[Federal Register Volume 64, Number 127 (Friday, July 2, 1999)]
[Rules and Regulations]
[Pages 35924-35928]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-16835]


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DEPARTMENT OF HEALTH AND HUMAN SERVICES

Food and Drug Administration

21 CFR Part 1020

[Docket No. 98N-0877]


Medical Devices; Performance Standard for Diagnostic X-Ray 
Systems; Amendment

AGENCY: Food and Drug Administration, HHS.

ACTION: Final rule.

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SUMMARY: The Food and Drug Administration (FDA) is issuing a final rule 
that amends the diagnostic x-ray systems performance standard for 
dental panoramic systems and mammography systems. This rule exempts 
panoramic dental x-ray units from the requirement that they be 
manufactured with exposure timers that automatically reset to zero upon 
premature termination of an exposure. Removing the automatic timer 
reset requirement will not compromise the quality of the radiographic 
image and will protect patients from being subject to unnecessary 
radiation due to repeat radiographs. This action also is intended to 
align the performance standard for mammography systems with the 
equipment requirements issued under the Mammography Quality Standards 
Act of 1992 (the MQSA).

EFFECTIVE DATE: September 30, 1999.
FOR FURTHER INFORMATION CONTACT: Richard V. Kaczmarek, Center for 
Devices and Radiological Health (HFZ-240), Food and Drug 
Administration, 1350 Piccard Dr., Rockville, MD 20850, 301-594-0865.

SUPPLEMENTARY INFORMATION:

I. Background

A. Panoramic Dental Radiograph

    The requirements in Sec. 1020.31 (21 CFR 1020.31) apply to 
diagnostic x-ray systems, including those used for dental radiography 
and mammography. Based on information from manufacturers, FDA had 
determined that the timer requirement in Sec. 1020.31(a)(2)(i) should 
not apply to panoramic dental units. As a result of that determination, 
FDA exercised its enforcement discretion and did not apply the timer 
requirement to panoramic dental units. Some States had adopted local 
standards that were identical in language to FDA's regulation, but did 
not exempt panoramic dental units from the timer requirement because 
those units were not expressly exempted in the Federal regulation. 
Those States were applying the timer requirement to dental panoramic 
units. To correct this inconsistency, FDA has amended the regulations 
to expressly exempt panoramic dental units from the timer requirement 
in Sec. 1020.31(a)(2)(i). This change should lead to consistency among 
government requirements.

B. Mammography X-Ray Devices

    The recent passage of the MQSA (Pub. L. 102-539) and issuance of 
the interim and final MQSA regulations have focussed attention on the 
mammography equipment requirements contained in 21 CFR part 1020. 
Although the MQSA is directed to facility requirements for maintaining 
mammography quality, both the interim and the final MQSA regulations 
address x-ray equipment that is also subject to the performance 
standard for diagnostic x-ray systems (58 FR 67558 and 58 FR 67565, 
December 21, 1993; and 62 FR 55976, October 28, 1997). The MQSA and 
FDA's regulations governing mammography establish quality standards for 
facilities performing mammography to ensure safe, reliable, and 
accurate mammography nationwide. FDA wanted to ensure that the 
standards applying to radiation emitting electronic products, including 
mammography equipment, and those applying to the facilities that use 
such equipment were in accord. To bring the standards into harmony, FDA 
has amended its performance standard for diagnostic x-ray systems.
    The MQSA standards also address the proper viewing of mammography 
films. The standard practice is that these films be read on view boxes 
(light boxes) with the ambient room light levels reduced. Unexposed 
film areas and parts of the light box not covered by exposed film 
should be masked to prevent the bright light surrounding the radiograph 
from interfering with reading the film.
    Extending the x-ray field to expose the borders of the film 
simplifies the work of the radiologist and accreditation bodies because 
they have to create only one mask size, rather than having to create 
individualized masks for each facility. With the current practice being 
to irradiate the same area of the same sized film for all patients, 
there is little evidence that allowing the x-ray field to completely 
darken the film will significantly raise the radiation safety risk to 
the patient. FDA has amended the diagnostic x-ray systems standard to 
allow fixed aperture and variable aperture beam-limiting device (BLD) 
systems, to open up or adjust the field size to cover the entire film 
and thus reduce the need to provide a different mask for each film. In 
certain instances, limiting the x-ray field to the size of the breast 
may be considered to be advantageous. Practitioners still retain this 
option, which may result in improved imaging quality due to the 
reduction of scattered radiation.
    To reduce unnecessary radiation exposure to the patient beyond the 
plane of the image receptor, FDA has requirements for x-ray field 
limitation and alignment. In the past, all systems in use for 
mammography had fixed aperture plates for x-ray field limitation. The 
advent of the variable aperture BLD for mammography is potentially a 
problem with respect to the primary barrier requirement if a BLD is 
opened so that the useful beam extends beyond the primary barrier 
provided by the image receptor support device. To prevent this problem, 
a variable aperture BLD must provide some restriction on the maximum 
field size to ensure that the entire useful beam at the plane of the 
image receptor is contained within the image receptor support device, 
which is also a primary barrier. In other words, for a fixed aperture 
or a variable aperture BLD with the collimator opened as wide as 
possible, the entire useful beam should not extend beyond the barrier, 
at any available source-image receptor distance (SID), except at the 
chest wall side, and the exposure level 5 centimeters beyond this 
barrier should not exceed 2.58X10-8 coulombs per kilogram 
(C/k) (0.1 milliroentgen (mR)) per exposure. This requirement is in 
agreement with the International Electrotechnical Commission (IEC) 
draft standard for mammography systems (IEC 62B/60601-2-45).

