Meta-analytic methods for fMRI, VBM and PET
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Introduction

Signed Differential Mapping is a statistical technique for meta-analyzing studies on differences in brain activity or structure which used neuroimaging techniques such as fMRI, VBM or PET. Meta-analyses using this method have been already published at high quality journals such as Arch Gen Psychiat , Am J Psychiatry , Biol Psychiat , Schizophrenia Bull , Br J Psychiat , Neurobiol Aging , Neuroimage , Psychol Med , Schizophr Res , J Clin Psychopharmacol , J Affect Disorders , Eur J Neurol , Eur Psychiat , Amyotroph Lateral Sc or Biol Mood Anxiety Disord .

The method

An introduction of the method can be found in the SDM Reference Manual.

Briefly, some of the features are:

• Possibility of combining group peak coordinates with parametric images.
• A criterion in the selection of the coordinates to avoid biases towards liberally thresholded regions.
• Use of specific gray or white matter templates.
• Accounting for different sources of spatial error (e.g. coregistration mismatch or the size of the cluster), peaks' effect-size, and signed maps to counteract positive and negative differences.
• Weights in the calculations: intra-study variance (i.e. studies with large sample sizes and/or lower error contribute more) and other optional weights.
• Use of the general linear model and inter-study heterogeneity to allow meta-analytical comparisons between groups and use of covariates.
• Complementary analyses such as exploration of heterogeneity (by means of heterogeneity maps, subgroup analyses and meta-regressions) and jackknife analyses (to assess the replicability of the results).

The software

Please feel free to download the software created by the SDM Project to carry out such meta-analyses.

References

Papers introducing relevant SDM methods:

• Radua J and Mataix-Cols D. Voxel-wise meta-analysis of grey matter changes in obsessive-compulsive disorder. Br J Psychiatry 2009; 195:393-402. (SDM method 1/3: original algorithms)
• Radua J, van den Heuvel OA, Surguladze S and Mataix-Cols D. Meta-analytical comparison of voxel-based morphometry studies in obsessive compulsive disorder vs other anxiety disorders. Arch Gen Psychiatry 2010; 67:701-711. (SDM method 2/3: comparisons and linear models)
• 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 2011; in Press. (SDM method 3/3: effect-sizes and variances)
• 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. (SDM specific white matter template)

Other studies using SDM:

• Bora E, Fornito A, Yücel M and Pantelis C. Voxelwise meta-analysis of gray matter abnormalities in bipolar disorder. Biol Psychiatry 2010; 67:1097-1105.
• Chen Z and Ma L. Grey matter volume changes over the whole brain in amyotrophic lateral sclerosis: A voxel-wise meta-analysis of voxel based morphometry studies. Amyotroph Lateral Scler 2010; 11:549-554.
• Bora E, Fornito A, Radua J, Walterfang M, Seal M, Wood SJ, Yücel M, Velakoulis D and Pantelis C. Neuroanatomical abnormalities in schizophrenia: A multimodal voxelwise meta-analysis and meta-regression analysis. Schizophr Res 2011; 127:46-57.
• E Via, J Radua, N Cardoner, F Happe and D Mataix-Cols. Meta-analysis of gray matter abnormalities in autism spectrum disorder. Arch Gen Psychiatry 2011; 68:409-418.
• Lai CH. Gray matter deficits in panic disorder: a pilot study of meta-analysis. J Clin Psychopharmacol 2011; 31:287-93..
• Richlan F, Kronbichler M and Wimmer H. Meta-analyzing brain dysfunctions in dyslexic children and adults. Neuroimage 2011; 56:1735-42.
• Bora E, Fornito A, Pantelis and Yücel M. Gray matter abnormalities in Major Depressive Disorder: A meta-analysis of voxel based morphometry studies. J Affect Disord 2011; in Press.
• Li J, Pan P, Song W, Huang R, Chen K and Shang H. A meta-analysis of diffusion tensor imaging studies in amyotrophic lateral sclerosis. Neurobiol Aging 2011; in Press.
• Pan PL, Song W and Shang HF. Voxel-wise meta-analysis of gray matter abnormalities in idiopathic Parkinson's disease. Eur J Neurol 2011; in Press.
• Bora E, Fornito A, Yücel M and Pantelis C. The effects of gender on grey matter abnormalities in major psychoses: a comparative voxelwise meta-analysis of schizophrenia and bipolar disorder. Psychol Med 2011; in Press.
• Nakao T, Radua J, Rubia K and Mataix-Cols D. Gray matter volume abnormalities in ADHD: Voxel-based meta-analysis exploring the effects of age and stimulant medication. Am J Psychiatry 2011; in Press.
• Murphy ML and Frodl T. Meta-analysis of diffusion tensor imaging studies shows altered fractional anisotropy occurring in distinct brain areas in association with depression. Biol Mood Anxiety Disord 2011; 1:3.
• Fusar-Poli P, Radua J, McGuire P and Stefan B. Neuroanatomical maps of psychosis onset: Voxel-wise meta-analysis of antipsychotic-naive VBM studies. Schizophrenia Bull 2011; in Press.

The authors | IoP King's College London | NeuroImageN