Severe Sepsis in Children - IMPRESS-C

Inclusion Criteria: For all patients: * Ability to assent (age 7-17 at time of participation in the study) * If taking antihypertensive medication, prescribing practitioner's written approval to participate For sAKI patients: * Hospitalization with a diagnosis of sepsis from 1998-2014 * Severe AKI as defined by the pEDRIFLE criteria during incident sepsis admission * Participation in cognitive survey study with completion of the PedsQL survey For healthy control patients: • Patients from the neurology service undergoing MRI with gadolinium as a part of their clinical care Exclusion Criteria: For all patients: * Known pre-existing CKD as defined by history of kidney transplant or long-term dialysis * Age greater than 17 years at the time of incident sepsis admission * AKI from primary kidney disease including acute glomerulonephritis and obstructive uropathy * Pregnancy at the time of enrollment * Known or suspected allergy to gadolinium based contrast * Known or suspected allergy to iodohippurate will be excluded from RPF measurement with iodohippurate * Heart failure or condition whereby the administration of 0.9% normal saline would be contraindicated * If taking antihypertensive medication, lack of prescribing practitioner's written approval to participate For healthy control patients: * Chronic kidney disease * History of acute kidney injury or GFR \<100 History of chronic illnesses deemed to predispose to renal or cardiovascular dysfunction or abnormalities Suspicion of infection * Neuro-vascular history such as encephalitis, meningitis, vascular anomalies of the brain or spinal cord or cerebrovascular infarct or ischemia will be excluded . * No indication for gadolinium administration for MRI