Numerical calculations of induced current – abstracts

Phys Med Biol. 2005 Mar 21;50(6):1047-70. Epub 2005 Feb 23. 
Development of the female voxel phantom, NAOMI, and its application to calculations of induced current densities and electric fields from applied low frequency magnetic and electric fields.

Dimbylow P.

National Radiological Protection Board, Chilton, Didcot, Oxon, OX11 0RQ, UK.

This paper outlines the development of a 2 mm resolution voxel model, NAOMI (aNAtOMIcal model), designed to be representative of the average adult female. The primary medical imaging data were derived from a high-resolution MRI scan of a 1.65 m tall, 23 year old female subject with a mass of 58 kg. The model was rescaled to a height of 1.63 m and a mass of 60 kg, the dimensions of the International Commission on Radiological Protection reference adult female. There are 41 tissue types in the model. The application of NAOMI to the calculations of induced current densities and electric fields from applied low frequency magnetic and electric fields is described. Comparisons are made with values from the male voxel model, NORMAN. The calculations were extended from 50 Hz up to 10 MHz. External field reference levels are compared with the ICNIRP guidelines.

Phys Med Biol. 2002 Apr 21;47(8):1391-8. 
Modelling fields induced in humans by 50/60 Hz magnetic fields: reliability of the results and effects of model variations.

Caputa K, Dimbylow PJ, Dawson TW, Stuchly MA.

Department of Electrical and Computer Engineering, University of Victoria, BC, Canada

This paper presents a comparison of anatomically realistic human models and numerical codes in the dosimetry of power frequency magnetic fields. The groups at the University of Victoria and the National Radiological Protection Board have calculated the induced electric fields in both their 'UVic and 'NORMAN' models using independently developed codes. A detailed evaluation has been performed for a uniform magnetic field at 60 Hz. Comparisons of all dosimetric metrics computed in each particular model agree within 2% or less. Since in situ measurements cannot be performed in humans, and achievable accuracy of measurements in models and animals is not likely to be better than 10-15%, the comparisons presented should provide confidence limits on computational dosimetry. An evaluation of the effect of model size, shape and resolution has also been performed and further illuminated the reasons for differences in induced electric fields for various human body models.

Phys Med Biol. 2000 Apr;45(4):1013-22. 
Current densities in a 2 mm resolution anatomically realistic model of the body induced by low frequency electric fields.

Dimbylow PJ.

National Radiological Protection Board, Didcot, Oxon, UK.

Current density distributions in a fine resolution (2 mm) anatomically realistic voxel model of the human body have been calculated for uniform, low frequency vertically aligned electric fields for a body grounded and isolated from 50 Hz to 10 MHz. The voxel phantom NORMAN is used which has a height of 1.76 m and a mass of 73 kg. There are 8.3 million voxels in the body differentiated into 37 tissue types. Both finite-difference potential and time-domain methods were used. Results are presented for the current density averaged over 1 cm2 in muscle, heart, brain and retina. Electric field values required to reach the NRPB and ICNIRP basic restrictions on current density are derived and compared with the external field guidelines from these standards.

Phys Med Biol. 1998 Feb;43(2):221-30.
Induced current densities from low-frequency magnetic fields in a 2 mm resolution, anatomically realistic model of the body.

Dimbylow PJ.

National Radiological Protection Board, Didcot, Oxon, UK.

This paper presents calculations of current density in a fine-resolution (2 mm) anatomically realistic voxel model of the human body for uniform magnetic fields incident from the front, side and top of the body for frequencies from 50 Hz to 10 MHz. The voxel phantom, NORMAN, has a height of 1.76 m and a mass of 73 kg. There are 8.3 million voxels in the body differentiated into 37 tissue types. Both the impedance method and the scalar potential finite difference method were used to provide mutual corroboration. Results are presented for the current density averaged over 1 cm2 in muscle, heart, brain and retina.