Difference between MRI vs MRA in runner with ankle injury

Let's say you had an ankle injury a long time ago. 

You sprained the ankle when you were out on a trail run, it got better , and you went right back to running.

But over time, you slowly got more and more pain in the ankle. 

In that case, you doctor might order an MRI of your ankle, or a similar imaging study called an MRA (instead of MRI). 

What's the difference between MRI or MRA in a runner with an old nagging ankle injury?

That's what we're talking about today on the Doc On The Run Podcast.