Safety and EEG data quality of concurrent high-density EEG and high-speed fMRI at 3 Tesla

Abstract

PurposeConcurrent EEG and fMRI is increasingly used to characterize the spatial-temporal dynamics of brain activity. However, most studies to date have been limited to conventional echo-planar imaging (EPI). There is considerable interest in integrating recently developed high-speed fMRI methods with high-density EEG to increase temporal resolution and sensitivity for task-based and resting state fMRI, and for detecting interictal spikes in epilepsy. In the present study using concurrent high-density EEG and recently developed high-speed fMRI methods, we investigate safety of radiofrequency (RF) related heating, the effect of EEG on cortical signal-to-noise ratio (SNR) in fMRI, and assess EEG data quality.Materials and methodsThe study compared EPI, multi-echo EPI, multi-band EPI and multi-slab echo-volumar imaging pulse sequences, using clinical 3 Tesla MR scanners from two different vendors that were equipped with 64- and 256-channel MR-compatible EEG systems, respectively, and receive only array head coils. Data were collected in 11 healthy controls (3 males, age range 18–70 years) and 13 patients with epilepsy (8 males, age range 21–67 years). Three of the healthy controls were scanned with the 256-channel EEG system, the other subjects were scanned with the 64-channel EEG system. Scalp surface temperature, SNR in occipital cortex and head movement were measured with and without the EEG cap. The degree of artifacts and the ability to identify background activity was assessed by visual analysis by a trained expert in the 64 channel EEG data (7 healthy controls, 13 patients).ResultsRF induced heating at the surface of the EEG electrodes during a 30-minute scan period with stable temperature prior to scanning did not exceed 1.0° C with either EEG system and any of the pulse sequences used in this study. There was no significant decrease in cortical SNR due to the presence of the EEG cap (p > 0.05). No significant differences in the visually analyzed EEG data quality were found between EEG recorded during high-speed fMRI and during conventional EPI (p = 0.78). Residual ballistocardiographic artifacts resulted in 58% of EEG data being rated as poor quality.ConclusionThis study demonstrates that high-density EEG can be safely implemented in conjunction with high-speed fMRI and that high-speed fMRI does not adversely affect EEG data quality. However, the deterioration of the EEG quality due to residual ballistocardiographic artifacts remains a significant constraint for routine clinical applications of concurrent EEG-fMRI.

Quantitative Analyses Help in Choosing Between Simultaneous vs. Separate EEG and fMRI

“…Quality comparison of EEG data has been investigated between simultaneous and separate recordings by visual inspection (Laufs et al, 2003; Foged et al, 2017) and simulation studies (Ihalainen et al, 2015). More quantitative spectral approaches for comparing measurements have been described.…”

“…We argue that for weaker effects this might not be the case. fMRI TR duration is considered of limited influence (Foged et al, 2017). The regional effects found in this study are somewhat different from these described in the literature (Luo and Glover, 2012; Ihalainen et al, 2015; Klein et al, 2015), underlining that for every individual set-up a quality test is advisable.…”

Exploring the advantages of multiband fMRI with simultaneous EEG to investigate coupling between gamma frequency neural activity and the BOLD response in humans

“…However, given the increase in temperature (∼0.8°C) in the Tp8 electrode, which also has a relatively long lead, the removal of the ECG lead alone is unlikely to ensure that high SAR sequences can be run safely with EEG system present. These findings are in general agreement with recent work that also considered safety implication of MB (Foged et al, ). It is also important to note that minimal heating effects were observed at the MRI scanner bore location suggesting that the MR scanning was not increasing the ambient temperature of the bore.…”

Investigation of True High Frequency Electrical Substrates of fMRI-Based Resting State Networks Using Parallel Independent Component Analysis of Simultaneous EEG/fMRI Data

“…This was necessary because it is not customary to acquire MB-EPI data simultaneously with EEG and at the time of the experiment, this was the first study to do so according to our knowledge. However, at the time that this report was being peer-reviewed, we learned that others had performed simultaneous multiband fMRI and EEG, albeit with different equipment (Lewis et al, 2016 ; Foged et al, 2017 ). In fact Foged et al showed, using temperature measurements, that it is safe to combine high density EEG with fast fMRI techniques such as multiband EPI (Foged et al, 2017 ).…”

“…However, at the time that this report was being peer-reviewed, we learned that others had performed simultaneous multiband fMRI and EEG, albeit with different equipment (Lewis et al, 2016 ; Foged et al, 2017 ). In fact Foged et al showed, using temperature measurements, that it is safe to combine high density EEG with fast fMRI techniques such as multiband EPI (Foged et al, 2017 ). Subsequent to our in-house testing, the procedure was approved by Auburn University's Institutional Review Board (IRB) as well as the MR safety committee.…”