Also ultrasound just isn't that good of an imaging technology, even with full aperture.
That said, it's non-ionising and if they can make this reasonably cheap (big if), then it's better than nothing at all. Probably decent for finding cancer, especially breast cancer (no pesky bones there!).
True, but ultrasound isn't entirely benign. Depending on what frequency and what power it can crack solid parts of the body (its used to break up kidney/gall stones) it also can heat things up (which is, assuming my understanding is correct, why doppler scans for blood flow are not done on <18 week pregancy)
My point is, phased arrays of ultrasound have the ability to be destructive. In the same way that a single MIMO wifi AP isn't going to cook you, but 10,000 MIMO arrays steering coherently over you will.
We have screening programs for a reason. We know the sensitivity and specificity of these. They are widely available in any rich country that doesn’t treat its citizens like shit. There will absolutely be better stuff out there as we progress, with better sensitivity/specificity and lower harm (everything medical has some harm quotient) but I have a hard time wrapping my head around how they will best physics to provide better than state of the art today with this technology (and bow they will beat availability of current screening systems)