resistivity index
Also written as: RI — Resistivity Index
Doppler parameter calculated from peak systolic and end-diastolic velocities to assess downstream vascular resistance and organ perfusion.
Full Definition
The resistivity index (RI) is a Doppler ultrasound parameter that reflects downstream vascular resistance and tissue perfusion characteristics. Calculated as (peak systolic velocity - end-diastolic velocity) / peak systolic velocity, the RI provides valuable information about organ function and vascular compliance. Normal RI values vary by organ system, with kidneys typically showing values below 0.70. Elevated RI may indicate increased downstream resistance due to various pathological conditions including chronic disease, acute rejection, or vascular compromise.
Usage
Usage note: Specify the organ system when reporting RI values, as normal ranges vary significantly.
In Context
- "The elevated resistivity index of 0.85 suggested compromised renal parenchymal function." — Renal ultrasound report
- "Serial resistivity index measurements showed improving organ perfusion following treatment." — Follow-up imaging study