[anax32]

Can anyone explain how this ultrasound can see through the skull?

I've worked on ultrasound devices and data, the shadows from bone, and distortions caused by tissue types were very difficult. If this device can deal with those distortions it would already be useful for lung imaging.

[DoctorOetker]

lungs are much harder than brain and bones (the acoustic impedances of solids and liquids is more similar than solids/liquids vs air: air is very thin)