Can Automated 3-Dimensional Dixon-Based Methods Be Used in Patients With Liver Iron Overload?

PURPOSE: Accurate quantification of liver iron concentration (LIC) can be achieved via magnetic resonance imaging (MRI). Maps of liver T2*/R2* are provided by commercially available, vendor-provided, 3-dimensional (3D) multiecho Dixon sequences and allow automated, inline postprocessing, which removes the need for manual curve fitting associated with conventional 2-dimensional (2D) gradient echo (GRE)-based postprocessing. The main goal of our study was to investigate the relationship among LIC estimates generated by 3D multiecho Dixon sequence to values generated by 2D GRE-based R2* relaxometry as the reference standard. METHODS: A retrospective review of patients who had undergone MRI scans for estimation of LIC with conventional T2* relaxometry and 3D multiecho Dixon sequences was performed. A 1.5 T scanner was used to acquire the magnetic resonance studies. Acquisition of standard multislice multiecho T2*-based sequences was performed, and R2* values with corresponding LIC were estimated. The comparison between R2* and corresponding LIC estimates obtained by the 2 methods was analyzed via the correlation coefficients and Bland-Altman difference plots. RESULTS: This study included 104 patients (51 male and 53 female patients) with 158 MRI scans. The mean age of the patients at the time of scan was 15.2 (SD, 8.8) years. There was a very strong correlation between the 2 LIC estimation methods for LIC values up to 3.2 mg/g (LIC quantitative multiecho Dixon [qDixon; from region of interest R2*] vs LIC GRE [in-house]: r = 0.83, P < 0.01; LIC qDixon [from segmentation volume R2*] vs LIC GRE [in-house]: r = 0.92, P < 0.01); and very weak correlation between the 2 methods at liver iron levels >7 mg/g. CONCLUSION: Three-dimensional-based multiecho Dixon technique can accurately measure LIC up to 7 mg/g and has the potential to replace 2D GRE-based relaxometry methods.

Quantitative Evaluation of Brain Echogenicity in Hypoxic-Ischemic Encephalopathy in Term Neonates Compared with Controls.

Purpose Neurosonography evaluation of neonatal hypoxic-ischemic encephalopathy (HIE) is mainly qualitative. We aimed to quantitatively compare the echogenicity of several brain regions in patients with HIE to healthy controls. Materials and Methods 20 term neonates with clinical/MRI evidence of HIE and 20 term healthy neonates were evaluated. Seven brain regions were assessed [frontal, parietal, occipital, and perirolandic white matter (WM), caudate nucleus head, lentiform nucleus, and thalamus]. The echogenicity of the calvarial bones (bone) and the choroid plexus (CP) was used for ratio calculation. Differences in the ratios were determined between neonates with HIE and controls. Results Ratios were significantly higher for HIE neonates in each region (p<0.05). The differences were greatest for the perirolandic WM, with CP and bone ratios being 0.23 and 0.22 greater, respectively, for the HIE compared to the healthy neonates (p<0.001). The perirolandic WM had a high AUC, at 0.980 for both the CP and bone ratios. The intra-observer reliability for all ratios was high, with the caudate to bone ratio being the lowest at 0.832 and the anterior WM to CP ratio being the highest at 0.992. Conclusion When coupled with internal controls, quantitative neurosonography represents a potential tool to identify early neonatal HIE changes. Larger cohort studies could reveal whether a quantitative approach can discern between degrees of severity of HIE. Future neurosonography protocols should be tailored to evaluate the perirolandic region, which requires posterior coronal scanning.

Rate of Change of Liver Iron Content by MR Imaging Methods: A Comparison Study.

