Determination of the inter-observer and inter-scanner variability in the measurement of the renal resistive and renal pulsatility indices in dogs

Renal Resistive Index (RRI) and Renal Pulsatility Index (RPI) are currently used in the diagnosis of ureteral obstruction, early diagnosis and follow-up of acute kidney injury, assessment of chronic kidney disease, and evaluation of transplanted kidneys. However, their inter-observer and inter-scanner variability has not been investigated in dogs, limiting the accuracy and clinical applicability of these indices. The objectives of this cross-sectional observational prospective study were to assess the inter-observer and inter-scanner variability of RRI and RPI and to determine whether operator experience influences measurement accuracy. RRI and RPI were measured in the left kidney of 10 client-owned dogs by four different operators with varying levels of experience, using two different ultrasound scanners. The intraclass correlation coefficient (ICC) between the two ultrasound scanners for both RRI and RPI were good to excellent in all four observers (ICC > 0.75 and p < 0.05). Similarly, a good to excellent correlation coefficient was observed between the measurements of the four operators for both indices across each ultrasound scanner (ICC > 0.75 and p < 0.05). These findings indicate that RRI and RPI are feasible and reproducible measurements with good inter-scanner and inter-observer agreement, regardless of operator experience. However, achieving high reproducibility requires adequate training and the use of a standardized protocol with strict but adaptable settings tailored to each patient's characteristics.