More accurate Talairach coordinates for neuroimaging using non-linear registration

Abstract

While the Talairach atlas remains the most commonly used system for reporting coordinates in neuroimaging studies, the absence of an actual 3-D image of the original brain used in its construction has severely limited the ability of researchers to automatically map locations from 3-D anatomical MRI images to the atlas. Previous work in this area attempted to circumvent this problem by constructing approximate linear and piecewise-linear mappings between standard brain templates (e.g. the MNI template) and Talairach space. These methods are limited in that they can only account for differences in overall brain size and orientation but cannot correct for the actual shape differences between the MNI template and the Talairach brain. In this paper we describe our work to digitize the Talairach atlas and generate a non-linear mapping between the Talairach atlas and the MNI template that attempts to compensate for the actual differences in shape between the two, resulting in more accurate coordinate transformations. We present examples in this paper and note that the method is available freely online as a Java applet.

Fig. 1. Scanning and Distortion Correction

The digital “Talairach” atlas was constructed by first scanning in the atlas and performing distortion correction on the scanned images to correct for distortions in both the original printed atlas and any distortions introduced by the scanning process. (Distortions result in the underlying graph paper used in the atlas not having orthogonal, equispaced lines). We semi-automatically located nine landmarks in each slice and then used these to map each scanned slice to the true orthogonal coordinate system using a thin-plate spline transformation.

Fig. 2. Digitized, Aligned and Segmented Axial Slices of the Talairach Atlas

The figure above shows selected slices from the digitized atlas with superimposed manual segmentations of the brain.

Fig. 3. MNI to Talairach Point-Based Registration

In this figure the results of progressively more complex registrations between the MNI brain surface and the Talairach brain surface are shown. In particular we show a thick section of outer brain surface of (i) Talairach Brain Mask (red) (ii) Colin Brain Mask (green) following rigid (left), affine (middle) and non-linear (right) point-based registration using RPM. Note especially the improved alignment in the frontal region (highlighted by a yellow ellipse.) We note that the affine registration is roughly equivalent to current piecewise linear methods (Brett et al. (2001)).

Fig. 4. MNI to Talairach Point-Based Registration, Image Overlay II

Another view of the result from Figure 3, where the surface from the Talairach atlas is overlaid on the Colin 27 brain. The result from the rigid transformation is shown in yellow, the affine transformation in green and the nonlinear transformation in red.

Fig. 5. A Direct Look at the Differences Between the MNI template and the Talairach Brain

Top, AC centered slices of MNI Template (Colin) Brain. Bottom: AC-centered slices of Colin Brain inversely mapped to Talairach space using the non-linear registration above. Note that the Talairach brain is, (i) Wider left to right, (ii) Shorter anterior to posterior and (iii) Appears to have no obvious distortions – demonstrating the smoothness of the overall nonlinear registration.

Fig. 6. Regional Volume Differences Between the MNI template and the Talairach Brain

In this figure we plot the magnitude of the Jacobian of the nonlinear mapping of the Talairach Brain to the MNI template. This is a measure of volume change which shows where the MNI template is substantially bigger (locally) than the Talairach brain. Note the relatively large difference in the temporal lobes.

Fig. 7. Improved Talairach Coordinates I: Axial Slices of Inferior Occipital Regions

Result from two locations (51,−75,8) and (51,−78,1). First Column: Slice z=−8 from the MNI template (top) and the Talairached Brain (bottom). Second Column: Top: The Talairach atlas slices for these locations. Middle: The location of this point on the original MNI template using a piecewise mapping (red cross-hairs). Bottom: The location of the same point on the Talairached-MNI brain. The third and fourth columns are repeats for location (51,−78,1). Note that in both cases these points are on the brain surface in the Talairached brain (as they should be, see the original atlas) whereas in the MNI brain they are located outside the brain.

Fig. 8. Improved Talairach Coordinates II: Axial Slices of Frontal Regions

Result from two locations (51,42,24) and (51,36,32). First Column: Slice z=24 from the MNI template (top) and the Talairached Brain (bottom). Second Column: Top: The Talairach atlas slices for these locations. Middle: The location of this point on the original MNI template using a piecewise mapping (red cross-hairs). Bottom: The location of the same point on the Talairached-MNI brain. The third and fourth columns are repeats for location (51,36,32).

Fig. 9. Improved Talairach Coordinates III: Coronal Slices of Frontal Regions

Result from two locations (−17,24,58) and (55,40,9). First Column: Slice y=24 from the MNI template (top) and the Talairached Brain (bottom). Second Column: Top: The location of this point on the original MNI template using a piecewise mapping (red cross-hairs). Bottom: The location of the same point on the Talairached-MNI brain. The third and fourth columns are repeats for location (55,40,9).

Fig. 10. Improved Talairach Coordinates IV: Coronal Slices of Superior Frontal/Premotor Regions

Result from two locations (50,−12,56) and (−32,−4,65). First Column: Slice y=−12 from the MNI template (top) and the Talairached Brain (bottom). Second Column: Top: The location of this point on the original MNI template using a piecewise mapping (red cross-hairs). Bottom: The location of the same point on the Talairached-MNI brain. The third and fourth columns are repeats for location (51,−78,1).

Fig. 11. The MNI to Talairach Conversion Applet