NAME

mri_convert

SYNOPSIS

mri_convert [options] <in volume> <out volume>

DESCRIPTION

mri_convert is a general purpose utility for converting between different file formats. The file type can be specified in two ways. First, mri_convert will try to figure it out on its own from the format of the file name (eg, files that end in .img are assumed to be in spm analyze format). Second, the user can explicity set the type of file using --in_type and/or --out_type.

Legal values for --in_tye (-it) and --out_type (-ot) are listed under optional flagged arguments.

A note on specifying orientation:

Do not use this to try to change the orientation for FSL. This is only to be used when the orientation information in the input file is *wrong*. If it is correct, this will make it wrong! If you are having problems with fslview displaying your data, consult the FSL website for methods to reorient.

Ideally, the orientation information is derived from a DICOM file so that you have some confidence that it is correct. It is generally pretty easyto determine which direction Anterior/Posterior or Inferior/Superior are. Left/Right is very difficult. However, if you have some way of knowing which direction is which, you can use these options to incorporate this information into the header of the output format. For analyze files, it will be stored in the output.mat file. For NIFTI, it is stored as the qform matrix. For bshort/bfloat, it is stored in the .bhdr file. For mgh/mgz it is internal.
First of all, determining and setting the orientation is hard. Don't fool yourself into thinking otherwise. Second, don't think you are going to learn all you need to know from this documentation. Finally, you risk incorporating a left-right flip in your data if you do it incorrectly. OK, there are two ways to specify this information on the command-line.
(1) explicitly specify the direction cosines with -iid, -ijd, -ikd. If you don't know what a direction cosine is, don't use this method.
(2) specify an orientation string with --in_orientation ostring and --out_orientation ostring
Supply the orientation information in the form of an orientation string (ostring). The ostring is three letters that roughly describe how the volume is oriented. This is usually described by the direction cosine information as originally derived from the dicom but might not be available in all data sets. You'll have to determine the correct ostring for your data. The first character of ostring determines the direction of increasing column. The second character of ostring determines the direction of increasing row. The third character of ostring determines the direction of increasing slice. Eg, if the volume is axial starting inferior and going superior the slice is oriented such that nose is pointing up and the right side of the subject is on the left side of the image, then this would correspond to LPS, ie, as the column increases, you move to the patients left; as the row increases, you move posteriorly, and as the slice increases, you move superiorly. Valid letters are L, R, P, A, I, and S. There are 48 valid combinations (eg, RAS LPI, SRI). Some invalid ones are DPS (D is not a valid letter), RRS (can't specify R twice), RAP (A and P refer to the same axis). Invalid combinations are detected immediately, an error printed, and the program exits. Case-insensitive. Note: you can use tkregister2 to help determine the correct orientation string.

POSITIONAL ARGUMENTS

REQUIRED-FLAGGED ARGUMENTS

None

OPTIONAL-FLAGGED ARGUMENTS

APPLYING TRANSFORMS (INCLUDING TALAIRACH)

SPECIFYING THE INPUT AND OUTPUT FILE TYPES
Legal values for --in_type (-it) and --out_type (-ot) are:

CONVERTING TO SPM-ANALYZE FORMAT
Converting to SPM-Analyze format can be done in two ways, depending upon whether a single frame or multiple frames are desired. For a single frame, simply specify the output file name with a .img extension, and mri_convert will save the first frame into the file. For multiple frames, specify the base as the output file name and add --out_type spm. This will save each frame as baseXXX.img where XXX is the three-digit, zero-padded frame number. Frame numbers begin at one. By default, the width the of zero padding is 3. This can be controlled with --in_nspmzeropad N where N is the new width.

OUTPUTS

EXAMPLE 1

APPLYING TRANSFORMS (INCLUDING TALAIRACH)
The volume can be resampled into another space by supplying a transform using the --apply_transform flag. This reads the transform file and applies the transform (when --apply_inverse_transform is used, the transform is inverted and then applied). An example of a transform file is talairach.xfm as found in subjectid/mri/transforms. To convert a subject's orig volume to talairach space, execute the following lines:
* cd subjectid/mri mkdir talairach mri_convert --apply_transform transforms/talariach.xfm --devolvexfm subjectid --ic 0 0 0 orig talairach
This properly accounts for the case where the input volume does not have it's coordinate center at 0.To evaluate the result, run:
* tkmedit -f $SUBJECTS_DIR/talairach/mri/orig -aux talairach
The main and aux volumes should overlap very closely. If they do not, use tkregister2 to fix it (run tkregister --help for docs).

EXAMPLE 2

From the subject directory: mri_convert -at mri/transforms/talairach_one.m3z mri/norm.mgz mri/norm_transformed_by_gca_one.mgz

BUGS

None

REPORTING

Report bugs to <freesurfer@nmr.mgh.harvard.edu>

SEE-ALSO

mris_convert