Is lumber puncture necessary before MRI result?

Hi, forgive me if this appears twice, I thought it had posted, but couldn’t find it anywhere!

Basically, I’ve got an appointment through for a lumber puncture on 27th Jan and a full brain and spine mri with contrast on 2nd Feb. Is it necessary to have the LP, or even advisable, before the scan results? I suffer with lower back pain, and severe migraine and don’t want to antagonise either, but fully admit to being a bit of a wuss too! I’m not sure what the point of the LP is, but as I need to let the hospital know if the appointment is convenient, I did wonder whether I could put it off till someone’s had a look at the scan results? or even refuse? would that put me in the neuro’s bad books?!

Any advice greatly appreciated