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vAnatomy Post Scanning Procedures

ComputeTalairach

The stanford MR toolbox command 'computeTalairach' will launch a GUI for specifying the 8 points needed to transform our vAnatomy coordinates into Talairach coordinates. This page describes how to use this tool.

After loading the vAnatomy file for which you wish to build the transform, You need to set the eight Talairach reference points (and a ninth intermediary point). You must set these points in order, but you can go back and change them at any time (although changing certain key points will reset other points).

In general, you select points by first clicking the button indicating which reference point you wish to select. Then, you must click once in the figure that you wish to select in (ie. coronal, axial, or sagittal view). You should then get 'cross-hairs'- click once one to select the point. You should see your selected point appear on all the slices. Note that once you click the button, you cannot change slices, so select the slice before clicking the button. Also note that the one exception to this procedure is the mid-sagittal. You will be forced to select this point in the coronal view, and no label for it will appear on your slices.

Here's a brief guide to finding the points in yor anatomy:

  1. Anterior Commissure (AC): the origin of the Talairach Atlas coordinate system. Use the axial view to find it, although it is sometimes clear from a mid-sagittal view, where it looks like a small spot of white matter just anterior to the thallamus. This structure is generally in the middle of the brain, above the brainstem but below the corpus callosum. It is a small fiber tract (3-5mm diameter) connecting the two hemispheres (separate from the much larger corpus callosum). Once you find the AC, be sure to mark its superior edge (it is several mm large). Talairach ( 0, 0, 0 ).
  2. Posterior Commissure (PC): use the axial view and look a couple of centimeters posterior of the AC, in about the same slice. The PC is very close to the brainstem and, in the sagittal view, it looks like a 'switch-back' in a small fiber tract connecting the cerebellum with the thallamus. Talairach ( 0, -24, 0 ).

    Once you specify the AC and the PC, the AC-PC line will automatically be drawn on your slices. Note that, if your AC and PC are not in the same slice, then this line will appear as segments across several slices. To find the PPC and AAC, find the slices where this line crosses the most anterior and the most posterior extent of the brain.

  1. Posterior to the PC (PPC): The point where the AC-PC line intersects the posterior extent of the brain at the AC-PC level. Talairach ( 0, -102, 0 ).
  2. Anterior to the AC (AAC): The point where the AC-PC line intersects the anterior extent of the brain at the AC-PC level. Talairach ( 0, 68, 0 ).

    3. The last four points require that two more axes be defined- the left-right axis and the superior-inferior axis. These must be orthogonal to the AC-PC line. To set up these axes, you must specify a mid-sagittal point somewhere near the AC. After you specify this point, the other two axes will be draw on your slices. Check to be sure that the superior-inferior axis provides a good compromise in dividing the two hemispheres. If it does not, select it again before continuing. As with the PPC and AAC, follow the relevant axis through the slices to the slice where the line segement reaches the end of the brain before selecting these points.

  3. Mid-sagittal point: An intermediate point that is not a Talairach reference. This point is used to define the superior-inferior and left-right axes. The program will force you to select it from the coronal view at the slice which contains the AC.
  4. Left of the AC (LAC): The point where a 'horizontal' line passing through the AC intersects the left extent of the brain in the coronal plane containing the AC. Talairach ( -62, 0, 0 ).
  5. Right of the AC (RAC): The point where a 'horizontal' line passing through the AC intersects the right extent of the brain in the coronal plane containing the AC. Talairach ( 62, 0, 0 ).
  6. Superior to the AC (SAC): The point where a 'vertical' line passing through the AC intersects the superior extent of the brain in the coronal plane containing the AC. Talairach ( 0, 0, 72 ).
  7. Inferior to the AC (IAC): The point where a 'vertical' line passing through the AC intersects the inferior extent of the brain (i.e., the inferior extents of the temporal lobes) in the coronal plane containing the AC. Talairach ( 0, 0, -42 ).
Given below are some of the images when the talairach points fall in one slice.
     
Some of the images when the talairach points fall in multiple slices.

 

You may find some of these links useful:

Talaraich Information from MedX Manual

The anatomic conventions of the Talairach Atlas are that anatomic right, superior and anterior directions are positive, while left, inferior and posterior directions are negative (Talairach Atlas Landmarks). Talairach Atlas Lanmarks are used to define the registration are as follows:

  1. The Anterior Commissure (AC), defined as the origin of the Talairach Atlas coordinate system, is assumed to be at location (0, 0, 0).
  2. The Posterior Commissure (PC) is assumed to be at location ( 0, -24, 0 ).
  3. The point where the AC-PC line intersects the posterior extent of the brain at the AC-PC level. This point is designated as the landmark 'Posterior to the Posterior Commissure' (PPC), and is assumed to be at location ( 0, -102, 0 ).
  4. The point where the AC-PC line intersects the anterior extent of the brain at the AC-PC level. This point is designated as the landmark 'Anterior to the Anterior Commissure' (AAC), and is assumed to be at location ( 0, 68, 0 ).
  5. The point where a 'horizontal' line passing through the AC intersects the left extent of the brain in the coronal plane containing the AC. This point is designated as the landmark 'Left of the Anterior Commissure' (LAC), and is assumed to be at location ( -62, 0, 0 ).
  6. The point where a 'horizontal' line passing through the AC intersects the right extent of the brain in the coronal plane containing the AC. This point is designated as the landmark 'Right of the Anterior Commissure' (RAC), and is assumed to be at location ( 62, 0, 0 ).
  7. The point where a 'vertical' line passing through the AC intersects the superior extent of the brain in the coronal plane containing the AC. This point is designated as the landmark 'Superior to the Anterior Commissure' (SAC), and is assumed to be at location ( 0, 0, 72 ).
  8. The point where a 'vertical' line passing through the AC intersects the inferior extent of the brain (i.e., the inferior extents of the temporal lobes) in the coronal plane containing the AC. This point is designated as the landmark 'Inferior to the Anterior Commissure' (IAC), and is assumed to be at location ( 0, 0, -42 ).

In order to best place the landmarks according to the assumptions used to determine their locations in Talairach Atlas space, it is recommended that you locate and place landmark vertices in specific orthogonal views, as follows:

  • AC, PC: Use sagittal and transverse views
  • SAC, IAC, RAC, LAC: Use coronal view
  • AAC, PPC: Use transverse view

    [END MedX quote]

 

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