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
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
1.- Symbol Digit Modalities Test (SDMT). In this task, the subjets
performed in blocks at two different sppeeds (2 and 2.5 seconds between
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
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.
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.
INCLIVA Health Research Centre
Avda. Menendez Pelayo,4