New support article on how to determine the nature of triggers and optimize configuration in EEG-fMRI recordings

by Dr. Alex Kreilinger – Technical Product Manager (Brain Products)
& Cilia Jäger, Ph.D. – Application Specialist EEG-fMRI (Brain Products)

Emblem EEG-fMRIFrom recurring feedback and our experience, we’ve learned that setting up the recording parameters for correct trigger information in EEG-fMRI is a common source of confusion.

The main problems with recording triggers in EEG-fMRI experiments are the following:

  • Triggers are especially important to correct for MR-based artifacts. Even more so, the triggers need to be precisely time-locked to the onset of these artifacts in order to properly remove them from the EEG signals.

  • It is often not easy to know what kind of trigger is coming from the MR device. It is reasonably straightforward to determine whether it’s optical or electrical, but then, the length and shape of the trigger pulses can only be determined by having access to the technical specifications of the MR device, or by actually looking at the signal (for example with an oscilloscope). If none of these two options are available, the user can try to deduce the type of trigger by connecting it to our TriggerBox (Plus) and checking the resulting markers in our recording and analysis software.

  • Even then, users are often tempted to draw the wrong conclusions, as it is not obvious whether resulting markers come from a pulse onset or offset. It gets even more complicated when trigger pulses are too short to be detected with the BrainAmp’s maximum sampling rate of 5000 Hz, thereby requiring the use of the TriggerBox (Plus)’ convenient bit stretcher.

In the new support article, we provide guidance on how to determine the type, shape, and length of triggers. Once these characteristics have been figured out, we demonstrate when and how to use the bit stretcher and point out how it affects the appearance of markers. Finally, we give advice on how to set up the digital port settings to receive triggers at the right time, depending on the combination of trigger type, shape, length, and use of the bit stretcher.

Go to full support article

By providing this article, we hope to make setting up the BrainAmp MR system in the MR environment easier. If you find important information missing or have follow-up questions, please do not hesitate to contact us.

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