If there's a concern, MRI first sounds like a good idea.  Anything large enough to worry about should show up, I'd think, though the research I've read suggests standard treatment for brain parasites is drugs and that there's not much else to be done unless it's a large mass and easily accesible surgically.  Your body will take care of/absorb the dead parasites over time.

If one doc wrote an rx for an MRI, why does the other need to sign off on it?  That seems odd.

If it were me, and it wouldn't take months to get the MRI, I'd do that first and consult the parasite doc if anything seemed abnormal.

Just my $0.02.