II. The Final Rule

    FDA believes that the final rule establishes reasonable 
requirements that can be implemented by the regulated industry without 
unnecessary burden. None of the comments on the proposed rule requested 
that FDA revise any of the changes proposed.

A. Panoramic Dental Radiograph

    The final rule exempts panoramic dental x-ray units from the 
requirement in Sec. 1020.31(a)(2)(i) that they be

[[Page 35925]]

manufactured with exposure timers that automatically reset to zero upon 
premature termination of an exposure. This change incorporates into 
regulation current FDA policy and should lead to consistency among 
Federal, State, and local requirements.

B. Mammography X-Ray Devices

    The MQSA requires that only x-ray equipment specifically designed 
for mammography can be used for mammography. Therefore, FDA has removed 
the reference in Sec. 1020.31(f)(3), which allowed the use of general 
purpose x-ray equipment with special attachments for mammography. This 
change harmonizes this regulation with the MQSA equipment requirements.
    Section 1020.31 permits the x-ray irradiation field at the plane of 
the image receptor to extend to the edges of the x-ray film. However, 
to protect the patient from unnecessary exposure to radiation, the 
mammographic field alignment requirement restricts the irradiation beam 
from extending beyond the edge of the receptor by no more than 2 
percent of the SID. The limit on x-ray transmission through the primary 
barrier (except on the chest wall edge) remains unchanged. FDA has 
added the words ``for transmission'' to Sec. 1020.31(m)(4) to further 
clarify the section.
    The definition for ``image receptor support device'' replaces the 
definition of ``image receptor support'' and clarifies that image 
receptor support devices must provide a primary protective barrier for 
any orientation of the x-ray tube and the image receptor support device 
(except the chest wall side). This revision maintains the requirement 
in the current Sec. 1020.31(m) that the image receptor support device 
must serve to provide a primary protective barrier that intercepts the 
useful beam. Equipment manufactured prior to the effective date of this 
rule has always been, and will continue to be, subject to the 
requirement that the primary barrier must intercept the useful beam.
    Unlike fixed aperture systems, which meet the established primary 
barrier requirement, with variable aperture collimation there is the 
possibility that the dimensions of the x-ray beam may be adjusted to 
exceed the area of the image receptor. This requirement confines the x-
ray beam to the dimensions of the primary barrier provided by the image 
receptor support device, except on the chest wall side.
     FDA has clarified the requirement that patient exposures not be 
permitted without an appropriate primary barrier in place, by stating 
the requirement explicitly. FDA further clarifies the requirement by 
adding the word appropriate prior to primary barrier. FDA wants to 
clarify that it is not appropriate for a mammographic x-ray system to 
generate x-rays with an inappropriate image receptor support device in 
place. To reduce radiation exposure to the patient, the rule provides 
that the image receptor support device, acting as the primary barrier, 
must be in place before a mammographic x-ray system can generate x-
rays. This requirement requires the image receptor support device be 
interlocked with the system so that an exposure cannot be made with the 
image receptor support device removed.

