PART 1020—PERFORMANCE STANDARDS FOR IONIZING RADIATION EMITTING PRODUCTS Authority: 21 U.S.C. 351, 352, 360e-360j, 360hh-360ss, 371, 381. Source: 38 FR 28632, Oct. 15, 1973, unless otherwise noted. § 1020.10 Television receivers. (a) Applicability. (b) Definitions. External surface (2) Maximum test voltage (3) Service controls (4) Television receiver (5) Usable picture (6) User controls (c) Requirements Exposure rate limit. (2) Measurements. (3) Test conditions. (i) On television receivers manufactured subsequent to January 15, 1970, measurements shall be made with all user controls adjusted so as to produce maximum x-radiation emissions from the receiver. (ii) On television receivers manufactured subsequent to June 1, 1970, measurements shall be made with all user controls and all service controls adjusted to combinations which result in the production of maximum x-radiation emissions. (iii) On television receivers manufactured subsequent to June 1, 1971, measurements shall be made under the conditions described in paragraph (c)(3) (ii) of this section, together with conditions identical to those which result from that component or circuit failure which maximizes x-radiation emissions. (4) Critical component warning. [38 FR 28632, Oct. 15, 1973, as amended at 88 FR 3654, Jan. 20, 2023] § 1020.20 Cold-cathode gas discharge tubes. (a) Applicability. (b) Definitions. Beam blocking device Cold-cathode gas discharge tube Exit beam Exposure −4 (c) Requirements Exposure rate limit. (ii) The divergence of the exit beam from tubes designed primarily to demonstrate the effects of x radiation, with the beam blocking device in the open position, shall not exceed (Pi) steradians. (2) Measurements. (ii) Measurements of exposure rates from tubes in enclosures from which the tubes cannot be removed without destroying the function of the tube may be made at a distance of thirty (30) centimeters from any point on the external surface of the enclosure, provided: ( a ( b (3) Test conditions. (ii) Measurements shall be made with the tube operated under forward and reverse polarity. (4) Instructions, labels, and warnings. (ii) Each enclosure or tube shall have inscribed on or permanently affixed to it, tags or labels, which identify the intended polarity of the terminals and: ( a b (iii) The tag or label required by this paragraph shall be located on the tube or enclosure so as to be readily visible and legible when the product is fully assembled for use. § 1020.30 Diagnostic x-ray systems and their major components. (a) Applicability. (i) The following components of diagnostic x-ray systems: (A) Tube housing assemblies, x-ray controls, x-ray high-voltage generators, x-ray tables, cradles, film changers, vertical cassette holders mounted in a fixed location and cassette holders with front panels, and beam-limiting devices manufactured after August 1, 1974. (B) Fluoroscopic imaging assemblies manufactured after August 1, 1974, and before April 26, 1977, or after June 10, 2006. (C) Spot-film devices and image intensifiers manufactured after April 26, 1977. (D) Cephalometric devices manufactured after February 25, 1978. (E) Image receptor support devices for mammographic x-ray systems manufactured after September 5, 1978. (F) Image receptors that are electrically powered or connected with the x-ray system manufactured on or after June 10, 2006. (G) Fluoroscopic air kerma display devices manufactured on or after June 10, 2006. (ii) Diagnostic x-ray systems, except computed tomography x-ray systems, incorporating one or more of such components; however, such x-ray systems shall be required to comply only with those provisions of this section and §§ 1020.31 and 1020.32, which relate to the components certified in accordance with paragraph (c) of this section and installed into the systems. (iii) Computed tomography (CT) x-ray systems manufactured before November 29, 1984. (iv) CT gantries manufactured after September 3, 1985. (2) The following provisions of this section and § 1020.33 are applicable to CT x-ray systems manufactured or remanufactured on or after November 29, 1984: (i) Section 1020.30(a); (ii) Section 1020.30(b) “Technique factors”; (iii) Section 1020.30(b) “CT,” “Dose,” “Scan,” “Scan time,” and “Tomogram”; (iv) Section 1020.30(h)(3)(vi) through (h)(3)(viii); (v) Section 1020.30(n); (vi) Section 1020.33(a) and (b); (vii) Section 1020.33(c)(1) as it affects § 1020.33(c)(2); and (viii) Section 1020.33(c)(2). (3) The provisions of this section and § 1020.33 in its entirety, including those provisions in paragraph (a)(2) of this section, are applicable to CT x-ray systems manufactured or remanufactured on or after September 3, 1985. The date of manufacture of the CT system is the date of manufacture of the CT gantry. (b) Definitions. Accessible surface Accessory component (1) A component used with diagnostic x-ray systems, such as a cradle or film changer, that is not necessary for the compliance of the system with applicable provisions of this subchapter but which requires an initial determination of compatibility with the system; or (2) A component necessary for compliance of the system with applicable provisions of this subchapter but which may be interchanged with similar compatible components without affecting the system's compliance, such as one of a set of interchangeable beam-limiting devices; or (3) A component compatible with all x-ray systems with which it may be used and that does not require compatibility or installation instructions, such as a tabletop cassette holder. Air kerma Kerma Air kerma rate (AKR) Aluminum equivalent 1 1 Articulated joint Assembler Attenuation block Automatic exposure control (AEC) Automatic exposure rate control (AERC) Beam axis Beam-limiting device C-arm fluoroscope Cantilevered tabletop Cassette holder Cephalometric device Coefficient of variation where: s = Estimated standard deviation of the population. X