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Etude par neuroimagerie IRM de la représentation centrale des mouvements de la main chez les sujets sains et chez les patients après chirurgie de la main

Abstract : After a sensory deprivation or a peripheral sensory rehabilitation, primary sensorimotor areas undergo anatomical and functional reorganization. The hand tendon transfer is a rehabilitative surgery that restores the hand extension function by changing the insertion of chosen flexor muscles. During rehabilitation, the central control of the flexion and extension movements is based on elementary processes of brain plasticity, still poorly understood, but known to be slow, taking up to one year and occurring simultaneously with manual recovery. We hypothesize that high-resolution functional MRI (fMRI) may reveal brain plasticity linked to motor-behavior recovery.This PhD thesis aims to develop fMRI methods for individual patient follow-up after hand tendon transfer surgery. We first defined reference maps, based on a group of healthy subjects, for fine cortical representation of voluntary hand movements. These maps were then used to evaluate brain plasticity linked to the hand tendon surgery. To better understand the representation of the hand’s movements of flexion and extension in the primary motor cortex, we carried out a high-resolution, functional MRI study (using a static magnetic field of 3 Tesla), on a group of 13 healthy subjects. It was necessary to register all individual brains into a common reference system in order to perform a group statistical analysis. However, the inter-individual anatomical variability of the primary motor areas prevented us from performing the registration by conventional methods. We evaluated various methods of nonlinear registration to ensure a robust inter-individual alignment of central sulci. We compared: 1. a local method (Demon), which allows for important local deformations, 2. a standard non-linear method (SPM), which allows for a global image alignment and 3. a global diffeomorphic registration method (DARTEL) with a large number of degrees of freedom. In addition, we applied a fourth, more recent method, in partnership with LSIS, (CNRS Marseille) which iteratively reinforces the alignment of identified sulci before applying DARTEL (DISCO+DARTEL). This adds a local sulci-based constraint to the global deformation. We found that the fourth method produced the best alignment according to both anatomical criteria (Hausdorff distance, mask tissues overlaps and characteristics of the deformations field) and functional criteria (localization accuracy and statistical robustness of activations detected). We were then able to establish high spatial resolution reference maps of the elementary movements of the hand. These maps showed multiple foci of activity and significant overlaps in the region known as the "hand-knob."This first step of testing completed, we entered into a second round of testing where we evaluated the reproducibility of our initial results by performing a second series of tests on the same control group (“test-retest”).Two patients were followed up: before surgery (M0) and 1 month (M1), 3 (M3), 6 (M6) and 12 months (M12) after surgery. Functional recruitment was observed during recovery in SMA, M1, ispilateral and contralateral S1 and lobules V-VI of the cerebellum. Compared with healthy subjects, these two patients presented compensatory cortex reorganization during progressive recovery of hand function.
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Fabrizio Pizzagalli. Etude par neuroimagerie IRM de la représentation centrale des mouvements de la main chez les sujets sains et chez les patients après chirurgie de la main. Médecine humaine et pathologie. Université de Grenoble, 2012. Français. ⟨NNT : 2012GRENS014⟩. ⟨tel-00906753⟩

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