Dear Teri

Subtle grey matter changes can be detected in the hippocampi of normal
subjects with VBM (which corroborate independent ROI measurements) see
Maguire et al, PNAS, 2000. See also Salmond et al, HBM 2000 regarding the
detection of bilateral hippocampal changes with VBM.
Mesial temporal sclerosis can be picked up on VBM using SPM 99 (unpublished
data) and hippocampal/amygdala changes can also be seen in elderly diseased
patients (unpublished data)
VBM pre-processing has advanced since the Woermann et al paper,
particularly the spatial normalisation and segmentation steps, and further
optimisations include modulation and automated brain extraction (Ashburner
& Friston, VBM-the methods, NeuroImage, 2000 and Good CD et al, NeuroImage
in press).
Although VBM is a fully automated procdure, attention to detail is
important. For example, I would suggest using customised (disease/age/sex
matched) templates for spatial normalisation  (which can also be used as
the priors for segmentation).These methods are not perfect, and inspection
of the segmented images for some elderly normal and diseased patients
reveals areas of relatively poor tissue classification). Another point to
be considered is the variance between subjects and between brain regions in
the same subjects. In areas of increased variance VBM may be less sensitive
to change, although this is the point of SPM which employs a regionally
specific estimate of variance. The spatial normalisation in VBM does not
aim to match each and every gyrus or deep brain structure, rather it aims
to match overall brain shape. If the normalisation was perfect, there would
be no differences between the normalised scans and all the differences
would be in the deformation maps. In regions of high variance a voxel of
interest may not represent exactly the same small structure for each
subject in the group. High dimensional warps and TBM or corical surface
mapping (Thompson et al, cerebral Cortex, 2001)are probably the best way to
solve some of these problems, athough they may be time intensive.

I hope this helps
Tina Good



There have been At 20:54 25/02/01 -0500, you wrote:
>Can someone please explain to me why gray matter changes in  the amygdala
>(and hippocampus) cannot be identified using VBM and SPM99?  I have read the
>Woermann et al paper  that describes visibly evident hippocampal damage in
>epileptic patients that was not detected using VBM.  The authors reason that
>small abnormalities are excluded due to normalization, segmentation, and
>smoothing.  Although that makes sense to me - it doesn't make sense that the
>hippocampal damage that could be seen with the naked eye could not be

>detected with this method.  They also state that automatic segmentation and

>voxel-by-voxel comparison of structural MRI is not suitable for

>investigating the amygdala and hippocampus.  Is it just these two regions?
>Why just these two regions?    I would greatly appreciate any references or
>help in resolving this issue.   Thanks all, teri-)
>
>
Dr Catriona Good
Clinical lecturer / Neuroradiologist
Wellcome Dept of Cognitive Neurology, ION
12 Queen Square
London WC1N 3BG

email: [log in to unmask]
phone  0207 8337485