Carotid ultrasonography is an

ultrasound Ultrasound is sound with frequency, frequencies greater than 20 Hertz, kilohertz. This frequency is the approximate upper audible hearing range, limit of human hearing in healthy young adults. The physical principles of acoustic waves apply ...

-based diagnostic imaging technique to evaluate structural details of the

carotid arteries In anatomy, the left and right common carotid arteries (carotids) () are arteries that supply the head and neck with oxygenated blood; they divide in the neck to form the external and internal carotid arteries. Structure The common carotid ...

. Carotid ultrasound is used to diagnose

carotid artery stenosis Carotid artery stenosis is a narrowing or constriction of any part of the carotid artery, carotid arteries, usually caused by atherosclerosis. Signs and symptoms The common carotid artery is the large artery whose Common carotid artery#Clinical ...

(CAS) and can assess

atherosclerotic plaque An atheroma, or atheromatous plaque, is an abnormal accumulation of material in the inner layer of an arterial wall. The material consists of mostly macrophage cells, or debris, containing lipids, calcium and a variable amount of fibrous conne ...

morphology and characteristics. Carotid duplex and contrast-enhanced ultrasound are two of the most common imaging techniques used to evaluate carotid artery disease.

Medical Uses

Carotid ultrasound is a low-cost, noninvasive, and accurate diagnostic imaging modality used to evaluate diseases of the carotid arteries. It is most often used to diagnose carotid artery stenosis, a form of

atherosclerosis Atherosclerosis is a pattern of the disease arteriosclerosis, characterized by development of abnormalities called lesions in walls of arteries. This is a chronic inflammatory disease involving many different cell types and is driven by eleva ...

, and has the capability to assess plaque morphology and characteristics. Carotid artery stenosis is a major risk factor for

stroke Stroke is a medical condition in which poor cerebral circulation, blood flow to a part of the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemor ...

, and risk assessment of atherosclerotic carotid plaques is a critical component of stroke prevention. Advances in imaging have allowed for risk stratification including degree of

stenosis Stenosis () is the abnormal narrowing of a blood vessel or other tubular organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture). ''Stricture'' as a term is usually used when narrowing ...

and how vulnerable the atherosclerotic plaque is to rupture. Other plaque features that contribute to stroke risk and can be evaluated by imaging are: intraplaque

hemorrhage Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, ...

, plaque

ulceration An ulcer is a discontinuity or break in a bodily membrane that impedes normal function of the affected Organ (biology), organ. According to Robbins's pathology, "ulcer is the breach of the continuity of skin, epithelium or mucous membrane caus ...

and

neovascularization Neovascularization is the natural formation of new blood vessels ('' neo-'' + ''vascular'' + '' -ization''), usually in the form of functional microvascular networks, capable of perfusion by red blood cells, that form to serve as collateral circu ...

, fibrous cap thickness, and presence of a lipid-rich necrotic core (LNRC). Carotid ultrasound is the preferred initial diagnostic test to evaluate carotid artery stenosis, and can also be used to monitor response to lipid-lowering therapy.

Alternative imaging modalities

Digital subtraction angiography Digital subtraction angiography (DSA) is a fluoroscopy technique used in interventional radiology to clearly visualize blood vessels in a bony or dense soft tissue environment. Images are produced using contrast medium by subtracting a "pre-cont ...

(DSA),

magnetic resonance angiography Magnetic resonance angiography (MRA) is a group of techniques based on magnetic resonance imaging (MRI) to image blood vessels. Magnetic resonance angiography is used to generate images of arteries (and less commonly veins) in order to evaluate ...

(MRA), and

CT angiography Computed tomography angiography (also called CT angiography or CTA) is a computed tomography technique used for angiography—the visualization of arteries and veins—throughout the human body. Using contrast injected into the blood vessels, im ...

(CTA) are confirmatory imaging techniques typically employed after ultrasound and prior to therapeutic intervention. DSA is the gold standard for evaluating CAS, and

MRI Magnetic resonance imaging (MRI) is a medical imaging technique used in radiology to generate pictures of the anatomy and the physiological processes inside the body. MRI scanners use strong magnetic fields, magnetic field gradients, and rad ...

is the gold standard for carotid plaque imaging.

Imaging Techniques

Duplex ultrasound

Duplex ultrasound Doppler ultrasonography is medical ultrasonography that employs the Doppler effect to perform imaging of the movement of tissues and body fluids (usually blood), and their relative velocity to the probe. By calculating the frequency shift of a ...

(duplex) combines standard B-mode ultrasound and

Doppler ultrasonography Doppler ultrasonography is medical ultrasonography that employs the Doppler effect to perform imaging of the movement of tissues and body fluids (usually blood), and their relative velocity to the probe. By calculating the frequency shift of a ...

to evaluate both structural details of the carotid arteries and blood flow through the arteries. During carotid duplex evaluation, the 2D B-mode structural image is superimposed with the doppler flow data, which provides a more realistic anatomical assessment. B-mode ultrasound is able to assess the structure of the carotid arteries and can identify areas of stenosis. B-mode is used identify stenotic lesions and to assess the echogenicity of plaques—strong correlation has been established between sonographic and histopathologic features of plaques. Plaque echolucency can signal an at-risk plaque, as it is the sonographic equivalent of a LNRC. Besides, other features such as intima-media thickness, surface of the plaque and presence of ulceration are also useful in predicting the possibility of stroke or heart attack in the future. Scanning through the eye can help to visualise carotid siphon (bend of internal carotid artery within the

cavernous sinus The cavernous sinus within the human head is one of the dural venous sinuses creating a cavity called the lateral sellar compartment bordered by the temporal bone of the skull and the sphenoid bone, lateral to the sella turcica. Structure The ...

