External Email - Use Caution
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:
1) 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
2) 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 http://secure-web.cisco.com/1uRUN3qw4_2ZQdVovG97ElQWo_5ofjkray9cxFwmREkCPYfV...http://secure-web.cisco.com/16jDYbTgO8Bi4O3L_8oBX-UxhLbIwNnO8u3tQFvD5bc-Ksr0wOUr6aPKXpKbq-JgTK4m5yMlEMw033cF-PNy4WuPATHg6tAPG5Y_haANNG1XYgW7LyzkeVT9q0vMg9Fe3SfvvpyMlnyl6B1NZ7-rtwuLzu6cxS9fC_nOWmnDdVOhiuG_XFC0ccbel7bcGn3Hva33DdiuClFanvCluaJqLdA/http%3A%2F%2Fwww.uniklinikum-dresden.de%2F
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}
External Email - Use Caution 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:
1. 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 2. 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 MailScanner has detected a possible fraud attempt from "secure-web.cisco.com" claiming to be http://www.uniklinikum-dresden.dehttp://secure-web.cisco.com/16jDYbTgO8Bi4O3L_8oBX-UxhLbIwNnO8u3tQFvD5bc-Ksr0wOUr6aPKXpKbq-JgTK4m5yMlEMw033cF-PNy4WuPATHg6tAPG5Y_haANNG1XYgW7LyzkeVT9q0vMg9Fe3SfvvpyMlnyl6B1NZ7-rtwuLzu6cxS9fC_nOWmnDdVOhiuG_XFC0ccbel7bcGn3Hva33DdiuClFanvCluaJqLdA/http%3A%2F%2Fwww.uniklinikum-dresden.de%2F
freesurfer@nmr.mgh.harvard.edu
-
Backhausen, Lea -
Fischl, Bruce