title: Safety in simultaneous EEG-fMRI at 3 T: temperature measurements.
abstract: BACKGROUND
  In simultaneous electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), safety of the EEG equipment is ensured by the manufacturer only for localizers and fMRI sequences. To conduct a clinically feasible simultaneous EEG-fMRI study, other sequences, e.g. anatomical and B0-correction sequences, have to be acquired in the same imaging session.
  
  
  OBJECTIVE
  To measure the temperature increase of the electrodes in different size EEG caps in a phantom and volunteers during magnetic resonance imaging (MRI) sequences typically used in clinical studies.
  
  
  METHODS
  A phantom with EEG caps of size 52, 56, and 60 was imaged using several sequences in two 3 T MRI scanners to determine the maximum and average temperature increases in the electrodes. Additionally, three volunteer studies were performed for the EEG caps of sizes 56 and 60. The sequences were gradient echo based echo planar imaging sequence, T2-weighted turbo spin echo (T2-TSE), spin echo multiecho for B0-correction, diffusion tensor imaging and T1-weighted 3D sequences.
  
  
  RESULTS
  In phantom studies the maximum temperature increase was 4.1℃ with a mean of 1.2 ± 1.1℃. In volunteer studies, the maximum temperature measured was 35.6℃ and the maximum temperature rise was 2.1℃ with a mean of 0.9 ± 0.7℃. Both were observed with a T2-TSE sequence.
  
  
  CONCLUSIONS
  The temperature of the electrodes did not exceed the limits set by the IEC 60601-1 standard (43℃) or manufacturer (45℃), thus indicating a safe EEG-fMRI protocol in this respect.
authors.affiliation: HUS Medical Imaging Center, Helsinki University Central Hospital, Finland Department of Physics, University of Helsinki, Helsinki, Finland linda.kuusela@hus.fi.
authors.forename: Linda
authors.initials: L
authors.lastname: Kuusela
authors.affiliation: HUS Medical Imaging Center, Helsinki University Central Hospital, Finland Department of Physics, University of Helsinki, Helsinki, Finland.
authors.forename: Sampsa
authors.initials: S
authors.lastname: Turunen
authors.affiliation: HUS Medical Imaging Center, Helsinki University Central Hospital, Finland.
authors.forename: Leena
authors.initials: L
authors.lastname: Valanne
authors.affiliation: HUS Medical Imaging Center, Helsinki University Central Hospital, Finland Department of Physics, University of Helsinki, Helsinki, Finland.
authors.forename: Outi
authors.initials: O
authors.lastname: Sipilä
mesh_terms: D004569:Electroencephalography / Q000009:adverse effects; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000009:adverse effects; D064847:Multimodal Imaging / Q000009:adverse effects; D019047:Phantoms, Imaging
keywords: Safety; functional magnetic resonance imaging; technical aspects