The ICA/CCA Velocity Ratio is a specialized measurement used in medical imaging to assess the health of arteries in the neck. This ratio provides insights into blood flow dynamics, helping healthcare professionals identify potential blockages or narrowings within these crucial vessels.
What Are ICA and CCA?
The common carotid artery (CCA) is a major blood vessel in the neck that branches from the aorta, carrying oxygenated blood from the heart to the head and brain. As it ascends, the CCA divides into two primary branches: the internal carotid artery (ICA) and the external carotid artery. The ICA supplies blood to the brain and eyes, making its unobstructed flow important for neurological function.
The measurement used in this ratio is the Peak Systolic Velocity (PSV), which represents the highest speed of blood flow during the heart’s contraction phase (systole). Doppler ultrasound, a non-invasive imaging technique, measures these velocities by sending sound waves into the arteries and detecting changes in their frequency as they reflect off moving red blood cells. These PSV readings from both the ICA and CCA are fundamental for calculating the ratio.
Why the Ratio Matters
The ICA/CCA Velocity Ratio serves as an important diagnostic tool, primarily for detecting and quantifying carotid artery stenosis, which is a narrowing of the carotid arteries. This narrowing often results from atherosclerosis, a condition where plaque builds up inside the artery walls. Significant stenosis can impede blood flow to the brain, increasing the risk of transient ischemic attacks (TIAs) or strokes.
Measuring this ratio helps overcome limitations of absolute velocity readings, as ratios are less affected by general circulatory conditions, such as a patient’s heart function or blood pressure. By comparing the velocity in the ICA to that in the CCA, the ratio provides a standardized and reliable indicator of localized blood flow acceleration, which is a key sign of arterial narrowing.
Calculating the Ratio
Calculating the ICA/CCA Velocity Ratio involves a straightforward formula that uses Peak Systolic Velocity (PSV) measurements from both arteries: ICA/CCA Velocity Ratio = PSVICA / PSVCCA. A medical professional uses Doppler ultrasound to obtain these values, which provides real-time images and blood flow information.
During the ultrasound examination, the PSV for the ICA is measured at the site of the highest velocity within any identified narrowing. The PSV for the CCA is taken from the distal common carotid artery, two to four centimeters proximal to the carotid bifurcation, where the CCA splits into the ICA and external carotid artery. This specific measurement location for the CCA helps ensure consistency and accuracy in the ratio calculation, providing a reliable baseline for comparison.
Both PSV measurements must be obtained from the same individual during the same examination to maintain consistency and allow for meaningful comparison. For example, if the PSV in the ICA is 250 cm/s and the PSV in the CCA is 80 cm/s, the ratio is 250 / 80 = 3.125. This calculated value then guides the interpretation of potential carotid artery health.
Interpreting Your Results
Interpreting the calculated ICA/CCA Velocity Ratio provides valuable information about the degree of narrowing, or stenosis, in the internal carotid artery. A normal ICA/CCA PSV ratio is considered less than 2.0, indicating healthy blood flow without significant blockages. In these cases, the ICA PSV is below 125 cm/s, and there is no visible plaque or thickening of the artery wall on ultrasound.
As the ratio increases, it suggests a greater degree of stenosis. For example, a ratio between 2.0 and 4.0 indicates moderate narrowing, in the range of 50% to 69% stenosis. In such cases, the ICA PSV falls between 125 cm/s and 230 cm/s. A ratio greater than 4.0, particularly if the ICA PSV exceeds 230 cm/s, points to severe stenosis, 70% or more. This level of narrowing signifies a significant impediment to blood flow, which may require further medical evaluation and intervention.
In cases of near total occlusion of the ICA, the velocity parameters can be variable, either very high or very low, or even undetectable. The diagnosis in these severe instances is often confirmed by observing a markedly narrowed lumen with “trickle flow” on color Doppler ultrasound. The precise interpretation of the ratio, along with other clinical findings and imaging details, helps healthcare providers determine the appropriate course of action for patient care.