Specifications

3. Set the SID to the value determined in the actual versus indicated SID test.
4. Reduce the X-Ray field to approximately 15 by 20 cm.
5. Make an exposure and develop the film.
6. To determine as accurately as possible the corners of the image recorded on the film, locate
two points on each of the four sides of the image. Through the two points on each side draw a
straight line. These four lines, when extended, intersect making a rectangle which is a close
approximation of the actual X-Ray field. Draw a diagonal across the image to determine the
center of the X-Ray image.
7. To determine the center of the X-Ray film draw diagonals across the film
(the point where these two lines cross is the center of the film), or fold
the film into quarters (the point where the two folds cross is the center of
the film).
8. The distance from the film center mark to the image center mark is
measured and recorded as the linear displacement or misalignment of
the centers of the X-Ray field and the image receptor.
D. VERIFICATION OF COMPLIANCE
Verify that this distance is less than or equal to 2 percent of the SID.
NEMA Standards 5-15-79
XR 8-2.18 INDICATION OF X-RAY FIELD SIZE
REQUIREMENT - Means shall be provided on the beam-limiting device to indicate field
size in the image receptor plane to within 2 percent of the SID (see 21 CFR 1020.31 (e)
(1) ).
A. GENERAL
The actual versus indicated SID test must be performed prior to beginning this
test.
November 2005 ( 5 - 17) Linear MC150-C Collimator
B. EQUIPMENT
A 24 by 30 centimeter or a 20 by 25 cm cassette with film.
C. PROCEDURE
1. Set the SID to the value determined in the actual versus indicated SID
test.