Geometric and Electric Characteristics

Geometic and electric characteristics of the layered sphere as reported by Roth et. al.[1]
Tissue	Radius (mm)	Conductivity(S/m)
Scalp	92.0	0.450
Skull	85.0	0.00563
Cortex	80.0	0.450

Conductivity (S/m) of the head tissues
	Source 1 [3]	Source 2 [4]	Source 3 [2]
Bone		0.010
White matter	0.117	0.133	0.129
Grey matter	0.228	0.400	0.200
Skin	0.346	0.778	0.270
CSF	1.611	1.538	1.668

[1] Roth,B.J.,Saypol.J. M., Hallet.,M. and Cohen,L.G. (1991 ) A theoretical calculation of the electric field induced in the cortex during magnetic stimulation. Electroencephalogaphv and Clinical Neurophyswlogy, 81 , 47-56.

[2] Holton, K. S. and Walker C. F. (1990) Correlation of a magnetic resonance brain image and tisue impedance. IEEE EMBS 92-93.

[3] Geddes L.A. and Baker L.E. (1967) 'The specific resistance of biological material: a compendium of data for the biomedical engineer and physiologist. Medical and Biological Engineering, 5 271 - 219.

[4] Geddes, L. A. (1989) Optimal stimulation duration for extracranial cortical stimulation. Neurosuyey, 20, 94-99.