Designation: F 640 79 (Reapproved 2000)

Standard Test Methods forRadiopacity of Plastics for Medical Use1

This standard is issued under the fixed designation F 640; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.This standard has been approved for use by agencies of the Department of Defense.

1. Scope1.1 These test methods cover the determination, by radiog-

raphy, of the radiopacity of plastic in the form of film, sheet,rod, tube, and moldings. The results of these measurements arean indication of the likelihood of locating the plastic partwithin the human body.

1.2 Types of Tests There are three methods of testsdescribed, differing in the method of calculating radiopacity.

1.2.1 Method ARadiopacity is determined as a specificdifference in optical density between the image of the plasticand the background on the X-ray film or equivalent.

1.2.2 Method BRadiopacity is determined by comparingthe images of the test piece and of a standard piece simulatingthe medical device.

1.2.3 Method CThe intrinsic radiopacity of a plastic isdetermined by measurements made on the image of a slab of aspecific thickness of the formulation.

1.3 The values stated in SI units are to be regarded as thestandard.

1.4 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents

2.1 ASTM Standards:B 209 Specification for Aluminum and Aluminum-Alloy

Sheet and Plate2D 1898 Practice for Sampling of Plastics3D 3182 Practice for RubberMaterials, Equipment, and

Procedures for Mixing Standard Compounds and Prepar-ing Standard Vulcanized Sheets4

E 7 Terminology Relating to Metallography5E 94 Guide for Radiographic Testing6E 135 Terminology Relating to Analytical Chemistry for

Metals, Ores, and Related Materials7E 142 Test Method for Controlling Quality of Radiographic

Testing8F 647 Practice for Evaluating and Specifying Implantable

Shunt Assemblies for Neurosurgical Application9

3. Terminology3.1 DefinitionsFor definitions of terms relating to X-ray

procedures, refer to Guide E 94 and Test Method E 142.3.2 Descriptions of Terms:3.2.1 optical densityin photographic photometry, the

logarithm to the base 10 of the ratio of the incident light to thetransmitted light (see Terminology E 135). The range of valuesof optical density expected in this test method is 0.5 to 1.5.

3.2.2 contrastin this test method, contrast is the differencebetween optical density measurements made on the back-ground (nominally 1.0 optical density) and on the test speci-men.

3.2.3 penetrametera device employed to obtain evidenceon a radiograph that the technique used is satisfactory. It is notintended for use in judging the size of discontinuities nor forestablishing acceptance limits for materials or products.

3.2.4 intrinsic radiopacityfor this application, where theplastic is part of a medical device, the X-ray linear absorptioncoefficient is important. The following definition is excerptedfrom Terminology E 7:absorption coefficientspecific factor characteristic of asubstance on which its absorption radiation depends. The rateof decrease of the natural logarithm of the intensity of a parallelbeam per unit distance traversed in a substance. For X rays, thelinear absorption coefficient is the natural logarithm of the ratioof the incident intensity of an X-ray beam incident intensity ofa beam of X rays, It the transmitted intensity, and X the

1 These test methods are under the jurisdiction of ASTM Committee F04 onMedical and Surgical Materials and Devices and are the direct responsibility ofSubcommittee F04.15 on Material Test Methods.

Current edition approved Oct. 26, 1979. Published January 1980.2 Annual Book of ASTM Standards, Vol 02.02.3 Annual Book of ASTM Standards, Vol 08.01.4 Annual Book of ASTM Standards, Vol 09.01.

5 Annual Book of ASTM Standards, Vol 03.01.6 Annual Book of ASTM Standards, Vol 03.03.7 Annual Book of ASTM Standards, Vol 03.05.8 Annual Book of ASTM Standards, Vol 03.03.9 Annual Book of ASTM Standards, Vol 13.01.

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Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

thickness of the absorbing material, then:It 5 Ie exp ~2X!.

Here is the linear absorption coefficient. The mass absorp-tion is given by /r where r is the density.

3.2.5 attenuationloss of energy per unit distance.

4. Summary of Test Methods4.1 The plastic specimen is laid on the cassette in the Xray

apparatus and a 10-mm thick sheet of aluminum is placed ontop of the specimen (or 15-mm thick, if so specified). Theapparatus is equivalent to that used in a hospital. Radiographsare made at specified voltages, times, and currents that aretypical of those used in the X-ray diagnosis of humans. Theradiopacity of the material or medical device is evaluated interms of the criteria described for the test method selected.Calibration is achieved by using both a standard specimen andan X-ray optical density standard.

5. Significance and Use5.1 Plastics, being composed principally of chemical ele-

ments of low atomic weight, have little opacity to X rays.Compounds of elements of higher atomic weight are deliber-ately mixed into plastics to obtain radiopacity.

5.2 These methods are intended to determine whether theplastic part has the degree of radiopacity specified for itsapplication as a medical device in the human body.

5.3 Degree of Contrast:5.3.1 Using Method A, it is recommended that a specific

difference in optical density between the background of 0.8 to1.2 optical density (3.2.1) and the image of the test specimenbe required in any specification for a radiopaque medicaldevice.

