[Code of Federal Regulations]
[Title 21, Volume 8]
[Revised as of April 1, 2003]
From the U.S. Government Printing Office via GPO Access
[CITE: 21CFR1020.31]
[Page 611-617]
TITLE 21--FOOD AND DRUGS
CHAPTER I--FOOD AND DRUG ADMINISTRATION, DEPARTMENT OF HEALTH AND HUMAN
SERVICES (CONTINUED)
PART 1020--PERFORMANCE STANDARDS FOR IONIZING RADIATION EMITTING PRODUCTS--Table of Contents
Sec. 1020.31 Radiographic equipment.
The provisions of this section apply to equipment for the recording
of images, except equipment involving use of an image intensifier or
computed tomography x-ray systems manufactured on or after November 28,
1984.
(a) Control and indication of technique factors--(1) Visual
indication. The technique factors to be used during an exposure shall be
indicated before the exposure begins, except when automatic exposure
controls are used, in which case the technique factors which are set
prior to the exposure shall be indicated. On equipment having fixed
technique factors, this requirement may be met by permanent markings.
Indication of technique factors shall be visible from the operator's
position except in the case of spot films made by the fluoroscopist.
(2) Timers. Means shall be provided to terminate the exposure at a
preset time interval, a preset product of current and time, a preset
number of pulses, or a preset radiation exposure to the image receptor.
(i) Except during serial radiography, the operator shall be able to
terminate the exposure at any time during an exposure of greater than
one-half second. Except during panoramic dental radiography, termination
of exposure shall cause automatic resetting of the timer to its initial
setting or to zero. It shall not be possible to make an exposure
[[Page 612]]
when the timer is set to a zero or off position if either position is
provided.
(ii) During serial radiography, the operator shall be able to
terminate the x-ray exposure(s) at any time, but means may be provided
to permit completion of any single exposure of the series in process.
(3) Automatic exposure controls. When an automatic exposure control
is provided:
(i) Indication shall be made on the control panel when this mode of
operation is selected;
(ii) When the x-ray tube potential is equal to or greater than 51
kilovolts peak (kVp), the minimum exposure time for field emission
equipment rated for pulsed operation shall be equal to or less than a
time interval equivalent to two pulses and the minimum exposure time for
all other equipment shall be equal to or less than 1/60 second or a time
interval required to deliver 5 milliamperes-seconds (mAs), whichever is
greater;
(iii) Either the product of peak x-ray tube potential, current, and
exposure time shall be limited to not more than 60 kilowatt-seconds
(kW's) per exposure or the product of x-ray tube current and exposure
time shall be limited to not more than 600 mAs per exposure, except when
the x-ray tube potential is less than 51 kVp, in which case the product
of x-ray tube current and exposure time shall be limited to not more
than 2,000 mAs per exposure; and
(iv) A visible signal shall indicate when an exposure has been
terminated at the limits described in paragraph (a)(3)(iii) of this
section, and manual resetting shall be required before further
automatically timed exposures can be made.
(4) Accuracy. Deviation of technique factors from indicated values
shall not exceed the limits given in the information provided in
accordance with Sec. 1020.30(h)(3);
(b) Reproducibility. The following requirements shall apply when the
equipment is operated on an adequate power supply as specified by the
manufacturer in accordance with the requirements of Sec. 1020.30(h)(3);
(1) Coefficient of variation. For any specific combination of
selected technique factors, the estimated coefficient of variation of
radiation exposures shall be no greater than 0.05.
(2) Measuring compliance. Determination of compliance shall be based
on 10 consecutive measurements taken within a time period of 1 hour.
Equipment manufactured after September 5, 1978, shall be subject to the
additional requirement that all variable controls for technique factors
shall be adjusted to alternate settings and reset to the test setting
after each measurement. The percent line-voltage regulation shall be
determined for each measurement. All values for percent line-voltage
regulation shall be within 1 of the mean value for all
measurements. For equipment having automatic exposure controls,
compliance shall be determined with a sufficient thickness of
attenuating material in the useful beam such that the technique factors
can be adjusted to provide individual exposures of a minimum of 12
pulses on field emission equipment rated for pulsed operation or no less
than one-tenth second per exposure on all other equipment.
