FY 2001 Wireless Technologies
- Evaluation of Quality Assurance Standard for the Measurement of Cellular Telephone Specific Absorption Rate
- Wireless Medical Telemetry
- Laboratory Testing of Cardiac and Electrical Stimulation Devices
- Development of a Standardized Test Method for Evaluating Interference from Electronic Security Systems
The wireless technology revolution, together with a flood of new medical devices incorporating sensitive microelectronics, is leading to a highly unstable situation. Dangerous malfunctions can be induced in devices via electromagnetic interference (EMI) from wireless equipment, such as cellular phones and magnetic-field emitting security devices.
OST's Division of Physical Sciences (DPS) is currently collaborating with the Federal Aviation Administration (FAA) on an investigation of the potential interaction between metal detectors and implanted medical devices, such as spinal and deep brain stimulators. This effort includes mapping electromagnetic fields emitted from security-screening systems, developing a simulator for testing medical devices for interference, and testing high-risk medical devices for susceptibility to EMI.
DPS has also responded to concerns about the radiation from handheld wireless (cellular) telephones by developing a cellular telephone measurement standard in conjunction with the IEEE. A well-defined measurement standard is necessary if both manufacturers and regulatory agencies are to have confidence in the measurements they make. To further this effort, OST developed standardized methods to measure the absorption of radiation in a human head model.
In addition to laboratory work, DPS routinely performs regulatory reviews of premarket submissions and post-market assessments of EMI, including 1) devices affected by EMI (implanted and external cardiac stimulation devices, powered wheelchairs and scooters); devices that can interfere with other medical devices (benign prostatic hyperplasia and cancer hyperthermia devices; and 3) MRI systems whose pulsed radio-frequency fields cause heating of metallic implants. In addition, DPS is developing labeling for 1) implanted medical devices to warn of heating that led to the deaths of two individuals in the past year. (These patients were inappropriately treated with radio-frequency diathermy, since they had metallic leads implanted in their central nervous system.); 2) electronic anti-theft security systems to avoid injuries to users of implantable medical devices; and 3) implanted nerve stimulation devices to avoid patient injuries from exposure to magnetic fields by security systems.
DPS also participates in numerous standards-setting activities, including 1) standards for EMI of implanted cardiac stimulation devices from wireless handheld phones and magnetic field-emitting security systems; 2) recommended practices for ad hoc EMI testing of medical devices with portable radio transmitters; 3) an international consensus standard for powered wheelchairs; 4) a measurement standard for microwave absorption from handheld wireless (cellular) telephones; and 5) a national consensus standards for hearing aid electromagnetic compatibility (EMC) with cellular telephones. In addition, DPS is participating in the development of an international draft position paper on harmful EMI effects to medical devices from security systems. This draft document was prepared by a working group sponsored by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).
Evaluation of Quality Assurance Standard for the Measurement of Cellular Telephone Specific Absorption Rate
Key words: cellular telephone, specific absorption rate, wireless, dosimetry, microwave
This project is being performed in support of an emerging standard being promulgated by the Institute of Electrical and Electronic Engineers. The voluntary standard is entitled "Recommended Practice for Determining the Spatial-Peak Specific Absorption Rate (SAR) in the Human Body Due to Wireless Communications Devices: Experimental Techniques." It sets forth the first consistent test methodology for measuring (dosimetry) the Specific Absorption Rate (SAR) induced in the human body by cellular telephones and wireless handsets that emit microwave radiation. The lack of a standardized test methodology has lead to widely varying results when the SAR induced by the same wireless device is measured at different laboratories with different simulated human head models. The inability to produce consistent results by different labs has caused consumer distrust, recalls, and regulatory confusion. In FY 2001, OST engineers developed and built an SAR measurement lab consisting of a data-acquisition system and three-dimensional, full-motion scanner to perform these tests. Then, in collaboration with the University of Maryland, they developed an SAR quality assurance (QA) system consisting of a simple model of a simulated wireless handset and human body phantom. This QA system will be circulated next year to many international labs to perform intercomparisons of SAR measurements.
Key words: wireless medical telemetry, electromagnetic interference (EMI), Wireless Medical Telemetry Services (WMTS), Federal Communications Commission (FCC),
During FY 2001, OST continued to work in partnership with the Federal Communications Commission (FCC), the American Hospital Association (AHA), telemetry manufacturers, and clinicians to help the FCC further refine and defend the use rules for the dedicated frequency bands of the new Wireless Medical Telemetry Services (WMTS). The WMTS provides unique protections against EMI and reduces the risk of interference to wireless medical telemetry from other in-band radio sources. This work addresses public health risks to wireless medical telemetry and positions the Center to focus on the correct areas for regulatory decisions.
Key words: electromagnetic interference (EMI), electromagnetic compatibility (EMC), electrical stimulation devices, nerve stimulation devices, cardiac stimulation devices, cellular telephone, metal detectors, wireless handset
This project is intended to assess the electromagnetic compatibility (EMC) of several high-priority ambulatory and implanted electrical stimulation medical devices. OST collaborated with personnel from ODE and OSB in a CDRH ad hoc group. This group identified over 20 reports of EMI of implanted neural stimulators that caused patient injuries. These reports included EMI from a variety of magnetic-field-emitting security systems. After identifying problematic devices, the Electrophysics Branch labs in OST continued to study potential interference of implanted and ambulatory medical devices by electromagnetic fields emitted from security systems. This work was performed in the EPB labs with support from the Federal Aviation Administration (FAA) under an interagency agreement between the FDA and FAA.
The OST laboratories also performed experiments to assess deep brain stimulators (DBS). This was done in response to clinical reports of serious patient injuries (including two deaths) from interactions with electromagnetic fields applied to the patients by radio frequency diathermy. These studies provided independent data supporting regulatory decisions that CDRH had to make regarding safety alerts about use of diathermy in patients with a DBS.
Development of a Standardized Test Method for Evaluating Interference from Electronic Security Systems
Key words: electromagnetic compatibility, EMC, interference, electromagnetic interference, EMI, metal detector, electronic surveillance system, cardiac pacemaker,
This project involves evaluating implantable medical devices for their susceptibility to electromagnetic interference (EMI) from electronic article surveillance systems (EASS), metal detectors and other security systems that emit low-frequency magnetic fields. EASS are used in many retail stores to prevent shoplifting by detecting special tags placed on merchandise. Security systems such as metal detectors are used to screen people for metal objects that can be used as weapons. The goal of this project is to develop a standardized laboratory test method to check the susceptibility of implanted medical devices with the magnetic fields emitted by these security systems. There is great similarity between EASS and metal detectors, in terms of the magnetic field exposures they produce for patients with medical devices implanted in their bodies. Magnetic field emissions from six different walk-through metal detectors were measured in detail. This project is closely associated with the OST project "Laboratory Testing of Cardiac and Electrical Stimulation Devices." The project also supports the work specified in the FDA interagency agreement with the Federal Aviation Administration for evaluating medical device EMI from emissions of airport security systems (metal detectors).