If you are wanting to do tractography I would think you would want at least
30 directions and 2.5x2.5x2.5mm resolution. 2x2x2mm resolution would be
better, but perhaps harder to get at 1.5T with reasonable SNR and a
reasonable amount of averages (i.e. scan time). You should acquire your
diffusion averages separately (not average on the scanner), and you should
not have any interpolation turned on.
How much scan time you have will determine how many averages and how many
directions you can get, but it is better to acquire more unique directions
rather than more averages (i.e. one average of 60 directions is better for
tractography than 2 averages of 30 directions).
At 3T, it is definitely worth correcting your data for EPI distortion with a
field map, however perhaps this is somewhat less important at 1.5T as the
distortion is less.
Peace,
Matt.
-----Original Message-----
From: FSL - FMRIB's Software Library [mailto:[log in to unmask]] On Behalf
Of Adil Javed
Sent: Thursday, March 04, 2010 9:23 PM
To: [log in to unmask]
Subject: [FSL] DTI question
Hi,
I am acquiring DTI images on our Phillips 1.5 T. I need to overlay T2 scans
on DTI to get lesion and non-lesion MD/FA/tractography info. My questions
are:
1-I am acquiring DTI images in 32 directions, b=1000, only 1 4D volume,
acquired in plane resolution of 0.87 x 0.87 with 3 mm slice thickness. The
reconstructed dimensions are 2.5mm x 2.5mm x 3mm. Reconstructed Voxel
resolution 256 x 256 x 60. Does this sound reasonable? I have seen other
publications acquire DTI at 2-to-3 x 2-to-3 x 5-to-6mm? with voxel
resolution of 90-128 x 90-128? Not sure if this too low of a resolution.
can anyone comment on this? What are advantages or disadvantages of lower vs
higher acquired resolutions? Also, some use an average of 3-9 images per
slice. Any advantage of this, b/c the scan time would be huge.
many thanks in advance,
aj
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