High field MRI: clinical applications and safety

1

Using MRI for the Direct Detection of Spontaneous
Alpha Wave Activity in the Brain
D. Konn, P. Gowland, R. Bowtell. Magnetic
Resonance Centre, School of Physics and
Astronomy, University of Nottingham.
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Why direct detection?

• Direct detection of neuronal activity
• Remove uncertainties in the location of the
  activity.
• Increase temporal resolution, as not limited by
  haemodynamic response.
• Bodurka J et al, J Magn Reson 1999137265-271

3
How?

• Associated magnetic fields cause phase change.
• Cortical activity modelled as current dipole of
  finite spatial extent.
• MEG - evoked activity 10 nAm
• - spontaneous alpha waves 100 nAm
• 8 nAm detectable phase change.
• Konn D, Gowland P, Bowtell R. Magn Reson Med
  20035040-49.

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What are alpha waves?

• 8 - 13 Hz oscillations.
• Prominent with eyes closed, blocked by visual
  stimulus.
• Parietal and occipital regions.

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MRI methodology

• 6 volunteers (5 useable), spherical phantom
• - 8 cycles
• - 60 secs eyes closed, 60 secs eyes open with
  6 Hz reversing checkerboard.

• Scanning on 3T system
• - Coronal, occipital lobe - flip angle 22
• - EPI - 64 x 64
• - TR 40 ms - 4 x 4 x 9 mm3
• - TE 24 ms

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Analysis

• Remove first 10 secs.
• Unwrap phase images.
• Correct for bulk motion.
• Normalise the phase images.
• Split each block into two. (16 cycles of 25 secs
  closed / open).

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Analysis

• Frequency spectrum of phase of each voxel during
  each time block.
• T-test eyes-closed v eyes-open.
• Greater power in phase oscillations with
  eyes-closed.
• 0.5 Hz or 1 Hz width optimum.
• Clusters of 3 voxels corrected Plt0.05.
• BOLD analysis.

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Results - spherical phantom (control)

• 5 of voxels active.
• Equal number with greater power in eyes open as
  eyes closed.
• No significant clusters.

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Results - volunteer RB
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Results- volunteer RB
BOLD
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Results - volunteer SG
10.9 - 11.4 Hz
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Results - volunteer JM
BOLD
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Further evidence

• No active clusters in magnitude at these
  frequencies.
• No clusters with greater power in eyes-open.

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Conclusions

• Clusters show behaviour that is characteristic of
  alpha wave activity.
• Further work needed to confirm results
• Simultaneous EEG
• Imaging at higher field strength.

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Acknowledgements
Prof. Richard Bowtell Dr. Penny Gowland Dr. Sue
Francis