You can have a basic ultrasound with only on channel. The following patent is from 1985, and has a pretty good overview of the field at the time. It appears tha

You can have a basic ultrasound with only on channel. The following patent is from 1985, and has a pretty good overview of the field at the time. It appears that most if not all untrasound transducers at the time were large single channel instruments. https://patents.google.com/patent/US4446395A https://patents.google.com/patent/US4446395A This patent, from 1989, indicates that most ultrasound transducers are either single element or linear arrays. It was the earliest patent I could find with a cursory look that had a 3 dimentional array. https://patents.google.com/patent/US5027820A/en https://patents.google.com/patent/US5027820A/en Regardless, even Wikipedia suggests that most of the arrays used for medical imaging use either a single element or a phased array: To generate a 2D-image, the ultrasonic beam is swept. A transducer may be swept mechanically by rotating or swinging. Or a 1D phased array transducer may be used to sweep the beam electronically. The received data is processed and used to construct the image. The image is then a 2D representation of the slice into the body. 3D images can be generated by acquiring a series of adjacent 2D images. Commonly a specialised probe that mechanically scans a conventional 2D-image transducer is used. However, since the mechanical scanning is slow, it is difficult to make 3D images of moving tissues. Recently, 2D phased array transducers that can sweep the beam in 3D have been developed. These can image faster and can even be used to make live 3D images of a beating heart. https://en.wikipedia.org/wiki/Medical_ultrasound#Sound_in_the_body https://en.wikipedia.org/wiki/Medical_ultrasound#Sound_in_th... Point being, I think you are wrong. I'm not an EE, so I can't speak towards signal processing, but I am a biologist by training, and I don't see a clear reason why sonar principles wouldn't work. We are basically a bag of salt water. Also, I am familiar enough with ultrasound to be sure that models with only a single transducer are very common. Hospitals and the like might be using the fancy-pants multi-dimensional arrays now, but the units we used to image things in college were definitely not multi-dimension. For one thing, they were older than the patent that demonstrated multi-dimensional arrays.