Background Previous studies have challenged the concept of contrast material-induced acute kidney injury (AKI) in adults; however, limited data exist for children and adolescents. Purpose To calculate the incidence and determine the risks of AKI in patients who received intravenous iodinated contrast media for CT. Materials and Methods This retrospective study was performed at a children's hospital from January 2008 to January 2018 and included patients aged 0-17 years in whom serum creatinine levels were measured within 48 hours before and after CT with or without contrast media. The incidence of AKI was measured according to the AKI Network guidelines. A subgroup analysis with propensity score matching of cases with control patients was performed. Differences before and after stratification based on estimated glomerular filtration rate (eGFR) were explored. Adjusted risk models were developed using log-binomial generalized estimating equations to estimate relative risk (RR). Results From a total of 54 000 CT scans, 19 377 scans from 10 407 patients (median age, 8.5 years; IQR, 3-14; 5869 boys, 4538 girls) were included in the analysis. Incidence rate of AKI for the entire sample was 1.5%; it was 1.4% (123 of 8844) in the group that underwent contrast-enhanced CT and 1.6% (171 of 10 533) in the group that did not ( = .18). In the contrast-enhanced CT group, AKI incidence was higher in the group with eGFR of at least 60 mL/min/1.73 m and in the group with eGFR lower than 60 mL/min/1.73 m (1.3% and 8.5%, respectively; < .001) compared with the noncontrast group (0.1% and 2.7%, respectively; < .001). Age was found to be a protective factor against AKI, with an RR of 0.96 (95% CI: 0.94, 0.99; = .01), and contrast media increased risk in the subgroup analysis, with an RR of 2.19 (95% CI: 1.11, 4.35; = .02). Conclusion The overall incidence of acute kidney injury after contrast-enhanced CT in children and adolescents was very low, and exposure to contrast media did not increase the risk consistently for acute kidney injury among different groups and analyses. © RSNA, 2022 See also the editorial by McDonald in this issue.

<p><strong>INTRODUCTION: </strong>Functional renal imaging, most commonly with MAG3 nuclear medicine renal scan, is recommended in the evaluation of children with urinary tract dilation (UTD) suspected of obstructive uropathy. Alternatively, renal function can be evaluated with functional Magnetic Resonance Urography (fMRU), which has superior anatomic detail. However, there are not enough data comparing both methods' equivalency. In this study, we compare the functional and obstruction parameters of fMRU and MAG3 in a pediatric cohort presenting with obstructive uropathy.</p>

<p><strong>STUDY DESIGN: </strong>This is an IRB-approved retrospective review of all children undergoing fMRU at a single, free-standing children's hospital between May 2008 and September 2017. Patients who also underwent a MAG3 renal scan within 6 months and who had no interval surgical intervention were included in the study. Bladder catheterization was performed prior to both imaging studies.</p>

<p><strong>RESULTS: </strong>735 children had 988 fMRU studies performed during the study period. 37 unique patients (13 girls and 24 boys) with median age of 6 months (range: 2 mo-19&nbsp;y) were included in the final sample. Median time interval between studies was 70 days (range 6-179 days). The majority of participants (26/37, 70.3%) presented with UTD P3 and had diagnosis of uretero-pelvic junction obstruction (UPJO) in 21/37. Differential renal function (DRF) was used to group 10 fMRU and 9 MAG3 patients as normal; 9 fMRU and 11 MAG3 as mild; 11 fMRU and 6 MAG3 as moderate; and 7 fMRU and 6 MAG3 as severe; Wilcoxon signed-rank test (p&nbsp;=&nbsp;0.5106). Results were similar for DRF among patients with and without duplex kidneys. In the analysis of obstruction, using reference standard T½ MAG3&nbsp;≥&nbsp;20&nbsp;min, a greater or equal than 6&nbsp;min renal transit time (RTT) from fMRU showed a specificity of 94%, a sensitivity of 62%, and an AUC of 0.827.</p>

<p><strong>DISCUSSION AND CONCLUSIONS: </strong>The differential renal function determined by MAG3 and fMRU in children was not statistically different, therefore we concluded that it was similar and potentially equivalent. Better correlation was shown in patients who had normal split kidney function. While the tests are clinically equivalent, the variability of DRF within each clinical category (i.e., normal, mild, moderate, severe) is not surprising, because MAG3 does not clearly differentiate the dilated collecting system from the functional parenchymal tissue, while fMRU does. Using MAG3 as the gold standard, fMRU was 94.74% specific and 5% more sensitive in detecting UPJO with a RTT of 6min vs. 8min.</p>

