Ee Gf Mri 2010 02 24
1
EEG Cap Specifications • 68-channel Aegis Array cap (Figure 2) • Wires run on inner side of cap from each electrode going into a cable located at base of cap • Electrodes pick up electric potential from the scalp to preamplifier • Cap is MRI compatible with vented lycra shell with low profile electrodes for subject comfort • Correct placement of EEG cap essential for accurate localization of EEG activity Challenges: There exists many challenges during the simultaneous acquisition of EEG and fMRI data (Figure 1). Gradient echo imaging (Figure 1A) and eye blinks (Figure 1B) introduce severe artifacts in the EEG signal that must be filtered by a software package called EMSE Suite in later processing steps. Other challenges include the precise head placement of the EEG cap, achieving low levels of impedance in order to obtain the highest quality EEG signal, and subject comfort during the scan. Purpose: To describe the methods used, challenges, and future applications of obtaining simultaneous EEG and functional MRI (EEG/fMRI). Rationale: EEG/fMRI is a safe and effective method of simultaneously evaluating the electrical activity in the brain (high temporal resolution with EEG) and the metabolic state of the brain (high spatial resolution with fMRI). When used in tandem, these techniques have the ability to create a high spatio-temporal image of both the metabolic state and neuronal signals in the brain. MRI Scan Specifications Functional MRI acquisition - 8-channel Sense head coil - Single shot fast field echo (FFE) echo planar imaging (EPI) - 35 slices (4 mm thick) in coronal plane for whole brain coverage - Repetition Time (TR) = 2000 msec; Echo Time (TE) = 38 msec - 150 dynamic scans, alternating eye blinking and rest condition every 15 scans (30 sec); scan time = 5 min, 8 sec T1 3D Anatomical Image Methods of Obtaining Simultaneous EEG and fMRI 1 Amanda Golsch, 3 Jane B. Allendorfer, 2 Leonid Rozhkov, 1 Ron Pratt, 1 Scott K. Holland, 1 , 3 Jerzy P. Szaflarski 1 Imaging Research Center and 2 Department of Neurology, Cincinnati Children’s Hospital Medical Center, and 3 Department of Neurology, University of Cincinnati Academic Health Center, Cincinnati, OH. Methods: The Imaging Research Center (IRC) at Cincinnati Children’s Hospital coordinates the use of a Philips 3T MRI system and the Electrode Arrays EEG system to obtain images and to record the electrical activity generated by neurons in the brain. Figure 1. EEG data obtained inside the scanner: artifacts induced by gradient echo imaging (A) and by eye blinks (B). A. Scanner starting B. Start of rapid eye blinking Figure 2 Impedance • Once the EEG cap is securely placed on subject’s head, then Egel (electrode gel) is applied. • Important for EGel to have direct contact with scalp • Rotate an Egel-filled syringe in clockwise and counter-clockwise motion to displace hair and slightly abrade scalp, then inject EGel • Check for low impedance levels (Figure 3) - Essential for obtaining a good EEG waveform - Dark blue or black color indicates low impedance - Hair products may increase impedance Figure 3 EEG System Components MRI-compatible preamplifier (Figure 4) • Cable that extends from base of cap is attached to preamplifier • Compares EEG electrode potentials with that from reference electrode and amplifies the difference from microvolts to millivolts Figure 4 Isolation unit • Converts electric potentials in the current-conducting wires into light pulses • Ensures no RF interference leakage in and out of MR suite Clinical and Research Applications in Epilepsy: Simultaneous EEG/fMRI is a non-invasive way for clinicians to map normal and pathological brain function and electrical activity allowing us to map brain areas involved in e.g., sleep- related activity (sleep spindles, vertex waves), wakefulness (alpha activity) or generation of epileptiform discharges in patients with epilepsy. This method may also provide additional localizing information in the presurgical work-up of epilepsy patients. Overall, Anatomical scan acquisition (T1 3D FFE) - 180 slices (1mm isotropic) in sagittal plane - flip angle of 8º; TR = 8.1 msec; TE = 3.7 msec total scan time = 5 min, 54 sec Figure 6. Fluctuations in MR signal intensity over 150 dynamic scans in combined visual and motor cortex regions (Figure 5 above). FMRI images in the coronal (A), axial (B) and sagittal (C) views. B A C • All electrodes placed according to the 10-20 international system: - FP1 and FP2 sensors must be located in middle of forehead slightly to the left and right of midline - CZ sensor must be aligned with central midline of the scalp • Precise EEG cap placement limited by non-homogeneous nature of skull FMRI data processing - Performed using Cincinnati Children’s Hospital Image Processing software - General linear modeling was performed to examine blood oxygenation level dependent (BOLD) response to eye blinks compared to rest condition (Figure 5) - Phasic pattern of MR signal intensity fluctuations over time corresponding to periods of eye blinking and rest (Figure 6) Figure 5. Comparison of BOLD response to eye blinks and resting condition in a single subject (uncorrected p<0.01). Regions in color indicate increased BOLD response to eye blinks, e.g. visual cortex (A) and motor cortex associated with facial movements (B). A B t=3. 4 t=10
description
EEG/fMRI Poster Presentation
Transcript of Ee Gf Mri 2010 02 24
EEG Cap Specifications• 68-channel Aegis Array cap (Figure 2)• Wires run on inner side of cap from each
electrode going into a cable located at base of cap
• Electrodes pick up electric potential from the scalp to preamplifier
• Cap is MRI compatible with vented lycra shell with low profile electrodes for subject comfort
• Correct placement of EEG cap essential for accurate localization of EEG activity
Challenges: There exists many challenges during the simultaneous acquisition of EEG and fMRI data (Figure 1). Gradient echo imaging (Figure 1A) and eye blinks (Figure 1B) introduce severe artifacts in the EEG signal that must be filtered by a software package called EMSE Suite in later processing steps. Other challenges include the precise head placement of the EEG cap, achieving low levels of impedance in order to obtain the highest quality EEG signal, and subject comfort during the scan.
