sdm-help-list > Meta-analysis includes both voxel-based and surface-based morphometry studies
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May 27, 2020  10:05 AM | Yen-Wen Chen
Meta-analysis includes both voxel-based and surface-based morphometry studies
Hi, 

I'm currently working on a meta-analysis project with structural MRI studies, and I found this SDM software developed by your research team from some readings. I sincerely appreciate that you share this amazing resource!

I'm new in meta-analysis, with only experiences from empirical MRI data processes. I have some questions regarding the SDM execution.

The studies included in my meta-analysis are restricted to whole-brain analysis studies from both voxel-based and surface-based morphometry.

I found an article from Li et al. (2019)*, talked about using a specific GM mask from FreeSurfer surface mask for pre-processing of SBM studies.

I found some previous posts from the SDM user's forum discussing the question of including both VBM and SBM studies in one meta-analysis. (specifically, this post and this post)

1. Should I create the specific mask for SBM studies on my own, or are there any existing masks from the software or the website that I can use?

2. From the SDM preprocessing step, how do I apply a custom-made mask, instead of the default masks in the scroll-down list?

3. From your response from this post, you mentioned that the "mask" should only include results from SBM.
    3.1. Does this mean that the preprocessing for VBM and SBM studies should be separately conducted? 
    3.2. Is there any way I can analyze the VBM and SBM studies together? Like adding a column with the data processing method?

* Li et al. (2019) Meta-analysis of cortical thickness abnormalities in medication-free patients with MDD

I appreciate your kind helps and look forward to your responses. 

Many thanks, 
Samantha
Jun 15, 2020  01:06 AM | Lydia Fortea - Instituto de Investigaciones Biom├ędicas August Pi i Sunyer (IDIBAPS)
RE: Meta-analysis includes both voxel-based and surface-based morphometry studies
Dear Samantha

It is possible to combine both, VBM and SBM studies, to perform the analysis. In the pre-processing step, you should use the SBM mask for all studies; and continue the analysis as normal.

Kind Regards,

Lydia
Jun 15, 2020  07:06 AM | Yen-Wen Chen
RE: Meta-analysis includes both voxel-based and surface-based morphometry studies
Dear Lydia, 

Thanks so much for replying!

I have some follow-up questions. 

1. I just noticed that there is "freesurfer" mask (with voxel size 2-mm) (sorry for my carelessness not noticing it earlier...). Is this the mask for SBM mask? 

2. In the Pre-processing step, is it recommended to use the default parameters, except the mask, for meta-analysis including both VBM and SBM studies. 

    (1) Modality: VBM - GM (or should I choose "Other"?)
    (2) Correlation template: GM
    (3) Anisotropy: 1
    (4) Isotropic FWHM: 20
    (5) Mask: freesurfer (?)
    (6) Voxel size: 2

3. Will you recommend to control for the processing method (i.e., voxel-based versus surface-based) for meta-analysis including both VBM and SBM (i.e., add processing method as covariate for Mean analysis step)?

Looking forward to your responses! Thank you so much!

Best wishes, 
Sam.
Jun 16, 2020  05:06 AM | Lydia Fortea - Instituto de Investigaciones Biom├ędicas August Pi i Sunyer (IDIBAPS)
RE: Meta-analysis includes both voxel-based and surface-based morphometry studies
Dear Samantha, 

1. Yes, indeed. freesurfer mask corresponds to the SBM data

2. It is recommended to use the default parameters (3), (4) and (6). The other paramters (1,2,5) has to be in accordande with tha data you want to analyze. In your case, should be
(1) VBM - gray matter
(2) GM
(5) freesurfer

3. Is not compulsory to control for the processing method; but it can be a good idea to perform a meta-regression with that variable to check if it's biasing your results. 

Kind regards,
Lydia
Jun 16, 2020  08:06 AM | Yen-Wen Chen
RE: Meta-analysis includes both voxel-based and surface-based morphometry studies
Hi Lydia, 

Thanks for the clarification and explanation! 

Best wishes, 
Sam.