Tools for NIfTI and ANALYZE image in MATLAB

(Click LINK HERE for the latest update)

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Description:

Frequently Asked Questions: http://www.rotman-baycrest.on.ca/~jimmy/NIfTI/FAQ.htm

• Feature of load_nii: It not only loads the file, but also converts data to RAS orientation while loading. This feature makes it different from other software, and it is proven to be a convenient way to tell the orientation immediately, especially in the Left/Right confusion.

• Feature of view_nii: With this function, the display can be embedded into your existing figure window. See detail at http://www.rotman-baycrest.on.ca/~jimmy/NIfTI/examples.txt.

• Feature of reslice_nii: It can interpolate any oblique images with non-orthogonal rotation or shearing and save them into orthogonal orientations that can be loaded with load_nii.

• Feature of save_nii: It can save any NIfTI data into ANALIZE compatible file extension (.img/.hdr), and can be used by other software that does not support NIfTI file format.

Basic Programs:

View fullsize image

1. load_nii.m:  Load N-Dimensional NIfTI data (where N can be from 3 to 7) or ANALYZE data (where N can be from 3 to 4), and apply header info (e.g. affine geometric transform, voxel intensity scaling, etc.) to the data. If your data has more than 3-Dimension (e.g. time series etc.), you can also specify a range to extract only 1 or several volumes.  For usage, type:  help load_nii

2. save_nii.m: Save N-Dimensional NIfTI data (where N can be from 3 to 7) that is loaded by "load_nii.m" or made by "make_nii.m". For usage, type: help save_nii

3. make_nii.m: Make N-Dimensional NIfTI data (where N can be from 3 to 7) based on the N-Dimensional matrix and other optional parameters (e.g. voxel_size, origin, etc.). Using "save_nii" command, the NIfTI data that is made by "make_nii" can be saved into a NIfTI file. For usage, type: help make_nii

4. make_ana.m: Make 3D ANALYZE data based on the 3D matrix and other optional parameters (e.g. voxel_size, origin, etc.). Using "save_untouch_nii" command, the ANALYZE data that is made by "make_ana" can be saved into an ANALYZE file in order to be compatible with some ANALYZE only programs. For usage, type: help make_ana

5. reslice_nii.m: Reslice 3D (or 4D) NIfTI data or ANALYZE data with affine matrix M in .mat file. The program will base on the affine matrix, which is especially useful for oblique images with non-orthogonal rotation or shearing that cannot be loaded with "load_nii.m". You can also specify voxel_size, etc. It will not cause negative effect, as long as you remember not to do slice time correction after using "reslice_nii.m". For usage, type: help reslice_nii

6. view_nii.m: View 3D (or 4D) NIfTI data or ANALYZE data that is loaded by "load_nii.m" or made by "make_nii.m". Activation map, ROI, etc. can be overlaid on top of a background image (see above picture). Plotted view can be embedded into your existing figure window. See detail at http://www.rotman-baycrest.on.ca/~jimmy/NIfTI/examples.txt. For usage, type: help view_nii

7. load_untouch_nii.m:  Load N-Dimensional NIfTI data (where N can be from 3 to 7) or ANALYZE data (where N can be from 3 to 4), but do not apply any changes indicated in the header. (Warning: Do not apply "view_nii.m" to the dataset loaded with "load_untouch_nii.m".  For usage, type:  help load_untouch_nii

8. save_untouch_nii.m: Save N-Dimensional NIfTI data (where N can be from 3 to 7) or ANALYZE data (where N can be from 3 to 4) that is loaded by "load_untouch_nii.m" or made by "make_ana.m". If you do not modify the loaded dataset, the header and data in the new saved file should be the same as those in the original file. For usage, type: help save_untouch_nii

Other Programs:

1. collapse_nii_scan.m: Integrate multiple single-scan NIfTI or ANALYZE files into a multiple-scan NIfTI file. For usage, type:  help collapse_nii_scan

2. expand_nii_scan.m: Break a multiple-scan NIfTI file into multiple single-scan NIfTI files. For usage, type:  help expand_nii_scan

3. flip_lr.m: Convert ANALYZE or NIfTI file to an L-R flipped NIfTI file. (Warning: please use this program with caution!). For usage, type:  help flip_lr

4. get_nii_frame.m: Return number of time frames of a NIfTI dataset. For usage, type:  help get_nii_frame

5. load_nii_ext.m: Load NIfTI header extension. For usage, type:  help load_nii_ext

6. mat_into_hdr.m: Integrate the affine matrix in old SPM MATLAB file into its .hdr header file to become NIfTI format file. For usage, type:  help mat_into_hdr

For NIfTI image, "load_nii.m" will take the affine matrix in its header and make appropriate space transformation. So the loaded dataset will always be in RAS orientation, i.e. X axis from Left to Right, Y axis from Posterior to Anterior, and Z axis from Inferior to Superior.

