Fast, free-breathing and motion-minimized techniques for pediatric body magnetic resonance imaging

Application of intranasal dexmedetomidine in magnetic resonance imaging of preterm infants: The ED50, efficacy and safety analysis

BACKGROUND

Infants undergoing magnetic resonance imaging (MRI) often require pharmacological sedation. Dexmedetomidine serves as a novel sedative agent that induces a unique unconsciousness similar to natural sleep, and therefore has currently been used as the first choice for sedation in infants and young children.

OBJECTIVE

To determine the 50% effective dose (ED50) and 95% confidence interval (95%CI) of intranasal dexmedetomidine for MRI in preterm and term infants, and to observe the incidence of adverse events. To explore whether there were differences in ED50 and 95%CI, heart rate (HR) and blood oxygen saturation (SpO2), the induction time and wake-up time and the incidence of adverse events between the 2 groups, so as to provide guidance for clinical safe medication for the meanwhile.

METHODS

A total of 68 infants were prospectively recruited for MRI examination under drug sedation (1 week ≤ age ≤ 23 weeks or weight ≤ 5kg). The children were divided into 2 groups according to whether they had preterm birth experience (Preterm group, Atterm group). The Dixon up-and-down method was used to explore ED50. The basic vital signs of the 2 groups were recorded, and the heart rate and SpO2 were recorded every 5 minutes until the infants were discharged from the hospital. The induction time, wake-up time and adverse events were recorded.

RESULTS

The ED50 (95%CI) of intranasal dexmedetomidine in the Preterm group and the Atterm group were 2.23 (2.03-2.66) μg/kg and 2.64 (2.49-2.83) μg/kg, respectively (P < .05). the wake-up time was longer in Preterm group (98.00min) than in Atterm group (81.00 min) (P < .05), the incidence of bradycardia in Preterm group was 3/33, which was higher than that in Atterm group (1/35). There was no difference in the induction time between the 2 groups (P > .05), and there was no significant difference in other adverse events.

CONCLUSIONS

Intranasal dexmedetomidine can be safely used for sedation in preterm infants undergoing MRI. Compared with term infants, preterm infants have a lower dose of dexmedetomidine, a higher incidence of bradycardia, and a longer weak-up time.

Variability in Surveillance Strategies Following Resection of Sacrococcygeal Teratoma

INTRODUCTION

Surveillance following sacrococcygeal teratoma (SCT) resection varies. The purpose of this study was to describe the clinical characteristics and outcomes of patients undergoing SCT resection and examine current institutional practices to detect recurrence.

METHODS

A single-institution retrospective review of children who underwent resection of an SCT from January 1, 2010 to December 31, 2020 was performed. Data were summarized and surveillance strategies compared between histopathologic subtypes using nonparametric methods.

RESULTS

Thirty six patients (75.0% female) underwent SCT removal at a median age of 8 d. Histopathology revealed 27 mature teratomas (75.0%), eight immature teratomas (22.2%), and one malignant germ cell tumor (2.8%). Median postoperative follow-up was 3.17 y (interquartile range [IQR]: 2.31-4.38 y). Patients had a median of 2.32 clinic visits per year (IQR: 2.00-2.70), alpha-fetoprotein levels were obtained at a median of 2.01 times per year (IQR: 0-1.66), and surveillance imaging was performed at a median of 2.31 times per year (IQR: 0-2.84). Patients with immature teratomas had alpha-fetoprotein laboratories obtained more frequently than patients with mature teratomas (3.10 times/year versus 0.93 times/year, P = 0.001). There was no significant difference in the number of imaging studies obtained between groups. Two patients (5.6%) developed recurrence, which were identified on magnetic resonance imaging at 191 and 104 d postresection, respectively.

CONCLUSIONS

Postoperative surveillance practices varied widely. Recurrence was noted in a single malignant case in the first year following resection. Multi-institutional studies are needed to determine the optimal surveillance strategy to detect recurrence of SCT.

Robust Unsupervised Super-Resolution of Infant MRI via Dual-Modal Deep Image Prior

Magnetic resonance imaging (MRI) is commonly used for studying infant brain development. However, due to the lengthy image acquisition time and limited subject compliance, high-quality infant MRI can be challenging. Without imposing additional burden on image acquisition, image super-resolution (SR) can be used to enhance image quality post-acquisition. Most SR techniques are supervised and trained on multiple aligned low-resolution (LR) and high-resolution (HR) image pairs, which in practice are not usually available. Unlike supervised approaches, Deep Image Prior (DIP) can be employed for unsupervised single-image SR, utilizing solely the input LR image for de novo optimization to produce an HR image. However, determining when to stop early in DIP training is non-trivial and presents a challenge to fully automating the SR process. To address this issue, we constrain the low-frequency k-space of the SR image to be similar to that of the LR image. We further improve performance by designing a dual-modal framework that leverages shared anatomical information between T1-weighted and T2-weighted images. We evaluated our model, dual-modal DIP (dmDIP), on infant MRI data acquired from birth to one year of age, demonstrating that enhanced image quality can be obtained with substantially reduced sensitivity to early stopping.

Evaluation of Artifact Appearance and Burden in Pediatric Brain Tumor MR Imaging with Compressed Sensing in Comparison to Conventional Parallel Imaging Acceleration

Clinical magnetic resonance imaging (MRI) aims for the highest possible image quality, while balancing the need for acceptable examination time, reasonable signal-to-noise ratio (SNR), and lowest artifact burden. With a recently introduced imaging acceleration technique, compressed sensing, the acquisition speed and image quality of pediatric brain tumor exams can be improved. However, little attention has been paid to its impact on method-related artifacts in pediatric brain MRI. This study assessed the overall artifact burden and artifact appearances in a standardized pediatric brain tumor MRI by comparing conventional parallel imaging acceleration with compressed sensing. This showed that compressed sensing resulted in fewer physiological artifacts in the FLAIR sequence, and a reduction in technical artifacts in the 3D T1 TFE sequences. Only a slight difference was noted in the T2 TSE sequence. A relatively new range of artifacts, which are likely technique-related, was noted in the 3D T1 TFE sequences. In conclusion, by equipping a basic pediatric brain tumor protocol for 3T MRI with compressed sensing, the overall burden of common artifacts can be reduced. However, attention should be paid to novel compressed-sensing-specific artifacts.

