Are there ways to detect whether the vas deferens near the ampulla is blocked by scars?

I believe: the development of MR (magnetic resonance) imaging has enabled the visualization of the vas deferens (there are two). The most natural abnormality of a vas is non-development/lack of it. Or, scarring could have resulted from a surgical procedure to cut them blocking sperm movement, i.e. a vasectomy. I'm not sure what the indication is for detecting this, but I'm certain your Urologist can help.