Physikalische und physiologische Grundlagen der transkraniellen Magnetstimulation

Zusammenfassung

Der Beitrag liefert einen Überblick über die technischen, biophysikalischen und physiologischen Grundlagen der transkraniellen Magnetstimulation (TMS). Ausgehend von der Technik eines Stimulators und des Wirkungsprinzips der TMS werden der zeitliche Verlauf eines Stimulationspulses sowie die räumliche Verteilung der im Kopf induzierten Felder dargestellt. Auf der Grundlage von Schwellenmessungen werden Umrechnungsfaktoren für verschiedene gängige Stimulatorkonfigurationen angegeben. Anschließend wird auf die Vergleichbarkeit von technischen Parametern zwischen Kernspinresonanztomographie und TMS eingegangen. Zum Schluss sind kurz mögliche technische Weiterentwicklungen dargestellt.

Summary

We present an overview on the technical, biophysical, and physiological fundamentals of transcranial magnetic stimulation (TMS). Starting with the stimulator technique and the active principle of TMS we illustrate the time course of a stimulation pulse and the spatial distribution of the induced fields. Based on threshold measurements transformation factors are given that allow the comparison of stimulation intensities using different stimulators. We discuss the comparability of technical parameters known from magnetic resonance imaging and TMS. Finally, we give an brief overview on putative further developments.

Schlüsselwörter

Stimulationspuls - monophasisch - biphasisch - Rundspule - Doppelspule - induzierte Feldverteilung - Nervenmodell - transkranielle Magnetstimulation

Keywords

Stimulation pulse - monophasic - biphasic - round coil - double coil - induced fields - nerve model - transcranial magnetic stimulation

