Ultrasound is usually a linear array of 256 or more transducers that can use timing information to direct an ultrasound signal in a range of directions. By moving the pulse origin left and right, and altering the direction, it is then possible to generate a 2d image of the area in contact with the probe.

It is possible to listen for echoes that are doppler shifted, to measure velocity of the bloodstream, for example. This information can be gathered in that same 2d image, to generate estimates of blood flow, and quite variety of other information without invasive procedures.