Motion compensated self supervised deep learning for highly accelerated 3D ultrashort Echo time pulmonary MRI

PURPOSE

To investigate motion compensated, self-supervised, model based deep learning (MBDL) as a method to reconstruct free breathing, 3D pulmonary UTE acquisitions.

THEORY AND METHODS

A self-supervised eXtra dimension MBDL architecture (XD-MBDL) was developed that combined respiratory states to reconstruct a single high-quality 3D image. Non-rigid motion fields were incorporated into this architecture by estimating motion fields from a lower resolution motion resolved (XD-GRASP) reconstruction. Motion compensated XD-MBDL was evaluated on lung UTE datasets with and without contrast and compared to constrained reconstructions and variants of self-supervised MBDL that do not account for dynamic respiratory states or leverage motion correction.

RESULTS

Images reconstructed using XD-MBDL demonstrate improved image quality as measured by apparent SNR (aSNR), contrast to noise ratio (CNR), and visual assessment relative to self-supervised MBDL approaches that do not account for dynamic respiratory states, XD-GRASP and a recently proposed motion compensated iterative reconstruction strategy (iMoCo). Additionally, XD-MBDL reduced reconstruction time relative to both XD-GRASP and iMoCo.

CONCLUSION

A method was developed to allow self-supervised MBDL to combine multiple respiratory states to reconstruct a single image. This method was combined with graphics processing unit (GPU)-based image registration to further improve reconstruction quality. This approach showed promising results reconstructing a user-selected respiratory phase from free breathing 3D pulmonary UTE acquisitions.

Turnaround time and efficiency of pediatric outpatient brain magnetic resonance imaging: a multi-institutional cross-sectional study

BACKGROUND

Aside from single-center reports, few data exist across pediatric institutions that examine overall MRI turnaround time (TAT) and the determinants of variability.

OBJECTIVE

To determine average duration and determinants of a brain MRI examination at academic pediatric institutions and compare the duration to those used in practice expense relative value units (RVUs).

MATERIALS AND METHODS

This multi-institutional cross-sectional investigation comprised four academic pediatric hospitals. We included children ages 0 to < 18 years who underwent an outpatient MRI of the brain without contrast agent in 2019. Our outcome of interest was the overall MRI TAT derived by time stamps. We estimated determinants of overall TAT using an adjusted log-transformed multivariable linear regression model with robust standard errors.

RESULTS

The average overall TAT significantly varied among the four hospitals. A sedated brain MRI ranged from 158 min to 224 min, a non-sedated MRI from 70 min to 112 min, and a limited MRI from 44 min to 70 min. The most significant predictor of a longer overall TAT was having a sedated MRI (coefficient = 0.71, 95% confidence interval [CI]: 0.66-0.75; P < 0.001). The median MRI scan time for a non-sedated exam was 38 min and for a sedated exam, 37 min, approximately double the duration used by the Relative Value Scale (RVS) Update Committee (RUC).

CONCLUSION

We found considerable differences in the overall TAT across four pediatric academic institutions. Overall, the significant predictors of turnaround times were hospital site and MRI pathway (non-sedated versus sedated versus limited MRI).

Pediatric magnetic resonance imaging: faster is better

Magnetic resonance imaging (MRI) has emerged as the preferred imaging modality for evaluating a wide range of pediatric medical conditions. Nevertheless, the long acquisition times associated with this technique can limit its widespread use in young children, resulting in motion-degraded or non-diagnostic studies. As a result, sedation or general anesthesia is often necessary to obtain diagnostic images, which has implications for the safety profile of MRI, the cost of the exam and the radiology department's clinical workflow. Over the last decade, several techniques have been developed to increase the speed of MRI, including parallel imaging, single-shot acquisition, controlled aliasing techniques, compressed sensing and artificial-intelligence-based reconstructions. These are advantageous because shorter examinations decrease the need for sedation and the severity of motion artifacts, increase scanner throughput, and improve system efficiency. In this review we discuss a framework for image acceleration in children that includes the synergistic use of state-of-the-art MRI hardware and optimized pulse sequences. The discussion is framed within the context of pediatric radiology and incorporates the authors' experience in deploying these techniques in routine clinical practice.

Interstitial fluid pressure as an emerging biomarker in solid tumors

The physical microenvironment of cancer is characterized by elevated stiffness and tissue pressure, the main component of which is the interstitial fluid pressure (IFP). Elevated IFP is an established negative predictive and prognostic parameter, directly affecting malignant behavior and therapy response. As such, measurement of the IFP would allow to develop strategies aimed at engineering the physical microenvironment of cancer. Traditionally, IFP measurement required the use of invasive methods. Recent progress in dynamic and functional imaging methods such as dynamic contrast enhanced (DCE) magnetic resonance imaging and elastography, combined with numerical models and simulation, allows to comprehensively assess the biomechanical landscape of cancer, and may help to overcome physical barriers to drug delivery and immune cell infiltration. Here, we provide a comprehensive overview of the origin of elevated IFP, and its role in the malignant phenotype. Also, we review the methods used to measure IFP using invasive and imaging based methods, and highlight remaining obstacles and potential areas of progress in order to implement IFP measurement in clinical practice.

