tips for toddler freaking out at the dr office?

20 month old, she's never had a "negative" (to us) experience at the dr, but she FREAKS OUT when we go, like screaming the entire time (even when we are just waiting in the office and no one is touching her). It's gotten worse as shes gotten older and more aware. We have 2 upcoming dr visits - one for a vaccine and one for an ultrasound that is needed. We try to make the visits as upbeat as possible, lots of distractions, but once she gets into panic mode it's hard to get her out of it. Anyone have any tips for how to make it more manageable for her? She is really understanding things - so I am thinking to prep her in the car ride and just explain where we are going and that we have to do it? I was also wondering if it's a bad idea to pair it with something like a "treat" after- like getting ice cream after.... as a little "hey look we went to the dr and you hated it but then you got this ice cream!" or is this a terrible idea... ?