The Pharmacokinetics of Dexmedetomidine in Children

Inclusion Criteria: * Age 3 - 11.9 years * 2 age groups: 3.0 - 5.9 years, 6.0 - 11.9 years * Patients will be equally distributed within each age group * Meets criteria to receive dexmedetomidine sedation for MRI: * Active, uncontrolled gastroesophageal reflux - an aspiration risk * Active, uncontrolled vomiting - an aspiration risk * Current (or within past 3 months) history of apnea requiring an apnea monitor * Active, current respiratory issues that are different from the baseline status (pneumonia,exacerbation of asthma, bronchiolitis, respiratory syncytial virus) * Unstable cardiac status (life threatening arrhythmias, abnormal cardiac anatomy,significant cardiac dysfunction) * Craniofacial anomaly, which could make it difficult to effectively establish a mask airway for positive pressure ventilation if needed * Current use of digoxin * Moya Moya Disease * New-onset stroke * Provide written consent to take part in the research study Exclusion Criteria: * Do not meet established sedation criteria * History of allergy, intolerance, or reaction to dexmedetomidine or hypersensitivity * Previous diagnosis of hepatic insufficiency/failure or a serum glutamate pyruvate transaminase level \> 2 times the normal limit determined by Children's Hospital Boston (TCH) * Current diagnosis of renal insufficiency/failure or a current serum creatinine level \> 1.5 times the normal limit determined by TCH * Have received digoxin in the past (no time limit) * Received phenobarbital, clonidine or valproic acid within 30 days * Current, repaired or risk of Moya-Moya disease * Recent stroke (cerebrovascular accident) within past 6 months * Uncontrolled hypertension * Concomitant use of beta antagonist, or calcium channel blocker * Participated in a clinical investigation within the past three months