Improving protocols for whole-body magnetic resonance imaging: oncological and inflammatory applications

Whole-body MRI is increasingly used in the evaluation of a range of oncological and non-oncological diseases in infants, children and adolescents. Technical innovation in MRI scanners, coils and sequences have enabled whole-body MRI to be performed more rapidly, offering large field-of-view imaging suitable for multifocal and multisystem disease processes in a clinically useful timeframe. Together with a lack of ionizing radiation, this makes whole-body MRI especially attractive in the pediatric population. Indications include lesion detection in cancer predisposition syndrome surveillance and in the workup of children with known malignancies, and diagnosis and monitoring of a host of infectious and non-infectious inflammatory conditions. Choosing which patients are most likely to benefit from this technology is crucial, but so is adjusting protocols to the patient and disease to optimize lesion detection. The focus of this review is on protocols and the elements impacting image acquisition in pediatric whole-body MRI. We consider the practical aspects, from scanner and coil selection to patient positioning, single-center generic and indication-specific protocols with technical parameters, motion reduction strategies and post-processing. When optimized, collectively these lead to better standardization of whole-body MRI, and when married to systematic analysis and interpretation, they can improve diagnostic accuracy.

Free-breathing magnetic resonance imaging with radial k-space sampling for neonates and infants to reduce anesthesia

BACKGROUND

Conventional chest and abdominal MRI require breath-holds to reduce motion artifacts. Neonates and infants require general anesthesia with intubation to enable breath-held acquisitions.

OBJECTIVE

We aimed to validate a free-breathing approach to reduce general anesthesia using a motion-insensitive radial acquisition with respiratory gating.

MATERIALS AND METHODS

We retrospectively enrolled children <3 years old who were referred for MRI of the chest or abdomen. They were divided into two groups according to MRI protocol: (1) breath-held scans under general anesthesia with T2-weighted single-shot fast spin-echo (SSFSE) and contrast-enhanced T1-weighted modified Dixon, and (2) free-breathing scans using radial sequences (T2-W MultiVane XD and contrast-enhanced T1-W three-dimensional [3-D] Vane XD). Two readers graded image quality and motion artifacts.

RESULTS

We included 23 studies in the free-breathing cohort and 22 in the breath-hold cohort. The overall imaging scores for the free-breathing radial T2-W sequence were similar to the scores for the breath-held T2-W SSFSE sequence (chest, 3.6 vs. 3.2, P=0.07; abdomen, 3.9 vs. 3.7, P=0.66). The free-breathing 3-D radial T1-W sequence also had image quality scores that were similar to the breath-held T1-W sequence (chest, 4.0 vs. 3.0, P=0.06; abdomen, 3.7 vs. 3.9, P=0.15). Increased motion was seen in the abdomen on the radial T2-W sequence (P<0.001), but increased motion was not different in the chest (P=0.73) or in contrast-enhanced T1-W sequences (chest, P=0.39; abdomen, P=0.15). The mean total sequence time was longer in free-breathing compared to breath-held exams (P<0.01); however, this did not translate to longer overall exam times (P=0.94).

CONCLUSION

Motion-insensitive radial sequences used for infants and neonates were of similar image quality to breath-held sequences and had decreased sedation and intubation.

“Low Dose MR” Dixon Technique for Imaging FDG PET-MR Lymphoma

Introduction  Hybrid PET-MR is a relatively new imaging modality with its major strength being the MR component offering superior soft tissue contrast. While PET/MRI offers the inherent advantage of reduced radiation dose, it has been shown to result in a markedly prolonged examination time becoming a challenge in children and sick patients. "Low dose MRI" is a term used in the nuclear medicine community to describe fast acquired PET-MR scan protocols that rely heavily on PET images for diagnosis. In this study, we sought to determine if the Dixon sequences obtained for attenuation correction could be used as a diagnostic sequence for interpreting PET-MRI lymphoma cases, potentially reducing scan time.

Materials and Methods  We retrospectively identified 40 patients who underwent ⁸⁸ FDG PET-MR body imaging studies for staging or restaging lymphoma. A radiologist and nuclear medicine physician initially reviewed top of the head to mid thigh PET images, attenuation correction coronal Dixon MRI sequences, and PET-MR fusion with Dixon sequence. The same physicians reviewed the PET images, multi-sequence MR including the attenuation correction Dixon, and multi-sequence PET-MR fusion images The lesions were further characterized based on their imaging characteristics, size, SUVmax, and malignant potency. A consensus read followed.

Results   All patients were adults with an average study age of 43.8 years. Our study consisted of 40 females and 48 males out of which 7 were for staging and 81 were for re-staging. All patients had systemic lymphoma. Thirty-seven of the studies had active lymph nodes on Dixon PET-MR that agreed with multi-sequence PET-MR which identified 33 positive cases (89.1%) having an average SUV 10.2 ± 7.74 SD. Four Dixon PET-MR cases did not detect lesions, with an average SUV 2.3 ± 0.55 SD, which was read as minimal residual activity. Multi-sequence MR identified 11 patients with enlarged lymph nodes without FDG uptake, which were not seen on Dixon MR. All 5 studies with bones lesions were detected by Dixon PET-MR as well as 2 soft tissue organ lesions. Multi-sequence MR identified 1 patient with non-active, healed bone lesion. Fifty-five of these studies were true negatives. Compared to multi-sequence PET-MR, Dixon PET-MR demonstrated 89.2% sensitivity, 100% specificity with no false positive studies.

Conclusion   The present study investigated the diagnostic potential of a fast protocol for integrated PET/MRI used for dedicated tumor staging of patients with lymphoma. In this retrospective study, Dixon PET-MR was shown to be sensitive and specific compared to multi-sequence PET-MR in the detection of lymphoma. The low number of these cases not detected had minimally active lymph nodes that resolved on subsequent imaging and probably were not clinically important.

Accelerating multi-echo chemical shift encoded water-fat MRI using model-guided deep learning

PURPOSE

To accelerate chemical shift encoded (CSE) water-fat imaging by applying a model-guided deep learning water-fat separation (MGDL-WF) framework to the undersampled k-space data.

METHODS

A model-guided deep learning water-fat separation framework is proposed for the acceleration using Cartesian/radial undersampling data. The proposed MGDL-WF combines the power of CSE water-fat imaging model and data-driven deep learning by jointly using a multi-peak fat model and a modified residual U-net network. The model is used to guide the image reconstruction, and the network is used to capture the artifacts induced by the undersampling. A data consistency layer is used in MGDL-WF to ensure the output images to be consistent with the k-space measurements. A Gauss-Newton iteration algorithm is adapted for the gradient updating of the networks.

