Hi Lee

It’s really hard to say. The change in voxel size might sound trivial, but it is a 30% change in volume (and hence SNR). The longer TE will counteract that by increasing T2* weighting.

Sorry I don’t have anything more conclusive to say except that it is obviously not ideal

Bruce

From: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> On Behalf Of Backhausen, Lea
Sent: Thursday, November 5, 2020 12:13 PM
To: 'freesurfer@nmr.mgh.harvard.edu' <freesurfer@nmr.mgh.harvard.edu>
Subject: [Freesurfer] Different Sequences Longitudinal Stream {Disarmed}

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Dear FreeSurfer experts,

I am currently working on a longitudinal data set with 4 time points, acquired at one site with the same Siemens Trio 3T scanner.

Unfourtunately, the T1 sequence differs slightly for one of these time points. These sequences have been measured:

repetition time (TR) = 2300 ms, echo time (TE) = 2.93 ms, inversion time (TI) = 900 ms, voxel size = 1.1 x 1.1 x 1.1mm, flip angle = 9°; matrix size = 256 x 256 x 160 mm
repetition time (TR) = 1900 ms, echo time (TE) = 2.26 ms, inversion time (TI) = 900 ms, voxel size = 1.0 x 1.0 x 1.0mm, flip angle = 9°; matrix size = 256 x 256 x 176 mm

Is it possible to process these different sequences in the longitudinal stream (if e.g. one participant would have 3 data sets of sequence 1 and one data set of sequence 2)?

Or would this cause too much bias?

Thank you very much, kind regards!

Lea Backhausen

------------------------------

Lea Backhausen

Ph.D. Student (M.Sc. Psychology/Neuroscience)

Department of Child and Adolescent Psychiatry, Faculty of Medicine of the TU Dresden, Germany
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