What are the dangers of therapeutic ultrasound massagers?

Risk ultrasound mass. Fda instructions say ultrasound waves should not come in contact with any vital organ of your body, followind organs heart, kidneys, liver, lungs, stomach, spleen, bowels, eyes, ears, ovaries, testicles, brain and spinal cord. Also there are other limitations it is safe&effective, but can cause pain due to cavitation/due to heating of the gas contained in tissue cell nuclei.