Voxel-based morphometry

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Voxel based morphometry (VBM) is a neuroimaging analysis technique that allows investigation of focal differences in brain volume. It can be regarded as a form of so-called statistical parametric mapping. Traditionally, brain volume is measured by drawing regions of interest (ROIs) on images from brain scanning and calculating the volume enclosed. However, this is time consuming and can only provide measures of large areas. Smaller differences in volume may be overlooked. VBM registers every brain to a template, which gets rid of most of the large differences in brain anatomy among people. Then the brain images are smoothed so that each voxel represents the average of itself and its neighbors. Finally, volume is compared across brains at every voxel.

One of the first VBM studies and one that came to attention in main stream media was a study on the hippocampus brain structure of London taxi drivers[1]. The VBM analysis showed the back part of the hippocampus was on average larger in the taxi drivers compared to control subjects while the frontal part was smaller. London taxi drivers need good spatial navigational skills and scientists have usually associated hippocampus with this particular skill.

A key description of the methodology of voxel-based morphometry is Voxel-Based Morphometry—The Methods[2] — one of the most cited articles in the journal NeuroImage.[3] The usual approach for statistical analysis is mass-univariate (analysis of each voxel separately), but multivariate analysis may also be used, e.g., for classifying patients from healthy.[4]

Contents

[edit] VBM for brain asymmetry

Usually VBM is performed for examining differencies across subjects, but it may also be used to examine neuroanatomical differencies between hemispheres detecting brain asymmetry.[5][6] A technical procedure for such an investigation may use the following steps:[7]

  1. Construction of a study-specific brain image template with a balanced set of left and right handed and males and females.
  2. Construction of white and grey matter templates from segmentation.
  3. Construction of symmetric grey and white matter templates by averaging right and left cerebral hemispheres.
  4. Segmentation and extraction of brain image, e.g., removal of scalp tissue in the image.
  5. Spatial normalization to the symmetric templates
  6. Correction for volume change (applying a Jacobian determinant)
  7. Spatial smoothing.
  8. Actual statistical analysis by the general linear model, i.e., statistical parametric mapping.

[edit] See also

[edit] References

  1. ^ Eleanor A. Maguire, David G. Gadian, Ingrid S. Johnsrude, Catriona D. Good, John Ashburner, Richard S. J. Frackowiak, and Christopher D. Frith (2000). "Navigation-related structural change in the hippocampi of taxi drivers". Proceedings of the National Academy of Sciences of the United States of America 97 (8): 4398–4403. doi:10.1073/pnas.070039597.  Commentary on the original article in the same issue: News story with an interview of the researcher:
  2. ^ John Ashburner and Karl J. Friston (June 2000). "Voxel-Based Morphometry—The Methods". NeuroImage 11 (6): 805–821. doi:10.1006/nimg.2000.0582. 
  3. ^ The number of citations is apparent from a search with Google Scholar (2007-12-07) [1].
  4. ^ Yasuhiro Kawasaki, Michio Suzuki, Ferath Kherif, Tsutomu Takahashi, Shi-Yu Zhou, Kazue Nakamura, Mie Matsui, Tomiki Sumiyoshi, Hikaru Seto and Masayoshi Kurachi (January 2007). "Multivariate voxel-based morphometry successfully differentiates schizophrenia patients from healthy controls". NeuroImage 34 (1): 235–242. doi:10.1016/j.neuroimage.2006.08.018. 
  5. ^ K.E. Watkins, T. Paus, J.P. Lerch, A. Zijdenbos, D.L. Collins, P. Neelin, J. Taylor, Keith J. Worsley and Alan C. Evans (September 2001). "Structural Asymmetries in the Human Brain: a Voxel-based Statistical Analysis of 142 MRI Scans". Cerebral Cortex 11 (9): 868–877. doi:10.1093/cercor/11.9.868. 
  6. ^ E. Luders, C. Gaser, L. Jancke & G. Schlaug (June 2004). "A voxel-based approach to gray matter asymmetries". NeuroImage 22 (2): 656–664. doi:10.1016/j.neuroimage.2004.01.032. 
  7. ^ Catriona D. Good, Ingrid Johnsrude, John Ashburner, Richard N. A. Henson, Karl J. Friston and Richard S. J. Frackowiak (September 2001). "Cerebral Asymmetry and the Effects of Sex and Handedness on Brain Structure: A Voxel-Based Morphometric Analysis of 465 Normal Adult Human Brains NeuroImage". NeuroImage 14 (3): 685–700. doi:10.1006/nimg.2001.0857. 

[edit] General technical references

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