For ANALYZE image, "load_nii.m" will load the image as is. Since an ANALYZE image could be in RAS or LAS depending on your assumption, many people are confused by its laterality, especially when an ANALYZE image is processed by different software. If you are still using ANALYZE image, I strongly suggest that you take a look at the table that I summarized:

http://www.rotman-baycrest.on.ca/~jimmy/UseANALYZE.htm

Because "load_nii.m" can only handle a subset of affine transform (flipping and orthogonal rotation with a total of 48 orientations), you should use "reslice_nii.m" to handle the rest of the space transformation (e.g. NIfTI files with non-orthogonal rotation, shearing etc.). It will not cause negative effect, as long as you remember not to do slice time correction after using "reslice_nii.m".

If you prefer the loaded dataset untouched, you have to use "load_untouch_nii.m" and " save_untouch_nii.m" program pair. In this case, the affine matrix in NIfTI header will not be applied to the loaded dataset, and the loaded dataset should not be used for other programs, like "view_nii.m" etc.

Two example datasets, "avg152T1_LR_nifti.nii" and "avg152T1_RL_nifti.nii", are provided under NIfTI web site http://nifti.nimh.nih.gov/nifti-1/data. As is indicated on NIfTI web site, "The first image (LR) is stored in radiological convention (LAS). The second image (RL) is stored in neurological convention (RAS). Any NIfTI compliant viewing software should display these images identically". When you load them with "load_nii.m", and display them with "view_nii.m", you can expect the same result.

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Update History:

• 2010-08-19: Thanks to Rembrandt from Radboud University Nijmegen (Netherlands), I made 2 small changes to handle the exceptions.
• 2010-04-13: Fixed a bug in "collapse_nii_scan" to collapse Analyze format data.
• 2010-01-06: "load_untouch_nii" now supports loading specific slices of NIfTI or Analyze format.
• 2009-09-09: While an N-Dimensional matrix can be saved into a NIfTI file using "make_nii / save_nii" command pair, a 3D matrix can also be saved into an ANALYZE file using "make_ana / save_untouch_nii" in order to be compatible with some ANALYZE only programs.
• 2009-07-03: Fixed several bugs, and posted informative table: http://www.rotman-baycrest.on.ca/~jimmy/UseANALYZE.htm.
• 2009-03-25: Thanks to the feedback of Kate Fissell from University of Pittsburgh, transformation matrix M will no longer be saved by save_untouch_nii.m.
• 2009-03-17:
  1. Thanks to the feedback of Bryce Wilkins from USC, a typo in one of my message display is fixed.
  2. Thanks to the suggestion of Ashish Raj from Cornell, 'expand_nii_scan.m' is modified and 'collapse_nii_scan.m' is added.
• 2008-12-05: Default data type for 'make_nii.m' now follows the data type of 'img' matrix, instead of float32.
• 2008-12-04: Fixed a bug in fliplr.m when reading files.
• 2008-10-23:
  1. Properly handle fread/'*char' problem with foreign characters in MATLAB 7 and above.
  2. Reordered input parameters for 'reslice_nii.m' program.
• 2008-09-04: Extended Load / Save / Make programs to N-Dimension, where N can be from 3 to 7 for NIfTI data and from 3 to 4 for ANALYZE data.
• 2008-08-28: Added "load_untouch_nii.m" and "save_untouch_nii.m" program pair. See detail in Description above and FAQ at: http://www.rotman-baycrest.on.ca/~jimmy/NIfTI/FAQ.htm.
• 2008-08-21: Added a "verbose" parameter for "reslice_nii.m" to provide an opportunity to disable the progress display.
• 2008-08-19:
  1. Program "load_nii.m" is modified to take tolerance parameter, which is the distortion allowed in the loaded image for a non-orthogonal affine matrix. If you set 'tolerance' to 0, it means that you do not allow any distortion. If you set 'tolerance' to 1, it means that you do not care any distortion. The image will fail to be loaded if it can not be tolerated. By default, it is 0.1 (10%).
  2. New program "reslice_nii.m" is provided to perform any 3D affine transform defined by a NIfTI format image, especially for those non-orthogonal affine transform (oblique image) that cannot be loaded by "load_nii.m".
  3. New program "reslice_nii.m" can also be applied to generate an isotropic image from either a NIfTI format image or an ANALYZE format image.
  4. New program "flip_lr.m" is provided for LAS->RAS (or RAS->LAS) conversion.
• 2008-07-07: Thanks to the feedback of Holger Krause from Heinrich-Heine University Dusseldorf, the bug in "mat_into_hdr.m" when input file containing a path has been fixed.
• 2008-04-08:
  1. Added a new feature to load and save NIfTI's header extension. Program nii.ext = load_nii_ext(NIfTI_file_name) will return empty if there is no header extension, and save_nii(nii, NIfTI_file_name) will save header extension if there is a valid nii.ext structure.
  2. Fixed a bug when loading qform data, which was introduced on 01-FEB-2008.
• 2008-02-01: Thanks to Jeff Gunter from Mayo who suggested to display a warning message instead of throwing an error for a very oblique image. Especially thanks to his code of checking qform rotation before applying voxel size modulation.
• 2007-05-03: Fixed a bug that caused the "value at crosshair" and "value at cursor" always displaying the value of the first 3D volume when viewing a 4D image using view_nii. Thanks to Ning Cao from UKY who reported and fixed this bug.
• 2007-04-26:
  1. Modified save_nii command, so earlier versions of SPM can also open it with correct originator.
  2. Modified http://www.rotman-baycrest.on.ca/~jimmy/NIfTI/FAQ.htm with several categories.
• 2007-04-19:
  1. Many users asked for a direct load of the affine matrix in the .mat file of earlier versions of SPM. Now if "load_nii" in the tools detects that the file you are loading is an Analyze file and there is a .mat file with the same file, it will automatically integrate the affine matrix in the .mat file into the .hdr structure.
  2. Fixed a bug in "mat_into_hdr.m" program.
• 2006-12-20:
  1. In "view_nii" window, a new menu item "Save displayed image as ..." is added in the "File" menu. This is especially helpful if people use "Convert orientation" item in the "Edit" menu to convert their old non-RAS Analyze image to RAS orientation. After conversion, the displayed RAS image can now be saved.
  2. Removed integer rounding for "hdr.hist.originator" in "load_nii", but origin voxel will still be rounded by "view_nii".
• 2006-12-15:
  1. Improved data scaling process. If scl_slope=1 and scl_inter=0, nothing has to be scaled, which is the same as scl_slope=0 situation. Otherwise, all values of scaled img will be stored in 32-bit rather than double precision, unless original img is 64-bit. This improvement dramatically reduced the size of the scaled image, unless the original image has double precision.
  2. Fixed a bug in calculating origin position when original origin position is [0 0 0] (an invalid origin).
• 2006-09-25: Added "mat_into_hdr.m" script to convert the ANALYZE 7.5 SPM Reoriented image file into NIfTI format, and integrate the affine matrix in its matlab file into its header file.
• 2006-07-26: Due to round-off of quaternions (quatern_b/c/d), sqrt(1.0-(b*b+c*c+d*d)) may become complex because value inside sqrt may go below 0 (e.g. -1e-6). Instead of complex, now 0 will be used in this case. Thanks to Jeff Gunter who reported this issue.
• 2006-07-04: Thanks to Michael Harms from WUSTL who reported and fixed some bugs in loading and making RGB data. He also added codes to save AnalyzeDirect compatible RGB data.
• 2006-06-28:
  1. "unxform_nii" from Jeff is included to provide an option of putting image orientation back to its original status.
  2. "expand_nii_scan" is modified so the expanded image files will be appended with a 4-digit number starting from 0000.
• 2006-06-03:
  1. There was a bug in converting some permuted images to RAS orientation. It has been fixed now. Thanks to Jeff Gunter from Mayo Clinic who reported this bug.
  2. hdr.dime.glmax and glmin are updated if hdr.dime.scl_slope is non-zero.
• 2006-04-20: Image data is now always loaded according to the size that is specified in its header. This is because that the size of some image data is incorrectly larger than what specified in "hdr.dime.dim" field, which has caused problem to load image data.
• 2006-03-22: It now supports both COMPLEX64 and COMPLEX128 data type.
• 2006-03-10: "nii.hdr.scl_slope" will take "avw.hdr.roi_scale" value, which is a non-ANALYZE7.5 field but exclusively used by SPM.
• 2006-03-07: Image data type will be converted to "double" in the case that "scl_slope" is used.
• 2006-02-24:
  1. Fixed a bug to reorder "pixdim" and "originator" field for some NIfTI data.
  2. Added "rot_orient" and "flip_orient" fields under "hdr.hist" if package make conversion of the NIfTI data into RAS orientation system.
• 2005-11-16: It now supports both new_RGB (RGB triple) & old_RGB (used by Analyze 6.0 from AnalyzeDirect Inc).
• 2005-11-07: Images whose cardinal planes are slightly off Cartesian coordinates will also be loaded. See detail in "xform_nii.m".

(Also available on MathWorks File Exchange)

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Contact: Please send your feed back to me (jimmy@rotman-baycrest.on.ca)