Enter the Peak Systolic Velocity and End Diastolic Velocity into the calculator to determine the Doppler Resistance Index. This calculator can also evaluate any of the variables given the others are known.

Doppler Resistance Index Formula

RI = (PSV - EDV) / PSV


  • RI is the Resistance Index
  • PSV is the Peak Systolic Velocity (cm/s)
  • EDV is the End Diastolic Velocity (cm/s)

To calculate the Doppler Resistance Index, subtract the End Diastolic Velocity from the Peak Systolic Velocity. Then, divide the result by the Peak Systolic Velocity. The result is the Resistance Index, which is a measure of the resistance to blood flow caused by changes in the blood vessel.

What is a Doppler Resistance Index?

The Doppler Resistance Index (RI) is a measure used in medical ultrasound imaging to quantify the resistance to blood flow in various organs and vessels. It is calculated based on the peak systolic and end diastolic velocities of the blood flow. A higher RI indicates greater resistance, which can be indicative of various pathological conditions such as renal artery stenosis or liver cirrhosis. It is a valuable tool in the diagnosis and monitoring of these and other conditions.

How to Calculate Doppler Resistance Index?

The following steps outline how to calculate the Doppler Resistance Index (RI).

  1. First, determine the Peak Systolic Velocity (PSV) in cm/s.
  2. Next, determine the End Diastolic Velocity (EDV) in cm/s.
  3. Next, gather the formula from above = RI = (PSV – EDV) / PSV.
  4. Finally, calculate the Doppler Resistance Index (RI).
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Peak Systolic Velocity (PSV) = 120 cm/s

End Diastolic Velocity (EDV) = 80 cm/s