Final answer:
The major disadvantages of MRI scans are the release of radiation and the need for a patient to be confined to a metal tube for up to 30 minutes.
Step-by-step explanation:
Two major disadvantages of MRI scans are a. release of radiation and poor quality images and d. release of radiation and the need for a patient to be confined to a metal tube for up to 30 minutes. MRI scans do not use radiation, so the release of radiation is not a disadvantage. Additionally, the need for shielding from the magnetic signals and the inadequate availability of equipment are not disadvantages of MRI scans. Instead, MRI scans provide detailed images of soft tissues, making them valuable diagnostic tools for conditions such as brain tumors and joint injuries.