resistive index
Also written as: RI — Resistive Index
A Doppler parameter calculated as (PSV - EDV)/PSV that reflects downstream vascular resistance.
Full Definition
The resistive index (RI) is a dimensionless Doppler ultrasound parameter calculated using the formula (peak systolic velocity minus end-diastolic velocity) divided by peak systolic velocity. This index provides information about downstream vascular resistance and organ perfusion, with normal values typically ranging from 0.5 to 0.7 depending on the organ system. Elevated resistive index values may indicate increased vascular resistance, while very low values can suggest arteriovenous shunting. In renal imaging, RI is particularly valuable for assessing transplant function and native kidney disease.
Usage
Usage note: Include normal reference values and clinical context when reporting.
In Context
- "The resistive index in the main renal artery was elevated at 0.85, suggesting increased downstream resistance." — Renal Doppler ultrasound report
- "Serial resistive index measurements showed progressive improvement following transplantation." — Follow-up imaging report