<p><strong>OBJECTIVES: </strong>To evaluate whether liver and spleen magnetic resonance elastography (MRE) can measure the severity of congenital hepatic fibrosis (CHF) and portal hypertension (pHTN) in individuals with autosomal recessive polycystic kidney disease (ARPKD), and to examine correlations between liver MRE and ultrasound (US) elastography.</p>

<p><strong>METHODS: </strong>Cross-sectional study of nine individuals with ARPKD and 14 healthy controls. MRE was performed to measure mean liver and spleen stiffness (kPa); US elastography was performed to measure point shear wave speed (SWS) in both liver lobes. We compared: (1) MRE liver and spleen stiffness between controls vs. ARPKD; and (2) MRE liver stiffness between participants with ARPKD without vs. with pHTN, and examined correlations between MRE liver stiffness, spleen length, platelet counts, and US elastography SWS. Receiver operating characteristic (ROC) analysis was performed to examine diagnostic accuracy of liver MRE.</p>

<p><strong>RESULTS: </strong>Participants with ARPKD (median age 16.8 [IQR 13.3, 18.9] years) had higher median MRE liver stiffness than controls (median age 14.7 [IQR 9.7, 16.7&nbsp;years) (2.55 vs. 1.92&nbsp;kPa, p = 0.008), but MRE spleen stiffness did not differ. ARPKD participants with pHTN had higher median MRE liver stiffness than those without (3.60&nbsp;kPa vs 2.49&nbsp;kPa, p = 0.05). Liver MRE and US elastography measurements were strongly correlated. To distinguish ARPKD vs. control groups, liver MRE had 78% sensitivity and 93% specificity at a proposed cut-off of 2.48&nbsp;kPa [ROC area 0.83 (95% CI 0.63-1.00)].</p>

<p><strong>CONCLUSION: </strong>Liver MRE may be a useful quantitative method to measure the severity of CHF and pHTN in individuals with ARPKD.</p>

<p><strong>PURPOSE: </strong>To determine the MRU imaging findings of calyceal diverticula in a large cohort of children and to compare the frequency of calyceal diverticula in our cohort with what has been previously reported.</p>

<p><strong>METHODS: </strong>This was a HIPAA-compliant, IRB-approved retrospective study of all patients with suspected CD based on their medical records. All patients in this study underwent MRU at our institution between 2010 and 2017. Two pediatric radiologists reviewed each MRU blinded to clinical information and other urologic imaging regarding the presence, size, location, and morphology of the cyst and presence/absence of contrast within it. The time when contrast first appeared within the cystic mass was recorded, and a χ test was used to determine significance on differences between the different characteristics of renal cysts and diverticula.</p>

<p><strong>RESULTS: </strong>Fifty children (29 girls and 21 boys; median age of 11.5&nbsp;years, IQR 7-16) with a total of 66 individual cystic masses were included. 21 (21/66, 31.8%) Cystic masses demonstrated contrast filling and were characterized as diverticula, resulting in a frequency of 26.6 cases per 1000 patients (21/787). The remaining 45 cystic masses (45/66, 68.1%) were cysts. The median diameter of CD was 2.5&nbsp;cm (IQR 1.5-3.7). Contrast was observed within the cystic mass on average at 4.6&nbsp;min (SD ± 2.4; range 1.5-13&nbsp;min). The agreement between both radiologists was 91% (k = 0.78). 6 Cysts and 18 CD were confirmed surgically, MRU demonstrated accurate diagnosis in 100% of those cases.</p>

<p><strong>CONCLUSION: </strong>Magnetic resonance urography is reliable in differentiating calyceal diverticula from renal cysts. On MRU, all diverticula were identified within 15&nbsp;min of contrast administration; hence longer delays in imaging are unnecessary.</p>

<p><strong>PURPOSE: </strong>The goal of our study is to compare hepatic stiffness measures using gradient-recalled echo (GRE) versus spin-echo echo planar imaging (SE-EPI)-based MR Elastography (MRE) at 3T used to measure hepatic stiffness in a patients with suspected liver diseases.</p>

<p><strong>MATERIALS AND METHODS: </strong>This retrospective study included 52 patients with liver disease who underwent a 3T MRE exam including both an investigational SE-EPI-based technique and a product GRE-based technique. Regions of interest (ROI) were placed on the elastograms to measure elastography-derived liver stiffness as well as the area included within the ROIs. The mean liver stiffness values and area of ROIs were compared.</p>