RESULTS

Compared with the compressed sensing water-fat separation (CS-WF) algorithm/2-step procedure algorithm, the MGDL-WF increased peak signal-to-noise ratio (PSNR) by 5.31/5.23, 6.11/4.54, and 4.75 dB/1.88 dB with Cartesian sampling, and by 4.13/6.53, 2.90/4.68, and 1.68 dB/3.48 dB with radial sampling, at acceleration rates (R) of 4, 6, and 8, respectively. By using MGDL-WF, radial sampling increased the PSNR by 2.07 dB at R = 8, compared with Cartesian sampling.

CONCLUSIONS

The proposed MGDL-WF enables exploiting features of the water images and fat images from the undersampled multi-echo data, leading to improved performance in the accelerated CSE water-fat imaging. By using MGDL-WF, radial sampling can further improve the image quality with comparable scan time in comparison with Cartesian sampling.

Assessing and conveying risks and benefits of imaging in neonates using ionizing radiation and sedation/anesthesia

Neonates represent a unique subset of the pediatric population that requires special attention and careful thought when implementing advanced cross-sectional imaging with CT or MRI. The ionizing radiation associated with CT and the sedation/anesthesia occasionally required for MRI present risks that must be balanced against the perceived benefit of the imaging examination in the unique and particularly susceptible neonatal population. We review the perceived risks of ionizing radiation and the more concrete risks of sedation/anesthesia in term and preterm neonates in the context of an imaging paradigm. When the expected diagnostic yield from CT and MRI is similar, and sedation is required for MRI but not for CT, CT likely has the higher benefit-to-risk ratio in the neonate. However, despite the risks, the most appropriate imaging modality should always be chosen after thoughtful consideration is given to each unique patient and informed discussions including radiology, anesthesia, neonatology and the parents/caregivers are pursued.

Signal intensity patterns in health and disease: basics of abdominal magnetic resonance imaging in children

Magnetic resonance imaging (MRI) is playing an increasing role in pediatric abdominal imaging, especially in the evaluation of diffuse parenchymal disease where other imaging modalities might be less sensitive. While quantitative imaging is slowly being incorporated into clinical imaging, qualitative assessment of visceral signal intensity should be part of the routine clinical workflow of all radiologists. Based on their T1 and T2 weighting, the liver, spleen, kidneys and pancreas have characteristic signal intensity patterns with respect to one another and to skeletal muscle. It is important to recognize normal signal intensity patterns of viscera and their evolution with patient age to be able to identify age-related variations and accurately identify diffuse parenchymal disease. Knowledge of normal signal intensity patterns can also help identify ectopic locations of normal tissue such as splenic rests and splenosis. In this review, we discuss normal signal intensity patterns of upper abdominal viscera and their variations on commonly used sequences in pediatric abdominal MRI. We also review normal variations in the perinatal period. Knowledge of these patterns can help pediatric radiologists become more astute in their interpretation of diffuse parenchymal disease in the abdomen.

Magnetic resonance imaging of Müllerian anomalies in girls: concepts and controversies

Female Müllerian anomalies are the result of failure of formation, fusion or resorption of the Müllerian ducts and are relatively common, with a prevalence of 5.5-7.0% in the general population. While some of these anomalies are asymptomatic, those presenting with obstruction require accurate identification for optimal clinical management including potential surgical treatment. MRI is a useful adjunct to sonography in the evaluation of Müllerian anomalies, typically allowing a more complete characterization of the malformation. Technical aspects, embryologic concepts and controversies regarding classification systems are highlighted in this review. Several Müllerian anomalies are discussed and illustrated in more detail utilizing various cases with pelvic MRI studies.

1.5 vs 3 Tesla Magnetic Resonance Imaging: A Review of Favorite Clinical Applications for Both Field Strengths-Part 2

ABSTRACT

The second part of this review deals with experiences in neuroradiological and pediatric examinations using modern magnetic resonance imaging systems with 1.5 T and 3 T, with special attention paid to experiences in pediatric cardiac imaging. In addition, whole-body examinations, which are widely used for diagnostic purposes in systemic diseases, are compared with respect to the image quality obtained in different body parts at both field strengths. A systematic overview of the technical differences at 1.5 T and 3 T has been presented in part 1 of this review, as well as several organ-based magnetic resonance imaging applications including musculoskeletal imaging, abdominal imaging, and prostate diagnostics.

Improved Image Quality for Static BLADE Magnetic Resonance Imaging Using the Total-Variation Regularized Least Absolute Deviation Solver

In order to improve the image quality of BLADE magnetic resonance imaging (MRI) using the index tensor solvers and to evaluate MRI image quality in a clinical setting, we implemented BLADE MRI reconstructions using two tensor solvers (the least-squares solver and the L1 total-variation regularized least absolute deviation (L1TV-LAD) solver) on a graphics processing unit (GPU). The BLADE raw data were prospectively acquired and presented in random order before being assessed by two independent radiologists. Evaluation scores were examined for consistency and then by repeated measures analysis of variance (ANOVA) to identify the superior algorithm. The simulation showed the structural similarity index (SSIM) of various tensor solvers ranged between 0.995 and 0.999. Inter-reader reliability was high (Intraclass correlation coefficient (ICC) = 0.845, 95% confidence interval: 0.817, 0.87). The image score of L1TV-LAD was significantly higher than that of vendor-provided image and the least-squares method. The image score of the least-squares method was significantly lower than that of the vendor-provided image. No significance was identified in L1TV-LAD with a regularization strength of λ= 0.4–1.0. The L1TV-LAD with a regularization strength of λ= 0.4–0.7 was found consistently better than least-squares and vendor-provided reconstruction in BLADE MRI with a SENSitivity Encoding (SENSE) factor of 2. This warrants further development of the integrated computing system with the scanner.

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.

