Renal ultrasound doppler effect

So I had the arteries around my kidneys checked today to make sure they weren’t constricted in any way.
They used an ultrasound machine, and somehow used the doppler effect to detect this.

Can someone explain to me how exactly the doppler effect is used? And does that mean the machine picks up soundwaves in the audible range as well?
I could hear my own heartbeat quite clearly during the test.
To forestall the ribbing that I’m already getting at work. Yes, I’m male. No, I’m not pregnant, thanks for asking. :slight_smile:

Well, poking around webmd, I think I found my own answer.
It must have been one of the color doppler machines.

Doppler Ultrasound