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Comment by gcanyon | Hacker News Reader

> In contrast, radiation affects everything in its path through the body.

The ultrasound has to pass through the body as well, right? Is it that ultrasound can be generated across a broader surface and below a certain threshold has no impact? Or is there some other reason the above statement makes sense?

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This technique causes cavitation at a precise depth. It's amazing.

https://www.youtube.com/watch?v=WqZLkzdNYuI - the video is 11 years old, from the same team. You can see them forming bubbles in precise shapes.

That’s the basic idea. You’ll still get some heating of tissue as ultrasound waves pass through other tissue but won’t be destructive.

Radiation therapies use similar principles but non-target tissue is still exposed to ionizing radiation which causes collateral damage.

There was an article weeks ago about the distinction being that the ultrasound could be focussed in where it imparts energy. However I’m not finding what i remember or i’d link to it.

That bit of the article seems incorrect... Alpha radiation dumps most of its energy in one region, according to the Bragg curve [1]

[1] - https://en.m.wikipedia.org/wiki/Stopping_power_(particle_rad...

The ultrasound waves are mechanical, so the amplitude can be focused while radiation can not be.

Think of making to waves in the bathtub so that they collide in the center and splash. That would be an mechanical wave. On the other hand, radiation would be be like shining two flashlights from either sides of the sink. The light simply passes through itself.

Could be that it's area of effect is only where the frequencies resonate.

I wonder if it's comparable to using a magnifying glass, in the sense that it's the hottest only at one specific point, even though the rays are traveling through the medium (air) at all points. So maybe it's like a magnifying glass for sound and the cancer is the ant that gets fried?

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