A duplex ultrasound is the technology used to measure blood flow during vascular surgery, according to University of Illinois at Chicago Department of Surgery. It may be used in tandem with an angiogram to make sure that an arm or leg bypass is operating properly.
A duplex ultrasound combines a Doppler ultrasound with a more traditional ultrasound, says MedlinePlus. The traditional ultrasound exam bounces sound waves off the patient's blood vessels. This creates pictures of the blood vessels that can be interpreted by a radiologist.
A Doppler ultrasound exam is a bit more sophisticated in that it can pick up the speed and direction of blood as it flows through blood vessels, according to WebMD. The way the blood flows causes a change in the pitch of the ultrasound, which appears as a graph on a computer screen that can also be understood by a radiologist. The sound waves are picked up by a device called a transducer.
An angiogram is an imaging test in which a contrast material, often an iodine dye, is injected into the artery or vein and captured by a special X-ray camera as it flows through the vessel, explains WebMD. The areas examined are usually near the heart, the lungs, the brain and the aorta, which is the largest artery in the body.