(c) Linearity. The following requirements apply when the equipment
is operated on a power supply as specified by the manufacturer in
accordance with the requirements of Sec. 1020.30(h)(3) for any fixed x-
ray tube potential within the range of 40 percent to 100 percent of the
maximum rated.
(1) Equipment having independent selection of x-ray tube current
(mA). The average ratios of exposure to the indicated milliampere-
seconds product (C/kg/mAs (or mR/mAs)) obtained at any two consecutive
tube current settings shall not differ by more than 0.10 times their
sum. This is: [verbar]X1-
X2[verbar][le]0.10(X1+X2); where
X1 and X2 are the average C/kg/mAs (or mR/mAs)
values obtained at each of two consecutive tube current settings or at
two settings differing by no more than a factor of 2 where the tube
current selection is continuous.
(2) Equipment having selection of x-ray tube current-exposure time
product (mAs). For equipment manufactured after May 3, 1994 the average
ratios of exposure to the indicated milliampere-seconds product (C/kg/
mAs (or mR/mAs)) obtained at any two consecutive mAs selector settings
shall not differ by more than 0.10 times their sum. This is:
[[Page 613]]
[verbar]X1-
X2[verbar][le]0.10(X1+X2); where
X1 and X2 are the average C/kg/mAs (or mR/mAs)
values obtained at each of two consecutive mAs selector settings or at
two settings differing by no more than a factor of 2 where the mAs
selector provides continuous selection.
(3) Measuring compliance. Determination of compliance will be based
on 10 exposures, made within 1 hour, at each of the two
settings. These two settings may include any two focal spot sizes except
where one is equal to or less than 0.45 millimeters and the other is
greater than 0.45 millimeters. For purposes of this requirement, focal
spot size is the focal spot size specified by the x-ray tube
manufacturer. The percent line-voltage regulation shall be determined
for each measurement. All values for percent line-voltage regulation at
any one combination of technique factors shall be within 1 of
the mean value for all measurements at these technique factors.
(d) Field limitation and alignment for mobile, portable, and
stationary general purpose x-ray systems. Except when spot-film devices
or special attachments for mammography are in service, mobile, portable,
and stationary general purpose radiographic x-ray systems shall meet the
following requirements:
(1) Variable x-ray field limitation. A means for stepless adjustment
of the size of the x-ray field shall be provided. Each dimension of the
minimum field size at an SID of 100 centimeters shall be equal to or
less than 5 centimeters.
(2) Visual definition. (i) Means for visually defining the perimeter
of the x-ray field shall be provided. The total misalignment of the
edges of the visually defined field with the respective edges of the x-
ray field along either the length or width of the visually defined field
shall not exceed 2 percent of the distance from the source to the center
of the visually defined field when the surface upon which it appears is
perpendicular to the axis of the x-ray beam.
(ii) When a light localizer is used to define the x-ray field, it
shall provide an average illuminance of not less than 160 lux (15
footcandles) at 100 centimeters or at the maximum SID, whichever is
less. The average illuminance shall be based upon measurements made in
the approximate center of each quadrant of the light field. Radiation
therapy simulation systems are exempt from this requirement.
(iii) The edge of the light field at 100 centimeters or at the
maximum SID, whichever is less, shall have a contrast ratio, corrected
for ambient lighting, of not less than 4 in the case of beam-limiting
devices designed for use on stationary equipment, and a contrast ratio
of not less than 3 in the case of beam-limiting devices designed for use
on mobile and portable equipment. The contrast ratio is defined as
I1 I2, where I1 is the illuminance 3
millimeters from the edge of the light field toward the center of the
field; and I2 is the illuminance 3 millimeters from the edge
of the light field away from the center of the field. Compliance shall
be determined with a measuring aperture of 1 millimeter.
