If a person had a normal with and without contrast 1.5 tesla mra, should he do 3.0 tesla mra to be sur that 1 to 2 mm cerebral aneurysm was not mised?

Not necessarily: MRA's ability to detect a 1-2 mm aneurysm depends on contrast vs. TOF technique, number of phase-encoded steps, and acquisition parameters. Field strength is another factor, but the data are equivocal for studies of coiled cerebral aneurysms (limited for de novo detection). See your neurologist or neurosurgeon for further discussion. http://link.springer.com/article/10.1007/s00234-008-0413-7