Table 1.

Data pre-processing techniques applied to MRI and fMRI images

Type	Ref.	Technique (applied methods)
Scaling	[36]	Image resize
	[8, 34, 37–39]	Image registration ( AR${}^2$, DARTEL${}^1$, LRg)
	[40–42]	Intensity non-uniformity correction (GW${}^1$, B1-NU${}^1$, N3${}^1$)
	[42]	Distortion correction (PB${}^1$)
	[43–45]	Bias correction/regularization (MICO${}^1$)
	[46]	Contrast enhancement (CLAHE${}^1$)
Correction	[31, 47–52]	Slice timing correction (HSI${}^2$, FEAT${}^2$, LSA${}^2$, 6-PST${}^2$)
	[31, 34, 40, 47–51, 53–55]	Motion correction (FSL-MCFLIRT${}^2$, LSA${}^2$, 6-PST${}^2$)
Stripping and trimming	[39, 40, 44, 46, 53, 56, 57]	Skull stripping (NRBAC${}^1$)
	[47]	Brain extraction (FSL-BET${}^1$ ${}^2$)
	[36]	Trim edges
Normalization	[33, 34, 37, 39, 42, 47, 49, 51, 56, 58, 59]	Normalization (SPM ${}^{1,2}$, SD${}^1$, ANTs${}^1$, EPI${}^2$)
	[36, 40]	Intensity normalization
	[31, 43, 45, 47, 50, 52, 54, 55]	Spatial normalization (ALT${}^1$ ${}^2$, FSL-FLIRT${}^2$, DARTEL${}^2$)
	[32]	Z-score normalization
	[39]	Numerical normalization
Filtering	[46, 50, 51]	Basic filtering (GSF${}^1$)
	[34]	Spatial filtering
	[34, 48, 49, 51]	Temporal filtering
	[8]	Weiner filtering
	[31, 47, 48, 53]	High-pass filtering
Smoothing	[45, 50, 58]	Basic smoothing (FWHM-GK${}^2$)
	[31, 47–49, 51, 52, 54, 59]	Spatial smoothing (FWHM-GK${}^2$)
Distinct techniques	[32]	Linear regression
	[49]	Linear detrend
	[31, 37, 43]	Modulation (JWF${}^1$)
	[38, 44, 59]	Segmentation (LLL${}^1$)
	[60]	Voxel-based morphometric
	[36]	Cortical reconstruction
	[34, 48]	Denoising (tCompCor${}^2$)
	[46, 57]	Data augmentation

FWHM-GK Full-width half-maximum (FWHM) Gaussian kernel, SPM statistical parametric mapping, SD standardization, ALT affine linear transformation, JWF Jacobian of wrap field, GSF Gaussian smoothing filter, FST Free Surfer Tool, ANTs advanced normalization tools, GW Gradwarp, B1-NU B1-non-uniformity, PB phantom based, FSL-BET FMRIB Software Library-Brain Extraction Tool, FSL-MCFLIRT motion correction using FMRIB’s linear image registration tool, FSL-FLIRT FMRIB’s linear image registration tool, FEAT FMRI expert analysis tool, CLAHE contrast limited adaptive histogram equalization, LLL local label learning, DARTEL diffeomorphic anatomical registration through exponentiated Lie algebra, LR linear registration, LSA least square approach, 6-PST 6 parameter spatial transformation, EPI echo planar imaging, NRBAC nonparametric region-based active contour, MICO multiplicative intrinsic component optimization

¹MRI

²fMRI