IVUS Flashcards
IVUS
Intravascular ultrasound (IVUS) is a diagnostic procedure that uses sound waves to create images of the inside of blood vessels. It’s also known as endovascular ultrasound or intravascular echocardiography.
**IVUS is used to: **
Evaluate the coronary arteries that supply the heart
Assess the degree of narrowing or thickening of an artery
Reveal plaque buildup that may have been missed during an angiogram or angioplasty
Aid in diagnosing or treating a heart condition
Provide detailed anatomic information about lesion characteristics
During an IVUS, a doctor threads a catheter with a small ultrasonic transducer through an artery or vein to the target location. The transducer then generates sound waves to produce images of the blood vessels.
IVUS is an invasive procedure and comes with the risks associated with any invasive procedure.
LIMA (L)
Lumen
LIMA (I)
Intima
Tunica intima
The inner layer that’s in direct contact with blood. It’s lined with endothelial cells that help blood flow smoothly. This layer also helps regulate blood pressure, prevent blood clots, and keep toxins out of the blood
LIMA (M)
Tunica media
The middle layer that contains elastic fibers and smooth muscle. This layer helps blood flow in the proper direction, and helps blood vessels contract and relax, which is called vasoconstriction and vasodilation. It’s usually the thickest layer of the blood vessel.
LIMA (A)
Tunica adventitia
The outer layer that provides structure and support to the blood vessel. It contains nerves and tiny vessels that deliver oxygen and nutrients to cells and help remove waste.
On a grey scale
Gray-scale intravascular ultrasound (IVUS) is a diagnostic imaging technique that uses grayscale to assess the coronary arteries and their vessel walls. It’s considered the standard for in vivo imaging of the coronary arteries
In intravascular ultrasound (IVUS), grayscale is used to classify plaque based on echogenicity:
Soft plaque: Lesion echogenicity is less than the surrounding adventitia
Fibrous plaque: Intermediate echogenicity between soft plaque and calcified plaques
Calcified plaque: Higher echogenicity than other types of plaque
Gray-scale IVUS is the standard for imaging the coronary artery wall and is used to assess coronary artery disease. However, the resolution of IVUS catheters can make it difficult to visually identify plaque morphology. To address this, new post-processing methods have been developed, such as virtual histology IVUS (VH-IVUS), iMAP-IVUS, Integrated Backscatter IVUS (IB-IVUS), and Automated Differential Echogenicity (ADE).
Some limitations of grayscale IVUS include:
Acoustic shadowing: Can be caused by calcification or necrotic tissue
Qualitative assessment: It can be difficult to visually identify plaque morphology
Soft plaque:
Appears as low echogenicity (darker on the image), indicating a high lipid content and considered more vulnerable to rupture.
Fibrous plaque:
Shows intermediate echogenicity (mid-range grey), representing a more stable plaque with a higher collagen content.
Calcified plaque:
Highly echogenic (bright white), easily identifiable due to its strong ultrasound reflection and often accompanied by an acoustic shadow.
OCT
OCT stands for optical coherence tomography, a noninvasive imaging procedure that uses infrared light to create 3D pictures of the inside of tissues and organs:
How it works
OCT uses a beam of light to create cross-sectional images of tissue structure. The images are made by a computer linked to the light source.
What it’s used for
OCT is most commonly used to image the retina and optic nerve in the eye. It can help diagnose and manage eye diseases like:
Diabetes-related retinopathy
Glaucoma
Age-related macular degeneration
Retinal tear
Retinal detachment
Central serous retinopathy
Macular hole
Macular pucker
Macular edema
Why it’s noninvasive
OCT is noninvasive, meaning it doesn’t touch or enter the eye. The infrared light used in standard OCT is invisible, making it more comfortable than imaging that uses visible light.
OCT is analogous to ultrasound imaging, but it uses light instead of sound.
echogenic
In the context of intravascular ultrasound (IVUS), “echogenic” refers to tissue that produces strong echoes on the ultrasound image, indicating a tissue type that readily reflects sound waves, typically signifying a calcified plaque within a blood vessel wall, which appears bright and distinct on the IVUS image compared to softer, less echogenic tissues like lipid-rich plaque.
Key points about echogenicity in IVUS:
High echogenicity:
Indicates dense calcified plaque, which appears bright on the image and can cast an acoustic shadow behind it, obscuring the underlying tissue.
Low echogenicity:
Represents softer tissue like lipid-rich plaque, appearing darker on the IVUS image.
Importance in plaque characterization:
By analyzing the echogenicity of different plaque components, clinicians can better assess the vulnerability of a plaque and guide treatment decisions.
echolucent
In the context of intravascular ultrasound (IVUS), “echolucent” refers to an area within a plaque that appears dark or low-echoing on the image, indicating a soft, lipid-rich tissue that does not reflect ultrasound waves as strongly as denser plaque components, often considered a sign of a vulnerable plaque with a high risk of rupture; essentially, it means a “low-echo” zone within the plaque on the IVUS image.