) and

ophthalmic artery The ophthalmic artery (OA) is an artery of the head. It is the first branch of the internal carotid artery distal to the cavernous sinus. Branches of the ophthalmic artery supply all the structures in the orbit around the eye, as well as some ...

. Doppler ultrasound allows for assessment of carotid arterial blood flow. Blood flow velocity is increased in areas of stenosis compared to normal. Therefore, doppler imaging substantially aids in the diagnosis of carotid artery stenosis by ultrasound.

Internal carotid artery The internal carotid artery is an artery in the neck which supplies the anterior cerebral artery, anterior and middle cerebral artery, middle cerebral circulation. In human anatomy, the internal and external carotid artery, external carotid ari ...

(ICA) is located posterolateral, and larger when compared to the

external carotid artery The external carotid artery is the major artery of the head and upper neck. It arises from the common carotid artery. It terminates by splitting into the superficial temporal and maxillary artery within the parotid gland. Structure Origin T ...

(ECA). ICA has low resistive pattern (difference between the blood velocities during heart

systole Systole ( ) is the part of the cardiac cycle during which some chambers of the heart contract after refilling with blood. Its contrasting phase is diastole, the relaxed phase of the cardiac cycle when the chambers of the heart are refilling ...

and

diastole Diastole ( ) is the relaxed phase of the cardiac cycle when the chambers of the heart are refilling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventricul ...

) when compared to ECA. ICA has sudden increase in velocity of blood flow during systole and persistent forward blood flow during diastole. ICA peak systolic velocity more than 125m/sec and diastolic velocity more than 40 m/sec signifies stenosis. ECA can be differentiated from the ICA by tapping

superficial temporal artery In human anatomy, the superficial temporal artery is a major artery of the head. It arises from the external carotid artery when it splits into the superficial temporal artery and maxillary artery. Its pulse can be felt above the zygomatic ar ...

of the same side. This will generate a saw-like appearance on ECA doppler. Temporary reversal of the direction of flow during early diastole in ECA is normal. ECA has triphasic flow pattern (forward flow in systole, reverse flow in early diastole, and forward flow in end diastole).

Vertebral artery The vertebral arteries are major artery, arteries of the neck. Typically, the vertebral arteries originate from the subclavian arteries. Each vessel courses superiorly along each side of the neck, merging within the skull to form the single, m ...

also has low resistive pattern similar to ICA.

Contrast-enhanced ultrasound

Contrast-enhanced ultrasound Contrast-enhanced ultrasound (CEUS) is the application of ultrasound contrast medium to traditional medical sonography. Ultrasound contrast agents rely on the different ways in which sound waves are reflected from interfaces between substances. T ...

(CEUS) is valuable because the contrast does not diffuse into surrounding tissues, and therefore all signals are intravascular. CEUS is used to assess plaque neovascularization and ulceration. Plaque enhancement on ultrasound has been proven to correlate with neovascularization, inflammation, and inflammation, and these features are associated with symptomatic carotid plaques. Intravenous contrast is able to improve the performance of carotid ultrasound in diagnosing carotid artery stenosis. Contraindications to the ultrasound contrast include

allergy Allergies, also known as allergic diseases, are various conditions caused by hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include Allergic rhinitis, hay fever, Food allergy, food al ...

heart failure Heart failure (HF), also known as congestive heart failure (CHF), is a syndrome caused by an impairment in the heart's ability to Cardiac cycle, fill with and pump blood. Although symptoms vary based on which side of the heart is affected, HF ...

acute coronary syndrome Acute coronary syndrome (ACS) is a syndrome due to decreased blood flow in the coronary arteries such that part of the heart muscle is unable to function properly or dies. The most common symptom is centrally located pressure-like chest pain, ...

endocarditis Endocarditis is an inflammation of the inner layer of the heart, the endocardium. It usually involves the heart valves. Other structures that may be involved include the interventricular septum, the chordae tendineae, the mural endocardium, o ...

ventricular arrhythmia Arrhythmias, also known as cardiac arrhythmias, are irregularities in the heartbeat, including when it is too fast or too slow. Essentially, this is anything but normal sinus rhythm. A resting heart rate that is too fast – above 100 beats ...

, and unstable respiration.

Limitations

While ultrasound is able to assess plaque morphology, it is limited in both specificity and sensitivity in assessing lipid-rich necrotic core, plaque hemorrhage, and ulceration when compared to the gold standard. When diagnosing carotid artery stenosis, carotid ultrasound has a lower sensitivity than MRA but is more sensitive than CTA. However, both CTA and MRA have a higher specificity. A major limitation of carotid ultrasound is a high degree of inter-/intraobserver variability; however, computerized algorithms used for evaluation of the intima-media thickness (IMT), a measure of plaque morphology, have helped minimize the degree of variability. Carotid ultrasound is dependent on operator skill, and other noted areas of limitation are poor insonation angle, poor blood flow, and deep artery location. CEUS is prone to overinterpretation of vessel wall abnormalities, known as pseudoenhancement.

References

{{Vascular procedures Medical ultrasonography