questions about 'Normalize to Symmetric Template'

Submitted by yaqiong on

Hi Chaogan,

I have a couple of questions about 'Normalize to Symmetric Template' in DPARSFA to ask you for help. 

1) Based on Zuo et al., 2010, normalization to symmetrica template was implimented after all the preprocessing steps but before VMHC analysis. I was wondering, does it matter to perform it at different steps, say after standard normalization or after smoothing?

2) I tried to implement 'normalization to symmetrica template' after standard normalization, but left and right hemispheres were still not symmetric and only the signal values changed a little. I checked the 'SymmetricGroupT1MeanTemplate' folder, and found that the 'SymmetricGroupT1MeanTemplate.nii' file was indeed more symmetric compared to 'GroupT1MeanTemplate.nii' file.  If the normalization to symmetirc template was based on 'SymmetricGroupT1MeanTemplate.nii', then the images should be symmetric. Is there something wrong? Could you please give me some suggestion?

Looking forward to your reply. Thank you very much.

Best,

Yaqiong

 

 

 

 

YAN Chao-Gan

Tue, 07/12/2016 - 02:35

Permalink

Hi Yaqiong,

1. It should not make a huge difference.

2. The individual normalized structural image was further reregistered to a SymmetricGroupT1MeanTemplate.nii, and then this refined transformation was applied to the functional data before VMHC calculation. Thus the functional images should be only changed a little. If the functional data is fully symmetric, the VMHC is 1 over all the brain.

Best,

Chao-Gan

Hi Chaogan,

Thanks very much for your reply.

For the second question, I thought the left and right hemispheres should be symmetric after 'Normalisation to symmetric template', but they are not, right? Is it because the registeration won't change the shape of the brain? As you said, the functional images should be only changed a little. Do the changes occur in both hemispheres?

And, I have a follow up question to ask you. C-PAC software uses a symmetric template for normalization in order to calculate VMHC. Do you think these two precedures (using a symmetric template for normalzation vs. normalization to symmetric template) are comparable?

Thank you.

Best,

Yaqiong

Hi Yaqiong,

It has effects on both hemishpere.

The symmetric template in C-PAC is not group specific. In general, this would not differ too much.

Best,

Chao-Gan

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