What is a ultrasonic bone density test?

A DXA alternative. The dual energy x-ray analysis (dexa or dxa) is considered the "gold standard" for measuring the mineral content of your bone. A similar measurement can be done with ct-scans or ultrasound, where the impedance of the sound wave can be correlated with bone mineral. None of these tests provide much definitive information about fracture risks. Ask you doctor for a frax clinical analysis first!
No radiation. Bone density is measured using x-ray which has radiation or by ultrasound which do not use radiation.