Ultherapy uses ultrasound to target the 4.5 mm SMAS layer, making it popular...

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

Ultherapy uses ultrasound to target the 4.5 mm SMAS layer, making it popular for lifting deep tissue without cutting. RF heats skin to around 40-45°C to boost collagen, great for mild tightening