The Influence of Age and Skull Conductivity on Surface and Subdermal Bipolar EEG Leads

Abstract

Bioelectric source measurements are influenced by the measurement location as well as the conductive properties of the tissues. Volume conductor effects such as the poorly conducting bones or the moderately conducting skin are known to affect the measurement precision and accuracy of the surface electroencephalography (EEG) measurements. This paper investigates the influence of age via skull conductivity upon surface and subdermal bipolar EEG measurement sensitivity conducted on two realistic head models from the Visible Human Project. Subdermal electrodes (a.k.a. subcutaneous electrodes) are implanted on the skull beneath the skin, fat, and muscles. We studied the effect of age upon these two electrode types according to the scalp-to-skull conductivity ratios of 5, 8, 15, and 30 : 1. The effects on the measurement sensitivity were studied by means of the half-sensitivity volume (HSV) and the region of interest sensitivity ratio (ROISR). The results indicate that the subdermal implantation notably enhances the precision and accuracy of EEG measurements by a factor of eight compared to the scalp surface measurements. In summary, the evidence indicates that both surface and subdermal EEG measurements benefit better recordings in terms of precision and accuracy on younger patients.

Interpreting EEG alpha activity

“…Thus, the age related decline seen in alpha amplitude across all areas of scalp (Chiang et al, 2011;Sebastián et al, 2011;Yordanova & Kolev, 1997) and the phenomenon of so called 'low amplitude alpha rhythm' could simply be associated with reduced conductivity as a function of increasing age (Wendel et al, 2010) or with genetically determined low volume tissue conductivity.…”

Applying Craniofacial Metrics to Adapt 3D Generic Head Models

“…These benefits will come from the adaptation of highly detailed generic volume conductor models assessing different electrode types and locations (Wendel, Väisänen, Seemann, Hyttinen & Malmivuo, 2010). Anthropometric data currently exists detailing deformations in craniometric landmarks; however, a database of landmark sizes coupled with age (Wendel, Väisänen, Seemann, Hyttinen & Malmivuo, 2010), gender (Wendel, Väisänen, Seemann, Hyttinen & Malmivuo, 2010), ethnic origin (Wendel, Osadebey & Malmivuo, 2009), and head shape (Wendel, Osadebey & Malmivuo, 2009) would improve the accuracy of the overly used fixed-geometry in highly complex models.…”

“…Anthropometric data currently exists detailing deformations in craniometric landmarks (Department of Defense, 1997;Donelson & Gordon, 1991;Farkas et al, 2005;Howells, 1973); however, a database of landmark sizes coupled with age (Wendel & Malmivuo, 2006;Wendel, Väisänen, Seemann, Hyttinen & Malmivuo, 2010), gender (Wendel, Osadebey & Malmivuo, 2009;Wendel, Väisänen, Seemann, Hyttinen & Malmivuo, 2010), ethnic origin (Wendel, Osadebey & Malmivuo, 2009), and head shape (Wendel, Osadebey & Malmivuo, 2009) would improve the accuracy beyond the overly used fixed-geometry of highly complex models such as from the Visible Human Project (Ackerman, 1991;National Institutes of Health (NIH), 1995). Future studies that will advance the field of source imaging will save time and money.…”

Bioimpedance technique for monitoring cerebral artery stenosis in a 3D numerical model of the head

“…1, and LMCA stenosis versions of the phantom were constructed. In these Table 1 Typical conductivities of tissues in the human head at 50 kHz, taken from [23][24][25]. versions, some of the circumferential voxels of the artery in a segment of about 1 cm length were given plaque conductivity.…”

“…In the present study a value of 0.021 S/m skull conductivity was used. This value was previously reported [23,24] and used in a modeling study [25]. In a carefully chosen procedure, in which sterility, a stable temperature, and relative humidity were guaranteed, the conductivity of the skull in patients undergoing epilepsy surgery was measured [24].…”