C. Effective Date

    This rule will be effective in 90 days. Usually, amendments to 
performance standards for electronic products become effective 1 year 
after the date of publication of the final rule to allow sufficient 
time for manufacturers to implement the changes in design or production 
practices (21 U.S.C. 360kk(c)). In the proposed rule, FDA explained its 
good cause basis for proposing a shorter timeframe, namely that the 
amendments were codifying current industry practice, making regulatory 
requirements consistent, or relaxing requirements, and requested 
comments on the proposed shortening of the timeframe. No comments were 
received. Consequently, this rule becomes effective September 30, 1999.

III. The Proposed Rule

    In the Federal Register of October 29, 1998 (63 FR 57957), FDA 
published a proposed rule to amend the performance standard for 
diagnostic x-ray systems (dental and mammographic systems 
requirements). The proposed rule contained the reasons for the proposed 
amendment, summarized the Technical Electronic Product Radiation Safety 
Standards Committee's recommendation regarding dental and mammographic 
systems, and delineated the statutory authority under which FDA issues 
this rule. The proposed rule also stated FDA's grounds showing good 
cause for prescribing an earlier effective date than 1 year after the 
date of publication of the final rule for these amendments to the 
performance standard and solicited specific comment on the timeframe 
for implementation of the final rule. Written comments were due January 
27, 1999.
    FDA received three comments, one each from a manufacturer, a 
professional society, and a State agency. All three comments supported 
the actions proposed in the rule. None of the comments commented on the 
timeframe for implementation of the final rule.

IV. Response to Comments

    All three comments supported the actions proposed in the rule. One 
of the comments requested clarification concerning Sec. 1020.31(m)(2), 
which would require that the x-ray tube shall not permit exposure 
unless the barrier is in place to intercept the useful beam. The 
concern was whether the manufacturer would be held responsible if an 
individual equipment owner chose to partially dismantle the system or 
bypass interlocks so that the x-ray tube could be operated with the 
primary barrier removed. The comment stated that such action would 
violate Sec. 1020.30(q)(2), which prohibits the owner of the equipment 
from modifying the equipment such that it would no longer comply with 
Sec. 1020.31. In such a case, the comment argued that FDA should cite 
the owner, not the manufacturer, for noncompliance.
    FDA agrees that a manufacturer should not be held responsible 
should an owner circumvent the interlocks to operate the system with 
the primary barrier removed. The regulation does not require the 
manufacturer to design an interlock that cannot be defeated. A 
modification by the owner that makes the unit noncompliant with 
Secs. 1020.31(m)(2) and 1020.30(q) may cause the device to be 
misbranded and adulterated. FDA could bring an action against the 
person who caused the misbranding and adulteration and also seek to 
enjoin use of the device.
    None of the comments include any recommendations on the timeframe 
for implementation of the final rule or suggest that FDA does not have 
good cause for shortening the customary 1-year period. FDA believes 
that unneeded delay in the implementation of these amendments could 
lead to difficulties for mammography facilities because of confusion 
over the requirements of the x-ray performance standard and standards 
issued under the MQSA. In addition, because the amendments clarify a 
provision of the Federal standard, FDA believes it is in the best 
interests of patients, facilities, and manufacturers to implement the 
dental x-ray equipment amendment expeditiously. For these reasons, the 
effective date of the final rule will be 90 days after date of 
publication in the Federal Register.

V. Environmental Impact

    The agency has determined under 21 CFR 25.30(a) and (i) and 
25.34(c) that

[[Page 35926]]

this action is of a type that does not individually or cumulatively 
have a significant effect on the human environment. Therefore, neither 
an environmental assessment nor an environmental impact statement is 
required.

