Radiographic Systems Other Than Fluoroscopic, Dental Intraoral,

Radiographic Systems Other Than Fluoroscopic, Dental Intraoral, Veterinarian, Computed Tomography, or Mammography Systems. 1. Beam Limitation. The useful beam shall be limited to the area of clinical interest. This shall be deemed to have been met if a positive beam-limiting device has been properly used or if evidence of collimation is shown on at least three sides or three corners of the film, (for example, projections from the shutters of the collimator, cone cutting at the corners, or borders at the film's edge). a. General Purpose Stationary and Mobile X-Ray Systems. i. The use of a variable-field beam limiting device providing stepless, independent adjustment of at least two dimensions of the x-ray field is required. ii. A method shall be provided for visually defining the perimeter of the x-ray field. 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. iii. The Agency may grant an exemption on noncertified x-ray systems to 1.6.6(1)(a)(i) and (ii) provided the registrant makes a written application for such exemption and in that application: i. demonstrates it is impractical to comply with 1.6.6(1)(a)(i) and (ii); and ii. the purpose of 1.6.6(1)(a)(i) and (ii) will be met by other methods. b. Additional Requirements for Stationary General Purpose X-Ray Systems. In addition to the requirements of 1.6.6(1)(a), all stationary general purpose x-ray systems shall meet the following requirements: i. A method 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. ii. The beam-limiting device shall indicate numerically the field size in the plane of the image receptor to which it is adjusted. iii. Indication of field size dimension and SID's shall be specified in inches and/or centimeters, 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. c. 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. d. Radiographic Systems Other Than Those Designated in 1.6.6(1)(a),(b), and (c). i. Means shall be provided 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. ii. 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. Compliance shall be determined with the axis of the x-ray beam perpendicular to the plane of the image receptor. iii. 1.6.6(1)(d)(i) and (ii) may be met with a system that meets the requirements for a general purpose x-ray system as specified in 1.6.6(1)(a) or, when alignment means are also provided, may be met with either: i. 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 with each such device having clear and permanent markings to indicate the image receptor size and SID for which it is designed; or ii. 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. 2. Radiation Exposure Control a. Exposure Initiation. Means shall be provided to initiate the radiation exposure by a positive action on the part of the operator, such as the depression of a switch. Radiation exposure shall not be initiated without such a positive action. In addition, it shall not be possible to initiate an exposure when the timer is set to a "zero" or "off" position if either position is provided. b. Exposure Termination. Means shall be provided to terminate the exposure at a preset time interval, preset product of current and time, a preset number of pulses, or a preset radiation exposure to the image receptor. Termination of an exposure shall cause automatic resetting of the timer to its initial setting or to "zero." i. Manual exposure control. An x-ray exposure control shall be incorporated into each x-ray system such that an exposure can be terminated by the operator at any time ("dead-man" switch) except for: i. exposure of 1/2 second or less; or ii. during serial radiography when means shall be provided to permit completion of any single exposure of the series in process. ii. Automatic exposure control. When an automatic exposure control is provided: i. indication shall be made on the control panel when this mode of operation is selected; ii. if the x-ray tube potential is equal to or greater than 50 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; iii. the minimum exposure time for all equipment other than that specified in 1.6.6(2)(b)(ii)(ii) shall be equal to or less than 1/60 second or a time interval required to deliver 5 mAs, whichever is greater; iv. either the product of peak x-ray tube potential, current, and exposure time shall be limited to not more than 60 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 that when the x-ray tube potential is less than 50 kVp, the product of x-ray tube current and exposure time shall be limited to not more than 2000 mAs per exposure; and v. a visible signal shall indicate when an exposure has been terminated at the limits required by 1.6.6(2)(ii)(iv), and manual resetting shall be required before further automatically timed exposures can be made. c. Exposure Indication. Means shall be provided