<p><strong>OBJECTIVE: </strong>To compare renal diffusion tensor imaging (DTI) parameters in patients with or without ureteropelvic junction (UPJ) obstruction.</p>

<p><strong>METHODS: </strong>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&nbsp;s/mm and b = 400&nbsp;s/mm. 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 &lt; 0.05.</p>

<p><strong>RESULTS: </strong>118 normal kidneys from 102 patients (median age 7&nbsp;years, IQR 6-15&nbsp;years; 58 males and 44 females) were compared to 22 kidneys from 16 patients (median age 13&nbsp;years, IQR 3-15&nbsp;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 &lt; 0.001). ADC was marginally significantly increased (p = 0.01) and track length was not significantly different (p = 0.24).</p>

<p><strong>CONCLUSION: </strong>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.</p>

<p><strong>PURPOSE: </strong>To describe the morphology and function of duplicated collecting systems in pediatric patients undergoing functional MR urography (fMRU).</p>

<p><strong>METHODS: </strong>This is a HIPAA compliant IRB approved retrospective study of all patients with duplicated renal collecting systems undergoing fMRU at our institution between 2010 and 2017. Two pediatric radiologists evaluated the studies to determine the presence, morphology and function of duplicated collecting systems using both T2-weighted and dynamic post-contrast fat saturated T1-weighted images. Assessed morphologic features included pelvic and calyceal dilation, partial or complete ureteral duplication, ureteral dilation, ectopic ureteral insertion and ureteroceles. Functional analysis was carried out per moiety.</p>

<p><strong>RESULTS: </strong>A total of 86 examinations (63 girls; 23 boys), median age 2.6 years (Standard Deviation 6.4 years, interquartile range: 0.4-10.3 years) and 107 kidneys (39 right; 30 left and 19 bilateral), which yielded 214 evaluable moieties, were included in the final sample. One hundred and sixty-three (76.1%) of the moieties had normal morphological features and normal functional results (average calyceal transit time and renal transit time of 2 min 28 s and 3 min 16 s, respectively). The remaining 51 moieties (23.8%) were hypoplastic or dysplastic. Seventy-seven (35.9%) had pelvic and calyceal dilation. Slightly more than half of the kidneys had complete ureteral duplication (60/107; 56%); 50 (50/107, 46.7%) had ectopic ureters (23 intra- and 27 extravesical) and 9 (9/107, 8.4%) had ureteroceles.</p>

<p><strong>CONCLUSION: </strong>fMRU provides comprehensive information regarding the morphology and function of duplicated renal collecting systems in children. In particular, fMRU is useful for assessing barely or non-functioning renal poles and ectopic ureters.</p>