Right ICA/CCA PSV Ratio

Blood velocity in the carotids depends on more than the artery's width. A strong heart, high blood pressure, anemia, an overactive thyroid, or a blocked carotid on the other side all push blood faster through a perfectly open vessel, and a young athlete's carotids can read high for no reason at all. Dividing the internal carotid's peak velocity by the common carotid's, measured in a normal segment just below the division, cancels that out: a narrowing raises the internal carotid number alone, so the ratio climbs, while a fast circulation raises both and the ratio stays put.

The bands are the 2003 Society of Radiologists in Ultrasound consensus: under 2.0 is a normal vessel or one narrowed by less than half, 2.0 to 4.0 is 50 to 69 percent, and over 4.0 is 70 percent or more. The 2023 Intersocietal Accreditation Commission update kept the ratio's line at 2.0 while loosening the velocity line, which makes the ratio the steadier of the two criteria. The report's stenosis grade is the reading physician's call across the ratio, the velocities and the image.