If you are having ANY concerns about having an MRI with and without contrast, I think the first thing you need to get answered is the question you stated in your post.

WHY is the test being ordered?

There are various reasons and various degrees of necessity behind a physician ordering any tests.

Is the doctor covering all bases? Is the doctor covering his butt? Does the doctor suspect something in particular and is looking to confirm or refute it? Is the doctor at a loss and is trying to find something?

Is the test essential? Are there other ways to find a proper diagnosis? What are the advantages and disadvantages of the test? The risks?

Some tests are absolutely necessary for a patient, some are not. Some are protocol for presenting with certain symptoms.

If you would feel better knowing the underlying reasons your physician has ordered your testing, do not hesitate to ask. After all, the patient is suppose to be FULLY informed, not just given a statement that you need to have a specific test or procedure.

Some patients WANT as much information as one can obtain from their physician and others prefer not to know. Physicians will not generally go into more detail than the patient requests, so if you want to know, please ask.