Objective: Magnetic resonance imaging (MRI) can accurately quantify liver iron concentration (LIC), eliminating the need for an invasive liver biopsy. Currently, the most widely used relaxometry methods for iron quantification are R2 and R2*, which are based on T2 and T2* acquisition sequences, respectively. We compared the rate of change of LIC as measured by the R2-based, FDA-approved commercially available third-party software with the rate of change of LIC measured by in-house analysis using R2*-relaxometry-based MR imaging in patients undergoing follow-up MRI scans for liver iron estimation. Methods: We retrospectively included patients who had undergone serial MRIs for liver iron estimation. The MR studies were performed on a 1.5T scanner; standard multi-slice, multi-echo T2- and T2*-based sequences were acquired, and LIC was estimated. The comparison between the rate of change of LIC by R2 and R2* values was performed via correlation coefficients and Bland−Altman difference plots. Results: One hundred and eighty-nine MR abdomen studies for liver iron evaluation from 81 patients (male: 38; female: 43) were included in the study. Fifty-nine patients had two serial scans, eighteen patients had three serial scans, three patients had four serial scans, and one patient had five serial scans. The average time interval between the first and last scans for each patient was 13.3 months. The average rates of change of LIC via R2 and R2* methods were −0.0043 ± 0.0214 and −0.0047 ± 0.012 mg/g per month, respectively. There was no significant difference in the rate of change of LIC observed between the two methods. Linearity between the rate of change of LIC measured by R2 (LIC R2) and R2* (LIC R2*) was strong, showing a correlation coefficient of r = 0.72, p < 0.01. A Bland−Altman plot between the rate of change of the two methods showed that the majority of the plotted variables were between two standard deviations. Conclusion: There was no significant difference in the rate of change of LIC detected between the R2 method and the R2* method that uses a gradient echo (GRE) sequence acquired with breath-hold. Since R2* is relatively faster and less prone to motion artifacts, R2*-derived LIC is recommended for iron homeostasis follow-up in patients with liver iron overload.

The role of apparent diffusion coefficient histogram metrics for differentiating pediatric medulloblastoma histological variants and molecular groups.

BACKGROUND: Medulloblastoma, a high-grade embryonal tumor, is the most common primary brain malignancy in the pediatric population. Molecular medulloblastoma groups have documented clinically and biologically relevant characteristics. Several authors have attempted to differentiate medulloblastoma molecular groups and histology variants using diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) maps. However, literature on the use of ADC histogram analysis in medulloblastomas is still scarce. OBJECTIVE: This study presents data from a sizable group of pediatric patients with medulloblastoma from a single institution to determine the performance of ADC histogram metrics for differentiating medulloblastoma variants and groups based on both histological and molecular features. MATERIALS AND METHODS: In this retrospective study, we evaluated the distribution of absolute and normalized ADC values of medulloblastomas. Tumors were manually segmented and diffusivity metrics calculated on a pixel-by-pixel basis. We calculated a variety of first-order histogram metrics from the ADC maps, including entropy, minimum, 10th percentile, 90th percentile, maximum, mean, median, skewness and kurtosis, to differentiate molecular and histological variants. ADC values of the tumors were also normalized to the bilateral cerebellar cortex and thalami. We used the Kruskal-Wallis and Mann-Whitney U tests to evaluate differences between the groups. We carried out receiver operating characteristic (ROC) curve analysis to evaluate the areas under the curves and to determine the cut-off values for differentiating tumor groups. RESULTS: We found 65 children with confirmed histopathological diagnosis of medulloblastoma. Mean age was 8.3 ± 5.8 years, and 60% (n = 39) were male. One child was excluded because histopathological variant could not be determined. In terms of medulloblastoma variants, tumors were classified as classic (n = 47), desmoplastic/nodular (n = 9), large/cell anaplastic (n = 6) or as having extensive nodularity (n = 2). Seven other children were excluded from the study because of incomplete imaging or equivocal molecular diagnosis. Regarding medulloblastoma molecular groups, there were: wingless (WNT) group (n = 7), sonic hedgehog (SHH) group (n = 14) and non-WNT/non-SHH (n = 36). Our results showed significant differences among the molecular groups in terms of the median (P = 0.002), mean (P = 0.003) and 90th percentile (P = 0.002) ADC histogram metrics. No significant differences among the various medulloblastoma histological variants were found. CONCLUSION: ADC histogram analysis can be implemented as a complementary tool in the preoperative evaluation of medulloblastoma in children. This technique can provide valuable information for differentiating among medulloblastoma molecular groups. ADC histogram metrics can help predict medulloblastoma molecular classification preoperatively.

