That's like asking how if a laser can cut through steel how lamps can be safe to have indoors.

Do you have a link or something that compares the power in both? I can't find one.

This is the summary I get from chatgpt - comparing Histotripsy and ultrasound imaging

| Property | Strongest Diagnostic / Imaging Ultrasound | Histotripsy (Therapeutic Ultrasound |

| Frequency | 2 – 10 MHz (obstetric: 2–5 MHz; high-res imaging up to 15 MHz) | 0.25 – 3 MHz (sometimes up to 6 MHz) |

| Pressure (Peak Negative) | Up to ~5–6 MPa (mechanical index limit ≈ 1.9) | 10 – 100 MPa (depending on type: intrinsic vs. boiling histotripsy) |

| Intensity (Spatial Peak, Temporal Average) | Typically < 0.1 W/cm²; upper safe limit ≈ 0.72 W/cm² (FDA/AIUM) | 100 – 10,000 W/cm² (very high peak intensities) |

| Pulse Duration | Microseconds (∼1–5 µs typical) | Microseconds to milliseconds (short bursts for mechanical disruption) |

Its kind of hard to know what this means - some of the numbers seem pretty close/crossover - but I don't think saying the difference is akin to a laser and a light.

There are 2 to 5 orders of magnitude difference in intensity. That alone is a pretty big difference.

It's a big difference, but it is not obvious to me that there can be no harmful impact from imaging.

You can vary the frequency, power, energy, focus... is not the SAME ultrasound.

But surely it could cause some damage at a lower frequency, power, etc anyway?

Why “surely”?

Most things that are harmless or even necessary at one level are deadly at another: heat, light, water, food, air… pretty much everything really.

“Dosis sola facit venenum” (only the dose makes the poison)

Using the example of a laser - you can have a powerful laser that can burn through metal. A far weaker laser (many magnitudes weaker) could still damage eye sight. Alternatively, water erodes mountains eventually.

I don't think you can argue that ultrasound imaging is harmless or a treatment/dose. It might be that it does nothing. It might also be that it does something (like when it destroys cancer cells) only its far milder, and not an obvious observation.

PS I know there are mild ultrasound devices to aid muscle recovery. These devices do something, presumably. If mild devices are acknowledged to impact muscles etc, some (mild probably) effect is occuring. Given there are occasions where these devices are known to have an impact on adults, why should we presume that there is no impact on the technology when it is looking at a developing foetus?

PPS Even in studies that say there is 'no effect' from ultrasound imaging, there is a tolerance of up to 10% difference between the control and the subjects.

PPPS And of course, sometimes the control is 'children who have only had 1 ultrasound' vs 'children who have 2 or more ultrasounds' - ie the control is not 'children who have who have had no ultrasounds' - ie we do not get true control studies.

Potentially, but these things are well controlled and understood: https://www.bmus.org/education-and-cpd/cpd-resources/top-tip...

Please don't be sarcastic for a possibility genuine question. It contributes to alienating the askers, not to mention the risk of some taking it quite literally.