LJK-Probability & Statistics Seminar

 

On Thursday February 23 2012 at 14h00 in Salle 1 - Tour IRMA

 

Seminary of Lotfi CHAARI (LJK / Mistis)

 

Approches bayésiennes variationnelles pour la détection-estimation des activations cérébrales en IRM fonctionnelle

 

Summary

 

In standard clinical within-subject analyses of event-related fMRI data, two steps are usually performed separately: detection of brain activity and estimation of the hemodynamic response.
Because these two steps are inherently linked, we propose in this work a joint detection-estimation procedure.
We adopt the so-called region-based Joint Detection-Estimation (JDE) framework that addresses this joint issue using a multivariate inference for detection and estimation.
JDE is built by making use of a regional bilinear generative model of the BOLD response and constraining the parameter estimation by physiological priors using temporal and spatial information in a Markovian modelling.
In contrast to previous works that use Markov Chain Monte Carlo (MCMC) techniques to approximate the resulting intractable posterior distribution, we recast the JDE into a missing data framework and derive a Variational Expectation-Maximization (VEM) algorithm for its inference. A variational approximation is used to approximate the Markovian model in the unsupervised spatially adaptive JDE inference and allow fine automatic tunig of spatial regularization parameters.
It follows a new algorithm that exhibits interesting properties compared to the previously used MCMC-based approach. Experiments on artificial and real data show that VEM-JDE is robust to model mis-specification and provides computational gain while maintaining good performance in terms of activation detection and hemodynamic shape recovery.