Dear Hector,
On 04/04/17 14:59, [log in to unmask] wrote:
> Dear Guillaume,
> On one hand, if I understand well your propose, inthe full factorial
> design, the factor would be GROUP and in "Cell" option in SPM12 you
> would have 3 cells (CONTROL, NO MHE and MHE, in other words healthy
> subjects, patients with MHE and patients without MHE) with one level, is
> it right?.
Yes, one factor with Name:Group and Levels:3. Then you specify 3 cells
with levels being 1, 2, and 3.
An identical alternative would have been to use the "One-way ANOVA" design.
> The "cell scans" would be the contrast images generated in the first
> level for each group, isn't it?
Yes, from your 2-back or SDMT task.
> At last in "multiple covariates" option I must put the diffrent
> covariates in my problem.
I would use the "covariates" options where you can specify covariates
one by one, with interactions and centering options.
> On the other hand, I understand that this factorial design specification
> creates automatically the different contrast.
This is optional. You can disable it and specify your contrasts of
interest by hand.
> Do you mind explain me, if it is possible with an example what is the
> exactly meaning of a F-contrast [0 0 0 1 -1 0; 0 0 0 0 1 -1 0]?
If you specify a single covariate, eg age, with options "Interactions"
and "Centering" set to "Factor 1, the design matrix will contain six
regressors and you can test for the main effect of group with contrast
[1 -1 0 0 0 0; 0 1 -1 0 0 0 0], and the group x age interaction with
contrast [0 0 0 1 -1 0; 0 0 0 0 1 -1 0].
Best regards,
Guillaume.
> Thank you very much in advance!
>
> Best regards,
> Hector
>
>
>
>
>
> El 2017-04-03 17:42, Guillaume Flandin escribió:
>> Dear Hector,
>>
>> You could use a full factorial design (one factor with 3 levels) and
>> add
>> your covariates there (with options "Interactions" and "Centering" set
>> to "Factor 1"). Then you can test for a group x covariate interaction
>> with an F-contrast [0 0 0 1 -1 0; 0 0 0 0 1 -1 0].
>>
>> Best regards,
>> Guillaume.
>>
>>
>> On 03/04/17 11:54, Hector Espinos wrote:
>>> Dear SPM user,
>>> I am relatively novice in the neuroimaging analysis and I would like
>>> to
>>> have your opinion as experts.
>>> I'm doing a study with fMRI imaging technique for detecting the
>>> Minimal
>>> Hepatic Encephalopathy (MHE) in early stages.
>>>
>>> I have done all the first level analysis and I am doing the second
>>> level
>>> analysis.
>>> The problem is the following:
>>>
>>> I have three groups previously analyzed:
>>> 17 healthy subjects as a control group
>>> 22 cirrhotic patients diagnosed with MHE using the PHES (Psychometric
>>> Hepatic Encephalopathy Score).
>>> 14 cirrhotic patients showing no symptoms of MHE on phychometric
>>> tests.
>>>
>>> These three groups done two taks for testing their cognitive
>>> capabilities:
>>>
>>> 1.- Symbol Digit Modalities Test (SDMT). In this task, the subjets
>>> performed in blocks at two different sppeeds (2 and 2.5 seconds
>>> between
>>> symbols).
>>> 2.- N-back, where the subjets did a letter identification task
>>> performed
>>> in blocks of two different modalities, O-back and 2-back, with resting
>>> periods between blocks.
>>>
>>> Also, it was registred the activity brain under no specific task
>>> (resting state).
>>>
>>> In the analysis of the first level, the study shows differences in
>>> brain
>>> activation between control subjets and cirrhotic patients.
>>> Additionally,
>>> it could see common areas affected between patients with MHE and
>>> no-MHE.
>>>
>>> Differences at O-back task involve mainly the lingual cyrus. The
>>> 2-back
>>> task show differences in activation of the caudate nucleus and putamen
>>> and in some regions of the frontal lobe.
>>> SDMT shows differences in activation on the middle temporal gyrus.
>>>
>>>
>>> On the other hand, we have a series of measured variables (covariates)
>>> for the three groups.
>>>
>>> Age
>>> Gender
>>> Stroop test scores
>>> Critical Flicker Frequency (CFF)
>>> Motor coordination (bimanual and visomotor)
>>> Attention test d2 scores
>>> Battery Wais scores
>>> Biochemical parameters (ammonium, cyclic GMP, IL-6, IL-18)
>>> Markers of oxidative / nitrosative damage (3-Nitrotyrosine,
>>> hydroxyideoxyguanine, carbonylated proteins, malondialdehyde).
>>>
>>>
>>> My problem is the following:
>>> I would like to do correlations between the aforementioned variables
>>> (covariates) and the different groups in order to be able to observe
>>> or
>>> identify significant differences in the responses in order to be able
>>> to
>>> identify which variables or parameters have greater influence and thus
>>> be able to identify or diagnose the MHE earlier (this is the major
>>> goal
>>> in this study).
>>>
>>> At this point, I do not know exactly what would be the best strategy
>>> to
>>> follow. Perform multiple regressions by trying to correlate the
>>> covariates for each of the groups or to perform a factorial design
>>> where
>>> groups, tasks and covariates are included?.
>>>
>>> I would appreciate any possible help to make the most effective design
>>> that it could provide the maximum information.
>>>
>>> Thank you very much in advance.
>>>
>>> Hector Espinos-Morato
>>> INCLIVA Health Research Centre
>>> Avda. Menendez Pelayo,4
>>> 46190 (Valencia-Spain)
>>>
--
Guillaume Flandin, PhD
Wellcome Trust Centre for Neuroimaging
University College London
12 Queen Square
London WC1N 3BG
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