In this video, we introduce a unique, EEG-fMRI recording protocol that can be used in both clinic and research settings. Simultaneous EEG-fMRI is a technique that provides synergy in the understanding and localization of seizure onset and epilepsy. Implementation of simultaneous EEG-fMRI can be used to map the spatial temporal processes of epileptic events, which can guide neurosurgical treatment for patients with medication refractory epilepsy, which is up to a third of the patients with epilepsy.
To begin, mark electrode positions on the patient's scalp based on the 10-20 system. After marking electrode placement positions, clean the patient's scalp using skin prep gel on gauze. Place conductive paste on one electrode cup and adhere it to the patient's scalp, following the channel name on the electrodes cable.
After placing the last electrode, secure all the electrodes to the scalp with glue on gauze. Then arrange all the electrode cables and place the cable junction far from the scalp by placing pads of gauze on the center of the patient's head. Place an elastic head cover to secure all the electrodes.
Connect the harness to the amplifier to monitor the patient's EEG synchronously with video recordings. In the monitoring room, connect the USB 2 adapter to the trigger box kit with a cable. Then connect the sync box to the USB adapter with a cable and connect one end of the fiber optic cable to the sync box.
Connect a USB port cable from the USB 2 adapter to the recording computer and connect a USB port cable from the sync box to the recording computer. Additionally, connect a USB port cable from the trigger box to the recording computer and the software license dongle to the recording computer. Confirm the trigger connection from the scanner.
In the scanning room, set up the EEG recording amplifier and the MR-sled kit inside the scanner. Connect the end of the fiber optic cable in the scanning room to the back of the amplifier and turn on the amplifier. Once the setup is complete in the scanning room, move to the monitoring room and then open the EEG recording software in the recording computer and create a workspace by clicking the new workspace menu under the File tab.
Scan the amplifier by clicking the Scan for Amplifier button and set up appropriate parameters including sampling rates and low and high cutoff frequencies for recording. Set the scanner parameters for the fMRI. Switch off the scanner helium pump in the scanning room to further reduce the introduction of artifacts into the EEG signal.
Transfer the patient to the scanning waiting room and explain the recording procedure to the patient. Clean the patient's back and right below the left shoulder for ECG lead placement. Apply an abrasive electrolyte gel on the ECG lead and place it on the left backside of the patient.
Apply adhesive tape around the ECG lead and cable to minimize scanning artifacts during the recording. Disconnect the EEG harness and connect the cable junctions to the interface box. Next in the scanning room, lay the patient down on the scanning table with the head in the open bottom half of the head coil.
Apply earplugs to reduce the scanner's noise and place a cushion around the patient's head to minimize head movement artifacts. Connect the top half of the head coil to close the bird cage coil around a patient's head. Adjust the bed height.
Connect the interface box to the amplifier and place the MR safe sandbags around the cables. Next in the monitoring room, click the impedance check button to check the impedance of the EEG electrodes. After confirming that the patient is ready for the recording, start the EEG recording by clicking the play button.
Run the fMRI acquisition scan. Open the EEG analysis software. For MR artifact correction, click on the Transformations, then Special Signal Processing and MR Correction tab.
In a newly created window, select Use Markers. Choose a trigger signal from the scanner and click Next. Select the interleaved and Based on Time options, insert the time information of the trigger signal and click on Next.
Check Enable Baseline Correction for Average and uncheck Compute Baseline Over the Whole Artifact. Insert the start and end values. Select Use Sliding Average Calculation.
Insert the Total Number of Intervals for Sliding Average. Check the Common Use of All Channels for Bad Intervals and Correction and click Next. In the following window, select Use All Channels for Correction and click Next.
Check Do Downsampling and choose 500 hertz for a new frequency. Check Apply Lowpass Filter, select Use FIR Filter, insert 70 hertz for a cutoff frequency and click Next. Select one Store Corrected Data option.
Then click Finish. To apply direct current removal by a high-pass filter, click on the Transformation. Then Data Filtering and IIR filters tab.
Check Enabled under Low Cutoff, insert a cutoff frequency of 0.5 hertz. Choose the filter order as two and click OK.To remove cardio ballistic artifacts, click the Transformations, then Special Signal Processing and CB Correction tab. On the window that subsequently opens, select Use Peak Detection and check Semiautomatic Mode.
Under the Search Pulse Template section, insert Start in seconds as 60 and Length in seconds as 20. Then check Mark Found Template to confirm appropriate ECG channel is chosen. Insert parameters for Pulse Rate and Correlation and Amplitude.
Insert R for mark pulses with our peak markers and click on Next. Check Use Whole Data to Compute the Time Delay and insert the Total Number of Pulse Intervals Used for Average. Under Correct Following Channels, move all the EEG channels to the right column, except the ECG channel and click Next.
On the next page, select one Store Corrected Data Option as preferred and click on Finish. Slide over the time axis at the bottom of the navigation bar and check where the base template ECG is highlighted with a blue shaded box to confirm the base template of the ECG is correctly marked. In the CB correction interactive mode window, check each marked ECG by double-clicking its corresponding row in the table.
Adjust the detected peak locations as needed by moving the red vertical lines. Once all ECGs are reviewed, click on Finish. To apply power line and alternating current noise removal by a notch filter, click on the Transformation then Data Filtering and IIR Filters tab.
Then check Notch Enabled, select Frequency and click OK.In the processed EEG data, clear focal left temporal slow waves are present, which is observed from the EEG recorded at the epilepsy monitoring unit. Our unique protocol provides a smooth transition for patients with epilepsy from the epilepsy monitoring unit to the scanning room, which can be further extended into the postictal window.