<p><strong>RESULTS: </strong>The mean liver stiffness was 3.72 kilopascal (kPa) ± 1.29 using GRE MRE and 3.78&nbsp;kPa ± 1.13 using SE-EPI MRE. Measurement of liver stiffness showed excellent agreement between the two pulse sequences with a mean bias of - 0.1&nbsp;kPa (range - 1.8 to 1.7&nbsp;kPa) between sequences. The mean measurable ROI area was higher with SE-EPI (313.8&nbsp;cm ± 213.8) than with the GRE technique (208.6&nbsp;cm ± 114.8), and the difference was statistically significant (P &lt; 0.05).</p>

<p><strong>CONCLUSIONS: </strong>Our data shows excellent agreement of measured liver stiffness between GRE and SE-EPI-based sequences at 3T. Our results show the advantage of a SE-EPI MRE sequence in terms of image quality, ROI size and acquisition time with equivalent liver stiffness measurements as compared to GRE-MRE sequence.</p>

<p>Imaging modalities for diagnosing kidney and urinary tract disorders in children have developed rapidly over the last decade largely because of advancement of modern technology. General pediatricians and neonatologists are often the front line in detecting renal anomalies. There is a lack of knowledge of the applicability, indications, and nephrotoxic risks of novel renal imaging modalities. Here we describe the clinical impact of congenital anomalies of the kidneys and urinary tract and describe pediatric-specific renal imaging techniques by providing a practical guideline for the diagnosis of kidney and urinary tract disorders.</p>

<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 compare the reproducibility and accuracy of R2-relaxometry MRI for estimation&nbsp;of liver iron concentration (LIC) between in-house analysis and FDA-approved commercially available third party results.</p>

<p><strong>METHODS: </strong>All MR studies were performed on a 1.5T scanner.&nbsp;Multi-echo spin-echo scans with a fixed TR and increasing TE values of 6&nbsp;ms, 9&nbsp;ms, 12&nbsp;ms, 15&nbsp;ms, and 18&nbsp;ms (spaced at 3&nbsp;ms intervals) were used. Post-processing of the images to calculate mean relaxivity, R2, included drawing of regions of interest to include the whole liver on mid-slice. The relationship between liver R2 values and estimated LIC calculated with in-house analysis and values&nbsp;reported by an external company (FerriScan, Resonance Health, Australia) were assessed with correlation coefficients and Bland-Altman difference plots. Continuous variables are presented as mean ± standard deviation. Significance was set at p value &lt; 0.05.</p>

<p><strong>RESULTS: </strong>474 studies from 175 patients were included in the study (mean age 10.4 ± 4.2&nbsp;years (range 1-18&nbsp;years); 254 studies from girls, 220 studies from boys). LIC ranged from 0.6 to 43&nbsp;mg/g dry tissue, covering a broad range from normal levels to extremely high iron levels. Linearity between proprietary and in-house methods was excellent across the observed range for R2 (31.5 to 334.8&nbsp;s); showing a correlation coefficient of r = 0.87, p &lt; 0.001. Bland-Altman R2 difference plot between the two methods shows a mean bias of + 21.5&nbsp;s (range - 47.0 to + 90.0&nbsp;s between two standard deviations). LIC reported by FerriScan compared with LIC estimated in-house with R2 as reported by FerriScan agreed strongly, (r = 1.0, p &lt; 0.001).</p>

<p><strong>CONCLUSION: </strong>R2 relaxometry MR imaging for liver iron concentration estimation is reproducible between proprietary FDA-approved commercial software and in-house analysis methods.</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>

<p>Three-dimensional (3-D) printing is gaining terrain in medical education, presurgical evaluation and recently as forensic evidence in court. Physicians, including radiologists, often provide expert testimony in court cases involving children with rib fractures and other injuries concerning for child physical abuse. Effectively communicating the complexities of fractures and other skeletal findings to nonmedical personnel using standard radiology studies can be challenging, especially during medical courtroom testimony. For this reason, we printed two 3-D models of the rib cage from the chest computed tomography (CT) scans of two patients with suspected non-accidental injury. The patients also had available chest radiographs. The DICOM (Digital Imaging and Communications in Medicine) data were 3-D reconstructed and segmented using two attenuation thresholds. We removed unwanted structures and printed them on a commercially available scanner. A pediatric radiologist, blinded to clinical data, reviewed both 3-D models, identified all rib lesions and classified them according to their healing stage. We compared the 3-D models and the chest radiograph against the chest CT as the standard of care. We convened a meeting with the Child Protection Team at out institution to get their feedback and opinions about the models. From our observations of our experts, three spontaneous interactions were observed. Instinctively, the experts picked up and grasped the models, rotating them, feeling them and angling them to better visualize the fractures from multiple angles. The experts expressed a willingness to consider using the models in court.</p>