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U.S. Department of Health and Human Services

About FDA

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FY 2001 Radiation Metrology

Radiation safety continues to be a significant concern for the Center. To help address this topic, OST maintains measurement and calibration facilities for x-ray, laser, non-coherent optical sources, and microwave measurements.

Each year FDA is responsible for the inspections of over 11,000 mammography facilities under the Mammography Quality Standards Act (MQSA). In addition, about 1,600 installations of general radiographic equipment are inspected against the mandatory performance standards mandated by the Radiation Control for Health and Safety Act (RCHSA). FDA also tests a number of industrial x-ray facilities each year. These inspection and testing programs involve measurements of ionizing radiation. OST provides OC, OHIP, ORA, and Agreement States with calibrated x-ray instruments and supplies for the various compliance inspection programs; support for special measurements as needed, such as measuring the ionizing radiation output from personnel security scanners, night vision devices, radioactive contamination of medical or consumer products, and CT beam profiles; and OST provides technical consultation. Traceability of measurements is achieved through the operation of a standard laboratory accredited by the National Voluntary Laboratory Accreditation Program (NVLAP).

In addition to ionizing radiation instrument calibrations, OST provides laboratory measurements and calibrations of light meters, laser measurement instrumentation, and microwave oven instruments for field enforcement of FDA performance standards. OST staff also provides pre- and post-market evaluations of selected products for compliance with FDA radiation standards.

The CDRH radiation measurement and calibration laboratories are internationally respected, and laboratory staff contribute significantly to the development of measurement protocols of new standards. For example, laboratory staff have been instrumental in establishing the national standard for mammography x-ray calibrations and continue to work closely with NIST. Additionally, staff have been closely involved in the effort to align the FDA Laser Standard with its international equivalents. The measurement and calibration program is a cost effective method of providing a large volume of high quality calibrations for a nationwide network of inspectors. FDA can be assured that compliance measurements are traceable to national standards. Traceability can be readily verified, because FDA is the sole custodian of the traceability chain. The laboratory's services are used for leveraging state agencies to test newly installed radiological equipment against FDA requirements, resulting in hundreds of additional inspections per year. The program allows both FDA and the states to avail themselves of traceable calibrations, which are independent of regulated industry, thus eliminating potential conflicts of interest.

Endoscope Hazard Evaluation

Key words: endoscopes, radiation, hazards

Work was initiated in FY 2000 to characterize the optical radiation emissions from endoscopes used in various minimally invasive diagnostic and therapeutic procedures. Data obtained from measurements of spectral radiant power showed that there is relatively little ultraviolet radiation emission below a wavelength of 370 nm and greatly attenuated emissions at wavelengths greater than about 700 nm.

In FY 2001, further tests were conducted of the spatial beam profiles from endoscopes. It was found that the spatial beam profiles from some of these devices is highly non-uniform, an unexpected result. A new test method was developed which uses a lens imaging beam profiler system to characterize non-uniform spatial profiles. In addition, a new field portable rapid scanning spectroradiometer system was obtained and characterized. This new system provides FDA with the capability of making rapid absolute spectral irradiance measurements under field conditions. These new measurement systems will be used in FY 2002 to complete a comprehensive evaluation of a wide variety of endoscopes. The data obtained in this work will be incorporated in reviewer guidance documents as a benchmark for evaluating the optical radiation safety of new devices and will provide the technical basis for setting safety limits to be included in international standards.

Ophthalmic Instruments Hazard Assessment

Key words: fundus cameras, radiation, hazards

Scientists started work in FY 2000 to determine the potential optical radiation hazards associated with the use of fundus cameras used to obtain photographs of the retina. Measurements were taken of the spectral integrated radiant exposure of the light emitted from pulsed Xenon light sources used in these devices. Preliminary data obtained showed relatively little ultraviolet and infrared radiation emissions from the device tested.

In order to evaluate the potential hazards to the retina, it is also necessary to characterize the spatial beam profile of the radiation on the retina. In FY 2001, a new test method to measure spatial beam profile was developed. The new test method uses a lens imaging beam profiler system. In addition, a new field portable rapid scanning spectroradiometer system to measure the pulsed light from fundus cameras was obtained and characterized. This new system provides FDA with the capability of making absolute spectral radiant exposure measurements under field conditions. These new measurement systems will be used in FY 2002 to complete the hazard evaluation of fundus cameras. The data obtained in this work will be incorporated in reviewer guidance documents as a benchmark for evaluating the optical radiation safety of new devices, and will provide the technical basis for setting safety limits to be included in international standards.

Ophthalmic Instrument Standards

Key words: standards, ophthalmic instruments, intraocular lenses

OST scientists were active participants in developing major amendments to the ISO 15004 ophthalmic instrument standard. This standard is particularly important to CDRH since it will be applicable to all instruments that direct optical radiation into the eye. This includes medical devices and radiologic products utilizing lasers, pulsed light, operation microscopes, and endoilluminators. Some of these devices have produced retinal burns during ocular surgical procedures. It is expected that the final committee draft will be reviewed by the full ISO TC172 committee in early 2002.

OST is also active in developing voluntary standards for ophthalmic devices through participation on the ANSI Z80 subcommittees for optical engineering issues. In FY 2001, the OST representative to ANSI Z80.11 was appointed as co-chair of the working group and chair of the Technical subcommittee. In FY 2001, ANSI Z80.7 (Intraocular Lenses) was harmonized with the ISO 11979 series. The revised standard was circulated for vote in the early part of FY 2001 and was approved. There are three additional standards being developed in ANSI Z80. These are Z80.11 (Laser Systems for Corneal Reshaping), Z80.12 (Multifocal Intraocular Lenses), and Z80.13 (Phakic Intraocular Lenses). Z80.12 and Z80.13 have also been submitted to, and accepted by, ISO TC 172/SC 7 as New Work Items (NWIs). Work on the Z80.11 document will continue through FY 2002.

