# SDM preparation

## TBSS preprocessing

Statistical parametric maps from diffusion-weighted studies employing FSL 'tract-based spatial statistics' (TBSS), cannot be straightforwardly meta-analyzed with ES-SDM, because the skeletons do not completely overlap across studies. Of course you can always use a text file with the peak coordinates, but maps should be preferred when available. In order to allow a correct overlap among the maps of TBSS studies and the specific SDM TBSS template, you should:

a) first retrieve a mass number of low-thresholded local peaks from the original t-statistical maps (see example below),

b) then combine positive and negative peaks in the same spreadsheet (remember that negative peaks must have negative t-values),

c) save the peaks and their t-values in a text file for ES-SDM (see "Preprocessing"),

d) and finally proceed to the ES-SDM preprocessing with the TBSS template.

### Example of how to retrieve the peaks with FSL

# Retrieve the local positive peaks

cluster -i ${1} --mm -n 100000 --olmax=${1}_pos.txt -t 0.1

# Create a negative image to subsequently extract negative peaks

fslmaths ${1} -mul -1 ${1}_neg.nii.gz

# Retrieve the local negative peaks

cluster -i ${1}_neg --mm -n 100000 --olmax=${1}_neg.txt -t 0.1

# Remove the negative image

rm ${1}_neg.nii.gz

### References

(TBSS preprocessing):
Peters BD, Szeszko PR, Radua J, Ikuta T, Gruner P, DeRosse P,
Zhang JP, Giorgio A, Qiu D, Tapert SF, Brauer J, Asato MR, Khong PL,
James AC, Gallego JA *and*
Malhotra AK. White matter development in adolescence: diffusion tensor imaging and meta-analytic results.
*Schizophrenia Bull* 2012; 38:1308-1317.
.