It’s actually a doctor does it with MRI contrast - that scared me too, when I realised it has to be a doctor - obviously it’s deemed higher risk than a mere blood test, but you do get a more senior person in attendance.
My doctor was an Aussie with a very black sense of humour. He said: "Right, tell me if you feel an excruciating pain, OK? 
"
“Thanks, Doc - you’re a great comfort! Rest assured you’ll know.”
There wasn’t pain, of course - he was a total wind-up merchant.
Tina