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.