X i n = Number of observations sampled. Computed tomography (CT) Control panel Cooling curve Cradle (1) A removable device which supports and may restrain a patient above an x-ray table; or (2) A device; (i) Whose patient support structure is interposed between the patient and the image receptor during normal use; (ii) Which is equipped with means for patient restraint; and (iii) Which is capable of rotation about its long (longitudinal) axis. CT gantry Cumulative air kerma Diagnostic source assembly Diagnostic x-ray system Dose Equipment Exposure (X) Field emission equipment Fluoroscopic air kerma display device Fluoroscopic imaging assembly Fluoroscopic irradiation time Fluoroscopy General purpose radiographic x-ray system Half-value layer (HVL) Image intensifier Image receptor Image receptor support device Isocenter Kerma tr tr tr Last-image-hold (LIH) radiograph Lateral fluoroscope Leakage radiation (1) The useful beam; and (2) Radiation produced when the exposure switch or timer is not activated. Leakage technique factors (1) For diagnostic source assemblies intended for capacitor energy storage equipment, the maximum-rated peak tube potential and the maximum-rated number of exposures in an hour for operation at the maximum-rated peak tube potential with the quantity of charge per exposure being 10 millicoulombs (or 10 mAs) or the minimum obtainable from the unit, whichever is larger; (2) For diagnostic source assemblies intended for field emission equipment rated for pulsed operation, the maximum-rated peak tube potential and the maximum-rated number of x-ray pulses in an hour for operation at the maximum-rated peak tube potential; and (3) For all other diagnostic source assemblies, the maximum-rated peak tube potential and the maximum-rated continuous tube current for the maximum-rated peak tube potential. Light field Line-voltage regulation Percent line-voltage regulation = 100(V n i i where: V n V i Maximum line current Mode of operation Movable tabletop Non-image-intensified fluoroscopy Peak tube potential Primary protective barrier Pulsed mode Quick change x-ray tube (1) The tube cannot be inserted in its housing in a manner that would result in noncompliance of the system with the requirements of paragraphs (k) and (m) of this section; (2) The focal spot position will not cause noncompliance with the provisions of this section or § 1020.31 or 1020.32; (3) The shielding within the tube housing cannot be displaced; and (4) Any removal and subsequent replacement of a beam-limiting device during reloading of the tube in the tube housing will not result in noncompliance of the x-ray system with the applicable field limitation and alignment requirements of §§ 1020.31 and 1020.32. Radiation therapy simulation system Radiography Rated line voltage Rated output current Rated output voltage Rating Recording Scan Scan time Solid state x-ray imaging device Source Source-image receptor distance (SID) Source-skin distance (SSD) Spot-film device Stationary tabletop Technique factors (1) For capacitor energy storage equipment, peak tube potential in kilovolts (kV) and quantity of charge in milliampere-seconds (mAs); (2) For field emission equipment rated for pulsed operation, peak tube potential in kV and number of x-ray pulses; (3) For CT equipment designed for pulsed operation, peak tube potential in kV, scan time in seconds, and either tube current in milliamperes (mA), x-ray pulse width in seconds, and the number of x-ray pulses per scan, or the product of the tube current, x-ray pulse width, and the number of x-ray pulses in mAs; (4) For CT equipment not designed for pulsed operation, peak tube potential in kV, and either tube current in mA and scan time in seconds, or the product of tube current and exposure time in mAs and the scan time when the scan time and exposure time are equivalent; and (5) For all other equipment, peak tube potential in kV, and either tube current in mA and exposure time in seconds, or the product of tube current and exposure time in mAs. Tomogram Tube Tube housing assembly Tube rating chart Useful beam Variable-aperture beam-limiting device Visible area X-ray control X-ray equipment (1) Mobile x-ray equipment (2) Portable x-ray equipment (3) Stationary x-ray equipment means X-ray field X-ray high-voltage generator X-ray subsystem X-ray system X-ray table X-ray tube (c) Manufacturers' responsibility. (d) Assemblers' responsibility. (1) Reports of assembly. https://www.fda.gov/about-fda/reports-manuals-forms/forms (2) Exceptions to reporting requirements. (i) Reloaded or replacement tube housing assemblies that are reinstalled in or newly assembled into an existing x-ray system; (ii) Certified accessory components; (iii) Repaired components, whether or not removed from the system and reinstalled during the course of repair, provided the original installation into the system was reported; or (iv)(A) Components installed temporarily in an x-ray system in place of components removed temporarily for repair, provided the temporarily installed component is identified by a tag or label bearing the following information: Temporarily Installed Component This certified component has been assembled, installed, adjusted, and tested by me according to the instructions provided by the manufacturer. Signature Company Name Street Address, P.O. Box City, State, Zip Code Date of Installation (B) The replacement of the temporarily installed component by a component other than the component originally removed for repair shall be reported as specified in paragraph (d)(1) of this section. (e) Identification of x-ray components. (1) Tube housing assemblies. (2) Replacement of tubes. (3) Quick-change x-ray tubes. (f) [Reserved] (g) Information to be provided to assemblers. (1) A statement of the rated line voltage and the range of line-voltage regulation for operation at maximum line current; (2) A statement of the maximum line