5.3.2 Method B requires that the image of the medicaldevice, or the image of the section of the medical device thatis radiopaque, give as much contrast (same background opticaldensity as above) as the image of a comparison standardsimulating the medical device.

NOTE 1It is expected that the dimensions and composition of thecomparison standard will be specified in the standard for the medicaldevice (see Appendix X1).

5.3.3 In Method C, the intrinsic radiopacity of a plastic isdetermined by comparison with an equal thickness of alumi-num, and by the calculation of the relative linear X-rayattenuation (3.2.5) of the plastic based on measurements ofoptical density of the image of the sample, and of the image ofthe comparison aluminum piece.

6. Apparatus6.1 X-Ray Machine, a medical-type (minimally full wave

rectified).6.2 Inherent X-Ray Beam Filtration, 2.5-mm aluminum

equivalent minimum.6.3 X-Ray Film, par-speed grade, used with par-speed in-

tensifying screens. A grid may be used.6.4 Penetrameters:6.4.1 MaterialThe aluminum sheet on top of the test

specimen and the step wedge (if used) shall be 99+ % alumi-num in accordance with Specification B 209 (typically, 1100

alloy). The comparison standard of Method B (7.1) shall be ofthe same metal, unless otherwise specified.

6.4.2 Aluminum Sheet A 10.0 6 0.15-mm thick aluminumsheet shall be used on top of the test specimen for all tests. Ifso specified in the standard for the medical device, a 15.0 60.15-mm thick sheet shall be placed on top of the testspecimen.

6.4.3 Step WedgeA step wedge may be used instead of thealuminum sheet specified in 6.4.2, if it has the requisitethickness steps.

6.5 Rubber Blankets Blankets incorporating X-ray ab-sorbers may be used to mask areas outside that covered by thepenetrameter (this prevents undercutting). Lead sheets mayalso be used for masking.

6.6 Back-Scatter Protection, as described in Guide E 94.6.7 Densitometer The densitometer shall be capable of

measuring the optical density over the range from 0.0 to 3.0optical density units, minimum. It shall have a measuringaccuracy of 6 0.02 optical density units or better. Thedensitometer shall have been calibrated within 6 monthspreviously by a method and calibration standard traceable tothe U.S. National Bureau of Standards.

6.8 Step Tablet, 10 for calibrating densitometers.

7. Comparison Standards7.1 Method BThe comparison standard shall be of similar

dimensions to the medical device. Its exact dimensions andcomposition (see 6.4.1) shall be specified in the standard forthe medical device.

7.2 Method CThe material of the comparison standardshall be Type 1100 aluminum (6.4.1), 2.0 mm thick, 25 mmwide, and 150 mm long.

8. Sampling8.1 Sample fabricated stock shapes or molded items in

accordance with Practice D 1898.

9. Test Specimens9.1 Film or Sheet The specimen shall be at least 150 mm

long and 25 6 1 mm wide. (For this specimen and thefollowing it is assumed that the penetrameter covers an area ofapproximately 150 by 50 mm.)

9.2 Rod or Tubing The specimen shall be at least 150 mmlong.

9.3 Molded Parts If the molded part has dimensions smallwith respect to the area covered by the penetrameter, thenseveral moldings shall be placed under the penetrameter.

9.4 Slab for Method CThe dimensions of the specimen ofthe plastic shall be 2.0 by 25 by 150 mm.

NOTE 2A 2.0-mm thick sheet is often molded especially for testing:for example, the description of sample in Practice D 3182.

10. Conditioning10.1 The test shall be performed at Class 1 conditions

(11.2.1), unless otherwise specified.

10 SRM 1001 has been found suitable for this purpose and is available fromNational Bureau of Standards, Office of Standard Reference Materials, Washington,DC 20234.

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10.2 If other combinations of kilovolt peaks andmilliampereseconds are used, these exact conditions shall bedescribed in the test report.

11. ProcedureMethod A11.1 Place the plastic test specimens on a cassette contain-

ing the X-ray film and the intensifying screens. Cover the testspecimen with the penetrameter.

11.2 X-Ray Exposure The recommended focus-film dis-tance for all classes of exposure is 1000 6 20 mm.

11.2.1 Class 1The conditions for Class 1 exposure shallbe:

80 to 85 kVp ~full2wave rectified!3.0 mAs ~must be varied!

11.2.2 The exposure shall be of such duration that an opticaldensity of 1.0 6 0.2 is obtained through a 10-mm thickness ofaluminum (or 15.0 mm, if specified in the standard for themedical device).

11.3 Film Development Develop the X-ray film in accor-dance with the manufacturers instructions.

11.4 Measurement of Optical Density:11.4.1 BackgroundMeasure the background optical den-

sity to determine whether it is in the specified range, 0.8 to 1.2.11.4.2 Medical Device ImageMeasure the optical density

of the image of the medical device.

12. ProcedureMethod B12.1 Expose the test specimen, with the comparison stan-

dard alongside it, to the X ray, in accordance with theprocedure described in 11.1-11.3, inclusive.

