FT_VOLUMEREALIGN
Note that this reference documentation is identical to the help that is displayed in MATLAB when you type “help ft_volumerealign”.
FT_VOLUMEREALIGN spatially aligns an anatomical MRI with head coordinates based on external fiducials or anatomical landmarks. This function does not change the anatomical MRI volume itself, but only adjusts the homogeneous transformation matrix that describes the mapping from voxels to the coordinate system. It also appends a coordsys-field to the output data, or it updates it. This field specifies how the x/y/z-axes of the coordinate system should be interpreted. For spatial normalisation and deformation (i.e. warping) an MRI to a template brain you should use the FT_VOLUMENORMALISE function. Different methods for aligning the anatomical MRI to a coordinate system are implemented, which are described in detail below: INTERACTIVE - Use a graphical user interface to click on the location of anatomical landmarks or fiducials. The anatomical data can be displayed as three orthogonal MRI slices or as a rendering of the head surface. The coordinate system is updated according to the definition of the coordinates of these fiducials. FIDUCIAL - The coordinate system is updated according to the definition of the coordinates of anatomical landmarks or fiducials that are specified in the configuration. HEADSHAPE - Match the head surface from the MRI with a measured head surface using an iterative closest point procedure. The MRI will be updated to match the measured head surface. You can optionally do an initial manual coregistration of the two head surfaces. SPM - Align the individual MRI to the coordinate system of a target or template MRI by matching the two volumes. FSL - Align the individual MRI to the coordinate system of a target or template MRI by matching the two volumes. Use as [mri] = ft_volumerealign(cfg, mri) or [mri] = ft_volumerealign(cfg, mri, target) where the first input is the configuration structure, the second input should be an anatomical or functional MRI volume and the third input is the the target anatomical MRI for SPM or FSL. The configuration can contain the following options cfg.method = string representing the method for aligning 'interactive' use the GUI to specify the fiducials 'fiducial' use pre-specified fiducials 'headshape' match the MRI surface to a headshape 'spm' match to template anatomical MRI 'fsl' match to template anatomical MRI cfg.coordsys = string specifying the origin and the axes of the coordinate system. Supported coordinate systems are 'ctf', '4d', 'bti', 'yokogawa', 'asa', 'itab', 'neuromag', 'acpc', and 'paxinos'. See http://tinyurl.com/ojkuhqz cfg.clim = [min max], scaling of the anatomy color (default is to adjust to the minimum and maximum) cfg.parameter = 'anatomy' the parameter which is used for the visualization cfg.viewresult = string, 'yes' or 'no', whether or not to visualize aligned volume(s) after realignment (default = 'no') When cfg.method = 'fiducial' and a coordinate system that is based on external facial anatomical landmarks (common for EEG and MEG), the following is required to specify the voxel indices of the fiducials: cfg.fiducial.nas = [i j k], position of nasion cfg.fiducial.lpa = [i j k], position of LPA cfg.fiducial.rpa = [i j k], position of RPA cfg.fiducial.zpoint = [i j k], a point on the positive z-axis. This is an optional 'fiducial', and can be used to determine whether the input voxel coordinate axes are left-handed (i.e. flipped in one of the dimensions). If this additional point is specified, and the voxel coordinate axes are left handed, the volume is flipped to yield right handed voxel axes. When cfg.method = 'fiducial' and cfg.coordsys = 'acpc', the following is required to specify the voxel indices of the fiducials: cfg.fiducial.ac = [i j k], position of anterior commissure cfg.fiducial.pc = [i j k], position of posterior commissure cfg.fiducial.xzpoint = [i j k], point on the midsagittal-plane with a positive Z-coordinate, i.e. an interhemispheric point above ac and pc The coordinate system will be according to the RAS_Tal convention i.e. the origin corresponds with the anterior commissure the Y-axis is along the line from the posterior commissure to the anterior commissure the Z-axis is towards the vertex, in between the hemispheres the X-axis is orthogonal to the YZ-plane, positive to the right When cfg.method = 'interactive', a user interface allows for the specification of the fiducials or landmarks using the mouse, cursor keys and keyboard.The fiducials