current of the x-ray system based on the maximum input voltage and current characteristics of the tube housing assembly compatible with rated output voltage and rated output current characteristics of the x-ray control and associated high-voltage generator. If the rated input voltage and current characteristics of the tube housing assembly are not known by the manufacturer of the x-ray control and associated high-voltage generator, the manufacturer shall provide information necessary to allow the assembler to determine the maximum line current for the particular tube housing assembly(ies); (3) A statement of the technique factors that constitute the maximum line current condition described in paragraph (g)(2) of this section. (h) Information to be provided to users. (1) All x-ray equipment. (i) Adequate instructions concerning any radiological safety procedures and precautions which may be necessary because of unique features of the equipment; and (ii) A schedule of the maintenance necessary to keep the equipment in compliance with this section and §§ 1020.31, 1020.32, and 1020.33. (2) Tube housing assemblies. (i) Statements of the leakage technique factors for all combinations of tube housing assemblies and beam-limiting devices for which the tube housing assembly manufacturer states compatibility, the minimum filtration permanently in the useful beam expressed as millimeters (mm) of aluminum equivalent, and the peak tube potential at which the aluminum equivalent was obtained; (ii) Cooling curves for the anode and tube housing; and (iii) Tube rating charts. If the tube is designed to operate from different types of x-ray high-voltage generators (such as single-phase self rectified, single-phase half-wave rectified, single-phase full-wave rectified, 3-phase 6-pulse, 3-phase 12-pulse, constant potential, capacitor energy storage) or under modes of operation such as alternate focal spot sizes or speeds of anode rotation which affect its rating, specific identification of the difference in ratings shall be noted. (3) X-ray controls and generators. (i) A statement of the rated line voltage and the range of line-voltage regulation for operation at maximum line current; (ii) A statement of the maximum line current of the x-ray system based on the maximum input voltage and output current characteristics of the tube housing assembly compatible with rated output voltage and rated current characteristics of the x-ray control and associated high-voltage generator. If the rated input voltage and current characteristics of the tube housing assembly are not known by the manufacturer of the x-ray control and associated high-voltage generator, the manufacturer shall provide necessary information to allow the purchaser to determine the maximum line current for his particular tube housing assembly(ies); (iii) A statement of the technique factors that constitute the maximum line current condition described in paragraph (h)(3)(ii) of this section; (iv) In the case of battery-powered generators, a specification of the minimum state of charge necessary for proper operation; (v) Generator rating and duty cycle; (vi) A statement of the maximum deviation from the preindication given by labeled technique factor control settings or indicators during any radiographic or CT exposure where the equipment is connected to a power supply as described in accordance with this paragraph. In the case of fixed technique factors, the maximum deviation from the nominal fixed value of each factor shall be stated; (vii) A statement of the maximum deviation from the continuous indication of x-ray tube potential and current during any fluoroscopic exposure when the equipment is connected to a power supply as described in accordance with this paragraph; and (viii) A statement describing the measurement criteria for all technique factors used in paragraphs (h)(3)(iii), (h)(3)(vi), and (h)(3)(vii) of this section; for example, the beginning and endpoints of exposure time measured with respect to a certain percentage of the voltage waveform. (4) Beam-limiting device. (i) Leakage technique factors for all combinations of tube housing assemblies and beam-limiting devices for which the beam-limiting device manufacturer states compatibility; and (ii) A statement including the minimum aluminum equivalent of that part of the device through which the useful beam passes and including the x-ray tube potential at which the aluminum equivalent was obtained. When two or more filters are provided as part of the device, the statement shall include the aluminum equivalent of each filter. (5) Imaging system information. (i) For each mode of operation, a description of the mode and detailed instructions on how the mode is engaged and disengaged. The description of the mode shall identify those technique factors and system controls that are fixed or automatically adjusted by selection of the mode of operation, including the manner in which the automatic adjustment is controlled. This information shall include how the operator can recognize which mode of operation has been selected prior to initiation of x-ray production. (ii) For each mode of operation, a descriptive example(s) of any specific clinical procedure(s) or imaging task(s) for which the mode is recommended or designed and how each mode should be used. Such recommendations do not preclude other clinical uses. (6) Displays of values of AKR and cumulative air kerma. (i) A schedule of maintenance for any system instrumentation associated with the display of air kerma information necessary to maintain the displays of AKR and cumulative air kerma within the limits of allowed uncertainty specified by § 1020.32(k)(6) and, if the capability for user calibration of the display is provided, adequate instructions for such calibration; (ii) Identification of the distances along the beam axis: (A) From the focal spot to the isocenter, and (B) From the focal spot to the reference location to which displayed values of AKR and cumulative air kerma refer according to § 1020.32(k)(4); (iii) A rationale for specification of a reference irradiation location alternative to 15 cm from the isocenter toward the x-ray source along the beam axis when such alternative specification is made according to § 1020.32(k)(4)(ii). (i) [Reserved] (j) Warning label. “Warning: This x-ray unit may be dangerous to patient and operator unless safe exposure factors, operating instructions and maintenance schedules are observed.” (k) Leakage radiation from the diagnostic source assembly. (l) Radiation from components other than the diagnostic source assembly. (m) Beam quality Half-value layer (HVL). 