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Magnetoencephalography

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

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  1. Magnetoencephalography Matt Martin 09/17/2004 APPM 4380

  2. Overview • Description • Applications • Issues

  3. 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)

  4. 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

  5. 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

  6. Magnetoencephalography - Apparatus • Clinical System by VSM Medtech • Screen is used for patient stimulation for functional mapping

  7. Magnetoencephalography - Applications • Epilepsy diagnosis • Functional Imaging and Mapping

  8. 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

  9. Magnetoencephalography – Epilepsy Diagnosis Epileptic seizure scan data and postprocessing

  10. 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.

  11. 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

  12. 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.

  13. 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

  14. 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

  15. 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

  16. Questions

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