RAVE-T2/T1 - Feasibility of a new hybrid MR-sequence for free-breathing abdominal MRI in children and adolescents

BACKGROUND

The new radial volumetric encoding RAVE-T₂/T₁ hybrid sequence is a modern three-dimensional sequence with multiparametric approach, which includes T₂- and T₁-weighted contrasts obtained in identical slice position during one measurement. However, the RAVE-T₂/T₁ hybrid sequence is not yet being used in clinical routine.

PURPOSE

The aim of this study was to evaluate the RAVE-T₂/T₁ hybrid sequence in a pediatric population with a clinical indication for an abdominal MRI examination to demonstrate that the hybrid imaging may be less challenging to perform on children.

MATERIALS AND METHODS

Our retrospective observational study included pediatric patients of all age groups and required for an abdominal MRI examination. Non-contrast standard axial T₁ DIXON and non-contrast RAVE-T₂/T₁ hybrid sequence were obtained at 3 T. MRI studies were analyzed independently by two pediatric radiologists using a 5-point Likert-type scale in five different categories. T₁- and T₂-weighted sequences were each compared with the RAVE-T₂/T₁-sequence using a Wilcoxon signed-rank test.

RESULTS

The analysis included 15 children (mean age, 11 years and 4 months, 7 girls and 8 boys). The Cohens Kappa of interrater agreement measured 0.62. The T₂ weighted part of the RAVE-T₂/T₁ sequence was significantly better than the standard T₂ HASTE sequence in four of five image quality categories: overall image quality (2.2 ± 0.7 vs 1.8 ± 0,7, p = 0.03), respiratory motion artefacts (3.8 ± 0.4 vs 2.0 ± 0.7, p <= 0.01), portal vein clarity (3.3 ± 0.8 vs 2.2 ± 0.7, p <= 0.01), hepatic margin sharpness (2.4 ± 1,0 vs 1.8 ± 0.7, p <= 0.01). The T₁ weighted part of the RAVE-T₂/T₁ sequence was significantly better than the standard T₁ DIXON weighted sequence in three of five image quality categories: respiratory motion artefacts (4.0 ± 0.2 vs 3.6 ± 0.8, p = 0.01), portal vein clarity (2.7 ± 0.9 vs 2.1 ± 0.7, p <= 0.01), hepatic margin sharpness (3.2 ± 0.7 vs 2.6 ± 0.9, p <= 0.01).

CONCLUSIONS

The RAVE-T₂/T₁ hybrid sequence is feasible and equal compared to standard T₁- and T₂-weighted sequences in the assessment of abdominal organs in a pediatric population. Due to non-inferiority to the current standard sequences for abdominal imaging, the RAVE-T₂/T₁ hybrid sequence is a good alternative for children who cannot be examined in breath-hold technique.

Free-breathing radial stack-of-stars three-dimensional Dixon gradient echo sequence in abdominal magnetic resonance imaging in sedated pediatric patients

BACKGROUND

There is a strong need for improvements in motion robust T1-weighted abdominal imaging sequences in children to enable high-quality, free-breathing imaging.

OBJECTIVE

To compare imaging time and quality of a radial stack-of-stars, free-breathing T1-weighted gradient echo acquisition (volumetric interpolated breath-hold examination [VIBE]) three-dimensional (3-D) Dixon sequence in sedated pediatric patients undergoing abdominal magnetic resonance imaging (MRI) against conventional Cartesian T1-weighed sequences.

MATERIALS AND METHODS

This study was approved by the institutional review board with informed consent obtained from all subjects. Study subjects included 31 pediatric patients (19 male, 12 female; median age: 5 years; interquartile range: 5 years) undergoing abdominal MRI at 3 tesla with a free-breathing T1-weighted radial stack-of-stars 3-D VIBE Dixon prototype sequence, StarVIBE Dixon (radial technique), between October 2018 and June 2019 with previous abdominal MR imaging using conventional Cartesian T1-weighed imaging (traditional technique). MRI component times were recorded as well as the total number of non-contrast T1-weighted sequences. Two radiologists independently rated images for quality using a scale from 1 to 5 according to the following metrics: overall image quality, hepatic edge sharpness, hepatic vessel clarity and respiratory motion robustness. Scores were compared between the groups.

RESULTS

Mean T1-weighted imaging times for all subjects were 3.63 min for radial exams and 8.01 min for traditional exams (P<0.001), and total non-contrast imaging time was 32.7 min vs. 43.9 min (P=0.002). Adjusted mean total MRI time for all subjects was 60.2 min for radial exams and 65.7 min for traditional exams (P=0.387). The mean number of non-contrast T1-weighted sequences performed in radial MRI exams was 1.0 compared to 1.9 (range: 0-6) in traditional exams (P<0.001). StarVIBE Dixon outperformed Cartesian methods in all quality metrics. The mean overall image quality (scale 1-5) was 3.95 for radial exams and 3.31 for traditional exams (P<0.001).

CONCLUSION

Radial stack-of-stars 3-D VIBE Dixon during free-breathing abdominal MRI in pediatric patients offers improved image quality compared to Cartesian T1-weighted imaging techniques with decreased T1-weighted and total non-contrast imaging time. This has important implications for children undergoing sedation for imaging.

[Imaging of tumor predisposition syndromes]

CLINICAL ISSUE

Tumor predisposition syndromes (TPS) are a heterogeneous group of genetic cancers. About 10% of the approximately 2200 malignancies in the childhood in Germany develop due to an inherited disposition, whereby TPS may be underdiagnosed. The focus of this review is set on imaging of Li-Fraumeni syndrome, neurofibromatoses, tuberous sclerosis, overgrowth, and neuroendocrine syndromes.

STANDARD RADIOLOGICAL METHODS

In order to detect tumors at an early stage, screening at specific time intervals for each TPS are required. Ultrasonography and magnetic resonance imaging (MRI), especially whole-body MRI, are particularly important imaging modalities.

METHODOLOGICAL INNOVATIONS

Innovative MRI techniques can increase image quality and patient comfort. MRI acquisition time can be significantly reduced through optimized acceleration factors, motion robust radial sequences and joint acquisition and readout of multiple slices during excitation. Thus, shorter MRI examinations can be performed in younger children without anesthesia.

