Scanning the extracranial arteries with ultrasound

Increase your confidence in carrying out a carotid artery scan. Following a set protocol and using a methodical approach will ensure that you have performed a detailed investigation of each vessel. In this Medmastery lesson, we will go through a step-by-step protocol for performing a comprehensive examination of the extracranial arteries using different planes, approaches, and ultrasound modalities.

Learn how to diagnose and treat extracranial vascular disease using ultrasound with this course. In this course, you’ll learn how to optimize the scanner controls as well as recognize and identify normal and atypical carotid, subclavian, and vertebral arteries using ultrasound images and flow patterns. You’ll learn how to make key measurements and use these to categorize disease and write a report.

The carotid, subclavian and vertebral arteries should be imaged according to a set protocol. This ensures a systematic approach and reduces the variability between sonographers. In this Medmastery lesson, we will go through a step-by-step protocol for performing a comprehensive examination of the extracranial arteries using different planes, approaches and ultrasound modalities.

The first step is to scan the right side of the patient's neck. Using a good amount of gel, position the probe on the patient's neck. Be careful not to exert too much pressure, particularly around the bifurcation where the vessels are very close to the skin and can easily be compressed. Starting with the B-mode, the carotid artery should be scanned in the transverse plane, there'll be an orientation marker on one side of the probe.

For transverse scan, this should be pointed to the patient's right side. The marker at the top left on the B-mode image will then represent the right side of the patient. In this course, the probe marker is usually represented by a yellow dot. A lateral approach through the sternocleidomastoid muscle in the neck provides a good ultrasonic window.

Identifying the common carotid artery and then starting at the base of the neck near the clavicle, move up slowly past the bifurcation and towards the mandible. This provides a good overall picture that will help identify the level and orientation of the bifurcation, and the location and extent of any disease present.

In some cases, such as when there's extensive disease or heavy calcification, switching on the color flow may help to identify the vessels and the presence of disease. Next, move back to the base of the neck and rotate the probe to image the proximal common carotid artery in the longitudinal plane.

The orientation marker should be pointing towards the patient's head. Here, the marker at the top left of the image will indicate the head end of the patient. Move up the neck using the knowledge gained from the transverse scan to help orientate the probe as you go. In some cases, it will be possible to image the bifurcation with the internal carotid artery and external carotid artery in the same plane, but they will often have to be imaged separately in a different plane.

These two vessels usually lie very close together so only small movements of the probe are required. Still scanning in the longitudinal plane, move back down towards the base of the neck and switch on the color flow, then travel back up the neck to help identify areas of high velocity and aliasing.

If significant disease is identified in the ICA it is really important to image as high up as possible into the distal ICA to confirm that it is patent or unobstructed and of good caliber. Next, the pulse Doppler should be used to attain quantitative measurements, including the peak systolic and end-diastolic velocities.

These should be measured in the distal CCA, proximal ICA, distal ICA, and proximal ECA. Any areas of suspected narrowing or stenosis should then be investigated. Having completed the assessment of the carotid arteries, move down to the base of the neck towards the subclavian artery. Scanning the subclavian arteries can be challenging due to the close proximity to the clavicle.

To help with this, ask the patient to relax their shoulder down, and turn the head a little further to the left, away from the side that is being scanned. Using plenty of gel, position the probe in the supraclavicular notch and adjust the position of the probe to obtain a longitudinal view of the subclavian artery.

Move the probe medially to image the subclavian artery as proximally as possible, and then laterally to image the distal subclavian artery. Use the color flow to help identify the vessel and any areas of stenosis, and then make sure to obtain a pulsed Doppler waveform which should have triphasic flow to help identify the presence of significant disease.

To complete the investigation, the vertebral artery needs to be assessed. This is usually best scanned with the patient's head positioned straight and using an anterior or lateral approach. The vertebral artery can be located by first imaging the mid CCA in the longitudinal plane. The transverse processes and vertebral artery should then come into view, just lateral and posterior to the CCA.

The transverse processes will be visualized as bright echoes with shadows behind them. In between each transverse process, a short segment of the vertebral artery and vertebral vein will be seen. The other segments of these vessels lies behind the bone of the transverse processes and cannot be visualized with ultrasound.

The probe position should be adjusted to optimize the view of the vertebral artery. For the color flow image, the color scale will usually need to be reduced and the gain increased to get good filling of the artery, shown here in red. The vertebral vein, shown here in blue, will be seen just above the artery. A pulse Doppler signal from the vertebral artery should also be obtained to confirm the direction of flow, which should be antegrade.

Once the scan of the right side is complete, the patient should be asked to turn their head to the right and the left side of the neck should be investigated following the same steps. As you can see, following a set protocol and using a methodical approach will ensure that you have performed a detailed investigation of each vessel.