Segmentation of ultrasound images

I have been provided with a database of ultrasound images consisting of neck and shoulder areas and I have to detect the exact location of the brachial plexus nerve cells.i have been provided with the ground truth but fail to understand on what basis they are choosing that area because there seems to be no change.

[Rik]

If you are not sure your ground truth is the actual truth, go talk to your supervisor, as that is not a Matlab question.