PRACTICAL RECOMMENDATION

Regular screening with ultrasound and MRI can reduce the morbidity and mortality of the patients affected with TPS.

Success of Nonsedated Neuroradiologic MRI in Children 1-7 Years Old

BACKGROUND. MRI use and the need for monitored anesthesia care (MAC) in children have increased. However, MAC is associated with examination delays, increased cost, and safety concerns. OBJECTIVE. The purpose of this study was to evaluate the success rate of nonsedated neuroradiologic MRI studies in children 1-7 years old and to investigate factors associated with success. METHODS. We retrospectively reviewed data from our institutional nonsedated MRI program. Inclusion criteria were outpatient nonsedated MRI referral, age 1-7 years old, and neuroradiologic indication. Exclusion criteria were MRI examinations for ventricular checks and contrast material use. Success was determined by reviewing the clinical MRI report. We recorded patient age and sex, type of MRI examination (brain, spine, craniospinal, head and neck, and brain with MRA), protocol length, presence of child life specialist, video goggle use, and MRI appointment time (routine daytime appointment or evening appointment). We used descriptive statistics to summarize patient demographics and clinical data and logistic regression models to evaluate predictors of success in the entire sample. Subset analyses were performed for children from 1 to < 3 years old and 3 to 7 years old. RESULTS. We analyzed 217 patients who underwent nonsedated MRI examinations (median age, 5.1 years). Overall success rate was 82.0% (n = 178). The success rates were 81.4% (n = 127) for brain, 90.3% (n = 28) for spine, 71.4% (n = 10) for craniospinal, 66.7% (n = 6) for head and neck, and 100% (n = 7) for brain with MRA. Age was significantly associated with success (odds ratio [OR], 1.33; p = .009). In children 1 to < 3 years old, none of the factors analyzed were significant predictors of success (all, p > .48). In children 3-7 years old, protocol duration (OR, 0.96; 95% CI, 0.93-0.99; p = .02) and video goggle use (OR, 6.38; 95% CI, 2.16-18.84; p = .001) were significantly associated with success. CONCLUSION. A multidisciplinary approach with age-appropriate resources enables a high success rate for nonsedated neuroradiologic MRI in children 1-7 years old. CLINICAL IMPACT. Using age as the primary criterion to determine the need for MAC may lead to overuse of these services. Dissemination of information regarding nonsedated MRI practice could reduce the rate of sedated MRI in young children.

Safety challenges related to the use of sedation and general anesthesia in pediatric patients undergoing magnetic resonance imaging examinations

The use of sedation and general anesthesia has facilitated the significant growth of MRI use among children over the last years. While sedation and general anesthesia are considered to be relatively safe, their use poses potential risks in the short term and in the long term. This manuscript reviews the reasons why MRI examinations require sedation and general anesthesia more commonly in the pediatric population, summarizes the safety profile of sedation and general anesthesia, and discusses an amalgam of strategies that can be implemented and can ultimately lead to the optimization of sedation and general anesthesia care within pediatric radiology departments.

Non-pharmacological strategies to obtain usable magnetic resonance images in non-sedated infants: Systematic review and meta-analysis

BACKGROUND

Although the use of sedation is commonly practiced to keep infants still while receiving magnetic resonance imaging, non-pharmacological strategies are a potential alternative.

OBJECTIVES

The purpose of this study was to determine the success rate of obtaining usable magnetic resonance images in infants with the sole use of non-pharmacological strategies.

DESIGN

Systematic literature review and meta-analysis SETTING: A search was conducted in PubMed, CINAHL and Cochrane Library.

PARTICIPANTS

Human infants from birth to 24 months of age who did not receive any sedation or anesthesia during magnetic resonance imaging METHOD: Articles that reported the success rate of obtaining usable images were included.

RESULTS

Of the 521 non-duplicate articles found, 58 articles were included in the systematic review with sample sizes ranging from 2-457, an average success rate of 87.8%, and an average scan time of 30 min. The most common non-pharmacological technique included feeding and swaddling infants before imaging to encourage infants to sleep during the scan. Meta-analysis performed on 53 articles comprising 3,410 infants found a success rate of 87%, but significant heterogeneity was found (I² = 98.30%). It was more difficult to obtain usable images solely with non-pharmacological techniques if infants were critically ill or a structural magnetic resonance imaging of the brain was required.

CONCLUSION

Non-pharmacological techniques are effective for obtaining usable magnetic resonance imaging scans in most but not all infants. Tweetable abstract: Non-pharmacological techniques are effective for obtaining usable magnetic resonance imaging scans in most infants.

Diagnostic equivalency of fast T2 and FLAIR sequences for pediatric brain MRI: a pilot study

BACKGROUND

Faster and motion robust magnetic resonance imaging (MRI) sequences are desirable in pediatric brain MRI as they can help reduce the need for monitored anesthesia care, which is a costly and limited resource that carries medical risks.

OBJECTIVE

To evaluate the diagnostic equivalency of commercially available accelerated motion robust MR sequences relative to standard sequences.

MATERIALS AND METHODS

This was an institutional review board-approved prospective study. Subjects underwent a clinical brain MRI using conventional multiplanar images at 3 Tesla followed by fast axial T2 and FLAIR (fluid-attenuated inversion recovery) sequences optimized for an approximately 50% reduction in acquisition time. Conventional and fast images from each subject were reviewed by two blinded pediatric neuroradiologists. The readers evaluated the presence of 12 findings. Intra-observer agreement was estimated for fast versus conventional sequences. For each set of sequences, interobserver agreement calculations and chi-square tests were used to evaluate differences between fast and conventional acquisitions. An independent third reader reviewed the intra-observer discrepancies and adjudicated them as being more conspicuous on fast sequence, conventional sequence or the equivalent. The readers also were asked to rate motion artifacts with a previously validated score.

