4-Layer Head-Size Sphere Phantom Model
The sphere is composed of four layers whose properties at 900 MHz are defined in Table 5 [9]. The brain average layer's properties are the average of brain gray matter and brain white matter. The bone average layer's properties are the average of bone marrow and bone cortical. The sphere has a radius of 0.108 m. A voxel and a tetrahedral CAD model are available for download. The voxel model was created from a set of images that contained slices of a sphere with a pixel resolution of 1/3 × 1/3 mm2 in the x-y plane and 1 mm resolution between slices in the z-direction, i.e., the same resolution as the Visible Human Male dataset that was used to construct the AustinMan model. These slices were then coarsened and extruded (using the 3-D coarsening method) in the same manner as the AustinMan model to produce the voxel model. The CAD model was generated using NX I-DEAS.
Table 5: 4-Layer Head-Size Sphere Definition
| Tissue | Layer [mm] | Rel. Perm. (εr) | Cond. (σ) [S/m] |
| Brain Avg. | 0 < r < 92 | 45.8055 | 0.76653 |
| Bone Avg. | 92 < r < 100 | 8.97915 | 0.091759 |
| Fat | 100 < r < 104 | 5.462 | 0.051043 |
| Skin | 104 < r < 108 | 41.405 | 0.86674 |
The sphere models were used in [14-20] and are available for validation purposes. The 4-layer head-size sphere models were added to the AustinMan website on 7/23/2012.
| Model Type | Element Resolution | Number of Elements | File Size |
| Voxel | 1×1×1 mm3 | 5,276,488 voxels | 1.4 GB |
| Voxel | 2×2×2 mm3 | 658,976 voxels | 174 MB |
| Voxel | 3×3×3 mm3 | 195,360 voxels | 52 MB |
| Voxel | 4×4×4 mm3 | 82,504 voxels | 23 MB |
| CAD | 0.29 mm3 | 19,589,664 tetrahedrons | 2.8 GB |
| CAD | 2.53 mm3 | 3,366,256 tetrahedrons | 480 MB |
| CAD | 14.73 mm3 | 443,040 tetrahedrons | 64 MB |
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