Required for outpatient procedures Prior authorization is required for the following outpatient radiology procedures through NIA. CT scan Nuclear exercise Tolerance test (ETT) MRI/MRA PET scan Obtaining authorization The ordering physician or clinic is responsible for getting authorization. If you are providing any of the services above, you should verify that the necessary authorization has been obtained. If you fail to do so, it could result in non-payment of your claim. Imaging procedures performed during an emergency room and/or urgent care visit or in observation and inpatient facilities do not require authorization.