Biomedical Engineering Reference
In-Depth Information
results to be more applicable to the population in general. In addition, it is com-
mon to use two different groups to contrast behavior, such as schizophrenics
and healthy volunteers. In either case, combining results for a group analysis
requires that the results from each individual be registered to a common space.
The standard image used for this registration can either be a selected mem-
ber of the group, some group average, or a general template (like a Talairach-
space template). Once this standard image is chosen, each of the individuals'
structural images are registered to the standard, and then the activation
results transformed into this space. All activation maps are then in the same
coordinate system, and the locations, sizes, and statistical values of the activa-
tions can be compared across or between groups.
8.5
Conclusion
fMRI is a powerful, noninvasive imaging technique for investigating brain
function. Registration plays a very important part in the analysis of fMRI
experiments. First, it is used for correction of subject motion during the scan-
ning sequence. This application is critical for avoiding detection of false,
motion-related activations, which can be considerable even when the motion
is subvoxel. Second, registration is used after statistical analysis to register
the activation map to individual structural scans or standard spaces like
Talairach space.
Since the raw functional images are tuned to be fast and give good BOLD
contrast, they tend to have relatively low spatial resolution (compared to ana-
tomical images) and poor anatomical contrast. Consequently, registration
involving these images is an important and challenging task that has consid-
erable scope for research into new methods as well as for improving and
extending the existing methods.
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