Hemodynamically informed parcellation of cerebral FMRI data

Standard detection of evoked brain activity in functional MRI (fMRI) relies on a fixed and known shape of the impulse response of the neurovascular coupling, namely the hemodynamic response function (HRF). To cope with this issue, the joint detection-estimation (JDE) framework has been proposed. This formalism enables to estimate a HRF per region but for doing so, it assumes a prior brain partition (or parcellation) regarding hemodynamic territories. This partition has to be accurate enough to recover accurate HRF shapes but has also to overcome the detection-estimation issue: the lack of hemodynamics information in the non-active positions. An hemodynamically-based parcellation method is proposed, consisting first of a feature extraction step, followed by a Gaussian Mixture-based parcellation, which considers the injection of the activation levels in the parcellation process, in order to overcome the detection-estimation issue and find the underlying hemodynamics

Physiologically Informed Bayesian Analysis of ASL fMRI Data

Arterial Spin Labelling (ASL) functional Magnetic Resonance Imaging (fMRI) data provides a quantitative measure of blood perfusion, that can be correlated to neuronal activation. In contrast to BOLD measure, it is a direct measure of cerebral blood flow. However, ASL data has a lower SNR and resolution so that the recovery of the perfusion response of interest suffers from the contamination by a stronger hemodynamic component in the ASL signal. In this work we consider a model of both hemodynamic and perfusion components within the ASL signal. A physiological link between these two components is analyzed and used for a more accurate estimation of the perfusion response function in particular in the usual ASL low SNR conditions

Les tècniques per a l’aprofitament de l’aigua a les possessions mallorquines (segles XVII-XIX)

En aquest article s’analitzen les infraestructures (fonts, safareigs, pous, sistemes de canalització, etc.) i les principals regulacions desenvolupades al llarg dels segles en el si de les grans explotacions agràries mallorquines (les possessions) amb l’objectiu d’aprofitar l’aigua amb distintes finalitats: agrícoles i ramaderes, transformadores, domèstiques i lúdiques. Una triple finalitat que està directament relacionada amb les distintes funcions d’una possessió: unitats de producció agrària i ramadera, lloc de residència de la família de l’arrendatari o del majoral i d’altres treballadors i centre d’esbarjo dels propietaris. Per a una millor comprensió del tema s’han escollit, tot i que també es treuen a col·lació altres exemples, dues possessions concretes: Son Fortesa d’Alaró (situada al Raiguer de Mallorca) i Raixa (ubicada als peus de la Serra de Tramuntana i de fàcil accés des de la capital). El motiu d’aquesta elecció es deu, en ambdós casos, al fet que es disposa de fonts de caire documental que permeten complementar l’anàlisi estrictament arquitectònica, alhora que comprendre el context en el qual sorgiren les infraestructures que s’analitzen. Així mateix, els dos casos seleccionats permeten posar l’accent en dos aspectes relacionats amb l’ús de l’aigua a les possessions mallorquines que han tingut gran transcendència fins a l’actualitat. D’una banda, l’aprofitament dels sistemes hidràulics d’origen musulmà, i, de l’altra, la combinació dels usos productius i estètics de l’aigua

Physiological models comparison for the analysis of ASL FMRI data

International audiencePhysiological models have been proposed to describe the processes that underlie the link between neural and hemodynamic activity in the brain. Among these, the Balloon model describes the changes in blood flow, blood volume and oxygen concentration when an hemodynamic response is ensuing neural activation. Next, an hemo-dynamic model links these variables to the blood-oxygen-level-dependent (BOLD) effect. Taken together, these equations allow the precise modeling of the coupling between the cerebral blood flow and hemodynamic response. However, several competing versions of the hemodynamic model and different physiological parameters values have been described in the literature. In this work, we analyse Arterial Spin Labelling (ASL) functional Magnetic Resonance Imaging (fMRI) data, which contains both perfusion and hemodynamic effects, to compare the impact of different settings in the coupling between blood flow and hemodynamic response

Variational Physiologically Informed Solution to Hemodynamic and Perfusion Response Estimation from ASL fMRI Data

International audienceFunctional Arterial Spin Labeling (fASL) MRI can provide a quantitative measurement of cerebral blood flow. A joint detection-estimation (JDE) framework has been considered to extract task-related perfusion and hemodynamic responses not restricted to canonical response function shapes. In this work, we provide a variational expectation-maximization (VEM) algorithm for hemodynamic and perfusion responses estimation. This approach provides a lower computational load compared to previous attempts, and facilitates the incorporation of prior knowledge and constraints in the estimation. Validation on simulated and real data sets has been performed