MRI physicist here as well. I have a basic understanding of ultrasound, and this looks like an array of transducers organized to perform tomography, just as CT did for Xray.

However Ultrasound quality depends highly on transducer-skin contact.

Any physicists here to comment on the effects of sonar through liquid and the effects on image resolution and field of view?

This is precisely why you do it in water - the water-skin contact is effectively perfect, as is the water-transducer interface, and the body of water is easily characterizable; in effect you are scanning one large object that consists of a body of water that just happens to have a human body in it, and then extracting the body from that scan.

This paper, “Whole Cross-Sectional Human Ultrasound Tomography”, goes into more detail.

https://arxiv.org/pdf/2307.00110