Intravascular ultrasound (IVUS) is a medical imaging technique using a specially designed catheter with a miniaturized ultrasound probe. This device allows clinicians to see inside blood vessels, with the catheter attached to a console that processes sound waves into real-time images. The technology applies high-frequency sound waves that bounce off the blood vessel walls, generating echoes that a computer translates into cross-sectional pictures. It is frequently used to examine the coronary arteries, which supply blood to the heart.
Purpose of IVUS Imaging
The primary purpose of IVUS imaging is to provide detailed anatomical information about a blood vessel that cannot be obtained through methods like angiography. While angiography produces a two-dimensional shadow image of the vessel’s open pathway, IVUS offers a 360-degree, cross-sectional view from inside the artery for a comprehensive assessment of its structure.
This interior view helps physicians accurately measure the vessel’s dimensions and quantify the amount of plaque buildup, known as plaque burden. This detailed imaging is used to guide treatment decisions for patients with coronary artery disease. It helps clinicians characterize the type of plaque present, assess the severity of a blockage, and determine the most appropriate intervention.
The IVUS Imaging Procedure
The IVUS procedure is performed in a cardiac catheterization laboratory. It is an invasive test, often conducted at the same time as other procedures like cardiac catheterization or angioplasty. Before the procedure, patients receive instructions regarding fasting and their regular medications. The patient is given a local anesthetic at the catheter insertion site and often a mild sedative to ensure they remain comfortable.
An interventional cardiologist begins by making a small incision, usually in the groin or wrist, and inserting a hollow plastic tube called a sheath into a blood vessel. The thin, flexible IVUS catheter is then inserted through this sheath. Guided by imaging like fluoroscopy (a type of X-ray), the cardiologist navigates the catheter through the blood vessel to the target coronary artery. The patient will not feel the catheter moving through their blood vessels.
Once the catheter’s tip is positioned just past the artery segment to be examined, the imaging process begins. The ultrasound probe emits sound waves as it is pulled back through the vessel by a motorized device. This device retracts the catheter at a controlled speed, such as 0.5 or 1.0 mm per second, to capture a continuous sequence of images.
Understanding IVUS Image Findings
The images produced by an IVUS system provide a detailed, cross-sectional view of the artery. These images allow physicians to clearly distinguish the different layers of the artery wall. The tunica media, a layer of smooth muscle, appears dark on the grayscale image because it does not reflect ultrasound waves, making it an easily identifiable landmark.
One of the main uses for these images is the identification and characterization of atherosclerotic plaque. The images reveal the extent of plaque buildup and provide clues about its composition, such as whether it is soft, fibrous, or contains hard, calcified deposits. This level of detail influences the choice of treatment strategy, as identifying heavily calcified plaque may prompt a different approach to preparing the artery for a stent.
When IVUS is used to evaluate a stent, the images show how well the metal struts of the stent are pressed against the vessel wall, a factor known as apposition. It also confirms whether the stent has been adequately expanded to open the artery. Physicians can also identify issues that may not be visible on an angiogram, such as small tears in the artery wall, called dissections, or the presence of blood clots.
Key Uses of IVUS in Medical Practice
In clinical practice, IVUS is frequently used to guide percutaneous coronary interventions (PCI), the procedures used to open blocked coronary arteries. Its detailed imaging helps cardiologists select the appropriately sized balloon or stent for a specific lesion. This precision is valuable for achieving a good outcome and reducing the chances of complications like artery re-narrowing (restenosis) or stent thrombosis.
The technology is also used for assessing lesions that appear ambiguous on a standard angiogram. An angiogram may not clearly show the severity of a blockage, and IVUS can provide the definitive measurements needed to decide whether an intervention is necessary. It is also a primary tool for investigating cases of in-stent restenosis, helping to determine why a previously placed stent has failed.
Beyond the coronary arteries, IVUS is also applied in peripheral artery interventions, such as those in the legs. Furthermore, IVUS plays a role in clinical research, where it is used to study the progression and regression of atherosclerosis over time, offering insights into how the disease develops and responds to therapy.