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Induced current densities from low-frequency magnetic fields in a 2 mm resolution, anatomically realistic model of the body
This article has been downloaded from IOPscience. Please scroll down to see the full text article. 1998 Phys. Med. Biol. 43 221 (http://iopscience.iop.org/0031-9155/43/2/001) Viewthe table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 190.248.30.139 The article was downloaded on 22/09/2010 at 19:59
Please note that terms and conditions apply.
Phys. Med. Biol. 43 (1998) 221–230. Printed in the UK
PII: S0031-9155(98)87773-7
Induced current densities from low-frequency magnetic fields in a 2 mm resolution,anatomically realistic model of the body
P J Dimbylow
National Radiological Protection Board, Chilton, Didcot, Oxon OX11 0RQ, UK Received 19 September 1997 Abstract. 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 Hzto 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.
1. IntroductionRestrictions on exposure of people to low-frequency magnetic fields are based on responses to induced current density. The National Radiological Protection Board’s guidance (McKinlay et al 1993) is intended to avoid the effects of induced electric currents on functions of the central nervous system such as the control of movement and posture, memory, reasoning and visual processing. This paperpresents 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. Its purpose is to provide the dosimetric link between applied external magnetic fields and the induced current density distribution within the body. Previous work hasbeen mostly based on the impedance method (see section 3.1) where the computational cells within the target volume are represented by a 3D impedance network. For each face of the cuboid cells the Kirchoff voltage equations are used with an electromotive force (emf) due to the incident magnetic fields. The equations are solved for the loop currents from which current densities are derived. Xi et al(1994) presented maximum and average current densities in heterogeneous models of mouse, rat and man. The human model comprised 37 000 cells with a resolution of 1.31 cm to give a mass of 70 kg. The scalar potential finite difference (SPFD) method promises to be a faster scheme with a smaller computational molecule (see section 3.3). The external magnetic field is represented by a vector potentialwhich enables the internal electric field to be represented by a scalar conduction potential. Dawson et al (1996) have applied their method to a 7.2 mm resolution model. Both of the above methods are used to provide mutual corroboration; firstly on a set of calculations at varying resolution, down to 4 mm, to demonstrate how the maximum values of current density increase with decreasing cell size andthe consequent need to average
0031-9155/98/020221+10$19.50 c 1998 IOP Publishing Ltd
221
222
P J Dimbylow
over a finite area, and secondly for the calculation with the 2 mm resolution of the fully detailed phantom. The latter calculations employ cells of discrete tissue type rather than a weighted mixture of properties required for the larger cell sizes. This is important for...
Search
Collections
Journals
About
Contact us
My IOPscience
Induced current densities from low-frequency magnetic fields in a 2 mm resolution, anatomically realistic model of the body
This article has been downloaded from IOPscience. Please scroll down to see the full text article. 1998 Phys. Med. Biol. 43 221 (http://iopscience.iop.org/0031-9155/43/2/001) Viewthe table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 190.248.30.139 The article was downloaded on 22/09/2010 at 19:59
Please note that terms and conditions apply.
Phys. Med. Biol. 43 (1998) 221–230. Printed in the UK
PII: S0031-9155(98)87773-7
Induced current densities from low-frequency magnetic fields in a 2 mm resolution,anatomically realistic model of the body
P J Dimbylow
National Radiological Protection Board, Chilton, Didcot, Oxon OX11 0RQ, UK Received 19 September 1997 Abstract. 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 Hzto 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.
1. IntroductionRestrictions on exposure of people to low-frequency magnetic fields are based on responses to induced current density. The National Radiological Protection Board’s guidance (McKinlay et al 1993) is intended to avoid the effects of induced electric currents on functions of the central nervous system such as the control of movement and posture, memory, reasoning and visual processing. This paperpresents 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. Its purpose is to provide the dosimetric link between applied external magnetic fields and the induced current density distribution within the body. Previous work hasbeen mostly based on the impedance method (see section 3.1) where the computational cells within the target volume are represented by a 3D impedance network. For each face of the cuboid cells the Kirchoff voltage equations are used with an electromotive force (emf) due to the incident magnetic fields. The equations are solved for the loop currents from which current densities are derived. Xi et al(1994) presented maximum and average current densities in heterogeneous models of mouse, rat and man. The human model comprised 37 000 cells with a resolution of 1.31 cm to give a mass of 70 kg. The scalar potential finite difference (SPFD) method promises to be a faster scheme with a smaller computational molecule (see section 3.3). The external magnetic field is represented by a vector potentialwhich enables the internal electric field to be represented by a scalar conduction potential. Dawson et al (1996) have applied their method to a 7.2 mm resolution model. Both of the above methods are used to provide mutual corroboration; firstly on a set of calculations at varying resolution, down to 4 mm, to demonstrate how the maximum values of current density increase with decreasing cell size andthe consequent need to average
0031-9155/98/020221+10$19.50 c 1998 IOP Publishing Ltd
221
222
P J Dimbylow
over a finite area, and secondly for the calculation with the 2 mm resolution of the fully detailed phantom. The latter calculations employ cells of discrete tissue type rather than a weighted mixture of properties required for the larger cell sizes. This is important for...
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