VI. Analysis of Impacts

    FDA has examined the impact of this final rule under Executive 
Order 12866 and the Regulatory Flexibility Act (5 U.S.C. 601-612) (as 
amended by subtitle D of the Small Business Regulatory Fairness Act of 
1996 (Pub. L. 104-121)), and the Unfunded Mandates Reform Act of 1995 
(Pub. L. 104-4). Executive Order 12866 directs agencies to assess all 
costs and benefits of available regulatory alternatives and, when 
regulation is necessary, to select regulatory approaches that maximize 
net benefits (including potential economic, environmental, public 
health and safety, and other advantages; distributive impacts; and 
equity). The agency believes this final rule is consistent with the 
regulatory philosophy and principles identified in the Executive Order. 
In addition, the final rule is not a significant regulatory action as 
defined by the Executive Order and therefore is not subject to review 
under the Executive Order.
    The Regulatory Flexibility Act requires agencies to analyze 
regulatory options that would minimize any significant impact of a rule 
on small entities. Because this final rule increases the flexibility of 
the performance standard and codifies current interpretations of 
Federal regulations in order to prevent inconsistent interpretations by 
State and local governments, and because none of the domestic 
manufacturers of panoramic dental units or mammography x-ray systems 
would be considered small entities, the agency certifies that the final 
rule will not have a significant economic impact on a substantial 
number of small entities engaged in manufacturing. Because dental and 
mammography facilities will buy machines with the changes to the 
performance standard allowed in this final rule only if it is 
economically advantageous to do so, the agency certifies that the final 
rule will not have a significant economic impact on a substantial 
number of small entities that are facilities (most, if not all, of 
which would be considered small entities). Therefore, under the 
Regulatory Flexibility Act, no further analysis is required.
    In the proposed rule, FDA conducted and published an initial 
regulatory flexibility analysis to ensure that impacts on small 
entities were assessed and to alert any potentially impacted entities 
to the opportunity to submit comments to this agency. No comments on 
the initial regulatory flexibility analysis were submitted. This final 
rule will not impose costs of $100 million or more in either the 
private sector or State, local, and tribal governments in the 
aggregate. Consequently, a summary statement of analysis under section 
202(a) of the Unfunded Mandates Reform Act of 1995 is not required.
    In part, the final rule codifies the equipment performance 
standards established under the MQSA by requiring only x-ray systems 
designed specifically for mammography be marketed for mammography. This 
rule updates the x-ray performance standard to reflect a standard 
already enforced under the MQSA. Consequently, FDA expects no economic 
impact from this portion of the final rule.
    The final rule also permits the x-ray irradiation field to extend 
to the edges of the x-ray film but not beyond the primary barrier 
provided by the image receptor support device. It further changes the 
definition of an image receptor support device, clarifying that it must 
provide a primary protective barrier and that exposures not be possible 
without the image receptor support device being in place, acting as the 
primary barrier. Exposing all of the film allows one size of film mask 
to be used for proper viewing of mammography films using light boxes 
and prohibiting extension of the beam beyond the primary barrier 
protects the patient from unnecessary exposure to radiation. The 
amendment to relax the field edge alignment criteria will not require 
any changes to x-ray mammography systems that are currently compliant; 
these systems will remain compliant after the effective date. The 
amendment will, however, allow the user to modify or purchase a 
collimator that has the ability to provide films without light borders 
as a convenience in simplifying viewing conditions. FDA believes that 
most of the image receptor support devices that are currently in use 
meet the requirements in the amendments to Secs. 1020.30(b) and 
1020.31(m). In addition, when the manufacturer's design of the cassette 
holder provides the primary barrier attenuation itself, then the 
cassette holder is considered a part of the image receptor support 
device. Therefore, FDA estimates that the amendments to 
Secs. 1020.30(b) and 1020.31(m) will impose minimal new costs. This 
rule also allows more flexibility for mammography facilities and 
accreditation bodies without compromising the public health and may 
reduce costs to mammography facilities and accreditation bodies by 
simplifying the masking of images.
    The final rule exempts panoramic x-ray dental units from the 
requirement that they be manufactured with exposure timers that 
automatically reset to zero or the initial setting upon premature 
termination of an exposure. For panoramic dental exposures, 
interrupting the exposure does not affect the quality of images already 
taken. Consequently, restarting the exposure at the initial starting 
point exposes patients to unnecessary radiation. This rule removes a 
regulatory requirement, while still protecting the public health, and 
may reduce costs to dental facilities and patients. FDA has identified 
no new reporting, recordkeeping, or other compliance requirements 
associated with this rule.
    The Safe Medical Devices Act of 1990 (Pub. L. 101-629) enacted on 
November 28, 1990, transferred the provisions of the Radiation Control 
for Health and Safety Act of 1968 (Pub. L. 90-602) from Title III of 
the Public Health Service Act (42 U.S.C. 201 et seq.) to Chapter V of 
the Federal Food, Drug, and Cosmetic Act (21 U.S.C. 201 et seq.). These 
provisions regulate electronic products that emit radiation. On October 
27, 1992, the MQSA was enacted to establish uniform, national quality 
standards for mammography. The MQSA (42 U.S.C. 263b(f)(1)(B)) requires 
the use of radiological equipment specifically designed for mammography 
to be used for mammography. Similarly, 21 CFR 900.12(b)(1) of the 
interim and final mammography regulations prohibits the use of 
conventional radiographic equipment for mammography.
    There are approximately 10,000 mammography facilities in the United 
States. Because this change in the performance standard only applies to 
components manufactured after the effective date of the final rule, the 
associated cost does not apply to those machines manufactured prior to 
that date. FDA estimates that approximately 10 percent of facilities 
replace their mammography machines in any one year. At this time, FDA 
is unable to estimate the demand for the modifications to systems 
currently in use. As discussed previously, the change concerning x-ray 
beam collimation is less restrictive than the present standard. FDA 
estimates the cost per system to be between $0 and $5,000, if the 
system modification is made during production.
    There are approximately 138,500 dental facilities in the United 
States of