Reference values for MRI-derived psoas and paraspinal muscles and macroscopic fat infiltrations in paraspinal muscles in children.

BACKGROUND: Sarcopenia, defined as loss of skeletal muscle mass, is a novel term associated with adverse outcomes in children. Magnetic Resonance Imaging (MRI) is a safe and precise technique for measuring tissue compartments and is commonly used in most routine paediatric imaging protocols. Currently, there is a lack of MRI-derived normative data which can help in determining the level of sarcopenia. This study aimed to introduce reference values of total psoas muscle area (tPMA), total paraspinal muscle area (tPSMA), and total macroscopic fat infiltrations of the PSMA (tMFI). METHODS: In this retrospective study, the local database was searched for abdominal and pelvic region MRI studies of children aged from 1 to 18 years (mean age (standard deviation (SD)) of 9.8 (5.5) years) performed in the years 2010-2021. Children with chronic diseases and a history of surgical interventions were excluded from the analysis. Finally, a total of 465 healthy children (n = 233 girls, n = 232 boys) were enrolled in the study. The values of the tPMA, tPMSA, and tMFI were measured in square centimetres (cm2 ) at the level of the L4/L5 intervertebral disc as the sum of the left and right regions. Age-specific and sex-specific muscle, fat, and body mass index percentile charts were constructed using the LMS method. Inter-observer agreement and intra-observer reproducibility were assessed using the Bland-Altman plots. RESULTS: Both tPMA and tPSMA showed continuous increases in size (in cm2 ) throughout all age groups. At the age of 18, the median tPMA areas reached 26.37 cm2 in girls and 40.43 cm2 in boys. Corresponding tPSMA values were higher, reaching the level of 40.76 cm2 in girls and 56.66 cm2 in boys. The mean value of tMFI within the paraspinal muscles was 5.0% (SD 3.65%) of their total area in girls and 3.5% (SD 2.25%) in boys with the actual difference between sexes up to 0.96 cm2 . Excellent intra-observer reproducibility and inter-observer agreement were noted. Actual mean differences for tPMA were at the level of 0.43 and 0.39 cm2 , respectively. Mean bias for tPSMA was 0.1 cm2 for inter-observer and 0.05 cm2 for intra-observer measurements. CONCLUSIONS: Our findings demonstrate novel and highly reproducible sex-specific MRI-derived reference values of tPMS, tPSMA, and tMFI at the level of the L4/L5 intervertebral disc for children from 1 to 18 years old, which may guide a clinician in the assessment of sarcopenia, a prognostic outcome marker in children.

Application of Apparent Diffusion Coefficient Histogram Metrics for Differentiation of Pediatric Posterior Fossa Tumors : A Large Retrospective Study and Brief Review of Literature.

PURPOSE: This study aimed to evaluate the application of apparent diffusion coefficient (ADC) histogram analysis to differentiate posterior fossa tumors (PFTs) in children. METHODS: A total of 175 pediatric patients with PFT, including 75 pilocytic astrocytomas (PA), 59 medulloblastomas, 16 ependymomas, and 13 atypical teratoid rhabdoid tumors (ATRT), were analyzed. Tumors were visually assessed using DWI trace and conventional MRI images and manually segmented and post-processed using parametric software (pMRI). Furthermore, tumor ADC values were normalized to the thalamus and cerebellar cortex. The following histogram metrics were obtained: entropy, minimum, 10th, and 90th percentiles, maximum, mean, median, skewness, and kurtosis to distinguish the different types of tumors. Kruskal Wallis and Mann-Whitney U tests were used to evaluate the differences. Finally, receiver operating characteristic (ROC) curves were utilized to determine the optimal cut-off values for differentiating the various PFTs. RESULTS: Most ADC histogram metrics showed significant differences between PFTs (p < 0.001) except for entropy, skewness, and kurtosis. There were significant pairwise differences in ADC metrics for PA versus medulloblastoma, PA versus ependymoma, PA versus ATRT, medulloblastoma versus ependymoma, and ependymoma versus ATRT (all p < 0.05). Our results showed no significant differences between medulloblastoma and ATRT. Normalized ADC data showed similar results to the absolute ADC value analysis. ROC curve analysis for normalized ADCmedian values to thalamus showed 94.9% sensitivity (95% CI: 85-100%) and 93.3% specificity (95% CI: 87-100%) for differentiating medulloblastoma from ependymoma. CONCLUSION: ADC histogram metrics can be applied to differentiate most types of posterior fossa tumors in children.

