Chapter 7
Page no. 686
JC-ELE-A-028.fm
GE Healthcare
Senographe DS
Revision 1
Service Information and Procedures Class A 2385072-16-8EN
Job Card ELE A028 - Collimation Checks
Insert the calculated value of Z
f
in the tables above.
3. Determine the global scaling factor (S) that you need to apply to Z
f
as follows:
a. From the RAW digital image in the AWS, use the
Segment
tool of the
Viewer
to measure the dis-
tance between two contiguous major reference markers.
b. Knowing that the distance between two contiguous major markers is 10 mm, calculate the global
scaling factor (S) using the following equation:
S = 1.063 x d / 10
Eq. 2
Note:
Because the reference plane of the
Segment
tool is 2 cm above the Breast Support surface, a
magnification factor 1.063 is applied to value of S as shown in the Eq 2 above.
Note:
You only need to calculate the global scaling factor (S) once for one of the field edges. You can
globally apply the determined global scaling factor (S) to each of the field edges.
Insert the determined global scaling factor (S) in the tables above.
4. Finally, determine the deviation of the x-ray field edge from the detector edge
in the plane of the
image
(Z
i
) by using the following equation:
Z
i
= S x Z
f
Eq. 3
Insert the calculated value of Z
i
in the table above and in the tables for action limit 2 on
Edge of light field
(in the plane of the film)
Edge of X-ray field
(in the plane of the film)
Y
f
= deviation between X-ray field and light field in the plane of the film
Edge of detector
Z
f
= deviation between X-ray field and detector in the plane of the film
Measure distance (d) in mm between two
contiguous major markers
