linked with the fluorescent screen assembly so that the useful beam at the fluorescent
screen is confined within the barrier irrespective of the panel-screen distance. For image
intensifiers, the useful beam shall be centered on the input phosphor. It should not
exceed the diameter of the input phosphor during fluoroscopy or cine-recording. For spot
film radiography with image intensifier equipment, the shutters should automatically
open to the required field size before the exposure.
(11) Beam-limiting devices such as collimators, adjustable diaphragms, or shutters,
shall provide the same degree of attenuation as is required of the tube housing.
(12) A fluoroscopic machine shall comply with either of the following:
(a) The x-ray field produced by nonimage-intensified fluoroscopic equipment shall
not extend beyond the entire visible area of the image receptor. Means shall be provided
to permit further limitation of the field. The minimum field size at the greatest SID shall
be equal to or less than 5 by 5 centimeters.
(b) For image-intensified fluoroscopic equipment, the total misalignment of the edges
of the x-ray field with the respective edges of the visible area of the image receptor along
any dimension of the visually defined field in the plane of the image receptor shall not
exceed 3% of the SID. The sum, without regard to sign, of the misalignment along any 2
orthogonal dimensions intersecting at the center of the visible area of the image receptor
shall not exceed 4% of the SID. For rectangular x-ray fields used with circular image
receptors, the error in alignment shall be determined along the length and width
dimensions of the x-ray field which pass through the center of the visible area of the
image receptor. Means shall be provided to permit further limitation of the field. The
minimum field size, at the greatest SID, shall be equal to or less than 5 by 5 centimeters.
(13) X-ray production in the fluoroscopic mode shall be controlled by a device which
requires continuous pressure by the operator for the entire time of an exposure. When
recording serial fluoroscopic images, the operator shall be able to terminate the x-ray
exposures at any time, but means may be provided to permit completion of any single
exposure of the series in progress.
(14) When the fluoroscope is operated at 80 kVp, the exposure rate at the position
where the beam enters the patient shall not exceed 3.2 R/mA-min and should not exceed
2.1 R/mA-min.
(15) Entrance exposure rate limits for fluoroscopic equipment shall be as follows:
(a) Machines with automatic exposure rate control shall not be operable at a
combination of tube potential and current which results in an a exposure rate in excess of
10 roentgens per minute at the point where the center of the useful beam enters the
patient, except during recording of fluoroscopic images or when an optional high level
control is provided.
Special means of activation of high level controls, such as
additional pressure applied continuously by the operator, shall be required to avoid
accidental use. A continuous signal audible to the fluoroscopist shall indicate that the
high level control is being employed.
(b) Machines without automatic exposure rate control shall not be operable at a
combination of tube potential and current which results in an exposure rate in excess of 5
roentgens per minute at the point where the center of the useful beam enters the patient,
except during recording of fluoroscopic images or when an optional high level control is
activated. Special means of activation of high level controls, such as additional pressure
applied continuously by the operator, shall be provided to avoid accidental use. A
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