Hi Xue,
It is an unusual appearance,
Part of me thinks it is just a bit, heterogeneous biceps anchor tendinosis.
Another suggestion would be some CPPD in the superior glenohumeral ligament just medial to the LHBT.
CPPD likes to walk through the SHGL and rotator suff cable.
Could you see any crystal deposition in the cuff cable when you did your short axis supraspinatus images?
The CPPD may show on a plain radiograph if you get one done.
Steve.