This guidance was written prior to the February 27, 1997 implementation of FDA's 
Good Guidance Practices, GGP's. It does not create or confer rights for or on any person 
and does not operate to bind FDA or the public. An alternative approach may be used if 
such approach satisfies the requirements of the applicable statute, regulations, or both. 
This guidance will be up dated in the next revision to include the standard elemnt s of GGP 's .  DEPARTMENT OF HEALTH 8t HUMAN SERVICES 
Public Health Service 
Memorandum 
Date 
horn 
Acting Chief, Diagnostic Devices Team, DOE I, OC 
CDRH (HFZ-300) 
Subject 
PBL and Other Changes to the Performance Standard; Small 
Target Angle X-Ray Tubes; Maximum EER  and Large Image 
To  Intensifiers 
Diagnostic X-Ray Compliance Testing Personnel and Selected 
Interested Federal and State Personnel 
Positive-Beam Limitation (PBL) Requirements 
Background 
On May 3, 1993, the FDA published a final rule in the Federal 
Register to amend the Performance Standard for Diagnostic 
X-Ray Systems and Their Major Components (Performance 
Standard).  This change allows assemblers to install manual 
beam-limiting devices (BLD) in stationary, general-purpose 
radiographic x-ray  (GP) systems.  The requirement that GP 
systems be equipped with PBL has been eliminated.  For those 
systems equipped with PBL, this proposal still contains the 
requirements that apply to PBL.  This change was effective 
June 2, 1993.  In our previous memorandum, dated April 15, 
1993, we provided interim guidance to field surveyors on the 
testing of certain radiographic systems. 
Policy 
This memorandum supersedes the April 15 memorandum.  All of 
the requirements for PBL still apply for assembled PBL 
systems.  The following represents testing guidance for GP 
systems: 
1.  Routine testing of GP systems equipped with an x-ray 
table should continue, using the Abovetable X-Ray Source 
Radiographic Systems (AR) test procedure, including the 
testing of the PBL.  Any PBL problems, such as failure of 
the PBL system to operate properly, will be valid 
noncompliances.  These violations include, but are not 
limited to, failure to prevent exposure until proper 
collimation has been accomplished, PBL size comparison, 
and failure to prevent exposures at source-image receptor 
distances (SID) at which the PBL is not designed to 
operate.  If a GP system is equipped with a manual BLD, 
then the answer to item 53 on the field test record would 
be ItCn as before.  This question will not generate a 
noncompliance.  The system testing should continue as  2 
before, with an "*I1 placed in data item 54.  Skip 
the rest of section 8 and all of section 9 of the 
instructions in the AR test procedure. 
2.  For those GP systems without a table which are equipped 
with a manual BLD, the Vertical Cassette Radiographic 
Systems (VC) test procedure should be used.  Failure to 
install PBL on these systems will not be cited as a 
violation. 
3.  If a GP system without a table is equipped with PBL, then 
the Chiropractic Supplement to the AR procedure (ARB) 
would apply. 
4.  When a system is tested involving a PBL collimator, you 
should determine whether the PBL mode of operation 
actually functions.  If not, then you should determine 
whether the PBL functioned at the time of installation. 
We allow the owner, under 21 CFR 1020.30(q)(2),  to modify 
a system under the following conditions: 
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 S  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, and provided the 
modification of the x-ray system does not 
result in a failure to comply with 
  1020.31,   1020.32, or 5  1020.33. 
If the user decided to disable his own PBL system for 
manual operation, this would not constitute a 
noncompliance.  If the user has modified the system in 
such a manner that the PBL mode is no longer operational, 
but all other aspects of the system appear compliant, 
record a I1Cm at item 53 on the field test record and add 
the following statement in the remarks section of the 
field test record: 
PBL mode disabled by user on [insert date of 
modification here]. 
We do not expect that many users will have their PBL 
systems disabled, since they can usually use the system 
in the override condition without a modification of the  hardware.  If, however, the user states that the PBL mode 
has not functioned since the date of installation, then 
this would still be a valid noncompliance.  Record an "Aw 
or "Bgg for the type of PBL at item 53 on the field test 
record and a "NW at item 54.  This will generate a 
noncompliance for fully certified systems. 
We have also attached a copy of a letter to manufacturers and 
assemblers, providing additional guidance as to how the new 
amendments will be enforced with respect to PBL. 
Change in Performance Standard (CFR) References 
As you should already be aware, the Performance Standard for 
Diagnostic X-Ray Systems and Their Major Components 
(Performance Standard) was amended on May 3, 1993 (Federal 
Register, Volume 58, Number 83, page 26386) to change various 
requirements, the most notable are those pertaining to 
positive beam limitation (PBL) and reassembly of components. 
With these changes in the Performance Standard, the references 
used have changed in certain circumstances.  To use the 
correct reference for the Performance Standard, please refer 
to the Federal Register publication.  This is especially 
important for FDA district offices when issuing diagnostic x- 
ray field test noncompliance letters. 
