The reasons ultrasound machines are expensive are not technical, it's mostly low volume and high overhead to comply with all rules and regulations.
You can make a useful ultrasound machine with just one transducer (e.g., to measure blood flow through the heart using Doppler, or using mechanical scanning).
You don't need fast CPU for processing, just downconvert to audio range and then 80286 is fast enough.
Source: wrote embedded software for one of those machines back in the day. 16 kB for everything, from keypad debouncing to GUI.
You are confusing several different thing under the vague notion of "ultrasound machines". Doppler mode is useful and cheap machines dedicated to that can and do exist. However even a basic machine able to do only a poor B-Mode needs at least vastly more processing power -- and vastly more channels.
Processing power is not a problem these days. Maybe if you feed all channels at ultrasound frequency to ADC and then try to do all processing in software. But you don't have to, it's oftentimes easier to have hardware (FPGA) pseudorandom signal generators and correlators to do the bulk of signal processing for you.
It depends. An FPGA able to do that is a big one, quite expensive. Today, an even more so tomorrow, you can afford to do that kind of computations in a CPU and/or a GPU.
Regardless of who is doing the beamforming, the TX and RX analog parts are intrinsically quite expensive with at least dozen of channels.
It isn't low volume per say: lots of women get (medically unnecessary) 3d ultrasounds when pregnant to get "a nicer picture" at independent clinics.
A lot of is regulatory, but not completely. - other issues include
1) expensive software integrations for EMR and billing reasons
2) that most machines have multiple wands to attach
3) That billing codes tend to support the use of expensive machines rather than cheap ones if a doctor wants to make money
is probably related to billing codes/other non-embedded software
You can make a useful ultrasound machine with just one transducer (e.g., to measure blood flow through the heart using Doppler, or using mechanical scanning).
You don't need fast CPU for processing, just downconvert to audio range and then 80286 is fast enough.
Source: wrote embedded software for one of those machines back in the day. 16 kB for everything, from keypad debouncing to GUI.