FLUOROSCOPIC UNIT QUALITY CONTROL TESTS
Section I. MINIMUM SOURCE TO TABLETOP DISTANCE TEST
The fluoroscope is the device, which enables you to see the shadows of x-rays
passing through the body. In other words, you can see on a screen exactly what you
are x-raying. Fluoroscopic procedures usually produce higher total exposure rates to
patients and medical personnel than conventional radiographic procedures. Yet,
fluoroscope units are often overlooked in a quality assurance program since it does
require more time and effort to perform the four necessary tests. Nevertheless,
installations with fluoroscopic capability should be concerned that these units are
operating correctly to avoid excessive exposure rates. Because radiation levels vary at
a rate inversely proportional to the squares of the distances in accordance with the
inverse square law, it is important that the minimum source to tabletop distance be
adequate. The shorter the source to tabletop distance, the greater the amount of
radiation the patient will receive. This test will enable you to find the proper minimum
distance from the fluoroscopic source to the tabletop. If this distance is out of the
prescribed range, the fluoroscope machine is out of adjustment.
a. One metallic object--3 inches long.
b. One metallic object--6 inches long.
Any lengths of metal strips will work as long as the length ratios are exactly
1:2. Another example would be one quarter and two quarters. Just be sure
to keep the ratios 1:2. The smaller one goes on the table; the larger object
goes on the imaging assembly (see figure 5-1).
Figure 5-1. Both objects used in minimum source to tabletop distance test.