Hifu

Someone who has had HIFU treatment done said:
I only see the result after a few weeks while you only undergo 1 treatment. And then keep it up by doing it once a year.
What gives this result?

The only thing I can think of for such a long-lasting result is that instead of collagen accretion, it is more likely to be ablative.
That is, in such case, collagen (in this case usually collagen I) is denatured at a temperature from above 42°C.
This is applied when cancer cells need to be ablated (destroyed).
With collagen, collagen fibres will then be broken down into fibrils and collagen molecules and amino acid chains. 
In this case, the collagen shortens and tightens the tissues around it. 
Sounds all nice but is not without danger and is also a medical act.

With capacitive RF (NBE 3000), collagen is produced and built up, giving more firmness and also creating stronger tissue. 
Collagen production by fibroblasts is a constant throughout life. It decreases with age and it is that which we counteract.