**Occupational Exposure to Magnetic Field in Transcranial Magnetic Stimulation Treatment Transcranial Magnetic Stimulation Treatment**

**Occupational Exposure to Magnetic Field in** 

DOI: 10.5772/intechopen.73224

Kjell Hansson Mild and Ole Jacob Møllerløkken Kjell Hansson Mild and Ole Jacob Møllerløkken Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.73224

#### **Abstract**

Transcranial magnetic stimulation (TMS) is used both as a diagnostic instrument and for therapy, available only at some psychiatric clinics for treatment of depression and at clinical neurophysiology where TMS is used for diagnosis of nerve damage. The Swedish National Board of Health and Welfare issued a referral edition about the use of repetitive TMS as an alternative treatment for depression. This may lead to a major increase in the application of TMS to treat depression. TMS is based on induction of an electric (E) field inside the brain by application of an external magnetic field with rapid rise and fall time. The E field in the brain has been calculated when different coils were used for the treatment. The reported E fields are of the order of tens to hundreds of volts per meter and the induced current density is estimated at tens of A/m2 . This field can depolarize neurons or modulate cortical excitability by selecting the appropriate parameters for stimulation and the duration of the treatment session. The mechanisms of action of neurostimulation still remain incompletely understood.

**Keywords:** staff, EU directive, health risk, precautionary principle

## **1. Introduction**

Transcranial magnetic stimulation (TMS) is used primarily in research and treatments of central nervous diseases, such as recurrent depressions, and has been used for several years. The non-invasive stimulation of the cortical cortex is accomplished through the application of pulsed magnetic fields generated by coils in different arrangements. The effects on major depressive disorder in adults have been reviewed by Perera et al. [1] and the Clinical TMS society, and they state that following the clinical recommendations given in their document it should result in continued safe and effective use of the TMS.

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

However, it is not yet so widespread, and today in Sweden and Norway, TMS equipment is available only at some psychiatric clinics for treatment of depression and at clinical neurophysiology where TMS is used for diagnosis of nerve damage. The Swedish National Board of Health and Welfare has issued a referral edition about the use of repetitive TMS as an alternative treatment for depression. The method is new, but it has been used with positive effects on persons with medium-to-severe depression. This may lead to a major increase in the application of TMS to treat depression.

However, although TMS have been reviewed several times, the potential exposure to the therapeutic staff has been neglected. The magnetic pulses can be targeted to selected cortical areas through the design and placement of the different coils used.

Occupational exposure limits have been recently revised in Europe and are given in the new EU directive [2] and the ICNIRP guidelines [3]. For the exposure experienced during TMS treatment, the limits are set to avoid stimulation of nerves. Studies by Karlström et al. [4] and Möllerlökken et al. [5] investigated the therapeutic staff exposure to pulsed magnetic fields during TMS/rTMS treatments in relation to the occupational exposure limits given and found that these limits may be exceeded close to the coil and safety measures are needed. In this paper, we will look closer into this exposure.
