Hi,

I try to answer but Eugenio may also add comments. Several points that are important:

- 1.5 Tesla and 1x1x1 mm3 are at the limit of what the algorithm can manage.

- Post-aquisition reslicing to a higher resolution does not really increase the information content. Internally the algorithm works at a much higher resolution, anyway.

- If possible, switch to 3 Tesla.

- If possible and this is a prospective study, add a coronal T2 image and use the bi-channel option. See papers of Iglesias et al. on this.

- What you could also do on a 1.5 T is acquire the T1WI double and average it after coregistration, this increases the SNR.

- Generally, isometric resolutions are good due to the symmetry, of course.

- Also on 1.5 T, you may go bit below 1 mm with good head immobilization, and a longer scanning time. BRAVO in general is a good T1 option.

Best,

Philipp

Von: freesurfer-bounces@nmr.mgh.harvard.edu <freesurfer-bounces@nmr.mgh.harvard.edu> im Auftrag von Ramesh Babu <mgrameshbabu2013@gmail.com>
Gesendet: Freitag, 2. April 2021 09:29
An: Freesurfer support list; Umesh Rurdrapatna
Betreff: Re: [Freesurfer] 2mm thick image for hippocampal segmentation.

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Dear experts,

Sorry for reposting. I am expecting some response from experts, so that I can proceed with confidence.

For our project work, we are looking for hippocampal and its subfield volumes. Using GE 1.5T scanner, we tried a 3D BRAVO sequence with 1x1x1 resolution, 256x256x160 dimension with 8* flip angle which produced images with a lot of noise. Then we tried the same sequence with 1x1x2 resolution, and 256x256x80 FOV, which produced a clean image without noise. When we reformatted the images, it produces 0.5x0.5x1 resolution with 512x512x172 dimension.

Is this sequence good for hippocampal volume estimation and subfield segmentation (also for whole-brain VBM analysis)?

Could you please suggest to me a correct sequence, if need to be changed?

Regards

Ramesh