MNI Coordinates, Talairach Coordinates and related issues

The Talairach atlas is widely used by the neuroimaging community to report locations of, for example, fMRI activation centroids. Many conversions from MNI coordinates to Talairach coordinates are crude approximations.

BioImage Suite incorporates ``the Nonlinear Yale MNI to Talairach Conversion Algorithm'', which will be documented in a forthcoming paper -- see also the slides from a recent talk for more details. This conversion is based on a nonlinear surface registration between the MNI Colin brain and the outline of the Talairach brain as reconstructed by digitizing the Talairach Atlas. As a convenience you may access this internal MNI to Talairach coordinate conversion used by BioImage Suite using our custom Java applet without downloading and installing BioImage Suite.

The assumption is that the brain on which coordinates are queries is either the MNI Colin brain or a brain that has been registered and resliced to have same number of slices as this.

Using the Nonlinear Talairach Coordinate Mapping

Once a brain image is registered – to the Colin brain, and resliced to have the same voxel dimensions (Axial 1x1x1 mm resolution, 181x217x181) as this, it is trivial to obtain Talairach coordinates.

First, examine whether the Y-coordinate in the image (i.e. the actual pixel ordering as represented by the Y-Coord in the viewer) is increasing from Anterior to Posterior (BioImage Suite default) or Posterior to Anterior.

Next, press either the "Col Rad" button in the "coordinate bar" (see Figure 1) if the y-coordinate increase from anterior to posterior or the "Col Neuro" button otherwise. Pressing either of these buttons for the first time may result in a slight delay (5-10 seconds) as the lookup table from Colin image coordinates to Talairach space is loaded. 

Now, simply navigate with the left mouse button in the viewer. The coordinates in the black label box, displayed in red, inside the "coordinate bar" are the Talairach coordinates under the mouse. (There are four numbers in the text box: the first three are the coordinates, the fourth number is the image intensity at this point). 

If the internal nonlinear map is used then the Talairach coordinates are printed in green with the prefix C_AP or C_PA (depending on whether the brain y-axis is anterior-to-posterior -- Rad, or posterior-to-anterior -- Neuro). The box below this (with the prefix MNI) shows the MNI Coordinates.

In addition you may access the internal MNI to Talairach coordinate conversion used by BioImage Suite using our custom Java applet without downloading and installing BioImage Suite.

References

• J. Talairach and P. Tournoux, Co-planar Stereotaxic Atlas of the Human Brain: 3-Dimensional Proportional System - an Approach to Cerebral Imaging Thieme Medical Publishers, New York, NY, 1988

An excellent summary/description of the issues, by Matthew Brett, can be found at the Cambridge Cognition and Brain Sciences Unit webpage. The nonlinear mapping used here fully addresses all of these issues.

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