[[Page 35927]]

which 40 percent provide access to panoramic dental x-ray units. An 
uncertain number of these facilities may request the manufacturer to 
remove the automatic reset of the exposure timer on their panoramic 
machines; however, they are not required to do so. FDA believes that 
the facility will only make this change if it is economically or 
clinically advantageous to do so. FDA estimates it will cost a facility 
an amount equal to what would be assessed for a routine service call 
(approximately $150.00 or less) to remove the automatic reset function 
for premature termination of an exposure for existing systems. FDA 
believes that manufacturers no longer manufacture panoramic dental x-
ray units with automatic reset exposure times.
    Most, if not all, of the mammography facilities and dental 
facilities would be considered small under the criteria establishment 
by the Small Business Administration. FDA's registration system shows 
five manufacturers of panoramic dental units. Of the domestic 
manufacturers, none would be considered small entities. There are 
approximately 10 manufacturers of mammography x-ray systems. Of these 
manufacturers, none would be considered small entities.
    For the mandatory changes to image receptor support devices, FDA 
believes that most of the image receptor support devices that are 
currently in use provide a primary barrier that is capable of meeting 
the requirements in the amendments to Secs. 1020.30(b) and 1020.31(m). 
There are approximately 10,000 mammography facilities in the United 
States. Because this change in the performance standard only applies to 
systems manufactured after the effective date of a final rule, the 
costs associated with any changes that may need to be made, would not 
apply to those machines manufactured prior to that date. FDA estimates 
that approximately 10 percent of facilities replace their mammography 
systems in any one year (10 percent of 10,000 = 1,000). FDA estimates 
the cost per system to be between $0 and $2,000 in the event that any 
manufacturers are required to implement design or production changes to 
ensure that exposures not be permitted on their systems without a 
primary barrier being in place. FDA estimates approximately 95 percent 
of systems currently being marketed already meet this requirement. With 
an annual mammography system replacement rate of 10 percent (i.e., 
1,000 new systems purchased per year), FDA estimates only approximately 
5 percent of these 1,000 systems may increase the cost to meet the 
requirement. To calculate the annual cost, FDA estimates a cost of $0 
to $2,000 per system multiplied by 50 systems (5 percent of 1,000 = 
50). Using this estimate, the costs are expected to be approximately $0 
to $100,000.
    Under these changes to the performance standard, FDA allows 
manufacturers and facilities to decide whether to implement any device 
modifications in response to the greater flexibility in these 
mammography collimation requirements. If the benefits associated with 
the flexibility in this rulemaking are outweighed by the costs to the 
facility, the facility can choose to not purchase a device that has 
been modified in response to the greater flexibility in this 
rulemaking. With regard to the mandatory change, FDA believes that the 
great majority of the image receptor support devices that are currently 
being manufactured provide a primary barrier that is capable of meeting 
the requirements in the amendment to Sec. 1020.31(m). Therefore, FDA 
does not anticipate that the amendment to Sec. 1020.31(m) will impose 
any significant costs.
    Because most of these changes to the mammography performance 
standard and the change to the timer requirement for panoramic dental 
systems do not increase regulatory burdens, FDA considered no 
alternatives to accomplish the stated objectives of the applicable 
statutes. For the primary barrier standard in Sec. 1020.31(m), FDA 
considered not requiring the primary barrier to be in place to 
intercept the useful beam. This alternative was rejected because 
without the primary barrier in place, patients would be exposed to 
unnecessary radiation.

