Should be
"is supposed to eliminate false *positives*"
of course. Sorry.
Cornelius
On Mon, Mar 1, 2010 at 2:46 PM, Cornelius Werner
<[log in to unmask]> wrote:
> Possibly they are referring to Oakes et al (2007): Integrating VBM
> into the General Linear Model with voxelwise anatomical covariates,
> Neuroimage 34, 500-508, where the authors show that different grey
> matter densities account for a considerable amount of inter-group
> variability. Correcting for that is supposed to eliminate false
> negatives as well as increase your sensitivity for true activations
> due to a smaller error term (probably similar to what you already
> know). You can do this pretty easily using FSL. See the manual on
> http://www.fmrib.ox.ac.uk/fsl/feat5/detail.html
> and search for "Number of additional, voxel-dependent EVs".
> As far as I know, it has not become a very widespread standard, but
> the rationale seems reasonable. It also depends on your view on VBM,
> of course.
>
> Hth,
> Cornelius
>
> On Fri, Feb 26, 2010 at 4:30 PM, GS <[log in to unmask]> wrote:
>> Hello,
>>
>> I am curious if anyone here has done a voxel-wise PVC on BOLD fMRI data
>> before. I am familiar with PVC in SPECT, PET, and ASL perfusion
>> measurements, but have not heard it done with BOLD data. A reviewer recently
>> criticised a proposal of ours for not having a protocol for voxel-wise PVC
>> of BOLD data, and I am stumped trying to find any reference to methods for
>> doing this.
>>
>> We are not using standard space for analysis but rather the 'functional ROI'
>> method of localizing a region in individuals in native space. The issue is
>> the anatomical structure where the fROI is localized may be a different size
>> between our two populations.
>>
>> Any thoughts or points in the right direction would be greatly appreciated!
>>
>>
>> My final niggling thought is: is PVC of BOLD even necessary when the
>> activation maps are difference images between two different activation
>> states (e.g., extrastriate cortex looking at house v objects)? I think this
>> is a different creature from resting glucose metabolism images from a PET
>> scanner, where less tissue looks like hypometabolism, as in BOLD data we
>> wouldn't expect CSF voxels to show significant changes in activity with two
>> activation states anyway.
>>
>
>
>
> --
> Dr. med. Cornelius J. Werner
>
> Department of Neurology
> RWTH Aachen University
> Pauwelsstr. 30
> 52074 Aachen
> Germany
>
> Institute of Neuroscience and Medicine
> MR Physics - INM4
> Research Centre Juelich
> 52425 Juelich
> Germany
>
> ::: Please encrypt confidential data :::
>
--
Dr. med. Cornelius J. Werner
Department of Neurology
RWTH Aachen University
Pauwelsstr. 30
52074 Aachen
Germany
Institute of Neuroscience and Medicine
MR Physics - INM4
Research Centre Juelich
52425 Juelich
Germany
::: Please encrypt confidential data :::
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