Ultherapy uses focused ultrasound to reach the 4.5 mm SMAS layer, which...

https://technivorz.com/why-is-imaging-such-a-big-deal-in-ultrasound-skin-tightening/

Ultherapy uses focused ultrasound to reach the 4.5 mm SMAS layer, which standard HIFU often can’t target as deeply. RF heats skin to 40-45°C for collagen boost but doesn’t reach the same depth