3)
4)
5)
6)
8)
The
Set a standard x-ray field size, 18 x 24 cm
(8 x 10"), using the appropriate numerical
indicator scale on the collimator.
Turn on the collimator light field and place
radiopaque markers on the table top to
delineate the edges of the light field.
Expose the cassette with a technique that
results in an optical density range of l-l.4
on the film.
Open collimator blades and without moving
the markers or cassette make a second
exposure using l/5 the mAs used in step 5.
This produces an image of the opaque markers.
7) Process the exposed film.
Repeat steps 2-7 using a larger x-ray field
size, 30 x 35 cm (11 x 14").
two field size evaluation is necessary since the
collimator blades on most units do not move in a linear
manner.
Any locks routinely used during this test which
do not hold properly
should be noted in
the
"Recommendations and Suggestions"
at the end of the
survey report.
X-ray/Light Field Congruence: I-6(a)
The size of the delineated light field and the size
of the x-ray field on the exposed radiographs should
agree within 2% of the SID (Reference #l). The shift
between the centers of the light field and x-ray field
should also be no greater than 2X of the SID (Reference
#l).
Both x-ray
films
should
be evaluated.
This
parameter should be measured at least annually or after
repairs which involve the removal of the collimator
from
the x-ray tube housing.
After the
x-ray/light field congruence at the table
cassette holder has been verified, the light field of the
collimator may be used to verify the alignment of the "x-
ray field" and center line of
any
wall mounted cassette
holders within the room.
X-ray Field/Image Receptor Alignment:
I-6(b)
Draw two sets of diagonals on each radiograph.
One
set should connect the corners of the x-ray field on each
radiograph; this represents
the x-ray field center. The
other set should be drawn to the corners of the x-ray
film; this indicates the center of the Bucky tray.
The
cross points of
each set of diagonals
should not be
separated by more than 2% of the SID (Reference
#1).
This parameter should be evaluated at least annually or
after any repair which could affect the alignment light
7
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