Détermination de l'activation neuronale dans la moelle épinière par imagerie intrinsèque
Abstract (summary)
The intrinsic imaging techniques have already managed to establish accurate maps of the neuronal activity in the cortex of small animals by recording the hemodynamic response. The high spatial and temporal resolutions of these methods make them the ideal tools for studying the coupling between the vascular and the neural responses. However, these studies have not been applied to the whole central nervous system, as the spinal cord has only been studied by a limited number of publications. The physiological problems, such as the different organization of the cortex and of the spinal cord, or the increased movements caused by respiration, make the imaging of this area more complex.
This thesis aims at applying two of the intrinsic imaging methods in order to record the hemodynamic response in the rat lumbar spinal cord. Intrinsic optical imaging consists in illuminating the region of interest by visible light, which is differentially absorbed by the oxygenated and the deoxygenated blood, and in recording the evolution of the absorbance, which is linked to the concentration of the chromophores. In addition, the statistical analysis of the speckle maps, originated from the illumination of the area with a coherent light produced by a laser, leads to the determination of the blood flow distribution over the image. The temporal evolution and the localization of the variations in concentration or in velocity, highlighted by signal processing techniques, consequently characterize the hemodynamic response.
In vivo experiences were conducted to check the viability of our acquisition system and a group study was carried out to study the reproducible characteristics of the response. Finally, the comparison with a group of rats, whose spinal cord was previously sectioned, pointed out some subsequent vascular and neuronal consequences.
Alternate abstract:
Les techniques d'imagerie intrinseque ont deja permis d'etablir des cartes precises de l'activite neuronale du cortex de petits animaux grace a renregistrement de la reponse hemodynamique. Leurs hautes resolutions spatiale et temporelle en font les outils ideaux pour etudier le couplage entre la reponse vasculaire et la reponse neuronale. Cependant, les etudes existantes sur ce sujet n'ont pas ete appliquees a l'ensemble du systeme nerveux central, la moelle epiniere n'ayant fait l'objet que d'un nombre tres restreint de publications. Les difficultes physiologiques apparentes, comme les differences d'organisation entre le cortex et la moelle, ou les mouvements plus consequents causes par la respiration, rendent l'imagerie intrinseque de cette zone plus delicate. Ce memoire propose d'appliquer deux des methodes d'imagerie intrinseque pour enregistrer la reponse hemodynamique dans la moelle epiniere du rat. L'imagerie optique intrinseque consiste a eclairer la zone d'interet par une lumiere absorbee differenciellement par le sang oxygene et par le sang deoxygene, puis a enregistrer les variations de la reflectance qui est reliee a la concentration des chromophores. Separement, 1'analyse statistique des cartes de speckle issues de l'eclairement de la region par une lumiere coherente permet de determiner la distribution des vitesses au sein de l'image. Les evolutions temporelles et la localisation des variations des concentrations et de la Vitesse, mises en relief par des methodes de traitement du signal, caracterisent alors la reponse hemodynamique.
La conduite d'experiences in vivo sur des rats nous a permis de valider la stabilite de notre systeme d'acquisition, puis de mener une etude de groupe afin d'etudier les caracteristiques reproductibles de la reponse. Enfin, la comparaison avec un groupe de rats ayant subi une section complete de la moelle a mis en evidence les changements vasculaires et neuronaux subsequents.
Indexing (details)
Biomedical engineering;
Optics
0541: Biomedical engineering
0752: Optics