RESULTS

Images from 77 children (mean age: 11.3 years) were analyzed. Intra-observer agreement (fast versus conventional) ranged between 89.2% and 92.3%. Interobserver agreement ranged between 86.1% and 88.4%. Interobserver agreement was significantly higher for conventional FLAIR relative to fast FLAIR for small (<5 mm) foci of T2 in the white matter. Otherwise, interobserver agreement was not different between the fast and conventional sequences. For awake subjects, fast sequences had significantly fewer artifacts (P<0.05).

CONCLUSION

Conventional T2 and FLAIR sequences can be optimized to shorten acquisition while maintaining diagnostic equivalency. These faster sequences were also less susceptible to motion artifacts.

MRI Techniques to Decrease Imaging Times in Children

Long acquisition times can limit the use of MRI in pediatric patients, and the use of sedation or general anesthesia is frequently necessary to facilitate diagnostic examinations. The use of sedation or anesthesia has disadvantages including increased cost and imaging time and potential risks to the patient. Reductions in imaging time may decrease or eliminate the need for sedation or general anesthesia. Over the past decade, a number of imaging techniques that can decrease imaging time have become commercially available. These products have been used increasingly in clinical practice and include parallel imaging, simultaneous multisection imaging, radial k-space acquisition, compressed sensing MRI reconstruction, and automated protocol selection software. The underlying concepts, supporting data, current clinical applications, and available products for each of these strategies are reviewed in this article. In addition, emerging techniques that are still under investigation may provide further reductions in imaging time, including artificial intelligence-based reconstruction, gradient-controlled aliasing sampling and reconstruction, three-dimensional MR spectroscopy, and prospective motion correction. The preliminary results for these techniques are also discussed. ^©RSNA, 2020 See discussion on this article by Greer and Vasanawala.

Impact of a fast free-breathing 3-T abdominal MRI protocol on improving scan time and image quality for pediatric patients with tuberous sclerosis complex

BACKGROUND

Magnetic resonance imaging (MRI) of the abdomen can be especially challenging in pediatric patients because of image quality degradation from respiratory motion. Abdominal MR protocols tailored for free-breathing children can potentially improve diagnostic image quality and reduce scan time.

OBJECTIVE

To evaluate the performance of a free-breathing 3-T MRI protocol for renal evaluation in pediatric patients with tuberous sclerosis complex (TSC).

MATERIALS AND METHODS

A single institution, Institutional Review Board-approved, retrospective database query identified pediatric TSC patients who underwent a free-breathing 3-T MR abdominal protocol including radial and respiratory-triggered pulse sequences and who also had a prior abdominal MRI on the same scanner using a traditional MR protocol utilizing signal averaging and Cartesian k-space sampling. Scan times and use of sedation were recorded. MR image quality was compared between the two protocols using a semiquantitative score for overall image quality and sharpness.

RESULTS

Forty abdominal MRI studies in 20 patients were evaluated. The mean scan time of the fast free-breathing protocol was significantly lower (mean: 42.5±9.8 min) compared with the traditional protocol (58.7±11.7 min; P=<0.001). Image sharpness was significantly improved for radial T2-weighted and T1-weighted triggered Dixon and radial T1-weighted fat-suppressed post-contrast images in the free-breathing protocol, while image quality was significantly higher on radial and Dixon T1-weighted sequences.

CONCLUSION

A free-breathing abdominal MR protocol in pediatric TSC patients decreases scan time and improves image quality and should be considered more widely for abdominal MRI in children.

Pediatric non-alcoholic fatty liver disease: current perspectives on diagnosis and management

Non-alcoholic fatty liver disease (NAFLD) represents the most common cause of chronic liver disease in childhood. To date, the “multiple-hit” hypothesis is largely recognized as an explanation of NAFLD pathogenesis and progression. Obesity and features of the metabolic syndrome have been closely linked to NAFLD development. Due to the increased prevalence of obesity worldwide, NAFLD has reached epidemic proportions over time. Given its unfavorable cardiometabolic burden (such as cardiovascular and metabolic consequences), it represents a worrying phenomenon needing a more comprehensive and successful management. Laboratory tests and classical imaging techniques play a pivotal role in NAFLD diagnosis, but novel noninvasive alternative methods to diagnose and monitor NAFLD have been investigated. Currently, lifestyle modifications remain the mainstay treatment, although its efficacy is poor because of the lack of compliance. Pediatric research is focusing on multiple alternative treatments targeting the main pathogenic factors such as insulin-resistance, dyslipidemia, gut-liver axis and microbiota, oxidative stress, and proinflammatory pathways. Results from these studies are promising but larger validation is needed. Innovative therapeutic approaches might add an important piece in the complex knowledge of pediatric NAFLD. We aimed to summarize recent insights into NAFLD diagnosis and treatment in children, with a focus on possible future perspectives in pediatric research.

Respiratory motion in children and young adults undergoing liver magnetic resonance imaging with intravenous gadoxetate disodium contrast material

BACKGROUND

Gadoxetate disodium, utilized in hepatobiliary magnetic resonance (MR) imaging, has been associated with transient respiratory motion during the arterial phase in adults.

OBJECTIVE

The purpose of this study was to determine the presence and severity of this phenomenon in children imaged awake versus under general anesthesia.

MATERIALS AND METHODS

This retrospective cohort study was approved by the institutional review board; informed consent was waived. One hundred thirty exams of children ≤18 years old who underwent dynamic liver MR imaging with gadoxetate disodium between October 2010 and January 2018 were reviewed. Three pediatric radiologists scored respiratory motion artifacts on all imaging phases using a 5-point Likert scale. Differences in mean motion scores were assessed with analysis of variance and Tukey's multiple comparisons test, and multivariable regression was used to identify predictors of arterial phase motion in awake patients.

RESULTS

One hundred thirty patients (50% [n=65] female; mean age: 9.8±3.7 years, 48.5% [n=63] awake) were included. There were significant differences in mean motion scores between phases in the awake cohort (P<0.0001) but not in the general anesthesia cohort (P=0.051). In the awake cohort, arterial phase motion score (mean: 3.52±0.83) was significantly higher than mean motion score in all other phases (P≤0.0003). There were no significant patient-specific predictors of arterial phase motion score in the awake cohort.

