Dear Steve, Mark, et al,
T1 MRI of the whole head was acquired in the sagittal plane (0.98 x 0.98,
256 x 256) with 128 slices (1.3047 mm thick). The volumes are 16 bits.
In some cases, the tip of the nose is located in the posterior coronal plane
(an artifact of the reconstruction process). It is easy to relocate 10-20
coronal slices to the anterior, effectively putting the nose back into its
proper real world location (there is a clear gap between the nose and the
back of the head).
A couple of simple questions...
Q1. Is it better to estimate and correct RF bias fields on the volume
before or after relocating the nose?
My guess would be that relocating the nose will lead to better RF bias field
estimation, especially with FAST. I assume, with FAST, that the RF bias
field estimation/correction is an integral part or product of the MRF
calculations. Furthermore, I assume that the MRF and neighbourhood
relationships can be calculated over the entire FOV of the volume, including
all head and non-head voxels (which would include artifacts and noise). I
presume that this information is then utilised for segmentation, that is,
the MRF and neighbourhood information is a continuous 3D function that is
generated and then utilised for refinement of segmentation into tissue
classes. If the neighbourhood information is more consistent by putting the
nose "back in place," this should result in better RF bias estimation.
Q2. We're using some software that is sensitive to RF bias. All we need is
an RF corrected volume, not the segmentation. Is it then reasonable to use
FAST on the whole FOV of the volume, before BET, just to extract the RF bias
corrected volume?
Take care, Darren
PS, all the best with the Oxford workshop.
--
Darren Weber, PhD Student
Cognitive Neuroscience, School of Psychology
Flinders University of SA, GPO Box 2100, Adelaide, SA 5001, Aust.
Ph: (61 8) 8201 3889, Fax: (61 8) 8201 3877
http://203.3.164.46/~dlw/homepages/index.html
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