Details of numerical calculations of induced currents and fields in the body

On other pages, we give

• an overview of induced currents in the body
• the effects of induced currents
• a summary of numerical calculations of induced currents
• the tissue conductivities used to do these calculations

In this page we give chapter and verse on the results of numerical calculations.  It is therefore necessarily quite detailed.

The calculations all come from Dimbylow 2005 (the results for the adult male were originally published in earlier papers Dimbylow 1998 and Dimbylow 2000).  The paper presents calculations for several different organs.  We have extracted the result for the "limiting case" organ, ie the organ where a given external field induced the highest current or internal field.  The focus is on the central nervous system but there are different definitions, some including the spinal cord and some not, so we give both alternatives.

External magnetic field

Induction of current

(averaged over 1 cm²)

• adult male: 5.50 mA/m² per mT = 1.82 mT per 10 mA/m² = 0.364 mT per 2 mA/m²
• adult female: 4.89 mA/m² per mT

both in the retina, for a lateral field.  From Dimbylow 2005 table 3.

The limiting case is therefore the male.  Because the limiting case is in the retina anyway, it makes no difference whether the spinal cord is included or not.

Induction of internal electric field

(99th percentile voxel)

• adult male: 48.6 mV/m per mT in spinal cord = 2.06 mT per 100 mV/m = 0.412 mT per 20 mV/m
• adult female: 31.4 mV/m per mT in brain

• adult male: 33.0 mV/m per mT in brain = 3.03 mT per 100 mV/m = 0.606 mT per 20 mV/m
• adult female: 31.4 mV/m per mT in brain

all for a lateral field.  From Dimbylow 2005 table 6.

The limiting case is therefore the male whether or not the spinal cord is included.

External electric field

Induction of current

(averaged over 1 cm²)

• adult male: 0.211 mA/m² per kV/m
• adult female: 0.217 mA/m² per kV/m = 46.1 kV/m per 10 mA/m² = 9.22 kV/m per 2 mA/m²

both in retina (value in heart is higher but is not part of central nervous system) for grounded person.  From Dimbylow 2005 table 4.

The limiting case is therefore the female. Because the limiting case is in the retina anyway, it makes no difference whether the spinal cord is included or not.

Induction of internal electric field

(99th percentile voxel)

• adult male: 3.42 mV/m per kV/m in spinal cord = 29.2 kV/m per 100 mV/m = 5.85 kV/m per 20 mV/m
• adult female: 2.92 mV/m per kV/m in spinal cord

• adult male: 1.65 mV/m per kV/m in brain
• adult female: 2.02 mV/m per kV/m in brain = 49.5 kV/m per 100 mV/m = 9.90 kV/m per 20 mV/m

all for grounded person.  From Dimbylow 2005 table 7.

The limiting case is therefore the male if the spinal cord is included and the female if it is not.