can be an investigation to detect the exact anatomic relation of the mass , if any underlying structure invasion or destruction present it can be identified. MRI can also detect any neck node if involved. Thyroid
mass can be of benign disease, but MRI can not comment surely on the malignancy . It can give a hint about the underlying pathology. As your doctor has suggested this investigation you should have done it . Consult your doctor for further discussion. take care.