Hi Erik, 

you should investigate why this is the case. Any difference in acquisition will cause effects and it will be impossible to distinguish these from real effects. 

Also you should never just resample one time point, as that will introduce processing bias. I would advise to
- find out why, and you need to report this in any analysis so that people are aware of this potential bias
- resample both time points to some 3rd space. Probably here simply conform them to 1mm isotropic. 

Best, Martin

On 15. May 2018, at 07:20, Erik O'Hanlon <erikohanlon@rcsi.ie> wrote:

Hi FS Experts,

I'm trying to run a longitudinal analysis across three timepoints and have run the cross steps for the data. I then ran the base step but found that my voxel dimensions are slightly different across the timepoints and I got the following error

ERROR: MultiRegistration::loadMovables: images have different voxel sizes.
  Currently not supported, maybe first make conform?
  Debug info: size(2) = 0.881117, 0.881117, 0.881117   size(0) = 0.884507, 0.884507, 0.884507
MultiRegistration::loadMovables: voxel size is different /projects/pi-vokeane/HPC_16_00925/MC_FS_testdata_EOH/freesurfer/subjects/abd025_tp3/mri/norm.mgz.


I assume I need to resample the data to the voxel size of the first time point and then rerun. Can you advise on what command to use to resample the images from time 2 and time 3 to those of time 1 before rerunning from scratch. I assume I can't avoid rerunning the initial reconall step once I resample my data.


Any guidance is much appreciated 

Best regards

Erik

Erik O'Hanlon 
Postdoctoral researcher
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RCSI Psychiatry 
Royal College of Surgeons in Ireland 
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T: 8093740 
E: erikohanlon@rcsi.ie W: www.rcsi.com

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