Thanks for the speedy replies,
I think that in case of a 3D acquisition, the bigger the volume the better the SNR (until a certain point, of course), and in this case the volume is bigger with 9,9%.
The parameters of the MPRAGE are:
TR/TE/TI: 1900/3.41/900 ms; FA: 9°; FOV: 210x240 mm2; 224x256 matrix; slice thickness: 0.94 mm;
160/176 slices; voxel size: 0.94x0.94x0.94 mm3; 180 Hz/pixel receiver bandwidth
But, (i know it can not be answered quantitatively, or at least hard) how big the influence of this effect in such comparison after all the preprocessing steps like intensity norm.
Ok, my last question was hypothetic,
I'm waiting for the answer from Andre van der Kouwe, for further help.
Thankx,
2011/1/20 Bruce Fischl fischl@nmr.mgh.harvard.edu
Hi Gergely,
I think this will be trouble. I'll cc Andre van der Kouwe, but for the 3D acquisitions, if you have a bigger field of view is has an effect on image SNR, so that will be a bias between your groups.
cheers Bruce
On Thu, 20 Jan 2011, Gergely Orsi wrote:
Hi Freesurfers,
I have a quick question:
I have two groups, both measured on the same scanner, with the same
sequence
(3D MPRAGE), and with almost the same parameters.
TR/TE/TI/BW/MATRIX/FOV/FOV-phase/Flip angle/Slice thickness/in-plane resolution... everything is the same, but the number of slices. Total measurement time was also the same.
One group was measured with 160 slices, the other with 176.
Can I compare the two groups in freesurfer?
Thanx,
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