Upper back 76604 & lower back 76705
Code 76705 (Ultrasound, abdominal, real time with image documentation; limited [e.g., single organ, quadrant, follow-up]) is appropriate for this lower back ultrasound.
You might be surprised to discover these other not-so-obvious anatomy/code pairings that CPT Assistant supports:
• chest wall, upper back: 76604 (Ultrasound chest [includes mediastinum], real time with image documentation)
• pelvic wall, buttock, perineum: 76857 (Ultrasound, pelvic [nonobstetric], real time with image documentation; limited or follow-up [e.g., for follicles])
• upper extremity, axilla, groin, lower extremity: 76881/76882 (Ultrasound, extremity, nonvascular, real time with image documentation).
http://codingnews.inhealthcare.com/coding-challenge/radiology-coding-education-is-76705-ok-for-back/
hope this helps for future readers!