VII. Paperwork Reduction Act of 1995

    This final rule contains no collections of information. Therefore, 
clearance by the Office of Management and Budget under the Paperwork 
Reduction Act of 1995 is not required.

List of Subjects in 21 CFR Part 1020

    Electronic products, Medical devices, Radiation protection, 
Reporting and recordkeeping requirements, Television, X-rays.
    Therefore, under the Federal Food, Drug, and Cosmetic Act and under 
authority delegated to the Commissioner of Food and Drugs, 21 CFR part 
1020 is amended as follows:

PART 1020--PERFORMANCE STANDARDS FOR IONIZING RADIATION EMITTING 
PRODUCTS

    1. The authority citation for 21 CFR part 1020 continues to read as 
follows:

    Authority: 21 U.S.C. 351, 352, 360e-360j, 360gg-360ss, 371, 381.

    2. Section 1020.30 is amended in paragraph (b) by removing the 
definition of ``image receptor support'' and adding a new definition in 
alphabetical order to read as follows:


Sec. 1020.30  Diagnostic x-ray systems and their major components.

* * * * *
    (b) * * *
    Image receptor support device means, for mammography x-ray systems, 
that part of the system designed to support the image receptor during a 
mammographic examination and to provide a primary protective barrier.
* * * * *
    3. Section 1020.31 is amended by revising paragraphs (a)(2)(i), 
(f)(3), and (m) to read as follows:

Sec. 1020.31  Radiographic equipment.

* * * * *
    (a) * * *
    (2) * * *
    (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.
* * * * *
    (f) * * *
    (3) Systems designed for mammography. (i) Mammographic beam-
limiting devices manufactured after September 30, 1999, shall be 
provided with means to limit the useful beam such that the x-ray field 
at the plane of the image receptor does not extend beyond any edge of 
the image receptor by more than 2 percent of the SID. This requirement 
can be met with a system that performs as prescribed in paragraphs 
(f)(4)(i), (f)(4)(ii), and (f)(4)(iii) of this section. For systems 
that allow changes in the SID, the SID indication specified in 
paragraphs (f)(4)(ii) and (f)(4)(iii) of this section shall be the 
maximum SID for which the beam-limiting device or aperture is designed.
    (ii) Each image receptor support device intended for installation 
on a system designed for mammography shall have clear and permanent 
markings to indicate the maximum image receptor size for which it is 
designed.
* * * * *

[[Page 35928]]

    (m) Primary protective barrier for mammography x-ray systems. For 
mammography x-ray systems manufactured after September 30, 1999:
    (1) At any SID where exposures can be made, the image receptor 
support device shall provide a primary protective barrier that 
intercepts the cross section of the useful beam along every direction 
except at the chest wall edge.
    (2) The x-ray tube shall not permit exposure unless the appropriate 
barrier is in place to intercept the useful beam as required in 
paragraph (m)(1) of this section.
    (3) The transmission of the useful beam through the primary 
protective barrier shall be limited such that the exposure 5 
centimeters from any accessible surface beyond the plane of the primary 
protective barrier does not exceed 2.58X10-8 C/kg (0.1 mR) 
for each activation of the tube.
    (4) Compliance for transmission shall be determined with the x-ray 
system operated at the minimum SID for which it is designed, at the 
maximum rated peak tube potential, at the maximum rated product of x-
ray tube current and exposure time (mAs) for the maximum rated peak 
tube potential, and by measurements averaged over an area of 100 square 
centimeters with no linear dimension greater than 20 centimeters. The 
sensitive volume of the radiation measuring instrument shall not be 
positioned beyond the edge of the primary protective barrier along the 
chest wall side.

    Dated: June 16, 1999.
Margaret M. Dotzel,
Acting Associate Commissioner for Policy Coordination.
[FR Doc. 99-16835 Filed 7-1-99; 8:45 am]
BILLING CODE 4160-01-F