Estimation of split renal function using different volumetric methods: inter- and intraindividual comparison between MRI and CT.

PURPOSE: This study aims to determine whether contrast-enhanced (CE)-magnetic resonance imaging (MRI) is comparable to CE-computed tomography (CT) for estimation of split renal function (SRF). For this purpose, two different kidney volumetry methods, the renal cortex volumetry (RCV) and modified ellipsoid volume (MELV), are compared for both acquisition types (CT vs. MRI) with regard to accuracy and reliability, subsequently referred to as RCVCT /RCVMRI and MELVCT /MELVMRI .

METHODS: This retrospective study included 29 patients (18 men and 11 women; mean age 62.8 ± 12.4 years) who underwent CE-MRI and CE-CT of the abdomen within a period of 3 months. Two independent readers (R1/R2) performed RCV and MELV in all datasets with corresponding semiautomated software tools. RCV was performed with datasets in the arterial phase and MELV in the venous phase. Statistics were calculated using one-way ANOVA, two-tailed Student's t test, Pearson´s correlation, and Bland-Altman plots with p ≤ 0.05 being considered statistically significant.

RESULTS: In all datasets, SRF was almost identical for both volumetry methods with a mean difference of < 1%. Bland-Altman analysis comparing RCV in CT and MRI showed very good agreement for R1/R2. Interreader agreement was strong for RCVCT and good for RCVMRI (r = 0.89; r = 0.69). MELVCT/MRI interreader agreement was only moderate (r = 0.54; r = 0.50) with a high range of values. Intrareader agreement was excellent for all measurements, except MELVMRI which showed a high mean bias and range of values (RCVCT : r = 0.93, RCVMRI : r = 0.98, MELVCT : r = 0.89, MELVMRI : r = 0.54).

CONCLUSION: Renal volumetric estimates of SRF are almost as accurate and reliable with CE-MRI as with CE-CT using RCV method. In distinction, the calculation of SRF using MELV was inferior to RCV with respect to accuracy and reliability. Thus, RCV method is recommended to estimate SRF, primarily using CT datasets. However, RCV with MRI datasets for kidney volumetry allows for comparable accuracy and reliability while sparing patients and healthy donors of unnecessary radiation exposure.