Can Ultrasound-Guided Xenon Delivery Provide Neuroprotection in Traumatic Brain Injury?

Traumatic brain injury (TBI) is associated with high mortality and morbidity in children and adults. Unfortunately, there is no effective management for TBI in the acute setting. Rodent studies have shown that xenon, a well-known anesthetic gas, can be neuroprotective when administered post-TBI. Gas inhalation therapy, however, the approach typically used for administering xenon, is expensive, inconvenient, and fraught with systemic side effects. Therapeutic delivery to the brain is minimal, with much of the inhaled gas cleared by the lungs. To bridge major gaps in clinical care and enhance cerebral delivery of xenon, this study introduces a novel xenon delivery technique, utilizing microbubbles, in which a high impulse ultrasound signal is used for targeted cerebral release of xenon. Briefly, an ultrasound pulse is applied along the carotid artery at the level of the neck on intravenous injection of xenon microbubbles (XeMBs) resulting in release of xenon from microbubbles into the brain. This delivery technique employs a hand-held, portable ultrasound system that could be adopted in resource-limited environments. Using a high-fidelity porcine model, this study demonstrates the neuroprotective efficacy of xenon microbubbles in TBI for the first time.

Feasibility of T2 Mapping of the Sacroiliac Joints in Healthy Control Subjects and Children and Young Adults with Sacroiliitis.

OBJECTIVE: To assess the feasibility of T2 mapping for evaluating pediatric SIJ cartilage at 3 Tesla (T) magnetic resonance imaging (MRI). METHODS: 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. RESULTS: 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. CONCLUSION: 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.

MRI-Derived Subcutaneous and Visceral Adipose Tissue Reference Values for Children Aged 6 to Under 18 Years.

The assessment of body composition in pediatric population is essential for proper nutritional support during hospitalization. However, currently available methods have limitations. This study aims to propose a novel approach for nutrition status assessment and introduce magnetic resonance imaging (MRI)-derived subcutaneous and visceral fat normative reference values. A total of 262 healthy subjects aged from 6 to 18 years underwent MRI examinations and anthropometric measurements. MRI images at the second lumbar vertebrae were used by two radiologists to perform the semi-automatic tissue segmentation. Based on obtained adipose tissue surface areas and body mass index (BMI) scores sex-specific standard percentile curves (3rd, 10th, 25th, 50th, 75th, 90th, 97th) and z-scores were constructed using LMS method. Additionally, 85th and 95th centiles of subcutaneous and visceral adipose tissue were proposed as equivalents of overweight and obesity. Bland-Altman plots revealed an excellent intra-observer reproducibility and inter-observer agreement. In conclusion, our findings demonstrate highly reproducible method and suggest that MRI-derived reference values can be implemented in clinical practice.

Potential benefits of functional magnetic resonance urography (fMRU) over MAG3 renal scan in children with obstructive uropathy.

INTRODUCTION: 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. STUDY DESIGN: 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. RESULTS: 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 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 = 0.5106). Results were similar for DRF among patients with and without duplex kidneys. In the analysis of obstruction, using reference standard T½ MAG3 ≥ 20 min, a greater or equal than 6 min renal transit time (RTT) from fMRU showed a specificity of 94%, a sensitivity of 62%, and an AUC of 0.827. DISCUSSION AND CONCLUSIONS: 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.

