title: Renal resistive indexes: variability in Doppler US measurement in a healthy population.
abstract: OBJECTIVE
  To determine the variability in resistive index (RI) in normal kidneys, possible causes of variability, and consequences of reporting a single value.
  
  
  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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Radiology, Duke University Medical Center, Durham, NC 27710, USA.
authors.forename: M T
authors.initials: MT
authors.lastname: Keogan
authors.forename: M A
authors.initials: MA
authors.lastname: Kliewer
authors.forename: B S
authors.initials: BS
authors.lastname: Hertzberg
authors.forename: D M
authors.initials: DM
authors.lastname: DeLong
authors.forename: R H
authors.initials: RH
authors.lastname: Tupler
authors.forename: B A
authors.initials: BA
authors.lastname: Carroll
mesh_terms: D000328:Adult; D000367:Age Factors; D000368:Aged; D000704:Analysis of Variance; D005260:Female; D006801:Humans; D007668:Kidney / Q000098:blood supply / Q000000981:diagnostic imaging*; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D012079:Renal Circulation / Q000502:physiology*; D018608:Ultrasonography, Doppler; D014655:Vascular Resistance / Q000502:physiology