Brain atlases have played an important role in many aspects of brain research by providing various types of anatomical information, such as brain structure names, locations, and boundaries. For neuroimaging, stereotaxic atlases have been especially useful, where a coordinate system (either through physical units, such as millimeters, or by relative units, such as one-eighth of the brain length) is employed to reference specific locations [1
One of the most widely used stereotaxic atlases was provided by Talairach and Tournoux [1
], as shown in . This histology-based atlas contains a detailed assignment of cortical regions, which can be referenced by physical or relative coordinates. If one has a brain image (histology, MRI, PET, etc.), the image can be transformed to the shape of the atlas and the coordinate system, and anatomical labels of the atlas can be transferred to the image. For example, if the image contains a lesion, the location, as well as the affected anatomical structures, can be reported in a systematic way, which allows us to directly compare results from different patients.
Comparison of MR-based images and atlases
Recently, MRI-based atlases have become widely available [6
]. There are many advantages of the MRI atlases. They are three-dimensional, with high anatomical fidelity (). The data are inherently in an electronic format, which makes it much easier to perform various image analysis procedures quantitatively. MRI images also enable more straightforward population-based analysis, because MRI data can be obtained within 1 h. shows an example of a population-averaged atlas (ICBM-152), which represents the averaged brain structures of a normal population [6
Although these atlases developed a systematic method for reporting and inter-participant comparison, they have been mostly used for studies of the gray matter structures and have not always been useful for white matter studies. This is because simple histology preparation and conventional MRI do not carry much contrast by which to delineate the detailed anatomy of the white matter. For example, the Talairach and Tournoux atlas shown in does not demonstrate labeling of white matter structures as extensively as that of the cortex, and many white matter regions are blank, without annotations. In the MRI-based atlases, the white matter resembles a large homogeneous field and lacks anatomical clues.
In this review, white matter atlases based on diffusion tensor imaging (DTI) are evaluated [13
]. The new anatomical information provided by DTI is apparent in . The homogeneous-looking white matter in can be readily compartmentalized by adopting the contrasts from DTI. For example, the four major white matter structures at this slice level, the corpus callosum, the cingulum, the corona radiata, and the superior longitudinal fasciculus (SLF), can be easily defined.