Seth J. Seidman

Dosimetric comparison of the specific anthropomorphic mannequin (SAM) to 14 anatomical head models using a novel definition for the mobile phone positioning

This paper presents new definitions for obtaining reproducible results in numerical phone dosimetry. Numerous numerical dosimetric studies have been published about the exposure of mobile phone users which concluded with conflicting results. However, many of these studies lack reproducibility due to shortcomings in the description of the phone positioning. The new approach was tested by two groups applying two different numerical program packages to compare the specific anthropomorphic mannequin (SAM) to 14 anatomically correct head models. A novel definition for the positioning of mobile phones next to anatomically correct head models is given along with other essential parameters to be reported. The definition is solely based on anatomical characteristics of the head. A simple up-to-date phone model was used to determine the peak spatial specific absorption rate (SAR) of mobile phones in SAM and in the anatomically correct head models. The results were validated by measurements. The study clearly shows that SAM gives a conservative estimate of the exposure in anatomically correct head models for head only tissue. Depending on frequency, phone position and head size the numerically calculated 10 g averaged SAR in the pinna can be up to 2.1 times greater than the peak spatial SAR in SAM. Measurements in small structures, such as the pinna, will significantly increase the uncertainty; therefore SAM was designed for SAR assessment in the head only. Whether SAM will provide a conservative value for the pinna depends on the pinna SAR limit of the safety standard considered.

EMC and wireless healthcare

Electromagnetic compatibility (EMC) is a critical part of addressing the risks related to the effects of electromagnetic interference (EMI) on active medical devices exposed to emissions from wireless technology. In addition, for wireless technology in healthcare to be safe, effective, reliable, and secure specific wireless issues must also be addressed including quality of service, coexistence with other wireless equipment, data integrity, and wireless security. Unfortunately, these issues pose risks that are poorly addressed in present medical devices standards or other consensus documents. This paper discusses risks for wireless technology in healthcare with examples from research examining the effects of emissions from wireless technology such as RFID on implantable cardiac pacemakers and defibrillators and EMC with other emitters. The paper goes into ways that the risks, including EMI, can be addressed and makes the case for substantive engagement by stakeholders, including the IT community, wireless developers, and clinical organizations. There is clear need to develop unbiased, consensus information and tools that will set the pathways and tools needed to meet the risks and challenges for widespread incorporation of wireless technology in healthcare.

Possible overexposure of pregnant women to emissions from a walk through metal detector

This paper presents a systematic procedure to evaluate the induced current densities and electric fields due to walk-through metal detector (WTMD) exposure. This procedure is then used to assess the exposure of nine pregnant women models exposed to one WTMD model. First, we measured the magnetic field generated by the WTMD, then we extracted the equivalent current source to represent the WTMD emissions and finally we calculated the induced current densities and electric fields using the impedance method. The WTMD emissions and the induced fields in the pregnant women and fetus models are then compared to the ICNIRP Guidelines and the IEEE C95.6 exposure safety standard. The results prove the consistency between maximum permissible exposure (MPE) levels and basic restrictions for the ICNIRP Guidelines and IEEE C95.6. We also found that this particular WTMD complies with the ICNIRP basic restrictions for month 1-5 models, but leads to both fetus and pregnant women overexposure for month 6-9 models. The IEEE C95.6 restrictions (MPEs and basic restrictions) are not exceeded. The fetus overexposure of this particular WTMD calls for carefully conducted safety evaluations of security systems before they are deployed.

Design of unique simulators to evaluate medical device susceptibility to radio frequency identification exposure

Background: The use of radiofrequency identification (RFID) in healthcare is increasing, but one of the biggest obstacles for widespread adoption is electromagnetic compatibility (EMC). Numerous studies have documented that RFID can interfere with medical devices. No recognized standard test methods currently exist to address medical device EMC from RFID emitters. This study identifies a potential protocol to test the effect of RFID exposure on medical devices. Methods: We developed four separate simulators which cover four distinct RFID frequency bands: Low frequency (LF): 125 kHz; High frequency (HF):13.56 MHz; Ultra high frequency (UHF): 915 MHz; and 2.4 GHz. The RFID Test Library includes actual RFID input signals and recommended field strength values for each simulator. The simulators consist of Helmholtz coils for LF and HF and use IEC 61000 4-3 exposure methods for UHF and 2.4 GHz. Discussion: The protocol presented in this paper represents one way to test if your medical device could be affected from exposure to RFID readers. The antennas chosen are used to produce repeatable tests. The input signals and field strengths are chosen to represent a wide variety of actual RFID reader technologies. Summary: The protocol needs to be tested with actual medical devices to understand the effects of the varying RFID test signals and to determine if the RFID Test Library is adequately defined. These tests are currently being conducted independently by the Food and Drug Administration (FDA) and MET Laboratories. Suggested maximum field levels are calculated and presented as a reasonable worst case exposure. It is the intent that after test validation this protocol will be submitted to the Association for Automatic Identification and Mobility (AIM) for publication.

Safety evaluation of walk-through metal detectors

In this paper, we describe a procedure to evaluate the electrical current, induced by walk-through metal detectors electromagnetic emission, inside a human model for safety assessment. This procedure consists of the measurement of the magnetic field, the derivation of equivalent current source, and the calculation of induced current using the impedance method. This procedure is applied to determine for a commercial walk-through metal detector the induced currents within an anatomical human model.

Characterizing the 2.4 GHz Spectrum in a Hospital Environment: Modeling and Applicability to Coexistence Testing of Medical Devices

The increasing use of shared, unlicensed spectrum bands by medical devices and nonmedical products highlights the need to address wireless coexistence to ensure medical device safety and effectiveness. This paper provides the first step to approximate the probability of a device coexisting in its intended environment by providing a generalized framework for modeling the environment. The application of this framework is shown through an 84day spectrum survey of the 2.4-2.48 GHz industrial, scientific, and medical band in a hospital environment in the United States. A custom platform was used to monitor power flux spectral density and record received power. Channel utilization of three nonoverlapping channels of 20 MHz bandwidth-relative to IEEE 802.11 channels 1, 6, and 11-were calculated and fitted to a generalized extreme value distribution. Low channel utilization was observed (<;10%) in the surveyed environment with sporadic occurrences of higher channel utilization (>50%). Reported findings can be complementary to wireless coexistence testing. This paper can provide input to the development of a consensus standard for wireless device coexistence test methods and a consensus document focused on wireless medical device coexistence risk management.