can be specified by pressing the corresponding key on the keyboard (n/l/r or a/p/z). When pressing q the interactive mode will stop and the transformation matrix is computed. This method supports the following options: cfg.viewmode = 'ortho' or 'surface', visualize the anatomical MRI as three slices or visualize the extracted head surface (default = 'ortho') cfg.snapshot = 'no' ('yes'), making a snapshot of the image once a fiducial or landmark location is selected. The optional second output argument to the function will contain the handles to these figures. cfg.snapshotfile = 'ft_volumerealign_snapshot' or string, the root of the filename for the snapshots, including the path. If no path is given the files are saved to the pwd. The consecutive figures will be numbered and saved as png-file. When cfg.method = 'headshape', the function extracts the scalp surface from the anatomical MRI, and aligns this surface with the user-supplied headshape. Additional options pertaining to this method should be defined in the subcfg cfg.headshape. The following option is required: cfg.headshape.headshape = string pointing to a file describing a headshape or a FieldTrip-structure describing a headshape, see FT_READ_HEADSHAPE The following options are optional: cfg.headshape.scalpsmooth = scalar, smoothing parameter for the scalp extraction (default = 2) cfg.headshape.scalpthreshold = scalar, threshold parameter for the scalp extraction (default = 0.1) cfg.headshape.interactive = 'yes' or 'no', use interactive realignment to align headshape with scalp surface (default = 'yes') cfg.headshape.icp = 'yes' or 'no', use automatic realignment based on the icp-algorithm. If both 'interactive' and 'icp' are executed, the icp step follows the interactive realignment step (default = 'yes') When cfg.method is 'fsl', a third input argument is required. The input volume is coregistered to this target volume, using FSL-flirt. Additional options pertaining to this method should be defined in the sub-structure cfg.fsl and can include: cfg.fsl.path = string, specifying the path to fsl cfg.fsl.costfun = string, specifying the cost-function used for coregistration cfg.fsl.interpmethod = string, specifying the interpolation method, can be 'trilinear', 'nearestneighbour', or 'sinc' cfg.fsl.dof = scalar, specifying the number of parameters for the affine transformation. 6 (rigid body), 7 (global rescale), 9 (traditional) or 12. cfg.fsl.reslice = string, specifying whether the output image will be resliced conform the target image (default = 'yes') When cfg.method = 'spm', a third input argument is required. The input volume is coregistered to this target volume, using SPM. You can specify the version of the SPM toolbox to use with cfg.spmversion = string, 'spm2', 'spm8', 'spm12' (default = 'spm8') Additional options pertaining to SPM2 and SPM8 should be defined in the sub-structure cfg.spm and can include: cfg.spm.regtype = 'subj', 'rigid' cfg.spm.smosrc = scalar value cfg.spm.smoref = scalar value Additional options pertaining to SPM12 are cfg.spm.sep = optimisation sampling steps (mm), default: [4 2] cfg.spm.params = starting estimates (6 elements), default: [0 0 0 0 0 0] cfg.spm.cost_fun = cost function string: 'mi' - Mutual Information (default) 'nmi' - Normalised Mutual Information 'ecc' - Entropy Correlation Coefficient 'ncc' - Normalised Cross Correlation cfg.spm.tol = tolerences for accuracy of each param, default: [0.02 0.02 0.02 0.001 0.001 0.001] cfg.spm.fwhm = smoothing to apply to 256x256 joint histogram, default: [7 7] With the 'interactive' and 'fiducial' methods it is possible to define an additional point (with the key 'z'), which should be a point on the positive side of the xy-plane, i.e. with a positive z-coordinate in world coordinates. This point will subsequently be used to check whether the input coordinate system is left or right-handed. For the 'interactive' method you can also specify an additional control point (with the key 'r'), that should be a point with a positive coordinate on the left-right axis. To facilitate data-handling and distributed computing you can use cfg.inputfile = ... cfg.outputfile = ... If you specify one of these (or both) the input data will be read from a *.mat file on disk and/or the output data will be written to a *.mat file. These mat files should contain only a single variable, corresponding with the input/output structure. See also FT_READ_MRI, FT_VOLUMERESLICE, FT_INTERACTIVEREALIGN, FT_ELECTRODEREALIGN, FT_DETERMINE_COORDSYS, SPM_AFFREG, SPM_NORMALISE, SPM_COREG
