Introduction to Vascular Ultrasonography

Ultrasound is a safe imaging modality that is used to form images of structures within the body. Unlike X-ray, ultrasound uses non-ionizing radiation in the form of sound waves. Ultrasonography can be used as a non-invasive examination of the blood vessels.

2D Ultrasound

• Two-dimensional (2D) ultrasound produces grayscale images. Clear fluid does not reflect sound waves, so the blood vessels are black structures on the sonogram. Other tissues produce echoes and are demonstrated as varying shades of gray. Plaque within an artery can be seen as a bright gray structure. Blood clots in a vein may not be seen if they are relatively new. Older blood clots may look dark or medium gray.

Pulsed Doppler

• Doppler measures the movement and speed of blood cells in the blood vessels. Pulsed Doppler produces waveforms that demonstrate the velocity of blood flow. The spectrum consists of a horizontal baseline. Waveforms moving upward and above the baseline demonstrate blood that is traveling away from the heart. Waveforms moving downward demonstrate blood that is moving toward the heart. In most arteries, each complete, arterial waveform demonstrates a slight flow reversal at some point in each waveform. Venous blood flow should almost always be below the baseline.

Color Doppler

• Color Doppler is used to demonstrate where the blood flow is and the direction of the blood flow in relation to the transducer, or camera. The color Doppler image is overlaid on the 2D image. The ultrasound system assigns the blood cells a color. The ultrasound settings are most often adjusted to demonstrate red within the artery. Blue indicates blood flow in the opposite direction.

Protocol

• Vascular imaging combines 2D imaging, pulsed wave Doppler, and color Doppler to acquire a complete examination. Generally, each section of an artery or vein is imaged with each technology. With venous imaging, 2D images of cross-sections of the vein are acquired. The cross-section images demonstrate an image of an open vein and an image of a closed vein resulting from pressure exerted by the sonographer.

Patient Preparation

• There is no necessary preparation prior to the examination. When the patient arrives, he will be asked to remove his pants and to put on a gown. The patient will be asked to lie down on an exam table. The torso may be elevated. Towels are used to protect any clothing from ultrasound gel. The gel is applied along the inside of the leg where the sonographer will scan. Vascular exams can last anywhere from 20 to 90 minutes.