Study of the Efficacy of Moderate Sedation With Intra-NAsal Dexmedetomidine Monitored by EEG MOnitoring

EEG monitoring will be performed in addition to the usual practice, before DEX administration and for 20 minutes before NMRI, to enable calculation of the PSI sedation score (at 0, 10, 20 minutes). Sedation will also be assessed by the PSSS clinical score at 0, 10, 20 minutes after DEX administration, as well as at 150 minutes after DEX.