for visual indication of x-ray production observable at or from the operator's protected position whenever x-rays are produced. In addition, a signal audible to the operator shall indicate that the exposure has terminated. d. Exposure Duration (Timer) Reproducibility. With a timer setting of 0.5 seconds or less, the difference between the maximum exposure time (Tmax) and the minimum exposure time (Tmin) shall be less than or equal to 10% of the average exposure time ( T ), when four timer tests are performed: e. Exposure Control Location. The x-ray exposure control shall be so placed that the operator can view the patient while making any exposure. f. Operator Protection, Except Veterinary Systems. i. Stationary systems. Stationary x-ray systems shall be required to have the x-ray exposure control permanently mounted in a protected area so that the operator is required to remain in that protected area during the entire exposure. ii. Mobile and portable systems. Mobile and portable x-ray systems which are: i. used continuously for greater than one week in the same location, i.e., a room or suite shall be considered as stationary systems under 1.6.6(2)(f)(i); and ii. used for less than one week in the same location shall be provided with either a protective barrier at least 6.5 feet (2 m) high for operator protection during exposures, or means shall be provided to allow the operator to be at least 12 feet (3.7 m) from the tube housing assembly during the exposure. iii. Operation Protection for Veterinary Systems. All stationary, mobile or portable x-ray systems used for veterinary work shall be provided with either a 6.5 foot (2 m) high protective barrier for operator protection during exposures, or shall be provided with means to allow the operator to be at least 12 feet (3.7 m) from the tube housing assembly during exposures. 3. Source-to-Skin Distance. All mobile or portable radiographic systems shall be provided with means to limit the source-to-skin distance to equal to or greater than 30 centimeters, except for veterinary systems. 4. Exposure Reproducibility. When all technique factors are held constant, including control panel selections associated with automatic exposure control (phototiming) systems, the coefficient of variation of exposure for both manual and phototimed systems shall not exceed 0.05. This requirement shall be deemed to have been met, if, when four exposures are made at identical technique factors, the difference between the maximum exposure (Emax) and the minimum exposure ( Emin) shall be less than or equal to 10% of the average exposure( ): 5. Radiation from Capacitor Energy Storage Equipment in Standby Status. Radiation emitted from the x-ray tube when the exposure switch or timer is not activated shall not exceed a rate of 2 milliroentgens (0.516 µC/kg) per hour at 5 centimeters from any accessible surface of the diagnostic source assembly, with the beam-limiting device fully open. 6. Accuracy. Deviation of technique factors from indicated values shall not exceed the limits specified for that system by its manufacturer. In the absence of manufacturer's specifications, the deviation shall not exceed 10% of the indicated value. 7. Linearity, Uncertified X-Ray Systems Only. The following requirements apply when the equipment is operated on a power supply as specified by the manufacturer for any fixed x-ray tube potential within the range of 40 percent to 100 percent of the maximum rated. a. Equipment having independent selection of x-ray tube current (mA). The average ratios of exposure to the indicated milliampere-seconds product mR/mAs (C/kg/mAs) obtained at any two tube current settings shall not differ by more than 0.10 times their sum. This is: where and are the average mR/mAs (C/kg/mAs) values obtained at any two tube current settings. b. Equipment having a combined x-ray tube current-exposure time product (mAs) selector, but not a separate tube current (mA) selector. The average ratios of exposure to the indicated milliampere-seconds product mR/mAs (C/kg/mAs) obtained at any two mAs selector settings shall not differ by more than 0.10 times their sum. This is: where and are the average mR/mAs (C/kg/mAs) values obtained at any two mAs selector settings. c. Measuring compliance. Determination of compliance shall be based on 4 exposures, of no less than 0.05 seconds each, taken within a time period of one hour, at each of the two settings. These two settings may include any two focal spot sizes provided that neither focal spot size is equal to or less than 0.45 millimeter, in which case the two settings shall be restricted to the same focal spot size. For purposes of this requirement, focal spot size is the nominal focal spot size specified by the x-ray tube manufacturer. 