apparently an MRA is just a MRI of the arteries and has been recommended by my cardiologist as last doppler ultrasound showed some blockage in one of my carotid arteries and he said the MRA is better. I found out it can be done without injecting a contrast so I made an appmt to have it done and was told no metal and jewellry allowed. I did some research and learned that metal in dental crowns put in many years ago could be a problem. Some of my crowns are 50yrs old =:0 and could possible be a danger. Has anyone heard of this issue?

Not a problem. There are some (poorly done) studies out there showing that MRIs cause mercury to be released from amalgam fillings, but that was only found when they used extremely powerful MRIs using 7 tesla, which is more than twice the power you'll be exposed to. It's really of no concern.