Measurement of renal volume using respiratory-gated MRI in subjects without known kidney disease: intraobserver, interobserver, and interstudy reproducibility

OBJECTIVE: Since renal volume is to be considered in managing renal diseases, a reproducible technique is needed. Our aim was to estimate intraobserver, interobserver, and interstudy reproducibility of renal volume measurement in subjects without known kidney disease using magnetic resonance (MR) imaging. MATERIALS AND METHODS: We studied 20 patients (age range 33-82 years) without known renal disease using 1.5-T MR imaging with a respiratory-gated two-dimensional coronal balanced steady state free precession sequence. Each patient repeated the study after 1h. Two readers independently segmented the area of both kidneys of the first study, subtracting cysts. After 1 week, the first reader segmented the second study and repeated the segmentation of the first study. The volume of each kidney was obtained by multiplying the renal area on each slice by the slice thickness and summing all the partial volumes. Reproducibility was assessed by Bland-Altman and Wilcoxon statistics. The coefficient of repeatability (CoR) was summed to the absolute value of bias; the ratio between this sum and the mean of the two data sets was used as a measure of variability while its complement to 100% was used as a measure of reproducibility. RESULTS: Acquisition time was 2-3min. Segmentation time was 20-25min. Intraobserver variability results in a CoR of 7ml and in a reproducibility of 95%, interobserver variability 8.8-9.8ml and 87-88%, interstudy variability 9.8-10.6ml and 91-93%, respectively. Considering both the effect of observer and the repetition of the study, the reproducibility was 83-87%. CONCLUSION: Renal volume measurement by MR imaging is highly reproducible.