(11) Identify the test film.
(12) Record your results on the data forms and film (i.e., the spot film format,
manual or automatic mode, and large or small focal spot).
If the density is insufficient to define the test tool, repeat the test with higher
mAs to obtain a test film of greater density.
5-10. EVALUATION AND INTERPRETATION
Since this test involves the analysis of several test radiographs, you must identify
each film as it is taken and record the identifying data on the data form.
a. From each of the radiographs, measure the total amount by which the
radiation field exceeds the visual field by both length and width.
(1) The clear area demonstrates the tips of the brass strips. Remember, the
brass strips represent the area that the radiated field should NOT exceed.
The dark area is the region actually exposed to radiation.
b. The sum of the lengths for one pair of opposing strips will give the excess
width. The sum of the other strips will be the excess length.
In the radiographic light field x-ray test, any misalignment is measured. In this
test we will measure only the differences representing excess radiation (that
is, where the radiation field exceeds the correct area). If the radiation is
within the visual field by any amount, it is not included.
c. Calculate the sum of excesses, that is, width plus length.
d. Record results of all films on the data forms.
e. For an image intensified system, the excess width and length should not
exceed 3% of the source (or focal spot) to table top distance (STD). The sum of excess
width plus length should not exceed 4%.
5-11. PREVENTIVE MAINTENANCE
Keeping the fluoroscopic beam to a minimum is vital to protect the patient from
excessive radiation. When you, as a radiologist, collimate to a given area of the body,
you need to be sure that what you see on the screen is exactly what is being exposed to
radiation and no more than that. Bearing this in mind, be sure to test the beam
restriction adequacy (or see that someone does) following each of the times or
situations listed below.