Novel Computerized Analytic Technique for Quantification of Amniotic Fluid Volume in Fetal MRI.

OBJECTIVE. Fetal MRI is increasingly used in the evaluation of suspected congenital anomalies. Assessment of amniotic fluid volume (AFV) is crucial, but no automated quantitative technique is currently available for MRI. The purpose of this study was to develop and evaluate an analytic technique for quantifying AFV in fetal MRI. MATERIALS AND METHODS. Two MRI phantoms containing known quantities of synthetic amniotic fluid were created. A 3D steady-state free precession sequence was used for 1.5-T MRI of the phantoms and as part of a standard clinical fetal MRI protocol. Software was developed and used to retrospectively calculate AFV for the phantom and 20 clinical MRI examinations. Times to completion were recorded. AFV was also calculated by a manual hand-tracing method. To evaluate performance, paired t tests were used to compare computer-generated measurements with known phantom volumes. Intraclass correlation coefficients were calculated to assess agreement between computer-generated and manual measurements. RESULTS. There was no significant difference between computer-generated measurements of known AFV in the MRI phantoms (p > 0.11). When the software program was applied to the clinical MRI examinations, the mean time to complete AFV measurement was 110 seconds. There was excellent reliability between total AFV calculated by the two software users and by means of manual measurements (intraclass correlation coefficient, 0.995; p < 0.01). CONCLUSION. The computerized analysis evaluated in this study rapidly and accurately quantifies AFV in fetal MRI. The results are concordant with known phantom volumes and manual measurements. The technique is promising for objective MRI evaluation of AFV and has the potential to improve prenatal diagnosis and management.

R2 relaxometry based MR imaging for estimation of liver iron content: A comparison between two methods.

PURPOSE: To compare the reproducibility and accuracy of R2-relaxometry MRI for estimation of liver iron concentration (LIC) between in-house analysis and FDA-approved commercially available third party results. METHODS: All MR studies were performed on a 1.5T scanner. Multi-echo spin-echo scans with a fixed TR and increasing TE values of 6 ms, 9 ms, 12 ms, 15 ms, and 18 ms (spaced at 3 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 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 < 0.05. RESULTS: 474 studies from 175 patients were included in the study (mean age 10.4 ± 4.2 years (range 1-18 years); 254 studies from girls, 220 studies from boys). LIC ranged from 0.6 to 43 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 s-1); showing a correlation coefficient of r = 0.87, p < 0.001. Bland-Altman R2 difference plot between the two methods shows a mean bias of + 21.5 s-1 (range - 47.0 to + 90.0 s-1 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 < 0.001). CONCLUSION: R2 relaxometry MR imaging for liver iron concentration estimation is reproducible between proprietary FDA-approved commercial software and in-house analysis methods.

Biexponential R2* relaxometry for estimation of liver iron concentration in children: A better fit for high liver iron states.

BACKGROUND: 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. PURPOSE/HYPOTHESIS: To evaluate a biexponential R2* relaxometry model in children with different ranges of iron overload. STUDY TYPE: Retrospective. POPULATION: In all, 181 children with different conditions associated with iron overload. FIELD STRENGTH/SEQUENCE: 1.5T, T2 *-weighted gradient echo sequence. ASSESSMENT: 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*fast ≥R2*slow were considered as having a predominant biexponential behavior. STATISTICAL TESTS: 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). RESULTS: The biexponential model was more suitable for patients with severe iron overload when compared with the other three LIC categories (P < 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. DATA CONCLUSION: The biexponential R2* relaxometry model is more suitable in children with severe iron overload. LEVEL OF EVIDENCE: 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1191-1198.

MRI of the Sacroiliac Joint in Healthy Children.

To listen to the podcast associated with this article, please select one of the following: iTunes, Google Play, or direct download. OBJECTIVE. 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. SUBJECTS AND METHODS. 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. RESULTS. 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 < 0.01) and in the upper quadrants (42.8% upper vs 27.1% lower, p = 0.01). CONCLUSION. We provide valuable reference MRI descriptions of the healthy pediatric sacroiliac joint that should improve our ability to distinguish between normal and pathologic findings.

