DRAFT Recommended Practice for Measurements and ...

1/29/98 121 C95.3-1991 Revision — 2 nd Draft
10/98 Draft
Fig D3 The calculated vertical currents passing through the various sections of a
6 x 6 x 6 mm MRI-based grounded model of the human body exposed to a 60 Hz
electromagnetic field.
Depending on the application, human body models may be crude approximations or
detailed meshes based on actual anatomy. Several suitable models have been
developed from CT and MRI scans of humans. One of the first, which was taken from
published anatomical cross sections, had a resolution of 6.55 mm [Gandhi and DeFord,
1988]. Models with resolutions of 2 x 2 x 2 mm [Dimbylow and Mann, 1994], 1.974 x
1.974 x 3 mm [Gandhi, 1995; Gandhi and Furse, 1995], 0.9 x 0.9 x 1.5 mm [Olley and
Excell, 1995], 1.7 to 5 mm using subgridding in some regions [Stuchly, et al., 1995] and 3
x 3 x 3 mm, based on MRI scans [Jensen and Rahmat-Samii, 1995; Luebbers, 1996]
have been reported. A popular source of anatomical data suitable as the basis of an
FDTD biological mesh is the Visible Human Project [Visible Human Project] of the
National Library of Medicine. Various types of data are available, with the most useful
perhaps being the cross sections. These are 1 mm slices for the male and 0.33 mm
slices for the female. Both have a cross-sectional resolution of 0.33 mm. FDTD
meshing of these data still requires considerable effort, especially in assigning the colors
of the slices to particular tissue types.
The Armstrong Laboratory, Radiofrequency Radiation Division, Brooks Air Force Base,
has a database of various animals that it uses as input for FDTD calculations. This
database consists of magnetic resonance imaging (MRI) scans of the Sprague-Dawley
rat, Rhesus monkey, and pigmy goat. In addition, the U.S. Naval Medical Research
Detachment at Brooks AFB has obtained MRI scans of a phantom Rhesus monkey that
was filled with a solution containing TX-150, polyethylene powder, sodium chloride and
water. The phantom was scanned in squatting and sitting positions. Each MRI scan
was converted to a TIF image for use with Adobe Photoshop software on the PC. All
images for each animal were aligned so as to eliminate some of the scanning artifacts
previously reported [Mason et al., 1995]. The phantom Rhesus monkey was assigned a
single Red-Green-Blue (RGB) value, whereas in the other models, each tissue type was
assigned a specific RGB color value as shown in Table D 1.
All 65,536 pixels on each image (81 images for the rat, 184 images for the monkey, and
276 images for the goat) were then "painted" manually with the RGB colors representing
the appropriate tissue types. Atlases and skeletons of the rat, monkey and goat were
used to identify the location of each tissue type [Barrett et al., 1994; Hopkins et al., 1972,
1973; Popesko et al., 1992]. Throughout the "painting" process, images were
Copyright © 1998 IEEE. All rights reserved. This is an unapproved IEEE Standards Draft,
subject to change.