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Discussion and Future Work
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8.3 Energy
8.3.1 Measured Phase-ring Image
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The measured phase-ring image might be used not only to create iso-eccentricity lines,
but also to improve the segregation of retinotopic visual areas. This is because iso-
eccentricity lines are expected to be perpendicular to the boundaries. Based on this, a
new energy component could be introduced.
8.3.2
Visual Field Sign Maps
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A further energy component could be based on the difference between the calculated
visual field sign map and the corresponding atlas image. Figure 16 (bottom right)
shows a visual field sign map atlas. However, when measured phase data is used, the
calculation of the derivative is problematic. When using unblurred data, the calculated
sign maps look like the one in Figure 16 (bottom left). In order to succeed, the calcula-
tion of visual field sign maps has to be improved. One way to do that is to blur in 3D,
i.e., in mrLoadRet. Blurring should be done in 3D because of distortions that are intro-
duced when flattening, and because of edge artifacts when blurring on the flat map.
Methods like anisotropic diffusion might be tried out.
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Like blurring, the derivative should be calculated based on distances that are taken
from 3D and not directly from the flat map because of the same reasons that are given
above.
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At this stage, mrFindBorders creates a sign map from measured data and a correspond-
ing atlas but they are not used in the matching process. Once the quality of the sign
map (calculated from the measured data) has been improved, it can be included easily
in the matching process.
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