Pediatric magnetic resonance angiography: to contrast or not to contrast.

Magnetic resonance (MR) angiography and MR venography imaging with contrast and non-contrast techniques are widely used for pediatric vascular imaging. However, as with any MRI examination, imaging the pediatric population can be challenging because of patient motion, which sometimes requires sedation. There are multiple benefits of non-contrast MR angiographic techniques, including the ability to repeat sequences if motion is present, the decreased need for sedation, and avoidance of potential risks associated with gadolinium administration and radiation exposure. Thus, MR angiography is an attractive alternative to CT or conventional catheter-based angiography in pediatric populations. Contrast-enhanced MR angiographic techniques have the advantage of increased signal to noise. Blood pool imaging allows long imaging times that result in high-spatial-resolution imaging, and thus high-quality diagnostic images. This article outlines the technique details, indications, benefits and downsides of non-contrast-enhanced and contrast-enhanced MR angiographic techniques to assist in protocol decision-making.

Prospective comparison of longitudinal change in hepatic proton density fat fraction (PDFF) estimated by magnitude-based MRI (MRI-M) and complex-based MRI (MRI-C).

PURPOSE: To compare longitudinal hepatic proton density fat fraction (PDFF) changes estimated by magnitude- vs. complex-based chemical-shift-encoded MRI during a weight loss surgery (WLS) program in severely obese adults with biopsy-proven nonalcoholic fatty liver disease (NAFLD). METHODS: This was a secondary analysis of a prospective dual-center longitudinal study of 54 adults (44 women; mean age 52 years; range 27-70 years) with obesity, biopsy-proven NAFLD, and baseline PDFF ≥ 5%, enrolled in a WLS program. PDFF was estimated by confounder-corrected chemical-shift-encoded MRI using magnitude (MRI-M)- and complex (MRI-C)-based techniques at baseline (visit 1), after a 2- to 4-week very low-calorie diet (visit 2), and at 1, 3, and 6 months (visits 3 to 5) after surgery. At each visit, PDFF values estimated by MRI-M and MRI-C were compared by a paired t test. Rates of PDFF change estimated by MRI-M and MRI-C for visits 1 to 3, and for visits 3 to 5 were assessed by Bland-Altman analysis and intraclass correlation coefficients (ICCs). RESULTS: MRI-M PDFF estimates were lower by 0.5-0.7% compared with those of MRI-C at all visits (p < 0.001). There was high agreement and no difference between PDFF change rates estimated by MRI-M vs. MRI-C for visits 1 to 3 (ICC 0.983, 95% CI 0.971, 0.99; bias = - 0.13%, p = 0.22), or visits 3 to 5 (ICC 0.956, 95% CI 0.919-0.977%; bias = 0.03%, p = 0.36). CONCLUSION: Although MRI-M underestimates PDFF compared with MRI-C cross-sectionally, this bias is consistent and MRI-M and MRI-C agree in estimating the rate of hepatic PDFF change longitudinally. KEY POINTS: • MRI-M demonstrates a significant but small and consistent bias (0.5-0.7%; p < 0.001) towards underestimation of PDFF compared with MRI-C at 3 T. • Rates of PDFF change estimated by MRI-M and MRI-C agree closely (ICC 0.96-0.98) in adults with severe obesity and biopsy- proven NAFLD enrolled in a weight loss surgery program. • Our findings support the use of either MRI technique (MRI-M or MRI-C) for clinical care or by individual sites or for multi-center trials that include PDFF change as an endpoint. However, since there is a bias in their measurements, the same technique should be used in any given patient for longitudinal follow-up.

Monitoring Fatty Liver Disease with MRI Following Bariatric Surgery: A Prospective, Dual-Center Study.

