Is ultrasound cavitation safe? I have heard it can damage the internal organs such as liver etc.

Ultrasound cavitation can be done safely by experienced doctors, but in my experience it's completely unnecessary, as I'm able to get comparable and excellent results with power- assisted liposuction that does not carry the risks of laser or ultrasound liposuction.  Be sure to discuss your goals and concerns with your board certified plastic surgeon and consider the pros and the cons. Be certain your surgeon is properly certified.  I've attached a link where you can start your search. 

Yes, in the right hands, this is a safe, effective procedure. I use VASER HI DEF with ThermRF and fat grafting to get the most fat removal, skin tightening, contour and definition. This combination will give you the most toned result. I recommend getting a formal evaluation with a hi definition physique expert. Best, Dr. Emer

Ultrasonic liposuction is safe.  In my opinion, good results can be obtained with many different lipo machines .  The right surgeon is the critical factor.