2 2 Table 1 X-Ray Tube Voltage Minimum HVL Designed Operating Range Measured Operating Potential Specified Dental Systems 1 I—Other X-Ray Systems 2 II—Other X-Ray Systems 3 Below 51 30 1.5 0.3 0.3 40 1.5 0.4 0.4 50 1.5 0.5 0.5 51 to 70 51 1.5 1.2 1.3 60 1.5 1.3 1.5 70 1.5 1.5 1.8 Above 70 71 2.1 2.1 2.5 80 2.3 2.3 2.9 90 2.5 2.5 3.2 100 2.7 2.7 3.6 110 3.0 3.0 3.9 120 3.2 3.2 4.3 130 3.5 3.5 4.7 140 3.8 3.8 5.0 150 4.1 4.1 5.4 1 2 3 (2) Optional filtration. (3) Measuring compliance. (n) Aluminum equivalent of material between patient and image receptor. Table 2 Item Maximum Aluminum Equivalent (millimeters) 1. Front panel(s) of cassette holders (total of all) 1.2 2. Front panel(s) of film changer (total of all) 1.2 3. Cradle 2.3 4. Tabletop, stationary, without articulated joints 1.2 5. Tabletop, movable, without articulated joint(s) (including stationary subtop) 1.7 6. Tabletop, with radiolucent panel having one articulated joint 1.7 7. Tabletop, with radiolucent panel having two or more articulated joints 2.3 8. Tabletop, cantilevered 2.3 9. Tabletop, radiation therapy simulator 5.0 (o) Battery charge indicator. (p) [Reserved] (q) Modification of certified diagnostic x-ray components and systems. (2) The owner of a diagnostic x-ray system who uses the system in a professional or commercial capacity may modify the system, provided the modification does not result in the failure of the system or component to comply with the applicable requirements of this section or of § 1020.31, § 1020.32, or § 1020.33. The owner who causes such modification need not submit the reports required by subpart B of part 1002 of this chapter, provided the owner records the date and the details of the modification in the system records and maintains this information, and provided the modification of the x-ray system does not result in a failure to comply with § 1020.31, § 1020.32, or § 1020.33. [71 FR 34028, June 10, 2006, as amended at 72 FR 17401, Apr. 9, 2007; 83 FR 13864, Apr. 2, 2018; 88 FR 3654, Jan. 20, 202] § 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 fluoroscopic image receptor, or computed tomography x-ray systems manufactured on or after November 29, 1984. (a) Control and indication of technique factors Visual indication. (2) Timers. (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. (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 (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. (b) Reproducibility. (1) Coefficient of variation. (2) Measuring compliance. (c) Linearity. (1) Equipment having independent selection of x-ray tube current (mA). 1 2 1 2 1 2 (2) Equipment having selection of x-ray tube current-exposure time product (mAs). 1 2 1 2 1 2 (3) Measuring compliance. (d) Field limitation and alignment for mobile, portable, and stationary general purpose x-ray systems. (1) Variable x-ray field limitation. (2) Visual definition. (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 I 1 2 1 2 (e) Field indication and alignment on stationary general purpose x-ray equipment. (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 Equipment for use with intraoral image receptors. (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. (3) Systems designed for mammography (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 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. (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). (1) Field size. (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. (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. (4) Operator initiated undersizing. (5) Override of PBL. 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. (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 (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 with means to limit the source-skin distance to not less than 30 cm. (j) Beam-on indicators. (k) Multiple tubes. (l) Radiation from capacitor energy storage equipment. (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 (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] § 1020.32 Fluoroscopic equipment. The provisions of this section apply to equipment for fluoroscopic imaging or for recording images from the fluoroscopic image receptor, except computed tomography x-ray systems manufactured on or after November 29, 1984. (a) Primary protective barrier Limitation of useful beam. −3 (2) Measuring compliance. (b) Field limitation Angulation. (2) Further means for limitation. (3) Non-image-intensified fluoroscopy. (4) Fluoroscopy and radiography using the fluoroscopic imaging assembly with inherently circular image receptors. (A) 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. (B) 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. (ii) For fluoroscopic equipment manufactured on or after June 10, 2006, other than radiation therapy simulation systems, the maximum area of the x-ray field in the plane of the image receptor shall conform with one of the following requirements: (A) When every linear dimension of the visible area of the image receptor measured through the center of the visible area is less than or equal to 34 cm in any direction, at least 80 percent of the area of the x-ray field overlaps the