Comparison of B-mode, conventional color Doppler, and superb microvascular imaging for evaluating renal cortical thickness in dogs without and with chronic kidney disease.

Objective: To identify the most reliable method for assessing renal function in dogs with chronic kidney disease (CKD) by comparing renal cortical thickness (RCT) evaluated using B-mode ultrasonography, conventional color Doppler imaging (CDI), and superb microvascular imaging (SMI).

Methods: This observational study included dogs with at least 2 stable serum creatinine measurements within 30 days. Dogs were classified into CKD stages 1 to 4 based on International Renal Interest Society (IRIS) guidelines. Dogs without renal abnormalities were included in the control group. Ultrasonographic measurements of renal dimensions and RCT normalized to aortic diameter (RCT:Ao ratio) were obtained in sagittal, transverse, and dorsal planes.

Results: 85 dogs were analyzed including 36 control dogs and 49 dogs with CKD, consisting of 19 at stage 1, 19 at stage 2, 6 at stage 3, and 5 at stage 4. The RCT:Ao ratio in SMI showed the strongest correlation with IRIS stages, followed by CDI. Color Doppler imaging and SMI demonstrated superior diagnostic performance over B-mode according to receiver operating characteristic curve analysis. The optimal cutoff values for the RCT:Ao ratio in CDI and SMI were 0.58, 0.56, 0.51, and 0.44 for IRIS stages 1 to 4 in the sagittal plane and 0.62, 0.57, 0.53, and 0.45 in the transverse and dorsal planes.

Conclusions: The RCT:Ao ratio measured using CDI and SMI correlated more strongly with IRIS stages than B-mode ultrasound and showed superior diagnostic performance, suggesting improved diagnostic utility.

Clinical relevance: Color Doppler imaging may improve the clinical assessment of RCT in dogs with CKD, enhancing its utility as a reliable indicator for diagnosing and staging CKD.