Relationship of renal apparent diffusion coefficient and functional MR urography in children with pelvicalyceal dilation.

OBJECTIVE: The aim is to evaluate the age-related changes and relationship of renal apparent diffusion coefficient (ADC) against the morphological and functional changes detected by functional magnetic resonance urography (fMRU) in children with pelvicalyceal dilation, with suspected or known ureteropelvic junction obstruction. MATERIALS AND METHODS: We retrospectively analyzed fMRUs with diffusion-weighted imaging (DWI) of the kidney in 35 subjects (25 males; median age: 7.1 years, range: 0.3-22.7 years) with 70 kidneys (40 with pelvicalyceal dilation and 30 with no pelvicalyceal dilation). Inclusion criteria were pelvicalyceal dilation, the absence of duplex kidneys and no ureteric dilation. DWI was performed with 3 diffusion gradient directions (b values = 0, 200, 500, 800 and 1,000 s/mm2). Metrics for fMRU included calyceal and renal transit times (CTT, RTT), time-to-peak (TTP), differential renal function based on volume (vDRF), Patlak number (pDRF) and combined volume and Patlak number (vpDRF). The grades of pelvicalyceal dilation, cortical thinning and corticomedullary differentiation were evaluated. The relationship between ADC values and the fMRU parameters was analyzed. RESULTS: ADC increases with age in kidneys without pelvicalyceal dilation (R2=0.37, P<0.001). Renal ADC does not correlate with any of the morphological or fMRU parameters (P>0.07). The median ADC of kidneys without pelvicalyceal dilation was 3.73×10-3 mm2/s (range: 2.78-5.37×0-3 mm2/s) and the median ADC of kidneys with pelvicalyceal dilation was 3.82×10-3 mm2/s (range: 2.70-5.70×10-3 mm2/s). There was no correlation between ADC and the absolute differences of vDRF or pDRF (P>0.33). CONCLUSION: Renal ADC does not correlate with morphological and functional results of fMRU changes in children with pelvicalyceal dilation due to suspected or known ureteropelvic junction obstruction.

Role of magnetic resonance urography in pediatric renal fusion anomalies.

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.

Intra- and inter-observer variability of functional MR urography (fMRU) assessment in children.

BACKGROUND: Functional MR urography (fMRU) provides comprehensive functional data that can be subject to variability. To interpret the results of fMRU, it is essential to know the intra- and inter-observer variability of the measured parameters. OBJECTIVE: To define the range of variability in fMRU, particularly that of the differential renal function based on volume (volumetric differential renal function) and Patlak differential renal function measurements in children. MATERIALS AND METHODS: We included 15 fMRU studies, 10 of non-duplicated and 5 of unilateral duplex kidneys. We recruited six observers with a range of fMRU experience, including two MRI technologists, one resident, one fellow, one pediatric radiologist and one pediatric urologist. The observers underwent intensive training in using the Children's Hospital of Philadelphia (CHOP)-fMRU freeware for analysis. They conducted the fMRU analysis on each case twice, at least 1 week apart. Mean and standard deviation were calculated for each set of absolute volume, absolute Patlak, volumetric differential renal function and Patlak differential renal function. We calculated the statistical significance of these deviations using the student's t-test. We also calculated interclass correlations for intra-observer and inter-observer agreement of both volume and Patlak measurements using SPSS software. RESULTS: Intra- and inter-observer variability did not differ significantly, measuring 6% and 4% for relative volume (volumetric differential renal function: P > 0.05) and 5% and 3% for relative function (Patlak differential renal function: P > 0.05). Absolute values of parameters showed more variability than the relative values. Intra- and inter-observer agreement was well above 0.90 (P < 0.001) for all volume measures except for duplex upper pole intra-observer measurements (0.80, P < 0.01). Intra- and inter-observer agreement for Patlak values were also above 0.90 (P < 0.001) except for duplex upper pole measurements, which were 0.54 (P = 0.13) and 0.81 (P < 0.01), respectively. CONCLUSION: Functional MRU analysis using CHOP-fMRU software is reproducible, with overall intra- and inter-observer variability rates of 5% for volumetric differential renal function and 4% for Patlak differential renal function. There was higher variability in volume and function measurements between upper and lower pole moieties of duplicated kidneys and for absolute volume and function values overall. A range of 45-55% for relative values of volumetric differential renal function and Patlak differential renal function could serve as the normal range.