visible area of the image. (B) When any linear dimension of the visible area of the image receptor measured through the center of the visible area is greater than 34 cm in any direction, the x-ray field measured along the direction of greatest misalignment with the visible area of the image receptor does not extend beyond the edge of the visible area of the image receptor by more than 2 cm. (5) Fluoroscopy and radiography using the fluoroscopic imaging assembly with inherently rectangular image receptors. (i) 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. (ii) 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. (6) Override capability. For X-ray Field Limitation System Failure (c) Activation of tube. (d) Air kerma rates. (1) Fluoroscopic equipment manufactured before May 19, 1995 (ii) Equipment provided without AERC shall not be operable at any combination of tube potential and current that will result in an AKR in excess of 44 mGy per minute (vice 5 R/min exposure rate) at the measurement point specified in § 1020.32(d)(3), except as specified in § 1020.32(d)(1)(v). (iii) Equipment 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 AKR in excess of 88 mGy per minute (vice 10 R/min exposure rate) in either mode at the measurement point specified in § 1020.32(d)(3), except as specified in § 1020.32(d)(1)(v). (iv) Equipment may be modified in accordance with § 1020.30(q) to comply with § 1020.32(d)(2). When the equipment is modified, it shall bear a label indicating the date of the modification and the statement: Modified to comply with 21 CFR 1020.32(h)(2). (v) Exceptions: (A) During recording of fluoroscopic images, or (B) When a mode of operation has an optional high-level control, in which case that mode shall not be operable at any combination of tube potential and current that will result in an AKR in excess of the rates specified in § 1020.32(d)(1)(i), (d)(1)(ii), or (d)(1)(iii) at the measurement point specified in § 1020.32(d)(3), 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. (2) Fluoroscopic equipment manufactured on or after May 19, 1995 (ii) Shall not be operable at any combination of tube potential and current that will result in an AKR in excess of 88 mGy per minute (vice 10 R/min exposure rate) at the measurement point specified in § 1020.32(d)(3), except as specified in § 1020.32(d)(2)(iii): (iii) Exceptions: (A) For equipment manufactured prior to June 10, 2006, during the recording of images from a fluoroscopic image receptor using photographic film or a video camera when the x-ray source is operated in a pulsed mode. (B) For equipment manufactured on or after June 10, 2006, during the recording of images from the fluoroscopic image receptor for the purpose of providing the user with a recorded image(s) after termination of the exposure. Such recording does not include images resulting from a last-image-hold feature that are not recorded. (C) When a mode of operation has an optional high-level control and the control is activated, in which case the equipment shall not be operable at any combination of tube potential and current that will result in an AKR in excess of 176 mGy per minute (vice 20 R/min exposure rate) at the measurement point specified in § 1020.32(d)(3). 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. (3) Measuring compliance. (i) If the source is below the x-ray table, the AKR shall be measured at 1 cm above the tabletop or cradle. (ii) If the source is above the x-ray table, the AKR shall be measured at 30 cm above the tabletop with the end of the beam-limiting device or spacer positioned as closely as possible to the point of measurement. (iii) In a C-arm type of fluoroscope, the AKR shall be measured at 30 cm from the input surface of the fluoroscopic imaging assembly, with the source positioned at any available SID, provided that the end of the beam-limiting device or spacer is no closer than 30 cm from the input surface of the fluoroscopic imaging assembly. (iv) In a C-arm type of fluoroscope having an SID less than 45 cm, the AKR shall be measured at the minimum SSD. (v) In a lateral type of fluoroscope, the air kerma rate shall be measured at a point 15 cm from the centerline of the x-ray table and in the direction of the x-ray source with the end of the beam-limiting device or spacer positioned as closely as possible to the point of measurement. If the tabletop is movable, it shall be positioned as closely as possible to the lateral x-ray source, with the end of the beam-limiting device or spacer no closer than 15 cm to the centerline of the x-ray table. (4) Exemptions. (e) [Reserved] (f) Indication of potential and current. (g) Source-skin distance. (2) For stationary, mobile, or portable C-arm fluoroscopic systems manufactured on or after June 10, 2006, having a maximum source-image receptor distance of less than 45 cm, means shall be provided to limit the source-skin distance to not less than 19 cm. Such systems shall be labeled for extremity use only. In addition, for those systems intended for specific surgical application that would be prohibited at the source-skin distances specified in this paragraph, provisions may be made for operation at shorter source-skin distances but in no case less than 10 cm. When provided, the manufacturer must set forth precautions with respect to the optional means of spacing, in addition to other information as required in § 1020.30(h). (h) Fluoroscopic irradiation time, display, and signal. Modified to comply with 21 CFR 1020.32(h)(2). (ii) As an alternative to the requirements of this paragraph, radiation therapy simulation systems may be provided with a means to indicate the total cumulative exposure time during which x-rays were produced, and which is capable of being reset between x-ray examinations. (2) For x-ray controls manufactured on or after June 10, 2006, there shall be provided for each fluoroscopic tube: (i) A