This is the last step of the preparations, and it consists in a) creating an SDM map for each original study; and b) permuting many times the location of the voxels creating randomized SDM maps.
To preprocess the studies
Press the button [Preprocessing]
Select [Preprocessing] in the Meta-analyses menu, to open the following dialogs:
Please be aware that this will remove the previous meta-analysis in this folder.
Statistical significance of Monte Carlo-based tests might vary slightly if you randomize the studies again. However, it is NOT recommended to repeatedly randomize the studies to find a set of randomizations which produce more liberal thresholds. Remember that the meta-analysis MUST be replicable by other colleagues.
A maximum and a minimum of each study will be written in a text file called pp.htm (note that these may not be the absolute maximum and minimum), and the recreated images will be separately saved in a set of NIfTI file called pp_(study).nii.gz, e.g. pp_Smith2000.nii.gz. These files are useful for checking that coordinates have been correctly read.
Several 2mm X 2mm X 2mm MNI-based masks and correlation templates are included in SDM software: gray matter (also usefull for fMRI and PET), white matter, fractional anisotropy, cerebrospinal fluid, brain and intracranial. Please contact should you need another mask or template.
Command-line and batch usage
pp correlation_template, degree_of_anisotropy, isotropic_fwhm, , mask, number_of_randomizations
pp fractional_anisotropy, 0.8, 20, white_matter, 20
(effect-sizes and variances): Radua J, Mataix-Cols D, Phillips ML, El-Hage W, Kronhaus DM, Cardoner N and Surguladze S. A new meta-analytic method for neuroimaging studies that combines reported peak coordinates and statistical parametric maps. Eur Psychiatry 2012; 27:605–611. .
(anisotropic kernels): Radua J, Rubia K, Canales-Rodriguez EJ, Pomarol-Clotet E, Fusar-Poli P and Mataix-Cols D. Anisotropic kernels for coordinate-based meta-analyses of neuroimaging studies. Front Psychiatry 2014; 5:13. .
(white matter template:) Radua J, Via E, Catani M and Mataix-Cols D. Voxel-based meta-analysis of regional white-matter volume differences in autism spectrum disorder versus healthy controls. Psychol Med 2011; 41:1539-1550. .
(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. .