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Renal resistive indexes: variability in Doppler US measurement in a healthy population
M T Keogan1, M A Kliewer, B S Hertzberg
1Department of Radiology, Duke University Medical Center, Durham, NC 27710, USA.
Purpose:
To determine the variability in resistive index (RI) in normal kidneys, possible causes of variability, and consequences of reporting a single value.
Materials And Methods:
Doppler ultrasound RI measurements were obtained in the upper, middle, and lower regions of 118 kidneys in 58 healthy subjects (aged 24-70 years; 35 women, 23 men) who subsequently underwent angiography. The effects of sampling a particular parenchymal region, vascular territory, or kidney were assessed.
Results:
Kidney region, vascular territory, and right versus left kidney had no consistently significant effect (P < or = .05) on RI. Age had a statistically significant effect. RI readings were highly correlated with each other both within a subject and within a kidney. The probability that a single RI value would exceed 0.70 in a healthy 45-year-old subject was 6%; this decreased to 3% when three readings were averaged.
Conclusion:
The variability of RI measurements in a kidney suggests that a number of RI readings should be averaged before a single representative value is reported.