display of the fluoroscopic irradiation time at the fluoroscopist's working position. This display shall function independently of the audible signal described in § 1020.32(h)(2)(ii). The following requirements apply: (A) When the x-ray tube is activated, the fluoroscopic irradiation time in minutes and tenths of minutes shall be continuously displayed and updated at least once every 6 seconds. (B) The fluoroscopic irradiation time shall also be displayed within 6 seconds of termination of an exposure and remain displayed until reset. (C) Means shall be provided to reset the display to zero prior to the beginning of a new examination or procedure. (ii) A signal audible to the fluoroscopist shall sound for each passage of 5 minutes of fluoroscopic irradiation time during an examination or procedure. The signal shall sound until manually reset or, if automatically reset, for at least 2 second. (i) Mobile and portable fluoroscopes. (j) Display of last-image-hold (LIH). (1) For an LIH image obtained by retaining pretermination fluoroscopic images, if the number of images and method of combining images are selectable by the user, the selection shall be indicated prior to initiation of the fluoroscopic exposure. (2) For an LIH image obtained by initiating a separate radiographic-like exposure at the termination of fluoroscopic imaging, the techniques factors for the LIH image shall be selectable prior to the fluoroscopic exposure, and the combination selected shall be indicated prior to initiation of the fluoroscopic exposure. (3) Means shall be provided to clearly indicate to the user whether a displayed image is the LIH radiograph or fluoroscopy. Display of the LIH radiograph shall be replaced by the fluoroscopic image concurrently with re-initiation of fluoroscopic exposure, unless separate displays are provided for the LIH radiograph and fluoroscopic images. (4) The predetermined or selectable options for producing the LIH radiograph shall be described in the information required by § 1020.30(h). The information shall include a description of any technique factors applicable for the selected option and the impact of the selectable options on image characteristics and the magnitude of radiation emissions. (k) Displays of values of AKR and cumulative air kerma. (1) When the x-ray tube is activated and the number of images produced per unit time is greater than six images per second, the AKR in mGy/min shall be continuously displayed and updated at least once every second. (2) The cumulative air kerma in units of mGy shall be displayed either within 5 seconds of termination of an exposure or displayed continuously and updated at least once every 5 seconds. (3) The display of the AKR shall be clearly distinguishable from the display of the cumulative air kerma. (4) The AKR and cumulative air kerma shall represent the value for conditions of free-in-air irradiation at one of the following reference locations specified according to the type of fluoroscope. The reference location shall be identified and described specifically in the information provided to users according to § 1020.30(h)(6)(iii). (i) For fluoroscopes with x-ray source below the x-ray table, x-ray source above the table, or of lateral type, the reference locations shall be the respective locations specified in § 1020.32(d)(3)(i), (d)(3)(ii), or (d)(3)(v) for measuring compliance with air-kerma rate limits. (ii) For C-arm fluoroscopes, the reference location shall be 15 cm from the isocenter toward the x-ray source along the beam axis. Alternatively, the reference location shall be at a point specified by the manufacturer to represent the location of the intersection of the x-ray beam with the patient's skin. (5) Means shall be provided to reset to zero the display of cumulative air kerma prior to the commencement of a new examination or procedure. (6) The displayed AKR and cumulative air kerma shall not deviate from the actual values by more than ±35 percent over the range of 6 mGy/min and 100 mGy to the maximum indication of AKR and cumulative air kerma, respectively. Compliance shall be determined with an irradiation time greater than 3 seconds. [70 FR 34039, June 10, 2005, as amended at 80 FR 19532, Apr. 13, 2015] § 1020.33 Computed tomography (CT) equipment. (a) Applicability. (2) The provisions of paragraphs (b), (c)(1), and (c)(2) are applicable to CT x-ray systems manufactured or remanufactured on or after November 29, 1984. (b) Definitions. (1) Computed tomography dose index (CTDI) where: z = position along a line perpendicular to the tomographic plane. D(z) = Dose at position z. T = Nominal tomographic section thickness. n = Number of tomograms produced in a single scan. This definition assumes that the dose profile is centered around z = 0 and that, for a multiple tomogram system, the scan increment between adjacent scans is nT. (2) Contrast scale where: μ w μ x (CT) w (CT) x (3) CT conditions of operation (4) CT number (5) [Reserved] (6) CT dosimetry phantom (7) Dose profile (8) Modulation transfer function (9) Multiple tomogram system (10) Noise n where: CS = Contrast scale. μ w s = Estimated standard deviation of the CT numbers of picture elements in a specified area of the CT image. (11) Nominal tomographic section thickness (12) Picture element (13) Remanufacturing (14) Scan increment (15) Scan sequence (16) Sensitivity profile (17) Single tomogram system (18) Tomographic plane (19) Tomographic section (c) Information to be provided for users. (1) Conditions of operation. (2) Dose information. (i) The CTDI at the following locations in the dosimetry phantom: ( a ( b ( c b b (ii) The CTDI in the center location of the dosimetry phantom for each selectable CT condition of operation that varies either the rate or duration of x-ray exposure. This CTDI shall be presented as a value that is normalized to the CTDI in the center location of the dosimetry phantom from