| (i) The fluoroscopic imaging assembly shall be provided
with a primary protective barrier that intercepts the entire cross
section of the useful beam at any SID.
(ii) The x-ray tube used for fluoroscopy shall not
produce x-rays unless the barrier is in position to intercept the
useful beam and the imaging device is in place and operable.
(iii) The exposure rate (air kerma rate) due to transmission
through the barrier with the attenuation block in the useful beam,
combined with radiation through the image intensifier if provided,
shall not exceed 3.34 x 10-3 % of the
entrance exposure rate (air kerma rate) at a distance of 10 cm from
any accessible surface of the fluoroscopic imaging assembly beyond
the plane of the image receptor.
(B) Measuring compliance of barrier transmission.
(i) The exposure rate (air kerma rate) due to transmission
through the primary protective barrier combined with radiation through
the image intensifier shall be determined by measurements averaged
over an area of 100 cm2 with no linear
dimension greater than 20 cm.
(ii) If the source is below the tabletop, the measurement
shall be made with the input surface of the fluoroscopic imaging assembly
positioned 30 cm above the tabletop.
(iii) If the source is above the tabletop and the SID
is variable, the measurement shall be made with the end of the beam-limiting
device or spacer as close to the tabletop as it can be placed, provided
that it shall not be closer than 30 cm.
(iv) Movable grids and compression devices shall be
removed from the useful beam during the measurement.
(v) The attenuation block shall be positioned in the
useful beam 10 cm from the point of measurement of entrance exposure
rate (air kerma rate) and between this point and the input surface
of the fluoroscopic imaging assembly.
(vi) The collimator shall be fully open when the measurement
is made.
(C) X-ray field.
(i) Compliance with clauses (ii) - (vi) of this subparagraph
shall be determined with the beam axis perpendicular to the plane
of the image receptor.
(ii) Fluoroscopic systems with a fixed SID and the
capability of a visible area of no greater than 300 cm2 shall be provided with either stepless adjustment
of the x-ray field or a means to further limit the x-ray field at
the image receptor to 125 cm2 or less.
If the equipment is provided with stepless adjustment, the minimum
x-ray field size at the maximum SID shall be less than or equal to
5 cm by 5 cm at the image receptor.
(iii) Fluoroscopic systems with a variable SID or a
fixed SID with the capability of a visible area of greater than 300
cm2 shall be provided with stepless adjustment
of the field size. The minimum x-ray field size at the maximum SID
shall be less than or equal to 5 cm by 5 cm at the image receptor.
(iv) 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 3.0% of the SID. The
sum of the excess length and the excess width shall be no greater
than 4.0% of the SID.
(v) 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 that pass through
the center of the visible area of the image receptor.
(vi) For fluoroscopic systems with only a manual mode
of collimation, the x-ray field produced shall be limited to the area
of the spot-film cassette at 16 inches above tabletop. Additionally,
during fluoroscopy, the beam shall be restricted to the area of the
input phosphor.
(vii) Spot-film devices 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 that has been selected
on the spot-film selector.
(-a-) 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.
(-b-) The total misalignment of the edges of the x-ray
field with the respective edges of the selected portion of the image
receptor along the length or width dimensions of the x-ray field in
the plane of the image receptor shall not exceed 3.0% of the SID when
adjusted for full coverage of the selected portion of the image receptor.
(-c-) The sum, without regard to sign of the misalignment
along any two orthogonal dimensions, shall not exceed 4.0% of the
SID.
(II) The center of the x-ray field in the plane of
the film shall be aligned with the center of the selected portion
of the film to within plus or minus 2.0% of the SID.
(2) Activation of the fluoroscopic tube. X-ray production
in the fluoroscopic mode shall be controlled by a device that requires
continuous pressure by the fluoroscopist for the entire time of the
exposure (continuous pressure type switch). When recording serial
fluoroscopic images, the fluoroscopist 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 process.
(3) Entrance exposure rate (air kerma rate) allowable
limits for fluoroscopic systems.
(A) The following requirements apply to fluoroscopic
systems manufactured prior to May 19, 1995.
(i) Fluoroscopic systems with AERC. Fluoroscopic systems
that are provided with AERC shall not be operable at any combination
of tube potential and current that will result in an exposure rate
(air kerma rate) in excess of 2.58 x 10-3 coulomb
per kilogram per minute (C/kg/min) (10 roentgens per minute (10 R/min)
or (100 mGy/min) at the point where the center of the useful beam
enters the patient, except:
(I) during recording of fluoroscopic images, excluding
last image hold; or
(II) when an optional high-level control is provided.
When so provided, the fluoroscopic system shall not be operable at
any combination of tube potential and current that will result in
an exposure rate (air kerma rate) in excess of 1.29 x 10-3 C/kg/min (5 R/min or 50 mGy/min) at the
point where the center of the useful beam enters the patient, unless
the high-level control is activated. Special means of activation of
high-level controls shall be required. The high-level control shall
be operable only when continuous manual activation is provided by
the operator. A continuous signal audible to the fluoroscopist shall
indicate that the high-level control is being employed.
(ii) Fluoroscopic systems without AERC (manual mode).
Fluoroscopic systems that are not provided with AERC shall not be
operable at any combination of tube potential and current that will
result in an exposure rate (air kerma rate) in excess of 1.29 x 10-3 C/kg/min (5 R/min or 50 mGy/min) at the
point where the center of the useful beam enters the patient, except:
(I) during recording of fluoroscopic images, excluding
last image hold; or
(II) when an optional high-level control is activated.
Special means of activation of high-level controls shall be required.
The high-level control shall be operable only when continuous manual
activation is provided by the operator. A continuous signal audible
to the fluoroscopist shall indicate that the high-level control is
being employed.
(iii) Fluoroscopic systems with both an AERC mode and
a manual mode. Fluoroscopic systems that are provided with both an
AERC mode and a manual mode shall not be operable at any combination
of tube potential and current that will result in an exposure rate
(air kerma rate) in excess of 2.58 x 10-3 C/kg/min
(10 R/min or 100 mGy/min) in either mode at the point where the center
of the useful beam enters the patient except:
(I) during recording of fluoroscopic images, excluding
last image hold; or
(II) when the mode or modes have an optional high-level
control, in which case that mode or modes shall not be operable at
any combination of tube potential and current that will result in
an exposure rate (air kerma rate) in excess of 1.29 x 10-3 C/kg/min (5 R/min or 50 mGy/min) at the
point where the center of the useful beam enters the patient, unless
the high level control is activated. Special means of activation of
high-level control shall be required. The high level control shall
be operable only when continuous manual activation is provided by
the operator. A continuous signal audible to the fluoroscopist shall
indicate that the high-level is being employed.
(iv) Measuring compliance. Compliance of entrance exposure
rate (air-kerma rate) for fluoroscopic systems shall be determined
as follows.
(I) If the source is below the x-ray table, the exposure
rate (air kerma rate) shall be measured at 1 cm above the tabletop
or cradle.
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