SDM   Seed-based d Mapping
formerly "Signed Differential Mapping"
Share on Facebook:   Facebook

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


(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. link .