After applying a water- soluble ultrasound transmission gel to the area to be assessed, your podiatrist will pass a handheld stick- like instrument called a ‘transducer’ over your skin. Podiatrists are highly trained in this technique and will then listen to the projected sounds and analyze the waveforms seen to assess the quality of blood flow in major vessels. This procedure is 100% pain free for the patient and highly evidence- based in the diagnosis or elimination of vessel disease.  

Your podiatrist might also apply a blood pressure cuff along with using the Doppler to assess pressures in your arm versus leg, a technique that is effective in gauging the risk of vessel disease in your legs or foot. How does it Work?

The transducer sends sound waves, which are then reflected according to the volume and velocity of blood flow under the skin (the Doppler effect). The sound waves, which return to the transducer are reflective of the time difference between signals (the Doppler frequency) and are processed by the machine to form waveforms. They are also amplified as sounds through a microphone. Your podiatrist then interprets the waveforms and sounds.

http://www.centrus.com.br/DiplomaFMF/SeriesFMF/doppler/capitulos-html/chapter_01.htm

http://www.webmd.com/a-to-z-guides/doppler-ultrasound