How to sperate a specific area marked using red lines from the background

I recently were diving into one kind of concer and got large sets of B-scan ultrasonography with target cell labled using red lines. However, the revelution and the quality of these pictures are not sufficient to make me seperate the nidus from the background using image binarization. I tried to find a function which could pick up the close area surrounded by the red lines. Due to the secrecy reason I just could offer a blur pic. Thank you for taking your time!

Did you try something?

…like using Google?