A. Limitation of useful beam.
(1) Primary Barrier.
(a) The fluoroscopic imaging assembly shall
be provided with a primary protective barrier, which intercepts the entire
cross section of the useful beam at any SID.
(b) The x-ray tube used for fluoroscopy shall
not produce x-rays unless the barrier is in position to intercept the entire
useful beam.
(2)
Fluoroscopic beam limitation.
(a) Certified
fluoroscopic systems, with or without spot film device neither the length nor
the width of the x-ray field in the plane of the image receptor shall exceed
that of the visible area of the image receptor by more than 3 percent of the
SID. The sum of the excess length and the excess width shall be no greater than
4 percent of the SID.
(i) Means shall be
provided to permit further limitation of the field. Beam limiting devices
manufactured after May 22, 1979, and incorporated in equipment with a variable
SID and/or a visible area of greater than 300 square centimeters shall be
provided with a means for stepless adjustment of the x-ray field;
(ii) All equipment with a fixed SID and a
visible area of 300 square centimeters or less shall be provided with either
stepless adjustment of the x-ray field or with means to further limit the x-ray
field size at the plane of the image receptor to 125 square centimeters or
less;
(iii) If provided, stepless
adjustment shall, at the greatest SID, provide continuous field sizes from the
maximum attainable to a field size of 5 centimeters by 5 centimeters or
fewer.
(iv) For equipment
manufactured after February 25, 1978, when the angle between the image receptor
and beam axis is variable, means shall be provided to indicate when the axis of
the x-ray beam is perpendicular to the plane of the image receptor;
and
(v) For rectangular x-ray
fields used with circular image reception, 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.
(b) For uncertified fluoroscopic
systems with a spot film device, the x-ray beam with the shutters fully opened
(during fluoroscopy or spot filming) shall be no larger than the largest spot
film size for which the device is designed. Measurements shall be made at the
minimum SID available but at no fewer than 20 centimeters table top to the film
plane distance.
(c) For uncertified
fluoroscopic systems without a spot film device, the requirements of
F.6.A(2)(a) apply.
(c) Other
requirements for fluoroscopic beam limitation:
(e) Spot-film devices, which are certified
components, shall meet the following additional requirements:
(i) Means shall be provided between the
source and the patient for adjustment of the x-ray field size in the plane of
the film to the size of that portion of the film, which has been selected on
the spot film selector. Such adjustment shall be automatically accomplished
except when the x-ray field size in the plane of the film is smaller than that
of the selected portion of the film. For spot film devices manufactured after
June 21, 1979, if the x-ray field size is less than the size of the selected
portion of the film, the means for adjustment of the field size shall be only
at the operator's option;
(ii) It
shall be possible to adjust the x-ray field size in the plane of the film to a
size smaller than the selected portion of the film;
(iii) The center of the x-ray field in the
plane of film shall be aligned with the center of the selected portion of the
film to within 2 percent of the SID; and
(iv) On spot-film devices manufactured after
February 25, 1978, if the angle between the plane of the image receptor and
beam axis is variable, means shall be provided to indicate when the axis of the
x-ray beam is perpendicular to the plane of the image receptor, and compliance
shall be determined with the beam axis indicated to be perpendicular to the
plane of the image receptor.