Medical Content Created by the Faculty of the
Harvard Medical School
After squirting some clear jelly onto the inside of one of your thighs to help the ultrasound sensor slide around easily, a technician or doctor places the sensor against your skin. Once it's in place, an image appears on a video screen, and the technician or doctor moves the sensor up and down along your leg — from the groin to the calf — to view the veins from different angles. The examiner presses the sensor into your skin firmly every few inches to see if the veins change shape under pressure. He or she then checks your other leg in the same way. As the machine measures the blood flowing through a vein, it makes a swishing noise in time with the rhythm of your heartbeat. This test usually takes 15-30 minutes. Most people don't feel any discomfort, but if your leg was swollen and sensitive to the touch before the test, the pressure of the sensor might cause some tenderness.