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Magnetoencephalography. Matt Martin 09/17/2004 APPM 4380. Overview. Description Applications Issues. Magnetoencephalography - Definition. Non-invasive brain imaging technique Passive measurement of minute current dipoles and corresponding magnetic moments

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magnetoencephalography

Magnetoencephalography

Matt Martin

09/17/2004

APPM 4380

overview
Overview
  • Description
  • Applications
  • Issues
magnetoencephalography definition
Magnetoencephalography - Definition
  • Non-invasive brain imaging technique
  • Passive measurement of minute current dipoles and corresponding magnetic moments
  • Magnetic field generated by neurons on the order of tens of femtoTeslas
  • High resolution in both space (2 - 3mm) and time (<1ms)
magnetoencephalography apparatus
Magnetoencephalography - Apparatus
  • Patient wears a helmet containing an array of 100+ sensitive magnetic field measurement devices
  • Measurement devices are called SQUIDs – Superconducting Quantum Interference Devices
  • Measurements must occur in costly magnetically shielded room
magnetoencephalography apparatus5
Magnetoencephalography - Apparatus
  • Prototype noise reducing helmet by Los Alamos National Labs
  • Lead shell must be kept below 8 Kelvin for superconducting properties
  • Surface Meissner currents expel external magnetic fields, reducing noise by six orders of magnitude
magnetoencephalography apparatus6
Magnetoencephalography - Apparatus
  • Clinical System by VSM Medtech
  • Screen is used for patient stimulation for functional mapping
magnetoencephalography applications
Magnetoencephalography - Applications
  • Epilepsy diagnosis
  • Functional Imaging and Mapping
magnetoencephalography epilepsy diagnosis
Magnetoencephalography – Epilepsy Diagnosis
  • Epilepsy is a condition wherein a patient suffers from repeated seizures that originate in the brain.
  • Manifested by extraordinarily high localized brain activity.
  • MEG ideal to locate such epileptic centers for surgical removal
magnetoencephalography epilepsy diagnosis9
Magnetoencephalography – Epilepsy Diagnosis

Epileptic seizure scan data and postprocessing

magnetoencephalography epilepsy diagnosis10
Magnetoencephalography – Epilepsy Diagnosis
  • Previous method: Intracranial Electroencephalography
  • Invasive surgery to lay EEG sensor network directly on the brain
  • Network connected to EEG monitor in hospital intensive care units.
magnetoencephalography functional imaging
Magnetoencephalography – Functional Imaging
  • Functional Imaging utilizes the high temporal resolution to generate real time brain scans
  • Doctors can use these scans to determine how the brain reacts to various stimuli
  • Multiple scans allow a brain map to be built, providing a base to begin research linking neural activity to specific classes of stimuli
magnetoencephalography functional imaging12
Magnetoencephalography – Functional Imaging
  • VSM's DataEditor: An averaged somato-sensory evoked response from a tactile stimulation of the second right digit.
  • VSM's MRIViewer: Dipole fit results for this scan.
issues
Issues
  • Noise – the background magnetic field of the earth is roughly 60 microTesla, approximately 9 orders of magnitude greater than that generated by the neurons of the brain
  • Reconstruction of imagery is inherently ill posed, as it is an inverse problem of Maxwell’s Equations
  • Mathematics of the reconstruction well beyond the scope of this presentation
sources
Sources
  • Belle Dumé: Brain Scans Made Easy.http://physicsweb.org/articles/news/8/5/5
  • CTF MEG Systems: http://www.ctf.com/products/meg/ctf/software.htm, http://www.ctf.com/products/meg/meg_apps/overview.htm
  • National Society for Epilepsy: Information on Epilepsy.http://www.epilepsynse.org.uk/pages/info/leaflets/explaini.cfm
additional readings
Additional Readings
  • Habib Ammari, et al: An Inverse Source Problem For Maxwell’s Equations In Magnetoencephalography.http://epubs.siam.org/sam-bin/getfile/SIAP/articles/37392.pdf
  • Takashi Suzuki: Parallel optimization applied to magnetoencephalography. http://www.sigmath.es.osaka-u.ac.jp/suzuki/preprint/pdf/04-4.pdf