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Spatial comparison between fMRI and MEG studies on human somatosensory brain function
NemoImage
13, Number
6, 2001, Part 2 of 2 Parts ID
METHODS
E al@
- ACQUISITION
Spatial Comparison between fMRI and MEG Studies on Human Somatosensory Brain Function J. He*, S. Francis*, A. Hilkbrandt,
G.R. Barnes?, R.W. Bowtell*, P.L. Furlong?, P.G. Morris*
*Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, UK. tThe Wellcome Trust Laboratory for MEG Studies, Neurosciences Research Institute, Aston University, Birmingham, UK. Introduction Magnetoencephalography (MEG) and functional magnetic resonance temporal resolution and spatial resolution respectively, providing somatosensory study has been performed to evaluate the feasibility
imaging (fMR1) are complementary techniques, an ideal combined tool for functional brain of combining data from these two techniques.
yielding high research’. A
Methods A sensory stimulator capable of delivering stimulation frequencies within the range 20-300Hz was used’. All stimuli were 150 microns in amplitude and took the form of sinusoidal waveforms. Stimuli of 40 and 200 Hz were applied to digits 2 and 5 of the right hand of each subject. Experiments were performed on 3 healthy, right-handed male subjects, aged 20-40 years. The stimulator did not interfere with the MEG or MRI signals. MRI
methods
T,’ weighted MBEST EPI images (128 x 128 matrix) were acquired on a 3 T scanner, using a 14 cm diameter surface coil, 35 ms echo time and 1.9 kHz gradient switching frequency. Ten contiguous sagitta14 mm slices were acquired every 2 s. Image data was registered, temporally smoothed, and high pass filtered. After correlation analysis, areas with corrected p-values of 0.001 were displayed. High-resolution anatomical images (256 x 256 matrix size, 13 mm voxel size) were acquired using a 3D MP-RAGE sequence. Using a 1Zparameter AIR co-registration algorithm, activation areas were then mapped onto the anatomical images. MEG
methods
MEG data were pcquired on a 151-channel whole head MEG system (CTF Systems, Inc.). Three reference coils yielded position information, thus defining the MEG co-ordinate system. A multi-start approach’ was used to fit 1 to 3 dipoles to the main temporal peaks of the evoked response. The solutions with the lowest reduced chi-squared value were further examined and results are presented for dipole solutions with a 95% confidence volume, obtained from Monte Carlo simulations. After the MEG recording, the individuals’ headshape and reference coils positions were digitised with a Polhemus (Isotrak) system. A surface matching procedure4 was then used to yield the transformation matrix between the fMRI and MEG co-ordinate systems. Results
and Discussion
Superposition of the ECD’s showed that the MEG sources lay bilaterally in the primary somatosensory cortex (SI - areas 1 and 3b), in the secondary somatosensory cortex (SII), and also the contralateral motor/premotor areas. Good agreement was found between the MEG dipoles and fMRI source locations, with 9 of the 10 dipole confidence limits overlapping in area 3b of SI, and 2 of 4 in SII and premotor, although only 3 of 8 dipoles coincided in area 1 of SI. The separation of the representation of digits 2 and 5 in area 3b was found to be comparable in fMR1 and MEG with an average separation of approximatey 7.5 mm. The proximity of MEG and fMRI is encouraging and provides the basis for further integration of the two modalities. References 111 [2] [31 [41
1995, 12, 406-431. JS George et al., J Clin Neurophysiol, 2000, 11, 188-202. ST Francis et al., Neuroimage, M Huang et al., Electroencephalography and Clinical Neurophysiology, D Schwart et al., Brain Topography, 1996, 9, 101-l 16.
s15
1998, 108, 23-44.
13, Number
6, 2001, Part 2 of 2 Parts ID
METHODS
E al@
- ACQUISITION
Spatial Comparison between fMRI and MEG Studies on Human Somatosensory Brain Function J. He*, S. Francis*, A. Hilkbrandt,
G.R. Barnes?, R.W. Bowtell*, P.L. Furlong?, P.G. Morris*
*Magnetic Resonance Centre, School of Physics and Astronomy, University of Nottingham, Nottingham, UK. tThe Wellcome Trust Laboratory for MEG Studies, Neurosciences Research Institute, Aston University, Birmingham, UK. Introduction Magnetoencephalography (MEG) and functional magnetic resonance temporal resolution and spatial resolution respectively, providing somatosensory study has been performed to evaluate the feasibility
imaging (fMR1) are complementary techniques, an ideal combined tool for functional brain of combining data from these two techniques.
yielding high research’. A
Methods A sensory stimulator capable of delivering stimulation frequencies within the range 20-300Hz was used’. All stimuli were 150 microns in amplitude and took the form of sinusoidal waveforms. Stimuli of 40 and 200 Hz were applied to digits 2 and 5 of the right hand of each subject. Experiments were performed on 3 healthy, right-handed male subjects, aged 20-40 years. The stimulator did not interfere with the MEG or MRI signals. MRI
methods
T,’ weighted MBEST EPI images (128 x 128 matrix) were acquired on a 3 T scanner, using a 14 cm diameter surface coil, 35 ms echo time and 1.9 kHz gradient switching frequency. Ten contiguous sagitta14 mm slices were acquired every 2 s. Image data was registered, temporally smoothed, and high pass filtered. After correlation analysis, areas with corrected p-values of 0.001 were displayed. High-resolution anatomical images (256 x 256 matrix size, 13 mm voxel size) were acquired using a 3D MP-RAGE sequence. Using a 1Zparameter AIR co-registration algorithm, activation areas were then mapped onto the anatomical images. MEG
methods
MEG data were pcquired on a 151-channel whole head MEG system (CTF Systems, Inc.). Three reference coils yielded position information, thus defining the MEG co-ordinate system. A multi-start approach’ was used to fit 1 to 3 dipoles to the main temporal peaks of the evoked response. The solutions with the lowest reduced chi-squared value were further examined and results are presented for dipole solutions with a 95% confidence volume, obtained from Monte Carlo simulations. After the MEG recording, the individuals’ headshape and reference coils positions were digitised with a Polhemus (Isotrak) system. A surface matching procedure4 was then used to yield the transformation matrix between the fMRI and MEG co-ordinate systems. Results
and Discussion
Superposition of the ECD’s showed that the MEG sources lay bilaterally in the primary somatosensory cortex (SI - areas 1 and 3b), in the secondary somatosensory cortex (SII), and also the contralateral motor/premotor areas. Good agreement was found between the MEG dipoles and fMRI source locations, with 9 of the 10 dipole confidence limits overlapping in area 3b of SI, and 2 of 4 in SII and premotor, although only 3 of 8 dipoles coincided in area 1 of SI. The separation of the representation of digits 2 and 5 in area 3b was found to be comparable in fMR1 and MEG with an average separation of approximatey 7.5 mm. The proximity of MEG and fMRI is encouraging and provides the basis for further integration of the two modalities. References 111 [2] [31 [41
1995, 12, 406-431. JS George et al., J Clin Neurophysiol, 2000, 11, 188-202. ST Francis et al., Neuroimage, M Huang et al., Electroencephalography and Clinical Neurophysiology, D Schwart et al., Brain Topography, 1996, 9, 101-l 16.
s15
1998, 108, 23-44.