paragraph (c)(2)(i) of this section, with the CTDI of paragraph (c)(2)(i) of this section having a value of one. As each individual CT condition of operation is changed, all other independent CT conditions of operation shall be maintained at the typical values described in paragraph (c)(2)(i) of this section. These data shall encompass the range of each CT condition of operation stated by the manufacturer as appropriate for CT of the head or body. When more than three selections of a CT condition of operation are available, the normalized CTDI shall be provided, at least, for the minimum, maximum, and mid-range value of the CT condition of operation. (iii) The CTDI at the location coincident with the maximum CTDI at 1 centimeter interior to the surface of the dosimetry phantom for each selectable peak tube potential. When more than three selections of peak tube potential are available, the normalized CTDI shall be provided, at least, for the minimum, maximum, and a typical value of peak tube potential. The CTDI shall be presented as a value that is normalized to the maximum CTDI located at 1 centimeter interior to the surface of the dosimetry phantom from paragraph (c)(2)(i) of this section, with the CTDI of paragraph (c)(2)(i) of this section having a value of one. (iv) The dose profile in the center location of the dosimetry phantom for each selectable nominal tomographic section thickness. When more than three selections of nominal tomographic section thicknesses are available, the information shall be provided, at least, for the minimum, maximum, and midrange value of nominal tomographic section thickness. The dose profile shall be presented on the same graph and to the same scale as the corresponding sensitivity profile required by paragraph (c)(3)(iv) of this section. (v) A statement of the maximum deviation from the values given in the information provided according to paragraph (c)(2) (i), (ii), (iii), and (iv) of this section. Deviation of actual values may not exceed these limits. (3) Imaging performance information. (i) A statement of the noise. (ii) A graphical presentation of the modulation transfer function for the same image processing and display mode as that used in the statement of the noise. (iii) A statement of the nominal tomographic section thickness(es). (iv) A graphical presentation of the sensitivity profile, at the location corresponding to the center location of the dosimetry phantom, for each selectable nominal tomographic section thickness for which the dose profile is given according to paragraph (c)(2)(iv) of this section. (v) A description of the phantom or device and test protocol or procedure used to determine the specifications and a statement of the maximum deviation from the specifications provided in accordance with paragraphs (c)(3) (i), (ii), (iii), and (iv) of this section. Deviation of actual values may not exceed these limits. (d) Quality assurance. (1) A phantom(s) capable of providing an indication of contrast scale, noise, nominal tomographic section thickness, the spatial resolution capability of the system for low and high contrast objects, and measuring the mean CT number of water or a reference material. (2) Instructions on the use of the phantom(s) including a schedule of testing appropriate for the system, allowable variations for the indicated parameters, and a method to store as records, quality assurance data. (3) Representative images obtained with the phantom(s) using the same processing mode and CT conditions of operation as in paragraph (c)(3) of this section for a properly functioning system of the same model. The representative images shall be of two forms as follows: (i) Photographic copies of the images obtained from the image display device. (ii) Images stored in digital form on a storage medium compatible with the CT x-ray system. The CT x-ray system shall be provided with the means to display these images on the image display device. (e) [Reserved] (f) Control and indication of conditions of operation Visual indication. (2) Timers. (ii) Means shall be provided so that the operator can terminate the x-ray exposure at any time during a scan, or series of scans under x-ray system control, of greater than one-half second duration. Termination of the x-ray exposure shall necessitate resetting of the CT conditions of operation prior to the initiation of another scan. (g) Tomographic plane indication and alignment. (2) For any multiple tomogram system, means shall be provided to permit visual determination of the location of a reference plane. The relationship of the reference plane to the planes of the tomograms shall be provided to the user in addition to other information provided according to § 1020.30(h). This reference plane can be offset from the location of the tomographic planes. (3) The distance between the indicated location of the tomographic plane or reference plane and its actual location may not exceed 5 millimeters. (4) For any offset alignment system, the manufacturer shall provide specific instructions with respect to the use of this system for patient positioning, in addition to other information provided according to § 1020.30(h). (5) If a mechanism using a light source is used to satisfy the requirements of paragraphs (g) (1) and (2) of this section, the light source shall allow visual determination of the location of the tomographic plane or reference plane under ambient light conditions of up to 500 lux. (h) Beam-on and shutter status indicators. (2) For systems that allow high voltage to be applied to the x-ray tube continuously and that control the emission of x-ray with a shutter, the radiation emitted may not exceed 0.88 milligray (vice 100 milliroentgen exposure) in 1 hour at any point 5 cm outside the external surface of the housing of the scanning mechanism when the shutter is closed. Compliance shall be determined by measurements average over