Inclusion Criteria:  Initiation of invasive mechanical ventilation in the Intensive Care Unit within 48 hours. Expected duration of invasive mechanical ventilation of at least 5 days.  Exclusion Criteria:  Body-mass-index (BMI) >40 Expected absence of active participation of the patient in study-related measurements after extubation Alcohol or drug abuse Non MRI compatible implant in the body Slipped disc Epilepsy Patients in an interdependence or with an employment contract with the principal investigator, Co-PI or his deputy.