Reaching Maximum Entrance Exposure Rate (EER) 
With the advent of larger field image intensifiers, there may 
be difficulties making sure that the maximum EER is measured 
when the automatic exposure rate control (AERC) mode is 
tested.  since AERC modes operate by monitoring the light 
level from the output phosphor of the image intensifier, the 
beam must be completely blocked by lead to drive the system to 
the maximum value of EER.  If the lead sheet included with the 
test kit is used (118 x 10 x low), it may not be large enough 
to completely cover a large field image intensifier.  When the 
x-ray field extends beyond the edge of the lead sheet and 
produces light on the output phosphor, the system will not 
- 
reach the maximum EER (see Figure 1  the table and test stand 
are not shown in this diagram).  To avoid this problem, the 
lead sheet may be moved closer to the x-ray tube and away from 
the image intensifier.  However, it might be easier to observe 
the following instructions: 
1.  For undertable-source fluoroscopic systems (UF), the 
x-ray field may be adjusted so that it is just larger 
than the MDH chamber.  The position of the chamber 
should be determined by viewing the monitor without the 
lead sheet in the beam.  Reduce the size of the field  and position the chamber in the center.  Insert the 
lead before the final EER measurement. 
For C-arm fluoroscopic systems (CF), the beam-defining 
assembly should be in slot 1 of the test stand.  With 
the lead sheet out of the beam, reduce the size of the 
x-ray field to slightly larger than the aperture (see 
Figure 2).  Only the aperture, with the MDH  chamber in 
the center, will be visible on the monitor (see 
Figure 3).  Insert the lead sheet before the final EER 
measurement. 
Small Target Angle X-Ray Tubes 
Recently, we received a copy of a diagnostic x-ray field test 
noncompliance letter where a General Electric assembler was 
notified that a system did not comply with the-PBL sizing 
requirements in 21 CFR 1020.31(g)(l)(i).  The testing was 
conducted with a 14" by 1711 film cassette at a source-image 
receptor distance (SID) of 36".  After the letter was sent to 
General Electric, they stated that the system tested uses an 11 
target angle x-ray tube insert.  They responded by indicating 
that the test was conducted at an SID where full film coverage 
was limited to certain film sizes.  They provided a copy of a 
page from the user's  information, which states these limits as 
follows: 
Target Angle (40"  SID)  Field Coverage 
While the PBL sizing requirements state that such a system must 
align the x-ray field with the image receptor at this SID, we 
believe that use of these film sizes under the above conditions 
does not constitute a public health concern.  We believe that the 
possibility of this type of undersizing becoming a problem in a 
real clinical situation in unlikely (see attached diagram for 
graphical representation of this scenario). 
If you have any questions, please contact Michael P. Divine of 
the Diagnostic Devices Branch at 301-594-4591. 
/ 
Thomas M.  @kub  Entrance Exposure Rate 
Large Field Image Intensifiers 
Figure 1  Figure 2 
\ 
X-Ray Field Larger  X-Ray Field Smaller 
- 
Than Lead Sheet  Than Lead Sheet 
- 
i 
A 
+7--'- 
c 
MDH Chamber 
\  I 
Beam Defining 
Assembly 
Field Size Reduced 
to Lead Aperture 
Opening 
Figure 3 
Entire chamber should 
be visible on monitor 
when viewed without lead  Small Target Angle 
X-Ray Tubes 
Tube Housing 
/ 
\ 
Colli 
Field 
Cutoff 
I 
Film 
SID = 90 cm 
Film 
SID = 110 cm  - 
DEPARTMENT OF HEALTH & HUMAN SERVICES 
Public Health Service 
s 
Food and Drug Administration 
1390 Piccard Drive 
Rockville MD 20850 
TO :  Manufacturers and Assemblers of Diagnostic X-Ray 
Systems 
SUBJECT :  Enforcement Policy for Positive-Beam Limitation (PBL) 
Requirements in 21 CFR 1020.31(g) 
On May 3, 1993, the FDA published a final rule in the Federal 
Register to amend the Performance Standard for Diagnostic X-Ray 
Systems and Their Major Components (Performance Standard).  This 
change allows assemblers to install manual beam-limiting devices 
(BLD) in stationary, general-purpose radiographic x-ray  (GP) 
systems.  The requirement that GP systems must be equipped with 
PBL was eliminated.  For those systems equipped with PBL, this 
rule still contains the requirements that apply to PBL,  This 
change was effective June 2, 1993. 
Recently, we have received questions from several different 
sources requesting clarification as to the requirements that 
apply to GP systems.  We hope this policy letter helps clarify 
our position with respect to the new amendments,  We have chosen 
a question and answer format to address some of the questions we 
have already received and others that we anticipate might be 
asked. 
If you have any questions on this 
Michael P.  Divine of the X-Ray 
Director 
Division of Compliance 
Center for Devices and 
Radiological Health 
Enclosure