[Code of Federal Regulations]
[Title 21, Volume 8]
[Revised as of April 1, 2008]
From the U.S. Government Printing Office via GPO Access
[CITE: 21CFR1020.31]

[Page 635-641]
 
                        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 radiography, 
except equipment for fluoroscopic imaging or for recording images from 
the

[[Page 636]]

fluoroscopic image receptor, or computed tomography x-ray systems 
manufactured on or after November 29, 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 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 milliampere-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 
(kWs) 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 
the air kerma 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

[[Page 637]]

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 air kerma to the indicated milliampere-
seconds product (mGy/mAs) obtained at any two consecutive tube current 
settings shall not differ by more than 0.10 times their sum. This is: 
[bond]X1 - X2[bond] <= 0.10(X1 + 
X2); where X1 and X2 are the average 
mGy/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.
    (2) Equipment having selection of x-ray tube current-exposure time 
product (mAs). For equipment manufactured after May 3, 1994, the average 
ratios of air kerma to the indicated milliampere-seconds product (mGy/
mAs) obtained at any two consecutive mAs selector settings shall not 
differ by more than 0.10 times their sum. This is: [bond]X1 - 
X2[bond] <= 0.10 (X1 + X2); where 
X1 and X2 are the average mGy/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 mm and the other is greater than 0.45 mm. 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 
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 (cm) shall be equal to 
or less than 5 cm.
    (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 cm or at the maximum SID, whichever is less. The 
average illuminance shall be based on 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 cm 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 mm 
from the edge of the light field toward the center of the field; and 
I2 is the illuminance 3 mm from the edge of the light field 
away from the center of the field. Compliance shall be determined with a 
measuring aperture of 1 mm.

[[Page 638]]

    (e) Field indication and alignment on stationary general purpose x-
ray equipment. Except when spot-film devices 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 SIDs 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 SIDs and image 
receptor dimensions in common clinical use (such as SIDs of 100, 150, 
and 200 cm and/or 36, 40, 48, and 72 inches and nominal image receptor 
dimensions of 13, 18, 24, 30, 35, 40, and 43 cm 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 cm or more, 
the x-ray field at the minimum SSD shall be containable in a circle 
having a diameter of no more than 7 cm; and
    (ii) If the minimum SSD is less than 18 cm, the x-ray field at the 
minimum SSD shall be containable in a circle having a diameter of no 
more than 6 cm.
    (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) Radiographic systems 
designed only for mammography and general purpose radiography systems, 
when special attachments for mammography are in service, manufactured on 
or after November 1, 1977, and before 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 at any designated SID except the edge of the image 
receptor designed to be adjacent to the chest wall where the x-ray field 
may not extend beyond this edge 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. When 
the beam-limiting device and image receptor support device are designed 
to be used to immobilize the breast during a mammographic procedure and 
the SID may vary, 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) Mammographic beam-limiting devices manufactured on or after 
September 30, 1999, shall be provided with a 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

[[Page 639]]

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.
    (iii) Each image receptor support device manufactured on or after 
November 1, 1977, 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.
    (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 cm;
    (iii) The x-ray beam axis is within 3 degrees 
of vertical and the SID is 90 cm to 130 cm inclusive; or the x-ray beam 
axis is within 3 degrees of horizontal and the SID 
is 90 cm to 205 cm 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

[[Page 640]]

image receptor through stepless adjustment of the field size. Each 
dimension of the minimum field size at an SID of 100 cm shall be equal 
to or less than 5 cm. 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 SIDs 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 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 cm; 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 
cm by 5 cm.
    (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 cm if operable above 50 kVp; or
    (ii) Ten cm if not operable above 50 kVp.
    (2) Mobile and portable x-ray systems other than dental shall be 
provided

[[Page 641]]

with means to limit the source-skin distance to not less than 30 cm.
    (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) An air kerma of 0.26 microGy (vice 0.03 mR exposure) in 1 minute 
at 5 cm 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 cm, with no linear dimension greater than 20 cm; and
    (2) An air kerma of 0.88 mGy (vice 100 mR exposure) in 1 hour at 100 
cm 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 air 
kerma 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 cm with no linear dimension greater than 20 cm.
    (m) Primary protective barrier for mammography x-ray systems--(1) 
For x-ray systems manufactured after September 5, 1978, and before 
September 30, 1999, which are designed only for mammography, the 
transmission of the primary beam through any image receptor support 
provided with the system shall be limited such that the air kerma 5 cm 
from any accessible surface beyond the plane of the image receptor 
supporting device does not exceed 0.88 microGy (vice 0.1 mR exposure) 
for each activation of the tube.
    (2) For mammographic x-ray systems manufactured on or after 
September 30, 1999:
    (i) At any SID where exposures can be made, the image receptor 
support device shall provide a primary protective barrier that 
intercepts the cross section of the useful beam along every direction 
except at the chest wall edge.
    (ii) The x-ray system shall not permit exposure unless the 
appropriate barrier is in place to intercept the useful beam as required 
in paragraph (m)(2)(i) of this section.
    (iii) The transmission of the useful beam through the primary 
protective barrier shall be limited such that the air kerma 5 cm from 
any accessible surface beyond the plane of the primary protective 
barrier does not exceed 0.88 microGy (vice 0.1 mR exposure) for each 
activation of the tube.
    (3) Compliance with the requirements of paragraphs (m)(1) and 
(m)(2)(iii) of this section 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 
cm with no linear dimension greater than 20 cm. 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.

[70 FR 34036, June 10, 2005]