Intersubject variability in a comprehensive numerical assessment of operator electromagnetic exposure to TMS

Area of Science:

• Biomedical Engineering
• Neuroscience
• Occupational Health

Background:

• Transcranial magnetic stimulation (TMS) is widely used in clinical and research settings.
• Operator safety during TMS procedures requires assessment of workplace exposure.
• Existing guidelines focus on patient safety, with limited data on operator exposure and anatomical variability.

Purpose of the Study:

• To evaluate the electric field (E-field) induced in TMS operators under realistic conditions.
• To assess the impact of inter-subject anatomical variability on TMS operator exposure.
• To compare induced E-field levels with international safety guidelines.

Main Methods:

• Numerical simulations using four detailed human models.
• Analysis of TMS coil positions at chest and abdomen.
• Varying coil-to-operator distances (12 cm, 22 cm, 40 cm).
• Computation of induced E-field using magneto-quasi-static solvers.

Main Results:

• Compliance with ICNIRP limits at 40 cm distance.
• Exceedance of occupational limits at 12 cm distance across all models.
• Partial exceedance at 22 cm, particularly in the abdominal region.
• Influence of anatomical features (e.g., adipose tissue) on E-field intensity.

Conclusions:

• Operator TMS exposure is a function of coil placement and individual anatomy.
• Increased distance is key for ensuring compliance and reducing exposure variability.
• Tailored assessments or mitigation strategies may be needed for closer TMS coil configurations.
• Inter-subject anatomical variability is crucial for accurate operator exposure evaluation.