Inclusion Criteria:  Subjects aged between 1-10 years old undergoing MRI ASA I-II Weighed between 1-30 kg  Exclusion Criteria:  Patients who had history of hypersensitivity reaction to dexmedetomidine or showed an allergic reaction due to sedation drugs during MRI examination. Patients with cardiorespiratory, liver, kidney problems, risk of difficult airway, undergoing digoxin or beta blocker therapy, and failed to be sedated after 45 minutes since drug administered.