Ultrasound technology is a non-invasive method used to detect and evaluate plaque buildup in arteries. This process, known as atherosclerosis, involves the accumulation of fatty deposits, cholesterol, and other substances within the artery walls. As these deposits grow, they form plaques that narrow the vessel and restrict blood flow. Ultrasound provides a safe, real-time method for visualizing these deposits and monitoring arterial health.
The Science of Visualizing Arterial Plaque
Ultrasound utilizes high-frequency sound waves that travel into the body and bounce back when they encounter different tissues, a process called echoing. These echoes are then processed by a computer to create a two-dimensional image of the artery and the surrounding structures. This method is called Brightness-mode, or B-mode, imaging, and it allows for the structural visualization of the arterial wall and any plaque present.
Plaque composition is determined by its echogenicity, or how brightly it appears on the B-mode image. Plaques containing soft lipids and blood appear dark (echolucent), while those with significant calcium deposits and dense fibrous tissue appear bright (echogenic).
Doppler ultrasound measures the speed and direction of blood flow by tracking the frequency shift of sound waves returning from moving red blood cells. When a plaque narrows the artery, the blood must accelerate to squeeze through the constricted area, creating higher-than-normal blood flow velocities and turbulence. The velocity measurements directly correlate with the severity of the narrowing, providing a functional measurement. Together, B-mode and Doppler imaging offer a comprehensive view of both the plaque’s structure and its impact on circulation.
Specific Ultrasound Tests Used for Diagnosis
The most common application for plaque detection is the Carotid Duplex Ultrasound, which focuses on the arteries in the neck leading to the brain. The carotid arteries are examined because plaque found here can be a marker for generalized atherosclerosis and is a direct risk factor for stroke.
The Carotid Duplex uses B-mode to visualize the plaque and Doppler to measure blood flow velocities. The images also allow clinicians to measure the thickness of the inner two layers of the artery wall, known as the Intima-Media Thickness (IMT). Increased IMT is one of the earliest signs of subclinical atherosclerosis.
Another routine procedure is Peripheral Artery Ultrasound, used to examine the arteries in the legs. This test diagnoses Peripheral Artery Disease (PAD), where plaque buildup restricts blood flow to the limbs. A specialized technique called Intravascular Ultrasound (IVUS) is used during invasive procedures like catheterizations. IVUS involves threading a tiny ultrasound probe inside the artery itself to obtain extremely high-resolution, cross-sectional images.
Understanding the Clinical Significance of the Scan
Clinical significance focuses on two measurements: the degree of stenosis and plaque characterization. The Degree of Stenosis refers to the percentage of arterial narrowing caused by the plaque, a measurement often determined by Doppler blood flow velocities. High-grade stenosis, defined as greater than 50% narrowing, significantly increases the risk of stroke.
Plaque Characterization distinguishes between stable and vulnerable plaques. Stable plaques are dense, highly calcified, and appear bright (echogenic) on the B-mode image. Vulnerable plaques are rich in soft lipids, contain intraplaque hemorrhage, and appear darker (echolucent or heterogeneous). Vulnerable plaques pose a greater risk because they are more likely to rupture, leading to a blood clot that can cause a heart attack or stroke.
Findings guide treatment decisions. High-grade stenosis or a vulnerable plaque may lead to intensive medical therapy, such as higher doses of cholesterol-lowering medication, or the need for a revascularization procedure. For patients with subclinical disease, the detection of increased IMT requires risk factor modification to prevent disease progression.