12.2 Measurement Compare the images of the medicaldevice with the comparison standard on the developed film asto optical density.

13. ProcedureMethod C13.1 Expose the test specimen (9.4), with the comparison

standard (7.2) alongside it, to the X ray, in accordance with theprocedure described in 11.1-11.3 inclusive.

13.2 Measurement Measure the optical density of theimages of the test specimen (plastic slab) and the comparisonstandard, as well as the optical density of the background underthe 10-mm thickness of aluminum.

14. Calculation14.1 Method AFrom the value of the optical density of the

background (11.4.1), subtract the optical density value of thetest specimen (11.4.2). Compare this difference, contrast(3.2.2), to the required contrast specified in the standard for themedical device.

14.2 Method BGiven that the background optical densityis in the correct range (0.8 to 1.2), note whether the optical

density of the image of the test specimen is less than, equal to,or greater than the optical density of the image of thecomparison standard, as measured in 12.2. The radiopacity ofthe medical device meets the requirements if the optical densityof its image on the developed film is less or equal to that of thecomparison standard.

14.3 Method CCalculate the percent relative linear at-tenuation coefficient, a, as follows:

a 5~B 2 S!~B 2 A! 3 100

where:B = background optical density, in the range 0.80 to 1.20,A = optical density under the 2.0-mm thickness of alumi-

num, andS = optical density of the image of the sample.

15. Report15.1 The report shall include the following:15.1.1 Test conditions, including the class, as described in

10, or the specific values of kVp and mAs shall be listed. Thefocus-film distance shall also be listed.

15.1.2 Specification requirements, including the thicknessof aluminum on top of the test specimen, the required contrast(Method A), the size of the comparison standard (Method B),or the percent relative linear attenuation coefficient (MethodC), as listed in the requirements of the standard specificationfor the medical device. The number and title of the medicaldevice specification shall also be listed.

15.1.3 Sample description, including name of manufacturer,type of device or plastic part, Catalog number or formulationnumber, dimensions of the test specimen, diameter, wallthickness, etc., and type of radiopaque additive and how itoccurs in the part, such as a uniform dispersion, line of specificcross section, etc.,

15.1.4 Optical density readings for all optical density mea-surements as described in 11.4, 12.2, and 13, and

15.1.5 Calculations, reporting the contrast as calculated in14.1, or whether the medical device is equivalent in contrast(optical density) to the comparison standard (14.2), or thepercent relative linear attenuation coefficient (14.3).

16. Precision and Bias16.1 The precision and bias of these test methods have not

yet been established.16.2 It is intended to develop data for the overall method

and the measurement of density from a round-robin test.

17. Keywords17.1 implants; plastic surgical devices; polymers; surgical

applications; radiopacity; test methods; surgical implants

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APPENDIXES

(Nonmandatory Information)

X1. VARIABLES IN RADIOPACITY OF PLASTICS IN MEDICAL DEVICES

X1.1 GeneralThe initial development of this standardwas based on the need to determine the location in the body ofplastic parts of small diameter. This led to a proposed require-ment for an optical density contrast measured on the medicaldevice. However, radiopacity is a property of many types ofmedical devices and its required numerical level is influencedby many variables, some of the principal being: type of plastic;size, thickness, and configuration; part of body or circulatorysystem; and X-ray energy applied in the procedure.

X1.2 Specification ValuesThis standard does not haveany requirements for minimum levels of radiopacity, nor that

there be a preferred test method (of the three described). It isexpected that a standard specification for the medical devicewill specify the required level of radiopacity, as determined bya particular test method (A, B, or C). The standard specificationfor the medical devices may also specify values for someparameters of the test method, such as: thickness of aluminumon top of the test specimen, whether 10 mm, 15 mm, or other;X-ray test voltage; and dimensions and composition of thecomparison standard (Method B).

X2. COMPARISON OF THE THREE TEST METHODS

X2.1 Method AIt has been proposed that, for manyapplications, an optical density contrast of 0.10 is satisfactory.For larger pieces and thin sections of the human body, acontrast of 0.05 optical density units may be adequate.

X2.2 Method BThis test method has been considered toassure the radiopacity of a medical device. The dimension ofthe comparison standard, especially thickness in the directionof the X-ray path, does not have to correspond to thedimensions of the medical device.

X2.3 Method C:X2.3.1 This test method is now being specified in Practice

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X2.3.2 This test method may be necessary where it isdifficult to characterize the radiopacity of the medical device,because of either its size or configuration. The remedy is torequire a minimum radiopacity in the plastics formulation.

X2.3.3 From available reports on the development of medi-cal devices, such as interuterine devices (IUDs) and fromcomments made by Committee F-4 members, it is obvious thatradiopaque formulations are often measured by Method C. Ithas usually been done by comparing materials. Due to thevariations in background optical density, it appears that a morereliable comparison and more reproducible test data can resultif No. 1100 aluminum or other material with well-known X-rayabsorption is used as a standard of radiopacity.

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