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National audience; L'imagerie par résonance magnétique (IRM) est la technique de choix pour l'exploration de la maturation cérébrale et de ses anomalies. La spectroscopie par résonance magnétique (SRM) est une technique de résonance magnétique nucléaire non invasive et spatialement localisée qui permet d'accéder au métabolisme intracérébral. Elle prend une place importante en neuroradiologie clinique au cours d'un examen par IRM standard. Cependant, les indications restent limitées à un petit groupe de pathologies, principalement les tumeurs, la souffrance cérébrale diffuse en particulier en période néonatale, et les maladies innées du métabolisme cérébral. Dans cet article sont revus les principaux noyaux étudiés en SRM, les méthodes d'acquisition et de post-traitement des données, les principaux métabolites détectables en SRM du proton et leurs variations au cours de la maturation cérébrale, et les principales applications cliniques dans la population pédiatrique.

International audience; Quantitative susceptibility mapping (QSM) is a recent MRI technique that measures tissue magnetic susceptibility mostly influenced by iron, myelin and calcium content in the brain that may provide additional biomarkers [1-3]. QSM involves advanced numerical methods designed to solve the complex inverse problem from the measured magnetic field inhomogeneity (derived from phase) to the spatial distribution of susceptibility. The reconstruction algorithms now become sufficiently robust to be implemented in routine brain exams. We present here the installation of an online reconstruction solution and initial in vivo results at high 3 T and ultra-high 7 T clinical fields. Clinical brain QSM acquisition and automated processing at 3T and 7T for routine use MRI systems and sequences: Siemens Verio 3T and Magnetom 7T were used (VB17 revision) with 32 channel head coils. A 3D multi-echo gradient echo sequence was applied. At 3T, the R2* mapping protocol designed for multicenter studies [4] was used (1 mm resolution, Tacq=10min); at 7T, isotropic 600 µm resolution were targeted (Tacq=12.5min). A modified reconstruction software (ICE functor) was used to generate proper combined phase images for QSM in which the first-echo individual coil images are used as a reference to solve the known issue in coil combination [5]. QSM reconstruction: The amplitude and phase DICOM images were sent to a separate DICOM server based on dicom toolkit (dcmtk open source software). Additional scripts were automatically triggered on reception to start the QSM post-processing. QSM reconstruction involved a field inhomogeneity calculation and unwrapping step from the multiple echoes, followed by a brain extraction (BET) step, an estimation of the internal field and the final MEDI reconstruction [2]. The BET algorithm was modified at 7T for an enhanced brain coverage. Images were then sent automatically back to the MRI when completed. Methods Conclusion References: 1. de Rochefort et al., MRM 2010;63:194. 2. Liu et al., MRM 2011;66:777 3. Eskreis-Winkler et al., NMR Biomed 2016. 4. D. Gay et al., ISMRM 2016, 5. Bernstein MA et al., MRM 1994; 32: 330-33. QSM can be readily applied to ongoing protocols involving 3D or 2D-multislice multi-echo gradient echo data providing additional quantitative information as compared to previously available qualitative SWI and quantitative R2* mapping. QSM seems more sensitive than R2*, with the possibility to easily separate diamagnetic and paramagnetic structures and with less sensitivity to magnetic field strength. 7T QSM should provide a significant gain in terms of achievable spatial resolution and sensitivity in routine clinical studies at our site. Results Fig.1 and 2 present typical results obtained at 3T in ongoing Parkinson and Multiple Sclerosis (MS) protocols, respectively, and Fig. 3 display 7T volunteer data. QSM images appeared on scanners within 10min with consistent image quality. Two-to-four cases per week in research protocols are currently performed. Figure 1-1-mm isotropic images obtained on a patient with Parkinson disease at 3T. The MEDIC image (square root of the squared magnitude over echoes) displays a limited T2* weighting. On the R2* map, CSF has low R2* as expected, WM/GM R2* and close to 20 s-1 , vessels, deep grey nuclei, calcifications then have higher R2* values. The QSM map, while cropping some brain boundaries, clearly separates paramagnetic structures (vessels, deep grey nuclei) from diamagnetic calcifications, and displays some WM/GM susceptibility differences. Figure 2-MEDIC, R2* map and QSM acquired at 3T on a 56 y.o. male MS patient on which MS lesions are easily identifiable by their paramagnetic values (the view is centered on one of them). While some reduction in R2* values can also be seen at the same location, the contrast is higher on the QSM maps. Figure 3-600-µm isotropic images obtained on a volunteer at 7T. The MEDIC image displays a limited T2* weighting. On the R2* map, CSF has low R2* as expected, WM/GM R2* and close to 40 s-1 , vessels, deep grey nuclei, calcifications have higher R2* values. The window level has been multiplied by 2 as compared to 3T, indicating the trend for linear increase of R2* with B0. The QSM map clearly separates paramagnetic structures (vessels, deep grey nuclei) from diamagnetic calcifications, and displays some WM/GM susceptibility differences with finer details as compared to 3T.

International audience; Resting-state connectivity has been widely studied in the healthy and pathological brain. Less well-characterized are the brain networks altered during pharmacological interventions and their possible interaction with vigilance. In the hopes of finding new biomarkers which can be used to identify cortical activity and cognitive processes linked to the effects of drugs to treat neurodegenerative diseases such as Alzheimer's disease, the analysis of networks altered by medication would be particularly interesting. Eleven healthy subjects were recruited in the context of the European Innovative Medicines Initiative 'PharmaCog'. Each underwent five sessions of simultaneous EEG-fMRI in order to investigate the effects of donepezil and memantine before and after sleep deprivation (SD). The SD approach has been previously proposed as a model for cognitive impairment in healthy subjects. By applying network based statistics (NBS), we observed altered brain networks significantly linked to donepezil intake and sleep deprivation. Taking into account the sleep stages extracted from the EEG data we revealed that a network linked to sleep is interacting with sleep deprivation but not with medication intake. We successfully extracted the functional resting-state networks modified by donepezil intake, sleep and SD. We observed donepezil induced whole brain connectivity alterations forming a network separated from the changes induced by sleep and SD, a result which shows the utility of this approach to check for the validity of pharmacological resting-state analysis of the tested medications without the need of taking into account the subject specific vigilance.

International audience; Longitudinal evaluation of brain sodium concentration in physiological conditions

International audience; Amyotrophic lateral sclerosis (ALS) is a rapidly fatal neurodegenerative disease characterized by upper (in brain) and lower (in spine) motor neuron degeneration. As conventional MRI fails to show brain motor neurons impairment in ALS, advanced techniques are needed to improve the diagnosis and to monitor the progression of the disease. In this study, brain ^\textrm23Na MRI was applied in 15 ALS patients and 31 controls. A common pattern of sodium accumulation was found in patients in the primary motor areas while no atrophy was detected. The occurrence of sodium accumulation without atrophy probably reflects early neuronal injury in ALS.