IntroductionImage Intensifier11-5Fi

Introduction
Image Intensifier
1
1-5
Figure 1-6. Placement of Collimator and B
eam Alignment Test Tools for Checking Fluoro Units
When this occurs, the alignment of the center of the
x-ray tube to the image intensifier can be checked by
noting if the image of the Collimator Tool is symmetr
ical, as seen on the TV monitor or mirror. While
observing the image of the centimeter
scales of the Collimator Tool, reco
rd the distance to the edge of the
viewing field for each of the four axes of the tool.
If the x-ray field is centered,
these distances should be
the same (Figure 1-6). If the centering is off by mo
re than 3% of the SID, it
should be corrected by
qualified service personnel.
Tape a large cardboard cassette, containing a fresh film
or a "Ready-Pac", to the input face of the image
intensifier. Open the fluoro collimator shutters as fa
r as possible, and expose the cassette in the fluoro
mode for about 15 seconds at 60 kVp and 1-2 mA. The sp
ot film device is not used
for this test exposure.
The processed film will show the imag
e of the Collimator Tool. The extent
of the actual field size at the
tabletop will be shown as the distance on the Collimator
Tool scale that is image
d for each axis of the
tool. The difference between the viewed
field size and the actual field
shown on the film
is a collimation
error. This test is
illustrated in Figure 1-7.
Nuclear Associates 07-661-7662
Operators Manual
1-6
Figure 1-7 Test of Viewed Field Versus Actual Field Size
This error for any given field edge must be less than 3% of
the SID. If the x-ray tube is 45 cm (18”) below
the table and the image intensifier is 30 cm (12”) above
the table, the allowed error is 2.25 cm (0.9”) in
any one direction.
1.6 Checking Spot Film Collimation
The spot film collimation may be checked in a simila
r manner. With the Beam Alignment and Collimator
Tools on the table, tape a loaded cardbo
ard cassette (that is larger than t
he spot film cassettes size) onto
the face of the spot film device or grid. Record the
size of the spot film cassette and make a full spot film
exposure. A loaded cassette can be placed in the spot
film device for this test. If the edges of the x-ray
field are visible in the spot film, the collimation is go
od, and film centering with respect to the x-ray field
can be checked. If the edges of t
he x-ray field are not visible on the s
pot film, the field size shown on the
larger film from the cardboard cassette will
indicate qualitatively the size of the actual
x-ray field.
References: Regulations for the Administration and
Enforcement of the Radiation Control Health and
Safety Act of 1968
. U.S. Department of Health,
Education, and Welfare. Food and Drug
Administration, July, 1980.
NOTE
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