Valič B1, 2, Gajšek P1, Miklavčič D2
1Institute of Non-Ionizing Radiation, Ljubljana, Slovenia
2Faculty of Electrical Engineering, University of Ljubljana, Ljubljana, Slovenia
Summary of research published in Bioelectromagnetics Vol. 30, No. 7, pp 591-599.
In modern medicine, many different prosthetic, therapeutic, diagnostic, or experimental implants are used. With the increasing number of implants, whether active or passive, an important question is raised: do current guidelines protect persons with the implants from the EMF adequately? Can the implant alter the electric and magnetic field distribution inside the human body in such a way that the basic restrictions are exceeded in spite of the fact that reference levels are not? The question of the protection of implanted persons is even more important in the working environment, where the employer is responsible for health and safety at work and must prove that the risks due to the EMF is minimal.
In recent years this question was addressed in a number of reports. But most of the papers deal either with RF fields, the exposure during MR imaging, or with the immunity of the active implants. We were unable to find any publication dealing with the effects of the implant on the current density distribution in the ELF (extreme low frequency) electric and magnetic field exposure situation.
In our study we used numerical modeling to calculate the current density distribution inside a human body with an intramedullary nail simultaneously exposed to ELF (50 Hz) electric and magnetic fields. We used an intramedullary nail in the femur because it is one of the longest implants used in humans. Thus, it is expected to alter the current density distribution significantly. The exposure conditions were corresponding to the reference levels for general public. To evaluate the influence of the implant, the current density distribution in the model with the implant was compared with the current density distribution in the model without the implant.
The results show that for the worst case exposure situation (the electric field is in the inferior to superior direction and the magnetic field in posterior to anterior direction) the implant increases the current density up to 10 times: from 0.9 mAm2 in the model without the implant to 9.5 mAm2 in the model with the implant in the region where the implant is in contact with soft tissue. This increase is significant since, in spite of complying with ICNIRP reference levels for general public, the basic restrictions on current density for general public are exceeded nearly five times. The region, where significant increase in the current density is observed, is however limited: in less than 8 cubic centimeters, ICNIRP basic restrictions are exceeded twice (current density higher than 4 mAm2).
The high increase of the current density means that the existing safety limits do not necessarily protect persons with implants to the same extent as they protect people without implants. The current density might consequentially exceed ICNIRP basic restrictions even though exposure is in compliance with ICNIRP reference levels. Cardiologists, traumatologists and other physicians who implant such implants and patients receiving them should attach importance to understanding of the electric and magnetic field distribution changes inside the human body due to conducting implants. In addition, the knowledge about the possible effects of the implants on the safety of the exposed patients is important for those preparing guidelines and standards about risk assessment and all involved in risk assessment in the working environment, where specific risks due to the effect of the implant should also be taken into account.