(e) Field indication and alignment on stationary general purpose x-
ray equipment. Except when spot-film devices or special attachments for
mammography are in service, stationary general purpose x-ray systems
shall meet the following requirements in addition to those prescribed in
paragraph (d) of this section:
(1) Means shall be provided to indicate when the axis of the x-ray
beam is perpendicular to the plane of the image receptor, to align the
center of the x-ray field with respect to the center of the image
receptor to within 2 percent of the SID, and to indicate the SID to
within 2 percent;
(2) The beam-limiting device shall numerically indicate the field
size in the plane of the image receptor to which it is adjusted;
(3) Indication of field size dimensions and SID's shall be specified
in centimeters and/or inches and shall be such that aperture adjustments
result in x-ray field dimensions in the plane of the image receptor
which correspond to those indicated by the beam-limiting device to
within 2 percent of the SID when the beam axis is indicated to be
perpendicular to the plane of the image receptor; and
(4) Compliance measurements will be made at discrete SID's and image
receptor dimensions in common clinical
[[Page 614]]
use (such as SID's of 100, 150, and 200 centimeters and/or 36, 40, 48,
and 72 inches and nominal image receptor dimensions of 13, 18, 24, 30,
35, 40, and 43 centimeters and/or 5, 7, 8, 9, 10, 11, 12, 14, and 17
inches) or at any other specific dimensions at which the beam-limiting
device or its associated diagnostic x-ray system is uniquely designed to
operate.
(f) Field limitation on radiographic x-ray equipment other than
general purpose radiographic systems--(1) Equipment for use with
intraoral image receptors. Radiographic equipment designed for use with
an intraoral image receptor shall be provided with means to limit the x-
ray beam such that:
(i) If the minimum source-to-skin distance (SSD) is 18 centimeters
or more, the x-ray field at the minimum SSD shall be containable in a
circle having a diameter of no more than 7 centimeters; and
(ii) If the minimum SSD is less than 18 centimeters, the x-ray field
at the minimum SSD shall be containable in a circle having a diameter of
no more than 6 centimeters.
(2) X-ray systems designed for one image receptor size. Radiographic
equipment designed for only one image receptor size at a fixed SID shall
be provided with means to limit the field at the plane of the image
receptor to dimensions no greater than those of the image receptor, and
to align the center of the x-ray field with the center of the image
receptor to within 2 percent of the SID or shall be provided with means
to both size and align the x-ray field such that the x-ray field at the
plane of the image receptor does not extend beyond any edge of the image
receptor.
(3) Systems designed for mammography. (i) Mammographic beam-limiting
devices manufactured after September 30, 1999, shall be provided with
means to limit the useful beam such that the x-ray field at the plane of
the image receptor does not extend beyond any edge of the image receptor
by more than 2 percent of the SID. This requirement can be met with a
system that performs as prescribed in paragraphs (f)(4)(i), (f)(4)(ii),
and (f)(4)(iii) of this section. For systems that allow changes in the
SID, the SID indication specified in paragraphs (f)(4)(ii) and
(f)(4)(iii) of this section shall be the maximum SID for which the beam-
limiting device or aperture is designed.
(ii) Each image receptor support device intended for installation on
a system designed for mammography shall have clear and permanent
markings to indicate the maximum image receptor size for which it is
designed.
(4) Other x-ray systems. Radiographic systems not specifically
covered in paragraphs (d), (e), (f)(2), (f)(3), and (h) of this section
and systems covered in paragraph (f)(1) of this section, which are also
designed for use with extraoral image receptors and when used with an
extraoral image receptor, shall be provided with means to limit the x-
ray field in the plane of the image receptor so that such field does not
exceed each dimension of the image receptor by more than 2 percent of
the SID, when the axis of the x-ray beam is perpendicular to the plane
of the image receptor. In addition, means shall be provided to align the
center of the x-ray field with the center of the image receptor to
within 2 percent of the SID, or means shall be provided to both size and
align the x-ray field such that the x-ray field at the plane of the
image receptor does not extend beyond any edge of the image receptor.
