproducibility for a x-ray unit in room 4:

5 mAs @ 60 kVp, 100 cm SID:

X_i = ith exposure measurement

 = mean value of exposure measurements

n = number of exposure measurements

C = 1/0.0128{[(0.013-0.0128)² * 8 + (0.012-0.0128)² * 2]/9}^1/2 = 0.03294


For the two extreme values 0.012 and 0.013:
(0.012-0.0128)/0.0128=-6.25%
(0.013-0.0128)/0.0128=1.56%

According to HARP, Coefficient of radiation for any 10 consecutive radiation should not be greater than 0.08. Mean value of 10 measurements should be within 20%.

According to SC35, Coefficient of radiation for any 10 consecutive radiation should not be greater than 0.05. Mean value of 10 measurements should be within 15%.

No matter which reference we choose, the x-ray unit in room 4 is within acceptable limits.