Carotid duplex ultrasound scanning is the most common and reliable imaging technique for the detection of plaque, which can cause narrowing of the carotid arteries that supply blood to the brain. Critical narrowing of these blood vessels or unstable, active plaque may cause mini-strokes (transient ischaemic attack or TIA) or stokes. Duplex ultrasound is an ideal technique to identify and classify the amount and type of plaque seen within these arteries. Carotid duplex scans are frequently performed for screening purposes before major surgery, when patients have experienced stroke or TIAs and for follow-up after surgery or stenting of the carotid arteries.
PATIENT PREPARATION AND EXAMINATION TECHNIQUE:
No special preparation is required from the patient.
The examination is performed in a quiet, darkened room with the patient lying on their back. The patient’s neck is exposed so that the sonographer has access to the carotid arteries that travel along both sides of the neck. Ultrasound gel is placed on the neck and the ultrasound scan is performed using an ultrasound probe or transducer. This transmits ultrasonic sound waves into the tissue, which are then reflected back to the probe allowing an image to be generated. Using B-mode the carotid vessels can be seen as can any plaque within these arteries. Classification of the type of plaque can be made. Using Doppler, measurement of the speed and direction of the blood flow within the arteries can be made. From the presence of plaque and the speed of the blood flow within the artery an estimation of the degree of stenosis or narrowing can be made. The vertebral arteries are also imaged to determine if they are patent and that the blood flow is in the right direction towards the brain.
The carotid duplex ultrasound scan will take between 15-30minutes depending on the degree of difficulty.
Degree of internal carotid artery stenosis (ICA) is graded as < 15%, 16-49%, 50-69%, 70-79%, 80-99% or completely occluded.