This CPB has been revised to state that Aetna considers "open" MRI units of any configuration, including MRI units that allow imaging when standing (Stand-Up MRI) or when sitting, to be an acceptable alternative to standard "closed" MRI units. This CPB has been revised to state that Aetna considers repeat MRI scans in different positions (such as flexion, extension, rotation and lateral bending) to be experimental and investigational.