8. Additional Requirements Applicable to Certified Systems Only. Diagnostic x-ray systems incorporating one or more certified component(s) shall be required to comply with the following additional requirement(s) which relate to that certified component(s). a. Linearity. When the equipment allows a choice of x-ray tube current settings and is operated on a power supply as specified by the manufacturer in accordance with the requirements of applicable Federal standards, for any fixed x-ray tube potential within the range of 40 to 100 percent of the maximum rating, the average ratios of exposure to the indicated milliampere-seconds product obtained at any 2 consecutive tube current settings shall not differ by more than 0.10 times their sum: where and are the average mR/mAs (C/kg/mAs) values obtained at each of 2 consecutive tube current settings. b. Beam Limitation for Stationary and Mobile General Purpose X-Ray Systems. i. There shall be provided a means of stepless adjustment of the size of the x-ray field. The minimum field size at an SID of 100 cm shall be equal to or less than 5 centimeters by 5 centimeters. ii. When a light localizer is used to define the x-ray field, it shall provide an average illumination of not less than 160 lux or 15 footcandles at 100 centimeters or at the maximum SID, whichever is less. The average illumination shall be based upon measurements made in the approximate center of each quadrant of the light field. Radiation therapy simulation systems manufactured on and after May 27, 1980, are exempt from this requirement. c. Beam Limitation for Portable X-Ray Systems. Beam limitation for portable x-ray systems shall meet the beam limitation requirements of 1.6.6(1)(a) and 1.6.6(7)(b). d. Field Limitation and Alignment on Stationary General Purpose X-Ray Systems. For stationary, general purpose x-ray systems which contain a tube housing assembly, an x-ray control, and, for those systems so equipped, a table, all certified in accordance with 21 CFR 1020.30(c): i. Positive beam limitation (PBL) shall be provided 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 each less than 50 centimeters; iii. The x-ray beam axis is within plus or minus 3 degrees of vertical and the SID is 90 centimeters to 130 centimeters inclusive; or the x-ray beam axis is within plus or minus 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 plus or minus 3 degrees; v. Neither tomographic nor stereoscopic radiography is being performed; and vi. The PBL system has not been intentionally overridden. This override provision is subject to 1.6.6(8)(d)(iii). ii. Positive beam limitation (PBL) shall prevent the production of x-rays when: i. Either the length or width of the x-ray field in the plane of the image receptor differs, except as permitted by 1.6.6(8)(d)(v), from the corresponding image receptor dimensions by more than 3 percent of the SID; or ii. The sum of the length and width differences as stated in 1.6.6 (8)(d)(ii)(i) without regard to sign exceeds 4 percent of the SID. iii. If a means of overriding the positive beam limitation (PBL) system exists, that means: i. Shall be designed for use only in the event of PBL system failure or if the system is being serviced; and ii. If in a position that the operator would consider it part of the operational controls or if it is referenced in the operator's manual or in other materials intended for the operator, i. shall require that a key be utilized to defeat the PBL; ii. shall require that the key remain in place during the entire time the PBL system is overridden; and iii. shall require that the key or key switch be clearly and durably labeled as follows: FOR X-RAY FIELD LIMITATION SYSTEM FAILURE iv. Compliance with 1.6.6(8)(d)(ii) shall be determined when the equipment indicates that the beam axis is perpendicular to the plane of the image receptor and the provisions of 1.6.6(8)(d)(i) are met. Compliance shall be determined no sooner than 5 seconds after insertion of the image receptor. v. The positive beam limitation system shall be capable of operation, at the discretion of the operator, such that the size of the field may be made smaller than the size of the image receptor through stepless adjustment of the field size. The minimum field size at a SID of 100 centimeters shall be equal to or less than 5 centimeters by 5 centimeters. vi. The positive beam limitation system shall be designed such that if a change in image receptor does not cause an automatic return to positive beam limitation function as described in 1.6.6(8)(d)(ii), then any change of image receptor size or SID must cause the automatic return. e. Timers. Except for dental panoramic systems, termination of exposure shall cause automatic resetting of the timer to its initial setting or to "zero." 9. Tube Stands for Portable X-Ray Systems. A tube stand or other mechanical support shall be used for portable x-ray systems so that the x-ray tube housing assembly need not be hand-held during exposures.