Optimizing functional MR urography: prime time for a 30-minutes-or-less fMRU.

BACKGROUND: Current protocols for functional MR urography (fMRU) require long scan times, limiting its widespread use. OBJECTIVE: Our goal was to use pre-defined criteria to reduce the number of sequences and thus the examination time without compromising the morphological and functional results. MATERIALS AND METHODS: The standard fMRU protocol in our department consists of eight sequences, including a 17-min dynamic post-contrast scan. Ninety-nine children and young adults (43 male, 56 female, mean age 7 years) were evaluated with this protocol. Each sequence was retrospectively analyzed for its utility and factors that affect its duration. RESULTS: Mean scan time to perform the eight sequences, without including the variable time between sequences, was 40.5 min. Five sequences were categorized as essential: (1) sagittal T2 for planning the oblique coronal plane, (2) axial T2 with fat saturation for the assessment of corticomedullary differentiation and parenchymal thickness, (3) coronal 3-D T2 with fat saturation for multiplanar and 3-D reconstructions, (4) pre-contrast coronal T1 with fat saturation to ensure an appropriate scan prior to injecting the contrast material and (5) the coronal post-contrast dynamic series. Functional information was obtained after 8 min of dynamic imaging in the majority of children. The coronal fat-saturated T2, coronal T1, and post-contrast sagittal fat-saturated T1 sequences did not provide additional information. Because of the effects of pelvicalyceal dilation and ureteropelvic angle on the renal transit time, prone position is recommended, at least in children with high-grade pelvicalyceal dilation. CONCLUSION: Comprehensive fMRU requires approximately 19 min for sequence acquisition. Allowing for time between sequences and motion correction, the total study time can be reduced to about 30 min. Four pre-contrast sequences and a shortened post-contrast dynamic scan, optimally with the child in prone position, are sufficient.

Dynamic gadolinium-enhanced MRI of the proximal femur: preliminary experience in healthy children.

OBJECTIVE: The purpose of this study is to use dynamic contrast-enhanced MRI to evaluate the perfusion characteristics of the proximal femur in the growing skeleton. MATERIALS AND METHODS: We evaluated 159 subjects (mean age, 5.67 years) who underwent a well-controlled protocol of contrast-enhanced MRI of the abdomen and hips. Perfusion and permeability parameters (enhancement ratio peak, AUC, time to peak, and rate of extraction) for six regions of the proximal femur were calculated. RESULTS: A decrease with age was found for all contrast kinetics parameters in all regions (p < 0.001). Perfusion parameters differed between the regions (p < 0.001). The highest perfusion and permeability parameters were found in the metaphyseal spongiosa, metaphyseal marrow, and periosteum. The metaphyseal spongiosa had a highly vascular pattern of enhancement and showed the highest enhancement ratio peak, AUC, and rate of extraction and the lowest time to peak. The metaphyseal marrow showed a vascular pattern of enhancement with a lower peak compared with the metaphyseal spongiosa. The periosteum showed prompt nonvascular contrast enhancement that reached a plateau that remained elevated. CONCLUSION: The highest enhancement was seen in areas involved with growth: the metaphyseal spongiosa, which is related to endochondral ossification, and the periosteal cambium, which is related to membranous ossification. The enhancement characteristics are radically different: in the spongiosa; enhancement is brisk and declines, with a vascular pattern, whereas contrast uptake increases with time in the periosteum. Recognition of normal enhancement patterns of the proximal femur is important for distinguishing normal development from pathologic processes.