Hepatic Artery Resistive Index Calculation and Clinical Applications

Understanding the Resistive Index Formula

The American College of Radiology recommends calculating the hepatic artery resistive index (RI) using the formula: RI = (Peak Systolic Velocity - End-Diastolic Velocity) / Peak Systolic Velocity, which requires Peak Systolic Velocity (PSV) and End-Diastolic Velocity (EDV) measurements 1, 2
The calculation of RI is based on the maximum velocity of blood flow during systole (PSV) and the minimum velocity of blood flow at the end of diastole (EDV) 1

Normal RI values typically range from 0.55 to 0.7 in healthy adults, according to the Journal of Hepatology and the American College of Radiology 3, 4
Elevated RI values (>0.8) may indicate poor prognosis in patients, and is a negative prognostic indicator for response to revascularization in renal disease, as stated by the American College of Radiology 1
Decreased RI values (<0.55) may suggest arteriovenous shunting, as reported by the Journal of Hepatology 3
In hereditary hemorrhagic telangiectasia, RI <0.55 is one criterion used in grading liver vascular malformations, according to the Journal of Hepatology 3

To accurately measure the hepatic artery resistive index, the American College of Radiology recommends taking multiple measurements (at least 3) and averaging the results for greater accuracy 2
The angle of insonation should be kept as close to 0° as possible, and measurements should be taken during suspended respiration when possible, as stated by the American College of Radiology 1, 2

The hepatic artery RI provides valuable diagnostic information, and its values should be interpreted in the context of the patient's clinical condition and other imaging findings, as recommended by the American College of Radiology 6, 2

Patient factors that can affect measurements include age and vascular compliance, atherosclerosis, hypertension, and heart rate, as reported by the American College of Radiology 5