by Dr. Tracy Warbrick
Application Specialist EEG-fMRI (Brain Products)
Standard MR-related artifact correction methods are sufficient for most applications, however, data susceptible to motion artifact can be more challenging. So, we are very pleased to announce that we will be introducing carbon wire loops (CWLs) for the BrainCap MR to help with handling motion-related artifact.
For EEG data acquired during fMRI scanning the gradient artifact and cardioballistic artifact are corrected using an average template subtraction approach. This relies on an artifact signal that repeats regularly; for gradient artifact it is the imaging volume that repeats over time and for cardioballistic artifact it is the cardiac cycle. Motion-related artifacts, on the other hand, are non-cyclic and unpredictable. Therefore, we need to consider a different approach.
Movement-induced signals can be measured by a loop moving inside a magnetic field (Faraday’s law of induction). As such, CWLs attached to the BrainCap MR can be used for obtaining reference signals inside the MRI scanner. The small movements of these CWLs in the magnetic field generate signals that can then be used to estimate and remove motion artifacts from the EEG.
CWLs have already been implemented successfully by some researchers, but until now a commercial solution has not been available. Our CWL solution consists of five bipolar loops permanently attached to cap fabric and situated; the centres of the loops are at AFz, T7, T8, CCPz, and Oz. Because the loops are bipolar, a BrainAmp ExG MR amplifier will be needed to record these signals. The CWLs can be included on any of our standard BrainCap MRs and can be used in MRI scanners up to 3T (subject to our general 3T EEG-fMRI conditions for use).
There are several approaches for detecting and correcting motion artifacts based on the CWL reference signals. Currently, our priority is to provide the CWLs and leave the choice of the correction method to our users who are experts in this field. There are open source software packages available for this correction method that can be integrated in the data processing pipeline.
As with all our products, we like to test them thoroughly and be able to make the most appropriate recommendations for our customers. We were in the final stages of data quality testing when the current global health situation arose. Therefore, we ask for your patience while we wait for the situation to improve so that we can continue our measurements without risk to us, our volunteers, or our cooperation partners. In the meantime, we are happy to discuss your research needs and whether Carbon Wire Loops for the BrainCap MR are a good solution for you.