My mri states: there is a single region of three foci of t2 prolongation within the white matter. neurologist isn't worried. what does this mean?

No worries: This report means that this tissue has different characteristics (has more water) than the surrounding tissue. That being said, the significance of any test finding - i.e., blood, ECG, imaging or other - depends on the context of your overall picture. So, in the greater scheme of things, your neurologist apparently feels these findings aren't significant. Hope that helps.