Having an mri of spine. does it matter if its done without contrast? should i make sure its done with and without? what's the difference?

Depends...: For looking at degenerative changes, like disc herniations and degree of spinal canal or neural foramen narrowing, no contrast is needed. If the exam is to look for any mass, infection, or if you have had back surgery before, then contrast would help.

If it is being done : For evaluation of back pain without any prior history of back surgery and one is not anticipating a diagnosis of a cancer or infection but looking for a disc problem, then one with non contrast is indicated. However, if prior back surgery or strong suspicion for a tumor or infection, then contrast would be recommended.