[glfharris]

Describing it as a best kept secret seems unnecessarily adversarial. The medical community aren't jealously guarding treatments from the populace.

Arguably shock wave lithotripsy, a common method for breaking up kidney stones, could be described as focused ultrasound.

[mmastrac]

I think it's a figure of speech meaning that it's just not widely known.

[jhallenworld]

It seems they are considering it for kidney stones, perhaps in addition to lithotripsy:

https://www.fusfoundation.org/diseases-and-conditions/kidney...

Lithotripsy is pretty limited, I think the preference in most cases is to use ureteroscopy (using holmium laser ablation to break up stones).. but as someone who's had this, I can tell you it's no fun- any progress would be welcome.