Talairach Atlases

The use of Cartesian coordinates as an anatomical nomenclature for the human brain was pioneered by Jean Talairach, a French neurosurgeon. Over the course of three decades, he published a series of atlases addressing the brain as a coordinate space [48-50]. The 1967 atlas was the earliest used for spatial normalization [14]. The 1967 atlas was not ideal for spatial normalization since its axial, sagittal, and coronal section images were from different brains. No single brain was adopted as the standard from the 1967 atlas, requiring transforms between various brains to achieve comparable Talairach coordinates [18,20,22]. This lack of standardization was resolved when the 1988 Talairach atlas was published with all three section images from the same brain, a 60-year-old right-handed European female. The 1988 Talairach atlas soon became the standard for human brain spatial normalization [19]. Though the original atlas concept was not coordinate specific, a right-handed Cartesian coordinate system has evolved with + x on the right, + y to the front, and + z to the top of the brain with the origin at the anterior commissure or AC (Figs 1 and 3) [32,35,37].

The 1988 atlas is well suited for global spatial normalization because it clearly defines all anatomical features needed for landmark-based coordinate transformations (Figs 3 and 6). The following features/landmarks are identifiable in highresolution MR images and serve as the basis for global spatial normalization:

• Location. A single landmark is needed to standardize location, and it is designated as the origin, or 0,0,0 coordinate, in Talairach space. The anatomical site of the origin is at the anterior commissure (AC), a very small midline site where a narrow band of callosal fibers crosses between hemispheres. More precisely, the origin is at the intersection of the interhemispheric fissure and the AC's posterior-superior margin. However, the visual center of the AC is usually selected in MR images since it is easier to see.

• Orientation. The interhemispheric plane and a line in this plane passing through both the AC and posterior commissure (PC) are used to standardize brain orientation. This AC-PC line defines the y-axis and the interhemispheric fissure defines the y-z plane needed to standardize orientation in Talairach space.

• Dimension. The dimensions of the 1998 Talairach Atlas brain in its standard orientation are 172 mm for A-P, 136 mm for L-R, and 118 mm for S-I [32,35]. While the A-P and L-R dimensions are clearly defined, the S-I dimension is from the top of the cortex to the most inferior margin of the temporal lobe. This is because the Talairach atlases were intended for normalization of the cerebrum, and little detail is provided for the cerebellum. These dimension measurements are sometimes called the bounding box dimensions for obvious reasons.

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