Key points about echolucent areas on IVUS:
Appearance:
On an IVUS image, echolucent areas appear as dark or low-intensity regions within the plaque, contrasting with brighter, more echogenic areas like calcified plaque.
Interpretation:
Echolucent zones are often associated with lipid-rich necrotic cores within a plaque, which are considered high-risk features due to their potential for rupture.
Clinical significance:
Identifying echolucent plaques can help guide treatment decisions, particularly in patients with coronary artery disease, as it may indicate a need for more aggressive management strategies to stabilize vulnerable plaques.
echobright
In the context of Intravascular Ultrasound (IVUS), “echobright” refers to areas within an image that appear bright or highly reflective on the ultrasound scan, indicating the presence of dense tissue like calcium deposits within a plaque, which strongly reflect the ultrasound waves, appearing as bright spots on the image compared to softer, less reflective plaque components like lipid-rich necrotic cores that appear darker.
Key points about echobright in IVUS:
Interpretation:
Bright areas on an IVUS image usually represent calcified plaque, which is considered “echobright” because it strongly reflects the ultrasound waves.
Contrast with echolucent:
Conversely, areas that appear dark on an IVUS image are called “echolucent” and often indicate the presence of soft, lipid-rich plaque material.
Clinical significance:
Identifying echobright areas on IVUS is important for assessing the composition of plaque and guiding treatment decisions, particularly during coronary interventions where understanding the presence of calcium can impact stent placement and deployment strategies.
tomographic view
A “tomographic view” in the context of intravascular ultrasound (IVUS) refers to a cross-sectional, 360-degree image of the blood vessel lumen and its walls, allowing for a detailed analysis of the vessel structure and plaque burden, unlike the 2D projection seen with angiography; essentially, it provides a “slice” of the vessel at a specific point, enabling a more comprehensive understanding of the vessel anatomy than just a luminal view.
Key points about IVUS tomographic view:
Detailed analysis:
Unlike angiography which only shows the lumen, IVUS provides a tomographic view, allowing for precise measurements of lumen size, plaque thickness, and vessel wall composition.
Cross-sectional imaging:
By rotating the ultrasound probe within the vessel, IVUS captures a cross-sectional image of the vessel at each point, providing a complete picture of the vessel wall structure.
Plaque assessment:
This tomographic view is crucial for accurately assessing the extent and nature of plaque within the vessel, which can be important for guiding treatment decisions like stent placement.
iFR
The instantaneous wave-free ratio (iFR) is a recently developed physiological index used to assess the severity of stenosis. The iFR is calculated by measuring the resting pressure gradient across a coronary lesion during the portion of diastole when microvascular resistance is low and stable.
iFR stands for instantaneous wave-free ratio, a medical index used to assess the severity of coronary artery stenosis. It’s a non-hyperaemic pressure index that’s measured during the wave-free period of diastole.
iFR is a diagnostic tool used during cardiac catheterization (angiography). It’s performed by placing invasive coronary pressure wires in the coronary arteries being assessed.
iFR has been shown to have similar diagnostic accuracy to fractional flow reserve (FFR), another index used to assess coronary artery stenosis. However, iFR has some advantages over FFR, including:
It can be obtained at rest without the use of vasodilators
It’s faster to perform
It has fewer adverse events
iFR and FFR can be used together in a hybrid approach to assess coronary artery stenosis. In this approach, iFR values between 0.86 and 0.93 are considered to be in a “grey-zone” and are confirmed by FFR.
FFR
FFR in medical terms stands for “Fractional Flow Reserve,” which is a measurement used during a cardiac catheterization to assess how well blood can flow through a narrowed coronary artery, essentially determining the functional significance of a blockage in the heart’s arteries and helping doctors decide if intervention is necessary to open it up; a lower FFR value indicates a more significant blockage impacting blood flow.
Key points about FFR:
Function:
It compares the blood pressure before and after a narrowed section of a coronary artery, calculating a ratio to determine the severity of the blockage in terms of blood flow impact.
Procedure:
A special pressure wire is inserted into the coronary artery during a cardiac catheterization to measure pressures at different points, allowing for FFR calculation.
Interpretation:
An FFR value below a certain threshold (usually around 0.75) indicates that the blockage is causing significant blood flow restriction and may warrant treatment like angioplasty or stent placement.
Where is plaque at
between the intima and media where plaque developes
depth penetration of vessel ultrasound
4-8 mm
This is one big advantage over OCT
This is why we can use IVUS for pheripherel imaging of large veins like the iliac or even the aorta for endovascular repair