These requirements may be met with:
(i) A system which performs in accordance with paragraphs (d) and
(e) of this section; or when alignment means are also provided, may be
met with either;
(ii) An assortment of removable, fixed-aperture, beam-limiting
devices sufficient to meet the requirement for each combination of image
receptor size and SID for which the unit is designed. Each such device
shall have clear and permanent markings to indicate the image receptor
size and SID for which it is designed; or
(iii) A beam-limiting device having multiple fixed apertures
sufficient to meet the requirement for each combination of image
receptor size and SID for which the unit is designed. Permanent, clearly
legible markings shall indicate the image receptor size and SID for
which each aperture is designed and shall indicate which aperture is in
position for use.
[[Page 615]]
(g) Positive beam limitation (PBL). The requirements of this
paragraph shall apply to radiographic systems which contain PBL.
(1) Field size. When a PBL system is provided, it shall prevent x-
ray production when:
(i) Either the length or width of the x-ray field in the plane of
the image receptor differs from the corresponding image receptor
dimension by more than 3 percent of the SID; or
(ii) The sum of the length and width differences as stated in
paragraph (g)(1)(i) of this section without regard to sign exceeds 4
percent of the SID.
(iii) The beam limiting device is at an SID for which PBL is not
designed for sizing.
(2) Conditions for PBL. When provided, the PBL system shall function
as described in paragraph (g)(1) of this section whenever all the
following conditions are met:
(i) The image receptor is inserted into a permanently mounted
cassette holder;
(ii) The image receptor length and width are less than 50
centimeters;
(iii) The x-ray beam axis is within 3 degrees of
vertical and the SID is 90 centimeters to 130 centimeters inclusive; or
the x-ray beam axis is within 3 degrees of horizontal and
the SID is 90 centimeters to 205 centimeters inclusive;
(iv) The x-ray beam axis is perpendicular to the plane of the image
receptor to within 3 degrees; and
(v) Neither tomographic nor stereoscopic radiography is being
performed.
(3) Measuring compliance. Compliance with the requirements of
paragraph (g)(1) of this section shall be determined when the equipment
indicates that the beam axis is perpendicular to the plane of the image
receptor and the provisions of paragraph (g)(2) of this section are met.
Compliance shall be determined no sooner than 5 seconds after insertion
of the image receptor.
(4) Operator initiated undersizing. The PBL system shall be capable
of operation such that, at the discretion of the operator, the size of
the field may be made smaller than the size of the image receptor
through stepless adjustment of the field size. Each dimension of the
minimum field size at an SID of 100 centimeters shall be equal to or
less than 5 centimeters. Return to PBL function as described in
paragraph (g)(1) of this section shall occur automatically upon any
change of image receptor size or SID.
(5) Override of PBL. A capability may be provided for overriding PBL
in case of system failure and for servicing the system. This override
may be for all SID's and image receptor sizes. A key shall be required
for any override capability that is accessible to the operator. It shall
not be possible to remove the key while PBL is overridden. Each such key
switch or key shall be clearly and durably labeled as follows:
For X-ray Field Limitation System Failure
The override capability is considered accessible to the operator if
it is referenced in the operator's manual or in other material intended
for the operator or if its location is such that the operator would
consider it part of the operational controls.
(h) Field limitation and alignment for spot-film devices. The
following requirements shall apply to spot-film devices, except when the
spot-film device is provided for use with a radiation therapy simulation
system:
(1) Means shall be provided between the source and the patient for
adjustment of the x-ray field size in the plane of the image receptor to
the size of that portion of the image receptor which has been selected
on the spot-film selector. Such adjustment shall be accomplished
automatically when the x-ray field size in the plane of the image
receptor is greater than the selected portion of the image receptor. If
the x-ray field size is less than the size of the selected portion of
the image receptor, the field size shall not open automatically to the
size of the selected portion of the image receptor unless the operator
has selected that mode of operation.
(2) Neither the length nor the width of the x-ray field in the plane
of the image receptor shall differ from the corresponding dimensions of
the selected portion of the image receptor by more than 3 percent of the
SID when adjusted for full coverage of the selected portion of the image
receptor. The sum, without regard to sign, of the length and width
differences shall not
[[Page 616]]
exceed 4 percent of the SID. 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.
(3) The center of the x-ray field in the plane of the image receptor
shall be aligned with the center of the selected portion of the image
receptor to within 2 percent of the SID.