• Literatur

• 1 Barker AT, Jalinous R, Freeston IL. Non-invasive magnetic stimulation of human motor cortex. Lancet 1985; 01: 1106-7.
• 2 Barker AT, Garnham CW, Freeston IL. Magnetic nerve stimulation: the effect of waveform on efficiency, determination of neural membrane time constants and the measurement of stimulator output. Electroenceph Clin Neurophysiol – Suppl 1991; 43: 227-37.
• 3 Cerri G, De Leo R, Moglie F, Schiavoni A. An accurate 3-D model for magnetic stimulation of the brain cortex. J Med Engineer Technol 1995; 19: 7-16.
• 4 Chen R, Classen J, Gerloff C, Celnik P, Wassermann EM, Hallett M, Cohen LG. Depression of motor cortex excitability by low-frequency transcranial magnetic stimulation. Neurology 1997; 48: 1398-403.
• 5 Classen J, Knorr U, Werhahn KJ, Schlaug G, Kunesch E, Cohen LG, Seitz RJ, Benecke R. Multimodal output mapping of human central motor representation on different spatial scales. J Physiol 1998; 512: 163-79.
• 6 Davey K, Epstein CM. Magnetic stimulation coil and circuit design. IEEE Trans Biomed Eng 2000; 47: 1493-9.
• 7 Heller L, van Hulsteyn DB. Brain stimulation using electromagnetic sources: theoretical aspects. Biophys J 1992; 63: 129-38.
• 8 Herwig U, Kolbel K, Wunderlich AP, Thielscher A, von Tiesenhausen C, Spitzer M, Schönfeldt-Lecuona C. Spatial congruence of neuronavigated transcranial magnetic stimulation and functional neuroimaging. Clin Neurophysiol 2002; 113: 462-8.
• 9 Hill AC, Davey NJ, Kennard C. Current orientation induced by magnetic stimulation influences a cognitive task. Neuroreport 2000; 11: 3257-9.
• 10 Hsu KH, Durand DM. Prediction of neural excitation during magnetic stimulation using passive cable models. IEEE Trans Biomed Eng 2000; 47: 463-71.
• 11 IEC. Particular requirements for the safety of magnetic resonance equipment for medical diagnosis. In: Diagnostic imaging equipment, publication IEC 60601-2-33, medical electrical equipment, Part 2. Genf: International Electrotechnical Commission (IEC); 1995.
• 12 Ilmoniemi RJ, Ruohonen J, Virtanen J. Relationsships between magnetic stimulation and MEG/EEG. In: Nilsson J, Panizza M, Grandori F. (eds). Advances in Magnetic Stimulation – Mathematical Modeling and Clinical Applications, Vol. 2/2. Pavia: Fondazione Salvatore Maugeri Edizioni; 1996: 65-72.
• 13 Ilmoniemi RJ, Ruohonen J, Karhu J. Transcranial magnetic stimulation- a new tool for functional imaging of the brain. Crit Rev Biomed Eng 1999; 27: 241-84.
• 14 Kammer T, Beck S, Erb M, Grodd W. The influence of current direction on phosphene thresholds evoked by transcranial magnetic stimulation. Clin Neurophysiol 2001; 112: 2015-21.
• 15 Kammer T, Beck S, Thielscher A, Laubis-Herrmann U, Topka H. Motor thresholds in humans. A transcranial magnetic stimulation study comparing different pulseforms, current directions and stimulator types. Clin Neurophysiol 2001; 112: 250-8.
• 16 Keck ME, Sillaber I, Ebner K, Welt T, Toschi N, Kaehler ST, Singewald N, Philippu A, Elbel GK, Wotjak CT, Holsboer F, Landgraf R, Engelmann M. Acute transcranial magnetic stimulation of frontal brain regions selectively modulates the release of vasopressin, biogenic amines and amino acids in the rat brain. Eur J Neurosci 2000; 12: 3713-20.
• 17 Krasteva V, Papazov S, Daskalov I. Magnetic stimulation for non-homogeneous biological structures. BioMedical Engineering OnLine 2002; 01: 3.
• 18 Kujirai T, Caramia MD, Rothwell JC, Day BL, Thompson PD, Ferbert A, Wroe S, Asselman P, Marsden CD. Corticocortical inhibition in human motor cortex. J Physiol 1993; 471: 501-19.
• 19 Maccabee PJ, Amassian VE, Eberle LP, Cracco RQ. Magnetic coil stimulation of straight and bent amphibian and mammalian peripheral nerve in vitro: locus of excitation. J Physiol 1993; 460: 201-19.
• 20 Marg E, Rudiak D. Phosphenes induced by magnetic stimulation over the occipital brain: description and probable site of stimulation. Optometry Vis Sci 1994; 71: 301-11.
• 21 Merton PA, Morton HB. Stimulation of the cerebral cortex in the intact human subject. Nature 1980; 285: 227.
• 22 Nagarajan SS, Durand DM, Warman EN. Effects of induced electric fields on finite neuronal structures- a simulation study. IEEE Trans Biomed Eng 1993; 40: 1175-88.
• 23 Nielsen JF, Klemar B, Kiilerich H. A new highfrequency magnetic stimulator with an oil-cooled coil. J Clin Neurophysiol 1995; 12: 460-7.
• 24 Pascual-Leone A, Valls-Solé J, Wassermann EM, Hallett M. Responses to rapid-rate transcranial magnetic stimulation of the human motor cortex. Brain 1994; 117: 847-58.
• 25 Ravazzani P, Ruohonen J, Tognola G, Anfosso F, Ollikainen M, Ilmoniemi RJ, Grandori F. Frequency-related effects in the optimization of coils for the magnetic stimulation of the nervous system. IEEE Trans Biomed Eng 2002; 49: 463-71.
• 26 Reilly JP. Peripheral nerve stimulation by induced electric currents: exposure to time-varying magnetic fields. Med Biol Eng Comput 1989; 27: 101-10.
• 27 Roth BJ, Basser PJ. A model of the stimulation of a nerve fiber by electromagnetic induction. IEEE Transactions on Biomedical Engineering 1990; 37: 588-96.
• 28 Roth BJ, Maccabee PJ, Eberle LP, Amassian VE, Hallett M, Cadwell J, Anselmi GD, Tatarian GT. In vitro evaluation of a 4-leaf coil design for magnetic stimulation of peripheral nerve. Electroenceph Clin Neurophysiol 1994; 93: 68-74.
• 29 Sakai K, Ugawa Y, Terao Y, Hanajima R, Furubayashi T, Kanazawa I. Preferential activation of different I wave by transcranial magnetic stimulation with a figure-of-eight-shaped coil. Exp Brain Res 1997; 113: 24-32.
• 30 Sarvas J. Basic mathematical and electromagnetic concepts of the biomagnetic inverse problem. Physics Med Biol 1987; 32: 11-22.
• 31 Schaefer DJ, Bourland JD, Nyenhuis JA. Review of patient safety in time-varying gradient fields. J Magn Reson Imaging 2000; 12: 20-9.
• 32 Thielscher A. Abschätzung zum Ort der Nervenstimulation durch Magnetfelder – Ein Beitrag zu den biophysikalischen Grundlagen der Transkraniellen Magnetstimulation. Dissertation: Universität Ulm. 2002
• 33 Thielscher A, Kammer T. Linking Physics with Physiology in TMS: A spherefield model to determine the cortical stimulation site in TMS. Neuroimage 2002; 17: 1117-30.
• 34 Wang H, Wang X, Scheich H. LTD and LTP induced by transcranial magnetic stimulation in auditory cortex. Neuroreport 1996; 07: 521-5.