1. What is Ultrasound Resistive Index?

Definition: Resistive Index (RI) is a Doppler ultrasound measurement that assesses blood flow resistance in organs and vascular systems.

Purpose: It helps evaluate vascular resistance in kidneys, liver, and other organs, aiding in diagnosis of various medical conditions.

2. How Does the Calculator Work?

The calculator uses the formula:

Where:

• \( RI \) — Resistive Index (dimensionless)
• \( S \) — Peak systolic velocity (cm/s)
• \( D \) — End-diastolic velocity (cm/s)

Explanation: The difference between peak systolic and end-diastolic velocities is divided by the peak systolic velocity.

3. Clinical Significance of Resistive Index

Details: RI values help assess vascular resistance and organ perfusion. Normal renal RI is typically 0.55-0.70. Elevated values may indicate renal disease or obstruction.

4. Using the Calculator

Tips: Enter the peak systolic and end-diastolic velocities from Doppler ultrasound measurements. Systolic must be greater than diastolic.

5. Frequently Asked Questions (FAQ)

Q1: What is a normal resistive index range?
A: Normal RI varies by organ: kidneys (0.55-0.70), liver (0.55-0.70), and other vascular beds have different normal ranges.

Q2: What does a high resistive index indicate?
A: High RI suggests increased vascular resistance, seen in conditions like renal artery stenosis, obstruction, or parenchymal disease.

Q3: Can RI be greater than 1?
A: Yes, when diastolic flow is reversed (negative D value), RI can exceed 1, indicating very high resistance.

Q4: How is RI different from pulsatility index?
A: RI uses only systolic and diastolic velocities, while pulsatility index incorporates mean velocity in its calculation.

Q5: What factors can affect RI measurements?
A: Patient age, heart rate, blood pressure, and technical factors like Doppler angle can influence RI values.