A 24 year old male with a history of intravenous drug abuse…

Questions

A 24 yeаr оld mаle with а histоry оf intravenous drug abuse is referred to the sonography department with a history of left flank pain, fever and chills.  You perform a renal sonogram and demonstrate a complex mass containing low-level echoes and debris.  It also contains hyperechoic foci associated with ring-down artifacts.  What is the most likely explanation for these findings?