10-144-220 Me. Code R. § F-7

Current through 2024-51, December 18, 2024

Section 144-220-F-7 - Radiographic systems other than fluoroscopic, dental intraoral or veterinarian systems

A. Beam limitation. The useful beam shall be limited to the area of clinical interest.

(1) General purpose stationary and mobile x-Ray systems.

(a) There shall be provided a means for stepless adjustment of the size of the x-ray field.

(b) For those units so designed, 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.

(c) The Agency may grant an exemption on non-certified x-ray systems to F.7.A.(1)(a) and (b) provided the registrant makes a written application for such exemption and in that application:

(i) Demonstrates it is impractical to comply with F.7.A.(1)(a) and (b); and

(ii) The purpose of F.7.A.(1)(a) and (b) will be met by other methods.

(2) Additional requirements for stationary general purpose x-ray systems. In addition to the requirements of F.7.A.(1), all stationary general purpose x-ray systems shall meet the following requirements:

(a) 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;

(b) The beam-limiting device shall indicate numerically the field size in the plane of the image receptor to which it is adjusted; and

(c) Indication of field size dimensions 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.

(3) 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.

(4) Mammography equipment standards. Only x-ray systems meeting the following standards shall be used:

(a) System design: The x-ray system shall be specifically designed for mammography.

(b) Image receptor: The image receptor systems and their individual components shall be specifically designed for or appropriate for mammography.

(c) Radiographic systems designed for mammography 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, which performs as prescribed in F.7.A.(5).

(5) Special purpose x-ray systems.

(a) 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.

(b) 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.

(c) F.7.A(5)(a) and (b) may be met with a system that meets the requirements for a general purpose x-ray system as specified in F.7.A(1) 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.

B. Radiation exposure control devices.

(1) Timers. 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. In addition, it shall not be possible to make an exposure when the time is set to a zero or off position if either position is provided.

(2) Manual Exposure Control.

(a) An x-ray control shall be incorporated into each x-ray system such that an exposure can be terminated by the operator at any time except for:

(i) Exposure of one-half 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.

(b) Each x-ray control shall be located in such a way as to meet the following requirements:

(i) Stationary x-ray systems shall be required to have the x-ray control permanently mounted in a protected area so that the operator is required to remain in that protected area during the entire exposure; and

(ii) Mobile and portable x-ray systems which are:

(a) Used for greater than one week in the same location, i.e., a room or suite, shall meet the requirements of F.7.B.(2)(b)(i)

(b) Used for greater than one hour and less than one week at the same location, i.e., one room or suite, shall meet the requirement of F.7.B.(2)(b)(ii)(a) or be provided with a 6.5 feet (1.98m) high protective barrier which is placed at least 6 (1.83m) feet from the tube housing assembly and at least 6 (1.83m) feet from the patient; or

(c) Used to make an exposure(s) of a patient at the use location shall meet the requirement of F.7.B.(2)(b)(ii)(a) or(b) or be provided with a method or x-ray control which will permit the operator to be at least six feet (3.66m) from the tube housing assembly during an exposure.

(iii) The x-ray control shall provide visual indication observable at or from the operator's protected position whenever x-rays are produced. In addition, a signal audible to the operator, if available with the unit, shall indicate that the exposure has terminated.

(3) Automatic exposure controls. When an automatic exposure control is provided:

(a) Indication shall be made on the control panel when this mode of operation is selected;

(b) 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;

(c) The minimum exposure time for all equipment other than that specified in F.7.B.(3)(b) shall be equal to or less than one-sixtieth second or a time interval required to deliver 5 mAs, whichever is greater;

(d) 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 in which case the product of x-ray tube current and exposure time shall be limited to not more than 2000 mAs per exposure; and

(e) A visible signal shall indicate when an exposure has been terminated at the limits required by F.7.B(3)(d), and manual resetting shall be required before further automatically timed exposures can be made.

(4) Reproducibility. With a timer setting of 0.5 seconds or less, the average exposure period (T) shall be greater than or equal to five times the maximum exposure period (Tmax) minus the minimum exposure (Tmin) when four timer tests are performed; i.e., T > 5 (Tmax -Tmin).

C. Source-to-skin distance. All mobile or portable radiographic systems shall be provided with means to limit the source-to-skin distance to not less than 30 centimeters.