CONCLUSION

Significantly increased arterial phase respiratory motion artifact in awake children undergoing dynamic liver MR imaging with gadoxetate disodium suggests that transient respiratory motion occurs in children. General anesthesia may suppress this phenomenon.

Recent Advances in Pediatric Brain, Spine, and Neuromuscular Magnetic Resonance Imaging Techniques

Magnetic resonance imaging (MRI) is a powerful radiologic tool with the ability to generate a variety of proton-based signal contrast from tissues. Owing to this immense flexibility in signal generation, new MRI techniques are constantly being developed, tested, and optimized for clinical utility. In addition, the safe and nonionizing nature of MRI makes it a suitable modality for imaging in children. In this review article, we summarize a few of the most popular advances in MRI techniques in recent years. In particular, we highlight how these new developments have affected brain, spine, and neuromuscular imaging and focus on their applications in pediatric patients. In the first part of the review, we discuss new approaches such as multiphase and multidelay arterial spin labeling for quantitative perfusion and angiography of the brain, amide proton transfer MRI of the brain, MRI of brachial plexus and lumbar plexus nerves (i.e., neurography), and T2 mapping and fat characterization in neuromuscular diseases. In the second part of the review, we focus on describing new data acquisition strategies in accelerated MRI aimed collectively at reducing the scan time, including simultaneous multislice imaging, compressed sensing, synthetic MRI, and magnetic resonance fingerprinting. In discussing the aforementioned, the review also summarizes the advantages and disadvantages of each method and their current state of commercial availability from MRI vendors.

Respiration resolved imaging with continuous stable state 2D acquisition using linear frequency SWEEP

Purpose

To investigate the potential of continuous radiofrequency (RF) shifting (SWEEP) as a technique for creating densely sampled data while maintaining a stable signal state for dynamic imaging.

Methods

We present a method where a continuous stable state of magnetization is swept smoothly across the anatomy of interest, creating an efficient approach to dense multiple 2D slice imaging. This is achieved by introducing a linear frequency offset to successive RF pulses shifting the excited slice by a fraction of the slice thickness with each successive repeat times (TR). Simulations and in vivo imaging were performed to assess how this affects the measured signal. Free breathing, respiration resolved 4D volumes in fetal/placental imaging is explored as potential application of this method.

Results

The SWEEP method maintained a stable signal state over a full acquisition reducing artifacts from unstable magnetization. Simulations demonstrated that the effects of SWEEP on slice profiles was of the same order as that produced by physiological motion observed with conventional methods. Respiration resolved 4D data acquired with this method shows reduced respiration artifacts and resilience to non‐rigid and non‐cyclic motion.

Conclusions

The SWEEP method is presented as a technique for improved acquisition efficiency of densely sampled short‐TR 2D sequences. Using conventional slice excitation the number of RF pulses required to enter a true steady state is excessively high when using short‐TR 2D acquisitions, SWEEP circumvents this limitation by creating a stable signal state that is preserved between slices.

Comparison of navigator-gated and breath-held image acquisition techniques for multi-echo quantitative dixon imaging of the liver in children and young adults

PURPOSE

Acquired over a breath hold, multi-echo Dixon (mDixon) magnetic resonance imaging (MRI) of the liver can be used to quantify proton density fat fraction (PDFF) and iron-related signal decay. However, young, obese, and co-morbid patients may have limited breath holding capacity and could benefit from a motion-robust mDixon acquisition. The purpose of this study was to compare hepatic PDFF and R2* values between navigator-gated and breath-held mDixon MRI acquisition techniques in children and young adults with suspected liver disease.

MATERIALS AND METHODS

This retrospective study was institutional review board-approved with a waiver of informed consent. Patients who underwent liver MRI with breath-held and navigator-gated mDixon sequences between January 2017 and July 2018 were included. One reviewer, blinded to sequence, measured PDFF and R2* on four images from each sequence. Another blinded reviewer graded respiratory motion (5-point Likert scale). Pearson correlation (r), Lin's concordance coefficients (r_c), and Bland-Altman analyses were used to assess agreement between techniques. Frequency of clinically limiting motion (score ≥ 3) was compared with Fisher's exact test.

RESULTS

Forty-two patients were included (15 female, 27 male; mean age: 15.7 ± 4.6 years). Mean PDFF and R2* were 16.6 ± 13.1% and 29.3 ± 4.7 s^-1 (breath-held) versus 17.0 ± 13.2% and 29.6 ± 5.2 s^-1 (navigator-gated). PDFF agreed almost perfectly between sequences (r_c = 0.997, 95% CI 0.994-0.998; mean bias: 0.3%; 95% limits of agreement: - 2.4 to +1.7%), while R2* values correlated very strongly but with poor agreement (r = 0.837, r_c = 0.832, 95% CI 0.716-0.910). Navigator-gated images exhibited significantly higher frequency of clinically limiting respiratory motion (88% vs. 48%, p = 0.0001).

CONCLUSION

Despite greater respiratory motion artifact, a free-breathing navigator-gated mDixon sequence produces PDFF values with almost perfect agreement to a breath-held sequence.

Techniques for minimizing sedation in pediatric MRI

MRI is used widely in infants and young children. However, in these young cases deep sedation or general anesthesia is often required to minimize motion artifacts during MRI examinations. Although the benefits of MR typically outweigh the potential risks of sedation when delivered by an experienced team, there are increasing concerns regarding the affect of sedation on young children. There continues to be a push to develop various strategies that can minimize the need for sedation. The present review summarizes several technical and clinical approaches that can help decrease the need for sedation in the pediatric patient. Optimization of the MRI environment, the role of child life specialists, feed-and-bundle and distraction techniques, noise-reduction methods, artificial intelligence, and MRI advances to decrease both scan times and motion artifacts will be discussed. Level of Evidence: 5 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2019.