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EEG-fMRI is a multimodal neuroimaging technique which enables the acquisition of EEG and fMRI data synchronously. The technique is now being used worldwide to evaluate normal brain function as well as brain function associated with recognized brain disorders.

Scalp EEG reflects the brain‘s electrical activity, more specifically it represents post-synaptic potentials in the cerebral cortex. fMRI detects haemodynamic changes throughout the brain known as the BOLD effect (Blood Oxygen Level Dependent). EEG-fMRI therefore enables the direct correlation of these two important measures of brain activity.

Simultaneous acquisition of EEG and fMRI data of good quality is a difficult task. Challenges with regards to subject safety and data quality cannot be underestimated. Careful preparation of the subject in accordance with established safety guidelines for EEG examination in the scanner is mandatory. Due care and attention is needed to avoid potential health risks. One such possible health and safety threat is the precipitation of induced currents dangerous to the subject. Such currents are induced by the MR image forming process if the subject is carelessly hooked up to the EEG acquisition system. Formal risk assessment according to recognized guidelines should be a matter of routine for all researchers working with combined EEG/fMRI protocols.

fMRI/EEG data quality is the other challenge. The MR is a very hostile environment at the best of times but presents particular problems where EEG acquisition is concerned. There are also challenges from the MR point of view. MR images are highly sensitive to contamination by foreign metal objects being placed in the scanner with the subject (even a simple tattoo can seriously distort the images). The EEG recording equipment – when placed in or near a scanner can certainly be described as a ‘foreign metal body’. However, for optimal EEG acquisition (with current available technology) the amplifier really needs to be placed inside the scanner at close proximity to the subject. Brain Products have addressed this dilemma uniquely by developing their BrainAmp MR from non magnetic materials, dedicated for use inside the scanner bore.

EEG was first recorded in an MR environment in 1993. The first continuous EEG-fMRI experiments were performed in 2000. Two main approaches to the integration of data acquisition have emerged in an attempt to overcome the technical difficulties encountered (described above).

The earliest approach was to acquire EEG data in the relatively noiseless periods in the scan during the ‘gaps’ between interleaved scan acquisitions. Each acquisition modality (EEG and fMRI) is interrupted in turn (periodically) to allow data of adequate quality to be recorded by the other modality. Subsequent approaches were developed to acquire high quality data from both modalities during continuous scan acquisitions.

Brain Products has focused on the latter approach and have offered state-of-the-art systems for EEG & fMRI since the year 2000. Brain Products offline as well as real-time gradient and pulse artifact correction software (Analyzer and RecView packages) are currently the ‘gold standard’ for EEG fMRI artifact correction. Subject safety and image quality are preserved by Brain Products unique amplifier technology as well as by special MR compatible and MR safe electrode caps.

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