Lower extremity deep vein thrombosis (DVT), a blood clot in the lower leg, only happens to a small percentage of the general population. When DVT is clinically suspected, imaging is typically done to evaluate the thrombus (blood clot) in the leg because the clot can move toward the lung. This creates a life-threatening condition called pulmonary embolism. DVT typically starts in the leg close to the ankle but it can come from further up the leg, above the knee, and in the pelvis.
Locating the area of the DVT is important because there is a greater risk of a pulmonary embolism if the DVT is above the knee. Ultrasound (US) duplex Doppler is used to find and diagnose suspected lower extremity DVT. Doppler imaging helps show blood flow and if the clot is totally blocking or partially blocking the blood vessel.
US is used because it is the most accurate test for diagnosing DVT close to the knee. It is not as accurate for diagnosing blood clots below the knee. In some patients, CT venography with contrast or MR venography with and without contrast or MR venography without contrast of the lower extremities is also appropriate to make the diagnosis of the blood clot in the leg. For more information, see the Blood Clots and Pulmonary Embolism pages.