<p><strong>OBJECTIVE: </strong>To assess the feasibility of T2 mapping for evaluating pediatric SIJ cartilage at 3 Tesla (T) magnetic resonance imaging (MRI).</p>

<p><strong>METHODS: </strong>Healthy control subjects and adolescents with sacroiliitis underwent a 3T MRI dedicated pelvic protocol that included a T2 mapping sequence consisting of multislice, multiecho acquisition. Healthy control subjects were prospectively recruited from our primary care practices as part of a larger imaging study, whereas adolescents with sacroiliitis were recruited specifically for this study. Regions of interest (ROIs) were hand-drawn by a senior pediatric radiologist twice and a radiology fellow twice to calibrate and test reliability using the intraclass correlation coefficient (ICC). T2 relaxation time between control subjects and cases was compared using univariate linear regression. We tested the association of T2 relaxation time in adolescents with sacroiliitis with patient-reported outcomes and the Spondyloarthritis Research Consortium of Canada sacroiliac joint (SIJ) inflammation and structural scores using Pearson correlation coefficients.</p>

<p><strong>RESULTS: </strong>Fourteen subjects were evaluable (six control subjects: median age 13.7 years [interquartile range (IQR): 12.2-15.5], 67% male patients; eight cases: median age 17.4 years [IQR: 12.5-20], 88% male patients]. Acquisition time for T2 mapping sequences was approximately 6 minutes, and segmenting the ROI for each SIJ took approximately 3 minutes. The intrarater and inter-rater ICCs were 0.67 and 0.46, respectively, indicating good to fair reliability. There was a trend, albeit statistically insignificant, in longer median T2 relaxation time in cases (43.04 ms; IQR: 41.25-49.76 ms) versus healthy control subjects (40.0 ms; IQR: 38.9-48.6 ms). Although not statistically significant, cases with longer T2 relaxation time tended to occur with poorer patient-reported outcomes. Correlations with the SIJ inflammation and structural lesion scores were weak.</p>

<p><strong>CONCLUSION: </strong>T2 mapping of the SIJ cartilage in children was feasible and reliable. Larger controlled and longitudinal assessments are needed to assess the validity and utility of these measurements for routine clinical practice and trials.</p>

<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>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>OBJECTIVE: </strong>Increasing reliance on MRI for the evaluation of sacroiliitis requires that radiologists be familiar with the normal appearance of the developing sacroiliac joint. We describe age-related MRI features of the sacroiliac joints in healthy children.</p>

<p><strong>SUBJECTS AND METHODS: </strong>Seventy healthy children from three age groups-prepubertal (8-10 years), peripubertal (11-13 years), and approaching skeletal maturity (14-17 years)-completed questionnaires and underwent sacroiliac joint MRI. Imaging studies were evaluated by three experienced pediatric radiologists. Metaphyseal-equivalent signal intensity, nonperiarticular osteitis, cartilage volume, joint fluid, enthesitis, and surface cortex irregularities were evaluated. Metaphyseal-equivalent signal intensity was evaluated using an ordinal grading system (types I-IV). Intraclass correlation coefficients were calculated to assess interrater reliability.</p>

<p><strong>RESULTS: </strong>Increased metaphyseal-equivalent signal intensity (types I and II) was present in most prepubertal children and in less than 10% of the group approaching skeletal maturity. More prepubertal girls had type I signal than boys, but signal progressed to type IV signal faster in girls than in boys. None of the subjects had subchondral marrow edema, but four subjects had nonperiarticular osteitis. Cartilage volumes decreased with advancing age in girls and, on average, were lower in girls than in boys of the same age. One subject had measurable joint fluid. Cortex irregularities were common (57.1%), most frequently seen along the iliac bone (51.4% ilium vs 11.4% sacrum, p &lt; 0.01) and in the upper quadrants (42.8% upper vs 27.1% lower, p = 0.01).</p>

<p><strong>CONCLUSION: </strong>We provide valuable reference MRI descriptions of the healthy pediatric sacroiliac joint that should improve our ability to distinguish between normal and pathologic findings.</p>

<p><strong>BACKGROUND: </strong>R2* relaxometry's capacity to calculate liver iron concentration (LIC) is limited in patients with severe overload. Hemosiderin increases in these patients, which exhibits a non-monoexponential decay that renders a failed R2* analysis.</p>

<p><strong>PURPOSE/HYPOTHESIS: </strong>To evaluate a biexponential R2* relaxometry model in children with different ranges of iron overload.</p>

<p><strong>STUDY TYPE: </strong>Retrospective.</p>

<p><strong>POPULATION: </strong>In all, 181 children with different conditions associated with iron overload.</p>

<p><strong>FIELD STRENGTH/SEQUENCE: </strong>1.5T, T *-weighted gradient echo sequence.</p>

<p><strong>ASSESSMENT: </strong>Bi- and monoexponential R2* relaxometry were measured in the liver using two regions of interest (ROIs) using a nonproprietary software: one encompassing the whole liver parenchyma (ROI-1) and the other only the periphery (ROI-2). These were drawn by a single trained observer. The residuals for each fitting model were estimated. A ratio between the residuals of the mono- and biexponential models was calculated to identify the best fitting model. Patients with 1) residual ratio ≥1.5 and 2) R2* ≥R2* were considered as having a predominant biexponential behavior.</p>

<p><strong>STATISTICAL TESTS: </strong>Nonparametric tests, Bland-Altman plots, linear correlation, intraclass correlation coefficient. Patients were divided according to their LIC into stable (n = 23), mild (n = 58), moderate (n = 61), and severe (n = 39).</p>

<p><strong>RESULTS: </strong>The biexponential model was more suitable for patients with severe iron overload when compared with the other three LIC categories (P &lt; 0.001) for both ROIs. For ROI-1, 37 subjects met criteria for a predominant biexponential behavior. The slow component (5.7%) had a lower fraction than the fast component (94.2%). For ROI-2, 22 subjects met criteria for a predominant biexponential behavior. The slow component (4.7%) had a lower fraction than the fast component (95.2%). The intraobserver variability between both ROIs was excellent.</p>

<p><strong>DATA CONCLUSION: </strong>The biexponential R2* relaxometry model is more suitable in children with severe iron overload.</p>

<p><strong>LEVEL OF EVIDENCE: </strong>3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019.</p>

<p>Renal fusion is on a spectrum of congenital abnormalities that occur due to disruption of the migration process of the embryonic kidneys from the pelvis to the retroperitoneal renal fossae. Clinically, renal fusion anomalies are often found incidentally and associated with increased risk for complications, such as urinary tract obstruction, infection and urolithiasis. These anomalies are most commonly imaged using ultrasound for anatomical definition and less frequently using renal scintigraphy to quantify differential renal function and assess urinary tract drainage. Functional magnetic resonance urography (fMRU) is an advanced imaging technique that combines the excellent soft-tissue contrast of conventional magnetic resonance (MR) images with the quantitative assessment based on contrast medium uptake and excretion kinetics to provide information on renal function and drainage. fMRU has been shown to be clinically useful in evaluating a number of urological conditions. A highly sensitive and radiation-free imaging modality, fMRU can provide detailed morphological and functional information that can facilitate conservative and/or surgical management of children with renal fusion anomalies. This paper reviews the embryological basis of the different types of renal fusion anomalies, their imaging appearances at fMRU, complications associated with fusion anomalies, and the important role of fMRU in diagnosing and managing children with these anomalies.</p>