an area of 100 square cm with no linear dimension greater than 20 cm. (i) Scan increment accuracy. (j) CT number mean and standard deviation. (2) The manufacturer shall provide specific instructions concerning the use of the method provided for calculation of CT number mean and standard deviation in addition to other information provided according to § 1020.30(h). [49 FR 34712, Aug. 31, 1984; 49 FR 37381, Sept. 24, 1984, as amended at 49 FR 47388, Dec. 4, 1984; 56 FR 36098, Aug. 1, 1991; 67 FR 9587, Mar. 4, 2002; 70 FR 34042, June 10, 2005] § 1020.40 Cabinet x-ray systems. (a) Applicability. (b) Definitions. (1) Access panel (2) Aperture (3) Cabinet x-ray system cabinet (4) Door (5) Exposure (6) External surface (7) Floor (8) Ground fault (9) Port (10) Primary beam (11) Safety interlock (12) X-ray system (13) X-ray tube (c) Requirements Emission limit. (ii) Compliance with the exposure limit in paragraph (c)(1)(i) of this section shall be determined by measurements averaged over a cross-sectional area of ten square centimeters with no linear dimension greater than 5 centimeters, with the cabinet x-ray system operated at those combinations of x-ray tube potential, current, beam orientation, and conditions of scatter radiation which produce the maximum x-ray exposure at the external surface, and with the door(s) and access panel(s) fully closed as well as fixed at any other position(s) which will allow the generation of x radiation. (2) Floors. (3) Ports and apertures. (ii) The insertion of any part of the human body through any aperture shall not be possible. (4) Safety interlocks. (ii) Each access panel shall have at least one safety interlock. (iii) Following interruption of x-ray generation by the functioning of any safety interlock, use of a control provided in accordance with paragraph (c)(6)(ii) of this section shall be necessary for resumption of x-ray generation. (iv) Failure of any single component of the cabinet x-ray system shall not cause failure of more than one required safety interlock. (5) Ground fault. (6) Controls and indicators for all cabinet x-ray systems. (i) A key-actuated control to insure that x-ray generation is not possible with the key removed. (ii) A control or controls to initiate and terminate the generation of x-rays other than by functioning of a safety interlock or the main power control. (iii) Two independent means which indicate when and only when x-rays are being generated, unless the x-ray generation period is less than one-half second, in which case the indicators shall be activated for one-half second, and which are discernible from any point at which initiation of x-ray generation is possible. Failure of a single component of the cabinet x-ray system shall not cause failure of both indicators to perform their intended function. One, but not both, of the indicators required by this subdivision may be a milliammeter labeled to indicate x-ray tube current. All other indicators shall be legibly labeled “X-RAY ON”. (iv) Additional means other than milliammeters which indicate when and only when x-rays are being generated, unless the x-ray generation period is less than one-half second in which case the indicators shall be activated for one-half second, as needed to insure that at least one indicator is visible from each door, access panel, and port, and is legibly labeled “X-RAY ON”. (7) Additional controls and indicators for cabinet x-ray systems designed to admit humans. (i) A control within the cabinet for preventing and terminating x-ray generation, which cannot be reset, overridden or bypassed from the outside of the cabinet. (ii) No means by which x-ray generation can be initiated from within the cabinet. (iii) Audible and visible warning signals within the cabinet which are actuated for at least 10 seconds immediately prior to the first initiation of x-ray generation after closing any door designed to admit humans. Failure of any single component of the cabinet x-ray system shall not cause failure of both the audible and visible warning signals. (iv) A visible warning signal within the cabinet which remains actuated when and only when x-rays are being generated, unless the x-ray generation period is less than one-half second in which case the indicators shall be activated for one-half second. (v) Signs indicating the meaning of the warning signals provided pursuant to paragraphs (c)(7) (iii) and (iv) of this section and containing instructions for the use of the control provided pursuant to paragraph (c)(7)(i) of this section. These signs shall be legible, accessible to view, and illuminated when the main power control is in the “on” position. (8) Warning labels. Caution: X-Rays Produced When Energized (ii) There shall be permanently affixed or inscribed on the cabinet x-ray system adjacent to each port a clearly legible and visible label bearing the statement: caution: Do Not Insert Any Part of the Body When System is Energized—X-ray Hazard (9) Instructions. (ii) Manufacturers of cabinet x-ray systems which are intended to be assembled or installed by the purchaser shall provide instructions for assembly, installation, adjustment and testing of the cabinet x-ray system adequate to assure that the system is in compliance with applicable provisions of this section when assembled, installed, adjusted and tested as directed. (10) Additional requirements for x-ray baggage inspection systems. (i) During an exposure or preset succession of exposures of one-half second or greater duration, the means provided shall enable the operator to terminate the exposure or preset succession of exposures at any time. (ii) During an exposure or preset succession of exposures of less than one-half second duration, the means provided may allow completion of the exposure in progress but shall enable the operator to prevent additional exposures. (d) Modification of a certified system. [39 FR 12986, Apr. 10, 1974]