A Doppler ultrasound is a noninvasive test that can be used to estimate the blood flow through your blood vessels by bouncing high-frequency sound waves (ultrasound) off circulating red blood cells. A regular ultrasound uses sound waves to produce images, but can't show blood flow.
See also the post below. Just buy a cheap electret condensor mic: onecall.farnell.com/pro-signal/abm-713-rc/electret-microphone-omni-pcb-pins/dp/2066499?st=microphone+condensor and connect it to your PC. Cut the tube and instead of the ear pieces push the mic into the tube. I'm sure you also get them with cable on ebay if you don't want to solder.