Coordinate Systems

The coordinate system used to equate brain topology with an index must include carefully selected features common to all brains. Further, these features must be readily identifiable and sufficiently distributed anatomically to avoid bias. Once defined, rigorous systems for matching or spatially normalizing a brain to this coordinate system must be developed. This allows individual data to be transformed to match the space occupied by the atlas. In the Talairach stereotaxic system [103,104], piecewise affine transformations are applied to 12 rectangular regions of brain, defined by vectors from the

FIGURE 2 Warping algorithms integrate multimodality brain data. Histologic tissue sections, stained here to reveal neurofibrillary tangle density in a subject with Alzheimer's disease, can be compared with functional imaging data acquired from the same subject in vivo [64]. Images of stained tissue sections (top left) are elastically warped back (bottom left) into their original configuration in the cryosection blockface (top right). An additional warp reconfigures the postmortem cryosection and histologic data back into their in vivo configuration, as imaged by premortem MRI. All maps can then be correlated with PET data acquired in vivo from the same patient (bottom right), which is aligned to the MR template using an additional cross-modality registration. (Data adapted from [64]). See also Plate 105.

FIGURE 2 Warping algorithms integrate multimodality brain data. Histologic tissue sections, stained here to reveal neurofibrillary tangle density in a subject with Alzheimer's disease, can be compared with functional imaging data acquired from the same subject in vivo [64]. Images of stained tissue sections (top left) are elastically warped back (bottom left) into their original configuration in the cryosection blockface (top right). An additional warp reconfigures the postmortem cryosection and histologic data back into their in vivo configuration, as imaged by premortem MRI. All maps can then be correlated with PET data acquired in vivo from the same patient (bottom right), which is aligned to the MR template using an additional cross-modality registration. (Data adapted from [64]). See also Plate 105.

FIGURE 3 Population-based maps of ventricular anatomy in normal aging and Alzheimer's disease, (a) 3D parametric surface meshes [106] were used to model a connected system of 14 tissue elements at the ventricular surface (partitioned along cytoarchitectural boundaries), based on high-resolution 3D MRI scans of 10 Alzheimer's patients (age: 71,9 + 10,9 yrs) and 10 controls matched for age (72,9 + 5,6 yrs), gender, and handedness [112] 3D meshes representing each surface element were averaged by hemisphere in each group, (b,c) The color map encodes a 3D RMS measure of group anatomic variability shown pointwise on an average surface representation for each group, in the Talairach stereotaxic space, Oblique side views reveal enlarged occipital horns in the Alzheimer's patients, and high stereotaxic variability in both groups, (d,e) A top view of these averaged surface meshes reveals localized patterns of asymmetry, variability, and displacement within and between groups, Asymmetry patterns at the ventricles and Sylvian fissure (see Fig, 4) emerge only after averaging of anatomical maps in large groups of subjects, Patterns of 3D variation can be encoded probabilistically to detect structural anomalies in individual patients or groups [110, 112], See also Plate 106,

[S"ormaJ Klderly

Alzheimer's Disease

anterior and posterior commissures to the extrema of the cortex, These transformations reposition the anterior commissure of the subject's scan at the origin of the 3D coordinate space, vertically align the interhemispheric plane, and horizontally orient the line connecting the two commissures, Each point in the incoming brain image, after it is registered into the atlas space, is labeled by an (x, y, z) address indexed to the atlas brain, Although originally developed to help interpret brainstem and ventricular studies acquired using pneumoencephalography [103], the Talairach stereotaxic system rapidly became an international standard for reporting functional activation sites in PET studies, allowing researchers to compare and contrast results from different laboratories [35,36,38,39],

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