OST continues to assess test methods which are designed to confirm the optical properties (refractive power and resolution) of intraocular lenses (IOLs). In FY 2002, OST will also participate in developing a method for computer modeling optical performance, in a model eye, of intraocular lens designs.

Laser Field Compliance Program

Key words: lasers, calibrations, product testing, technical support

During FY 2001, OST continued to provide support to the laser field compliance program through consultations on optical radiation measurements. The OST Laser Calibration Laboratory maintains equipment for conducting high-precision optical measurements, which provide validity to measurements made in compliance testing programs nationwide. The laboratory measurement standard is a C-series calorimeter built by the National Institute of Standards and Technology (NIST). To assure the validity of measurements made by OST, periodic intercomparisons are conducted with NIST, and in-house quality assurance procedures are followed. During the later half of FY 2001, work commenced to convert the C-series calorimeter control system to one similar to that used by NIST.

Microwave Oven Leakage Instrument Calibration

Key words: microwave ovens, instrument calibration, precision calibration, microwave leakage, non-ionizing radiation

Twenty-five microwave leakage survey instruments were calibrated in OST’s Electrophysics Branch calibration facility to provide an independent source of data supporting the enforcement of the Federal Microwave Oven Performance Standard (21 CFR 1030). The calibrations were based on precision calibrations transferred from the old EPB Precision Anechoic Chamber that has since been demolished. OST continued to design and specify instrument positioning equipment and a chamber fire system to convert an existing shielded room in the new OST laboratory into an anechoic calibration chamber for precision microwave instrument calibration.

Laser Performance Standard

Key words: lasers, standards, harmonization

FDA is in the process of amending the performance standard for laser products to bring it into closer harmonization with the international standards issued by the International Electrotechnical Commission (IEC) [IEC 60825-1 and IEC 60601-2-22]. OST is providing support to this effort through membership on the CDRH workgroup.

Standard for Personnel Security Screening Systems

Key words: security screening, x-ray

A current issue of concern to FDA is the use of ionizing radiation for the security screening of individuals. Several installations of x-ray security scanners are currently in operation in this country and many more are being considered following the attacks of September 11. FDA has regulatory jurisdiction over these devices. OST has led the effort to develop an ANSI/HPS consensus standard to address the radiation safety issues of this practice. In fiscal year 2001, the Task Group completed a proposed draft standard and submitted the draft to the ANSI/HPS N43 Committee for review and balloting.

X-ray Instrument Calibration

Key words: calibration, x-ray measurement, laboratory accreditation.

OST laboratories provide traceability to the national standards for all x-ray measurements related to enforcing FDA regulations, including those promulgated under the Mammography Quality Standards Act (MQSA) and the Radiation Control for Health and Safety Act (RCHSA). This program supplies the following: calibrated x-ray instruments for routine compliance programs and all related field supplies; support for special measurements needed such as measuring the ionizing radiation output from personnel security scanners, night vision devices, contaminated medical and consumer products, CT beam profiles, etc.; specifications and procurement of instrumentation; and technical experts for developing standards for radiation safety for non-medical uses of radiation. The laboratory is presently accredited for calibrating three classes of x-ray instruments in radiation fields typical of general radiography, mammography, and electronic product radiation.

X-ray measurement traceability is achieved by operating a secondary standard laboratory accredited by the National Voluntary Laboratory Accreditation Program (NVLAP). In fiscal year 2001, a total of 1,375 accredited calibrations of radiation-measuring instruments were performed by irradiation in known x-ray fields. In addition, 606 electrical instrument pre-calibrations and 122 calibrations of non-invasive kVp were performed. Since many state agencies perform FDA inspections and sometimes use their own equipment, states rely heavily on this CDRH calibration service. In FY 2001, 64% of the calibrations were for instruments owned by FDA, 29% for instruments owned by state agencies, and 5% for instruments owned by other federal agencies. A large percentage of the instruments calibrated– 64%--were designated for testing compliance with the Radiation Control for Health and Safety Act of 1968 (RCHSA). Twenty-three percent of the instruments were designated for testing compliance with the Mammography Quality Standards Reauthorization Act of 1998 (MQSA), and five percent of the instrument calibrations were in support of the Nationwide Evaluation of X-ray Trends (NEXT).

OST keeps track of approximately 2,800 pieces of equipment at over 500 inspector stations throughout the country and U.S. territories, instrument usage and calibration data. As required by NVLAP, the laboratory this year has participated in a Proficiency Test administered by the National Institute of Standards and Technology (NIST), has undergone an internal audit of operating procedures and of the Quality System, and has been subject to a site inspection by NVLAP assessors. The laboratory complies with NIST Special Publication 812: Criteria for the Operation of Federally Owned Secondary Calibration Laboratories (Ionizing Radiation); NIST Handbook 150: NVLAP Procedures and General Requirements; and ISO Guide 25: General Requirements for the Competence of Calibration and Testing Laboratories.

The calibration program is a cost-effective method of providing a large volume of calibrations for a nationwide network of inspectors. Through this program, FDA and states can avail themselves of traceable calibrations that are independent of the regulated industry, thus eliminating potential conflicts of interest.