1. What is Resistive Index?

Definition: Resistive Index (RI) is a dimensionless parameter used in Doppler ultrasound to assess blood flow resistance in organs.

Purpose: It helps evaluate vascular resistance in kidneys, liver, and other organs, aiding in diagnosis of conditions like renal artery stenosis.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( RI \) — Resistive Index (dimensionless)
• \( PSV \) — Peak Systolic Velocity (m/s)
• \( EDV \) — End Diastolic Velocity (m/s)

Explanation: The difference between peak and end diastolic velocities is normalized by the peak velocity to create a ratio independent of absolute velocity values.

3. Importance of Resistive Index

Details: RI is crucial for assessing vascular resistance in organs. Normal values typically range from 0.55-0.70 in kidneys, with higher values indicating increased resistance.

4. Using the Calculator

Tips: Enter PSV and EDV values obtained from Doppler ultrasound measurements. PSV must be greater than EDV for valid calculation.

5. Frequently Asked Questions (FAQ)

Q1: What is a normal resistive index value?
A: Normal RI varies by organ but is typically 0.55-0.70 in kidneys. Consult clinical guidelines for specific applications.

Q2: What does a high resistive index indicate?
A: Elevated RI (>0.70 in kidneys) suggests increased vascular resistance, possibly due to obstruction, vasoconstriction, or parenchymal disease.

Q3: What does a low resistive index mean?
A: Low RI (<0.55 in kidneys) may indicate low resistance flow, seen in hyperemia, arteriovenous malformations, or severe stenosis.

Q4: How is PSV and EDV measured?
A: Using Doppler ultrasound by placing the sample volume in the vessel of interest and measuring peak and end-diastolic velocities.

Q5: Can RI be greater than 1?
A: Yes, when EDV is negative (reverse flow), RI can exceed 1, indicating very high resistance.