Resistive Index Calculator for Doppler Ultrasound

More about the Doppler Resistive Index (RI) Calculator:

The Resistive Index (RI), also known as the Pourcelot index, is a key Doppler ultrasound parameter used to assess vascular resistance in arterial beds. It is calculated using the formula:

RI = (Peak Systolic Velocity – End Diastolic Velocity) / Peak Systolic Velocity

This dimensionless value provides crucial insight into the downstream resistance of blood flow, making it an essential part of evaluating renal, hepatic, testicular, and transplant vascular integrity. The RI is especially valuable because it is noninvasive, easily obtainable, and reproducible, making it widely used in clinical practice.

Renal Applications

The most common clinical use of RI is in renal Doppler ultrasound, where it helps assess intrarenal arterial flow and resistance. In native kidneys, an RI value less than 0.7 is generally considered normal, while values above this threshold may suggest intrinsic renal disease, such as acute tubular necrosis, glomerulonephritis, or obstructive uropathy. In renal transplants, elevated RI values can indicate graft dysfunction due to rejection, obstruction, or vascular complications.

Hepatic and Splenic Vascular Assessment

In the liver and spleen, the RI can aid in evaluating conditions such as portal hypertension, hepatic artery stenosis, or venous outflow obstruction. A high hepatic artery RI in a transplant setting may suggest graft dysfunction or hepatic artery thrombosis.

Testicular and Ovarian Evaluation

In scrotal Doppler ultrasound, a low or absent diastolic flow with a high RI may indicate testicular torsion or infarction. Similarly, in ovarian Doppler studies, abnormal RI values can suggest torsion, infarction, or neoplasms altering the blood supply.

Clinical Relevance and Limitations

• Advantages: RI is noninvasive, reproducible, and easy to calculate using spectral Doppler data. It provides a quick snapshot of vascular health and can be trended over time.
• Limitations: The RI is influenced by factors such as heart rate, age, vascular compliance, and systemic hemodynamic conditions. It should always be interpreted in conjunction with the clinical context and other imaging findings.

How the Calculator Helps

Our Doppler RI calculator allows quick and accurate calculation using input from spectral Doppler waveforms. It eliminates manual error and provides real-time, evidence-based guidance for interpreting vascular resistance in different organ systems.

Whether used in nephrology, transplant follow-up, reproductive health, or hepatology, the Resistive Index remains a cornerstone of functional Doppler ultrasound evaluation. Integrating this calculator into clinical workflows promotes efficiency, diagnostic confidence, and improved patient care.