(4) Means shall be provided to reduce the x-ray field size in the
plane of the image receptor to a size smaller than the selected portion
of the image receptor such that:
(i) For spot-film devices used on fixed-SID fluoroscopic systems
which are not required to, and do not provide stepless adjustment of the
x-ray field, the minimum field size, at the greatest SID, does not
exceed 125 square centimeters; or
(ii) For spot-film devices used on fluoroscopic systems that have a
variable SID and/or stepless adjustment of the field size, the minimum
field size, at the greatest SID, shall be containable in a square of 5
centimeters by 5 centimeters.
(5) A capability may be provided for overriding the automatic x-ray
field size adjustment in case of system failure. If it is so provided, a
signal visible at the fluoroscopist's position shall indicate whenever
the automatic x-ray field size adjustment override is engaged. Each such
system failure override switch shall be clearly labeled as follows:
For X-ray Field Limitation System Failure
(i) Source-skin distance--(1) X-ray systems designed for use with an
intraoral image receptor shall be provided with means to limit the
source-skin distance to not less than:
(i) Eighteen centimeters if operable above 50 kVp; or
(ii) Ten centimeters if not operable above 50 kVp.
(2) Mobile and portable x-ray systems other than dental shall be
provided with means to limit the source-skin distance to not less than
30 centimeters.
(j) Beam-on indicators. The x-ray control shall provide visual
indication whenever x-rays are produced. In addition, a signal audible
to the operator shall indicate that the exposure has terminated.
(k) Multiple tubes. Where two or more radiographic tubes are
controlled by one exposure switch, the tube or tubes which have been
selected shall be clearly indicated before initiation of the exposure.
This indication shall be both on the x-ray control and at or near the
tube housing assembly which has been selected.
(l) Radiation from capacitor energy storage equipment. Radiation
emitted from the x-ray tube shall not exceed:
(1) 8.6x10-9 C/kg (0.03 mR) in 1 minute at 5 centimeters
from any accessible surface of the diagnostic source assembly, with the
beam-limiting device fully open, the system fully charged, and the
exposure switch, timer, or any discharge mechanism not activated.
Compliance shall be determined by measurements averaged over an area of
100 square centimeters, with no linear dimension greater than 20
centimeters; and
(2) 2.58x10-5 C/kg (100 mR) in 1 hour at 100 centimeters
from the x-ray source, with the beam-limiting device fully open, when
the system is discharged through the x-ray tube either manually or
automatically by use of a discharge switch or deactivation of the input
power. Compliance shall be determined by measurements of the maximum
exposure per discharge multiplied by the total number of discharges in 1
hour (duty cycle). The measurements shall be averaged over an area of
100 square centimeters with no linear dimension greater than 20
centimeters.
(m) Primary protective barrier for mammography x-ray systems. For
mammography x-ray systems manufactured after September 30, 1999:
(1) At any SID where exposures can be made, the image receptor
support device shall provide a primary protective barrier that
intercepts the cross
[[Page 617]]
section of the useful beam along every direction except at the chest
wall edge.
(2) The x-ray tube shall not permit exposure unless the appropriate
barrier is in place to intercept the useful beam as required in
paragraph (m)(1) of this section.
(3) The transmission of the useful beam through the primary
protective barrier shall be limited such that the exposure 5 centimeters
from any accessible surface beyond the plane of the primary protective
barrier does not exceed 2.58X10-8 C/kg (0.1 mR) for each
activation of the tube.
(4) Compliance for transmission shall be determined with the x-ray
system operated at the minimum SID for which it is designed, at the
maximum rated peak tube potential, at the maximum rated product of x-ray
tube current and exposure time (mAs) for the maximum rated peak tube
potential, and by measurements averaged over an area of 100 square
centimeters with no linear dimension greater than 20 centimeters. The
sensitive volume of the radiation measuring instrument shall not be
positioned beyond the edge of the primary protective barrier along the
chest wall side.
[58 FR 26401, May 3, 1993; 58 FR 31067, May 28, 1993, as amended at 64
FR 35927, July 2, 1999]