Purpose To longitudinally monitor liver fat before and after bariatric surgery by using quantitative chemical shift-encoded (CSE) MRI and to compare with changes in body mass index (BMI), weight, and waist circumference (WC). Materials and Methods For this prospective study, which was approved by the internal review board, a total of 126 participants with obesity who were undergoing evaluation for bariatric surgery with preoperative very low calorie diet (VLCD) were recruited from June 27, 2010, through May 5, 2015. Written informed consent was obtained from all participants. Participants underwent CSE MRI measuring liver proton density fat fraction (PDFF) before VLCD (2-3 weeks before surgery), after VLCD (1-3 days before surgery), and 1, 3, and 6-10 months following surgery. Linear regression was used to estimate rates of change of PDFF (ΔPDFF) and body anthropometrics. Initial PDFF (PDFF0), initial anthropometrics, and anthropometric rates of change were evaluated as predictors of ΔPDFF. Mixed-effects regression was used to estimate time to normalization of PDFF. Results Fifty participants (mean age, 51.0 years; age range, 27-70 years), including 43 women (mean age, 50.8 years; age range, 27-70 years) and seven men (mean age, 51.7 years; age range, 36-62 years), with mean PDFF0 ± standard deviation of 18.1% ± 8.6 and mean BMI0 of 44.9 kg/m2 ± 6.5 completed the study. By 6-10 months following surgery, mean PDFF decreased to 4.9% ± 3.4 and mean BMI decreased to 34.5 kg/m2 ± 5.4. Mean estimated time to PDFF normalization was 22.5 weeks ± 11.5. PDFF0 was the only strong predictor for both ΔPDFF and time to PDFF normalization. No body anthropometric correlated with either outcome. Conclusion Average liver proton density fat fraction (PDFF) decreased to normal (< 5%) by 6-10 months following surgery, with mean time to normalization of approximately 5 months. Initial PDFF was a strong predictor of both rate of change of PDFF and time to normalization. Body anthropometrics did not predict either outcome. Online supplemental material is available for this article. © RSNA, 2018.

Longitudinal Assessment of Renal Perfusion and Oxygenation in Transplant Donor-Recipient Pairs Using Arterial Spin Labeling and Blood Oxygen Level-Dependent Magnetic Resonance Imaging.

OBJECTIVES: The aims of this study were to assess renal function in kidney transplant recipients and their respective donors over 2 years using arterial spin labeling (ASL) and blood oxygen level-dependent (BOLD) magnetic resonance imaging (MRI) and to prospectively evaluate the effect of losartan on functional MRI measures in recipients. MATERIALS AND METHODS: The study included 15 matched pairs of renal transplant donors and recipients. Arterial spin labeling and BOLD MRI of the kidneys were performed on donors before transplant surgery (baseline) and on both donors and recipients at 3 months, 1 year, and 2 years after transplant. After 3 months, 7 of the 15 recipients were prescribed 25 to 50 mg/d losartan for the remainder of the study. A linear mixed-effects model was used to evaluate perfusion, R2*, estimated glomerular filtration rate, and fractional excretion of sodium for changes across time or associated with losartan treatment. RESULTS: In donors, cortical perfusion in the remaining kidney decreased by 50 ± 19 mL/min per 100 g (11.8%) between baseline and 2 years (P < 0.05), while cortical R2* declined modestly by 0.7 ± 0.3 s-1 (5.6%; P < 0.05). In transplanted kidneys, cortical perfusion decreased markedly by 141 ± 21 mL/min per 100 g (34.2%) between baseline and 2 years (P < 0.001), while medullary R2* declined by 1.5 ± 0.8 s-1 (8.3%; P = 0.06). Single-kidney estimated glomerular filtration rate increased between baseline and 2 years by 17.7 ± 2.7 mL/min per 1.73 m (40.3%; P < 0.0001) in donors and to 14.6 ± 4.3 mL/min per 1.73 m (33.3%; P < 0.01) in recipients. Cortical perfusion at 1 and 2 years in recipients receiving 25 to 50 mg/d losartan was 62 ± 24 mL/min per 100 g higher than recipients not receiving the drug (P < 0.05). No significant effects of losartan were observed for any other markers of renal function. CONCLUSIONS: The results suggest an important role for noninvasive functional monitoring with ASL and BOLD MRI in kidney transplant recipients and donors, and they indicate a potentially beneficial effect of losartan in recipients.

High specificity targeting and detection of human neuroblastoma using multifunctional anti-GD2 iron-oxide nanoparticles.

AIM: To develop biocompatible, tumor-specific multifunctional iron-oxide nanoconstructs targeting neuroblastoma, an aggressive pediatric malignancy. MATERIALS & METHODS: Clinical-grade humanized monoclonal antibody (hu14.18K322A), designed to target GD2 antigen on neuroblastoma with reduced nonspecific immune interactions, was conjugated to hydroxyethyl starch-coated iron-oxide nanoparticles. Targeting capability in vitro and in vivo was assessed by immunofluorescence, electron microscopy, analytical spectrophotometry, histochemistry and magnetic resonance R2* relaxometry. RESULTS: The biocompatible nanoconstructs demonstrated high tumor specificity in vitro and in vivo, and low background uptake in a mouse flank xenograft model. Specific accumulation in tumors enabled particle visualization and quantification by magnetic resonance R2* mapping. CONCLUSION: Our findings support the further development toward clinical application of this anti-GD2 iron-oxide nanoconstruct as diagnostic and therapeutic scaffold for neuroblastoma and potentially other GD2-positive malignancies.