DTI of the kidney in children: comparison between normal kidneys and those with ureteropelvic junction (UPJ) obstruction

Objective To compare renal diffusion tensor imaging (DTI) parameters in patients with or without ureteropelvic junction (UPJ) obstruction. Methods Patients that underwent functional MR urography (MRU) with renal DTI were retrospectively selected. Kidneys deemed normal on T2-weighted images and functional parameters were used as controls and compared to those kidneys with morphologic and functional findings of UPJ obstruction. DTI included a 20-direction DTI with b values of b = 0 s/mm(2) and b = 400 s/mm(2). Diffusion Toolkit was used for analysis and segmentation. TrackVis was used to draw regions of interest (ROI) covering the entire volume of the renal parenchyma, excluding the collecting system. Fibers were reconstructed using a deterministic fiber tracking algorithm. Whole kidney ROI-based analysis was performed to obtain cortico-medullary measurements (FA, ADC and track length) for each kidney. T tests were performed to compare means and statistical significance was defined at p < 0.05. Results 118 normal kidneys from 102 patients (median age 7 years, IQR 6-15 years; 58 males and 44 females) were compared to 22 kidneys from 16 patients (median age 13 years, IQR 3-15 years; 9 males and 7 females) with UPJ obstruction. Mean FA values were significantly lower (0.31 +/- 0.07; n = 22) in kidneys with UPJ obstruction than normal kidneys (0.40 +/- 0.08; n = 118) (p < 0.001). ADC was marginally significantly increased (p = 0.01) and track length was not significantly different (p = 0.24). Conclusion Our results suggest that DTI-derived metrics including FA and ADC are potential biomarkers to differentiate kidneys with UPJ obstruction and assess renal parenchymal damage.