Fa_template resolution


#1

Hi,
My DWI data has 2mm isotropic resolution but the fa_template created by “dwiintensitynorm” has 2.2x2.3x2.3mm resolution.
Why this happens and how can I modify it?

Thanks,
Mahmoud


#2

This is caused by the way we calculate the unbiased voxel-grid in case of rotated input images. You can find a discussion here. population_template has a -voxel_size option to modify this behaviour but this option is not accessible from dwiintensitynorm.

If you’re after an FA template with specific resolution, I’d convert the DWI images to FA images and create a population template using population_template.


#3

Thanks, Max.
I’d like to know more about how “population_template” creates the template. Like what are the steps, what types of registrations are used … . Is there a document that explains those details?


#4

Not a document but population_template prints an overview of what it is going to perform as info messages to the terminal at the beginning of the processing. After initial alignment, the template is iteratively refined (“stages”) by registering each subject to the template, and averaging the transformed subject images to form a new template.

Here is an overview of the registration stages performed by default, for more options see the docs:


#5

Thanks for your response, Max.

1- Would you please elaborate what does initial alignment do?
2- Is it possible to introduce an initial template to start with it? like with FSL fnirt and fnirt commands.
3- After creating the fa_template using the “population_template”, I’d like to register the individual T2 images to that template. What’s the best way to do that?