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?.
The "cell scans" would be the contrast images generated in the first
level for each group, isn't it?
At last in "multiple covariates" option I must put the diffrent
covariates in my problem.
On the other hand, I understand that this factorial design specification
creates automatically the different contrast.
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]?
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)
>>
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