Hi Worried,
He will just lie on a bed going through a tube with loud annoying mechanistic noises for 45 minutes, hopefully drowned out by headphones.
He may have an injection of dye into the vein on his wrist half-way through.
You would waste your time sitting outside, and you won’t hear the results for a week or two, so let him go on his own.
Make sure you accompany him to the follow-up appointment with all your potential questions written down. If there is nothing untoward found you can tear them up like confetti and shower the consultant with them.
Best of luck.
Cheers, John.