Reliability of total renal volume computation in polycystic kidney disease from magnetic resonance imaging

Rationale and Objectives: Total renal volume (TRV) is an important quantitative indicator of the progression of autosomal dominant polycystic kidney disease (ADPKD). The Consortium for Radiologic Imaging Studies of Polycystic Kidney Disease proposes a method for TRV computation based on manual tracing and geometric modeling. Alternative approaches for TRV computation are represented by the application of advanced image processing techniques. In this study we aim to compare TRV estimates derived from these two different approaches. Materials and Methods: The nearly-automated technique for the analysis of MR images was tested on 30 ADPKD patients. TRV was computed from both axial (KVax) and coronal (KVcor) acquisitions, and compared to measurements based on geometric modeling (KVap) by linear regression and Bland Altman analysis. In addition, to assess reproducibility, intra-observer and inter-observer variabilities were computed. Results: Linear regression analysis between KVax and KVcor resulted in an excellent correlation (KVax=1KVcor-0.78; r2=0.997). Bland-Altman analysis showed a negligible bias and narrow limits of agreement (bias:-11.7ml; SD:54.3ml). Similar results were obtained by comparison of volumes obtained applying the nearly-automated method and the one based on geometric modeling (y=0.98x+75.9; r2=0.99); bias:-53.7ml; SD: 108.1ml). Importantly, geometric modeling doesn’t provide reliable TRV estimates in huge kidney affected by regional deformation. Intra- and inter-observer variability resulted in very small percentage error less than 2%. Conclusion: The results of this study provide the feasibility of using a nearly-automated approach for accurate and fast evaluation of TRV also in markedly enlarged ADPKD kidneys including exophytic cysts.