D. Exposure reproducibility. The coefficient of variation of exposure shall not exceed 0.10 when all technique factors are held constant. This requirement shall be deemed to have been met if, when four exposures are made at identical technique factors, that the value of the average exposure (E) is greater than or equal to five times the maximum exposure (Emax) minus the minimum exposure (Emin), i.e., E > 5 (Emax - Emin).

E. 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 mC/kg) per hour at 5 centimeters from any accessible surface of the diagnostic source assembly with the beam-limiting device fully open.

F. 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).

(1) Reproducibility. When the equipment is operated on an adequate power supply as specified by the manufacturer in accordance with the requirements of applicable Federal standards, the estimated coefficient of variation of radiation exposures shall be no greater than 0.05, for any specific combination of selected technique factors.

(2) 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, any fixed x-ray tube potential within the range of 40 percent to 100 percent of the maximum rating, the average ratios of exposure to the indicated milliampere-seconds product, i.e., mR/mAs, obtained at any two consecutive tube current settings shall not differ by more than 0.10 times their sum,

X1-X2 < 0.10 (X1 + X2),

where X1 and X2 are the average mR/mAs values obtained at each of two consecutive tube current settings.

(3) Accuracy. Deviation of technique factors from indicated values shall not exceed the limits specified for that system by its manufacturer. In the absence of the manufacturer's specifications the deviation shall not exceed 10% of the indicated value.

(4) Beam limitation for stationary and mobile general purpose x-ray systems.

(a) There shall be provided a means of stepless adjustment of the size of the x-ray field.

(b) 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 or after May 27, 1980, are exempt from this requirement.

(c) The edge of the light field at 100 centimeters or at the maximum SID, whichever is less, shall have a contrast ratio, corrected for ambient lighting, of not less than 4 in the case of beam-limiting devices designed for use on stationary equipment, and a contrast ratio of not less than 3 in the case of beam-limiting devices designed for use on mobile equipment. The contrast ratio is defined as I1/I2 when I1 is the illumination 3 millimeters from the edge of the light field toward the center of the field; and I2 is the illumination 3 millimeters from the edge of the light field away from the center of the field. Compliance shall be determined with a measuring instrument aperture of 1 millimeter in diameter.

(5) Beam limitation for portable x-ray systems. Beam limitation for portable x-ray systems shall meet the beam limitation requirements of F.7.A.(1). and F.7.F.(4).

(6) 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):

(a) Positive beam limitation (PBL) when present shall function 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;

(vi) 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 F.7.F(6)(c).

(b) 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 F.7.F(6)(e) 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 F.7.F(6)(b)(i) without regard to sign exceeds 4 percent of the SID.

(c) If a means of overriding the positive beam limitation 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,

(a) Shall require that a key be utilized to defeat the PBL;

(b) Shall require that the key remain in place during the entire time the PBL system is overridden; and

(c) Shall require that the key or key switch be clearly and durably labeled as follows:

FOR X-RAY FIELD LIMITATION SYSTEM FAILURE

(d) Compliance with F.7.F.6(b) shall be determined when the equipment indicates that the beam axis is perpendicular to the plane of the image receptor and the provisions of F.7.F(6)(a) are met. Compliance shall be determined no sooner than five seconds after insertion of the image receptor.

(e) 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.

(f) 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 F.7.F.(6)(b), then any change of image receptor size or SID must cause the automatic return.

(7) Timers. Except for dental panoramic systems, termination of exposure shall cause automatic resetting of the timer to its initial setting or to zero.

(8) Transmission limit for image receptor supporting devices used for mammography. For x-ray systems manufactured after September 5, 1978 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 exposure 5 centimeters from any accessible surface beyond the plane of the image receptor supporting device does not exceed 0.1 milliroentgen (25.8 nC/kg) for each activation of the tube. Exposure shall be measured with the system operated at the minimum SID for which it is designed. Compliance shall be determined at the maximum rate peak tube potential for the system and at the maximum rated product of the tube current and exposure time (mAs) for that peak tube potential. Compliance shall be determined by measurements averaged over an area of 100 square centimeters with no linear dimension greater than 20 centimeters.

10-144 C.M.R. ch. 220, § F-7