Purpose: To describe the methods used, challenges, and future applications of obtaining simultaneous EEG and functional MRI (EEG/fMRI).
Rationale: EEG/fMRI is a safe and effective method of simultaneously evaluating the electrical activity in the brain (high temporal resolution with EEG) and the metabolic state of the brain (high spatial resolution with fMRI). When used in tandem, these techniques have the ability to create a high spatio-temporal image of both the metabolic state and neuronal signals in the brain.
MRI Scan Specifications Functional MRI acquisition- 8-channel Sense head coil- Single shot fast field echo (FFE) echo planar imaging (EPI)- 35 slices (4 mm thick) in coronal plane for whole brain coverage- Repetition Time (TR) = 2000 msec; Echo Time (TE) = 38 msec- 150 dynamic scans, alternating eye blinking and rest condition every 15 scans (30 sec); scan time = 5 min, 8 sec
T1 3D Anatomical Image
Methods of Obtaining Simultaneous EEG and fMRI1Amanda Golsch, 3Jane B. Allendorfer, 2Leonid Rozhkov, 1Ron Pratt, 1Scott K. Holland, 1,3Jerzy P. Szaflarski
1Imaging Research Center and 2Department of Neurology, Cincinnati Children’s Hospital Medical Center, and 3Department of Neurology, University of Cincinnati Academic Health Center, Cincinnati, OH.
Methods: The Imaging Research Center (IRC) at Cincinnati Children’s Hospital coordinates the use of a Philips 3T MRI system and the Electrode Arrays EEG system to obtain images and to record the electrical activity generated by neurons in the brain.
Figure 1. EEG data obtained inside the scanner: artifacts induced by gradient echo imaging (A) and by eye blinks (B).
A. Scanner starting
B. Start of rapid eye blinking
Figure 2
Impedance• Once the EEG cap is securely placed on subject’s head, then Egel (electrode gel) is applied.• Important for EGel to have direct contact with scalp• Rotate an Egel-filled syringe in clockwise and counter-clockwise motion to displace hair and slightly abrade scalp, then inject EGel• Check for low impedance levels (Figure 3) - Essential for obtaining a good EEG waveform - Dark blue or black color indicates low impedance - Hair products may increase impedance
Figure 3
EEG System Components MRI-compatible preamplifier (Figure 4)• Cable that extends from base of cap is attached to preamplifier • Compares EEG electrode potentials with that from reference electrode and amplifies the difference from microvolts to millivolts
Figure 4
Isolation unit • Converts electric potentials in the current-conducting wires into light pulses• Ensures no RF interference leakage in and out of MR suite
Clinical and Research Applications in Epilepsy: Simultaneous EEG/fMRI is a non-invasive way for clinicians to map normal and pathological brain function and electrical activity allowing us to map brain areas involved in e.g., sleep-related activity (sleep spindles, vertex waves), wakefulness (alpha activity) or generation of epileptiform discharges in patients with epilepsy. This method may also provide additional localizing information in the presurgical work-up of epilepsy patients. Overall, it allows us to gain greater understanding of the neurobiology of electrical brain signals.
Anatomical scan acquisition (T1 3D FFE)- 180 slices (1mm isotropic) in sagittal plane - flip angle of 8º; TR = 8.1 msec; TE = 3.7 msec total scan time = 5 min, 54 sec
Figure 6. Fluctuations in MR signal intensity over 150 dynamic scans in combined visual and motor cortex regions (Figure 5 above).
FMRI images in the coronal (A), axial (B) and sagittal (C) views.
BA C
• All electrodes placed according to the 10-20 international system: - FP1 and FP2 sensors must be located in middle of forehead slightly to the left and right of midline - CZ sensor must be aligned with central midline of the scalp• Precise EEG cap placement limited by non-homogeneous nature of skull
FMRI data processing- Performed using Cincinnati Children’s Hospital Image Processing software- General linear modeling was performed to examine blood oxygenation level dependent (BOLD) response to eye blinks compared to rest condition (Figure 5)- Phasic pattern of MR signal intensity fluctuations over time corresponding to periods of eye blinking and rest (Figure 6)
Figure 5. Comparison of BOLD response to eye blinks and resting condition in a single subject (uncorrected p<0.01). Regions in color indicate increased BOLD response to eye blinks, e.g. visual cortex (A) and motor cortex associated with facial movements (B).
A
B
t=3.4 t=10
