Voxel-based morphometry

Voxel based morphometry (VBM) is a neuroimaging analysis technique that allows investigation of focal differences in brain anatomy, using the statistical approach of so-called "statistical parametric mapping". In traditional morphometry, volume of the whole brain or its subparts 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 rather 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, the image 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 [cite journal
title = Navigation-related structural change in the hippocampi of taxi drivers
author = Eleanor A. Maguire, David G. Gadian, Ingrid S. Johnsrude, Catriona D. Good, John Ashburner, Richard S. J. Frackowiak, and Christopher D. Frith
journal = Proceedings of the National Academy of Sciences of the United States of America
volume = 97
issue = 8
pages = 4398–4403
year = 2000
url = http://www.pnas.org/cgi/content/full/97/8/4398
doi = 10.1073/pnas.070039597Commentary on the original article in the same issue:
* cite journal
author = Alejandro Terrazas and Bruce L. McNaughton
title = Brain growth and the cognitive map
volume = 97
issue = 9
pages = 4414–4416
journal = Proceedings of the National Academy of Sciences of the United States of America
url = http://www.pnas.org/cgi/content/extract/97/9/4414
doi = 10.1073/pnas.97.9.4414
year = 2000News story with an interview of the researcher:
* cite news
author = BBC
publisher = BBC News
title = Taxi drivers' brains 'grow' on the job
url = http://news.bbc.co.uk/2/hi/science/nature/677048.stm
date = 2000-03-14
accessdate = 2007-03-06] . 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" [Cite journal
author = John Ashburner and Karl J. Friston
title = Voxel-Based Morphometry—The Methods
journal = NeuroImage
year = 2000
volume = 11
issue = 6
month = June
pages = 805–821
doi = 10.1006/nimg.2000.0582
url = http://www.fil.ion.ucl.ac.uk/spm/doc/papers/john_vbm_methods.pdf] — one of the most cited articles in the journal "NeuroImage". [The number of citations is apparent from a search with Google Scholar (2007-12-07) [http://scholar.google.com/scholar?as_publication=Neuroimage] .] 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. [Cite journal
author = Yasuhiro Kawasaki, Michio Suzuki, Ferath Kherif, Tsutomu Takahashi, Shi-Yu Zhou, Kazue Nakamura, Mie Matsui, Tomiki Sumiyoshi, Hikaru Seto and Masayoshi Kurachi
title = Multivariate voxel-based morphometry successfully differentiates schizophrenia patients from healthy controls
journal = NeuroImage
volume = 34
issue = 1
month = January
year = 2007
pages = 235–242
doi = 10.1016/j.neuroimage.2006.08.018 ]

VBM for brain asymmetry

Usually VBM is performed for examining differences across subjects, but it may also be used to examine neuroanatomical differencies between hemispheres detecting brain asymmetry. [Cite journal
author = K.E. Watkins, T. Paus, J.P. Lerch, A. Zijdenbos, D.L. Collins, P. Neelin, J. Taylor, Keith J. Worsley and Alan C. Evans
title = Structural Asymmetries in the Human Brain: a Voxel-based Statistical Analysis of 142 MRI Scans
journal = Cerebral Cortex
volume = 11
issue = 9
pages = 868–877
month = September
year = 2001
url = http://cercor.oxfordjournals.org/cgi/content/abstract/11/9/868
doi = 10.1093/cercor/11.9.868] [Cite journal
author = E. Luders, C. Gaser, L. Jancke & G. Schlaug
title = A voxel-based approach to gray matter asymmetries
journal = NeuroImage
volume = 22
issue = 2
year = 2004
month = June
pages = 656–664
doi = 10.1016/j.neuroimage.2004.01.032] A technical procedure for such an investigation may use the following steps: [Cite journal
author = Catriona D. Good, Ingrid Johnsrude, John Ashburner, Richard N. A. Henson, Karl J. Friston and Richard S. J. Frackowiak
title = Cerebral Asymmetry and the Effects of Sex and Handedness on Brain Structure: A Voxel-Based Morphometric Analysis of 465 Normal Adult Human BrainsNeuroImage
volume = 14
issue = 3
month = September
year = 2001
pages = 685–700
doi = 10.1006/nimg.2001.0857
journal = NeuroImage]
# Construction of a study-specific brain image template with a balanced set of left and right handed and males and females.
# Construction of white and grey matter templates from segmentation.
# Construction of symmetric grey and white matter templates by averaging right and left cerebral hemispheres.
# Segmentation and extraction of brain image, e.g., removal of scalp tissue in the image.
# Spatial normalization to the symmetric templates
# Correction for volume change (applying a Jacobian determinant)
# Spatial smoothing.
# Actual statistical analysis by the general linear model, i.e., statistical parametric mapping.

See also

* Jacobian
* Change of variable

References

General technical references

* [http://www.tina-vision.net/docs/memos/2003-011.pdf Tutorial: A Critical Analysis of Voxel Based Morphometry (VBM)]
* [http://pni.med.jhu.edu/methods/bookstein.pdf Voxel-Based Morphometry Should Not Be Used with Imperfectly Registered Images]
* [http://www.fil.ion.ucl.ac.uk/spm/doc/papers/john_should.pdf Why Voxel-Based Morphometry Should Be Used]
* [http://www.bic.mni.mcgill.ca/software/VBM/ Voxel Based Morphometry at the BIC]
* [http://pni.med.jhu.edu/methods/vbm.htm Voxel-Based Morphometry at Johns Hopkins University]
* [http://en.wikibooks.org/wiki/SPM/VBM Voxel-Based Morphometry at Wikibooks]