PURPOSE: Motion artifacts remain a major challenge in applying multi-shot 2D imaging to motion prone patient populations. Through-plane motion is especially problematic, where the lack of encoding cannot be easily recovered, even using deep-learning (DL)-regularized reconstruction. We demonstrate the benefits of combining prospective and retrospective motion correction, where the Scout Accelerated Motion Estimation and Reduction (SAMER) technique is utilized for on-the-fly motion estimation with field-of-view (FoV) updates along with retrospective correction of potential residual motion.

METHODS: Four prospective motion correction (pMoCo) strategies were implemented within a custom 2D turbo-spin-echo (TSE) SAMER enabled sequence. They were evaluated in vivo across representative subject motion, with associated simulations to characterize artifacts and the correction performance. In addition, motion trajectories measured during inpatient clinical exams were used to further demonstrate the robustness of the combined motion correction approach.

RESULTS: Prospectively applying FoV updates significantly improved the image quality of SAMER reconstructions. Simulated artifact patterns were shown to closely match those observed in vivo, and across 274 simulations using clinical motion trajectories, the combined approach reduced NRMSE in 90% of moderate-to-severe motion cases and significantly decreased the overall reconstruction error.

CONCLUSION: Utilizing on-the-fly SAMER motion estimates, a combined prospective and retrospective motion correction approach was demonstrated for 2D TSE imaging. The proposed method improved image quality in several representative in vivo motion experiments and across simulations of a wide range of clinical inpatient motion conditions. In addition, simulated artifact patterns were shown to closely match those observed in vivo. This capability should enable on-the-fly prediction of motion artifacts for efficient/intelligent acquisition strategies for the most challenging motion scenarios.

Characterizing in-utero brain development is essential for understanding typical and atypical neurodevelopment. Building on prior spatiotemporal fetal brain MRI atlases, we present the CRL-2025 fetal brain atlas, a spatiotemporal (4D) atlas of the developing fetal brain between 21 and 37 gestational weeks. This atlas is constructed from MRI scans of 159 fetuses with typically developing brains using a diffeomorphic deformable registration framework integrated with kernel regression on age. CRL-2025 uniquely includes detailed tissue segmentations, transient white matter compartments, and parcellation into 126 anatomical regions. It offers significantly enhanced anatomical details over the CRL-2017 atlas and is presented along with a re-release of the CRL diffusion MRI atlas featuring newly created tissue segmentation and labels. We release de-identified, processed subject-level fetal MRI datasets used to generate CRL-2025, providing input-output transparency and reproducibility. We also provide FetalSEG, a deep learning-based multiclass segmentation tool to facilitate automatic fetal brain MRI segmentation. The CRL-2025 atlas and its tools enable scalable fetal brain MRI segmentation, analysis, and neurodevelopmental research for the broader community.

BACKGROUND: Measuring differential renal function (DRF) is critical for managing children with congenital and acquired urological diseases. MAG-3 renal scintigraphy is the most widely used clinical technique; dynamic contrast-enhanced MRI (DCE-MRI) provides a radiation-free and high-resolution alternative method for assessing DRF.

OBJECTIVE: To evaluate the agreement between DRF values derived from DCE-MRI and MAG-3 scintigraphy-derived DRF in pediatric patients.

MATERIALS AND METHODS: This retrospective study included 23 pediatric patients (age range, 3 months-20 years; mean±SD, 8.3±7.4 years) who underwent DCE-MRI embedded in MR urography (MRU) protocol and MAG-3 studies within 6 months. DCE-MRI was performed using a golden-angle radial dynamic stack-of-stars acquisition with golden-angle sparse parallel (GRASP) reconstruction, and analyzed the renal filtration rate with a two-compartment tracer kinetic model. DRF values from DCE-MRI were compared with those from MAG-3, using both default (n=23) and C-shaped background regions for MAG-3 analysis, where raw data were available (n=16). Agreement was evaluated using Bland-Altman analysis, Pearson and concordance correlations, and paired statistical tests.

RESULTS: With default MAG-3 background analysis (n=23), mean DRF difference (MAG-3 minus DCE-MRI) was 0.4% (95% CI, -3.3% to 4.2%), with 95% limits of agreement of -16.7% to +17.5%. Concordance correlation coefficient (CCC) was 0.870 (95% CI, 0.718-0.942). Within the pre-defined clinically acceptable margin of ±10%, 78.3% (18/23) of cases fell, with a mean absolute difference of 6.1%. With C-shaped background subtraction in the subset with available raw MAG-3 data (n=16), mean difference was -2.3% (95% CI, -6.7% to 2.0%), limits of agreement -18.3% to +13.6%, and CCC 0.845 (95% CI, 0.614-0.943). Pearson correlation was strong in both analyses (n=23: r=0.872, 95% CI, 0.719-0.945; n=16: r=0.866, 95% CI, 0.648-0.953; both P<0.001). No clinically significant systematic or proportional bias was detected in either analysis.

CONCLUSION: DCE-MRI demonstrates strong linear association and concordance with MAG-3 scintigraphy for pediatric differential renal function assessment with no clinically significant systematic bias, though the observed measurement variability indicates caution is warranted when comparing values near surgical decision thresholds. C-shaped background correction is recommended for MAG-3 in hydronephrotic kidneys to optimize inter-modality agreement.

BACKGROUND: The stria of Gennari (SoG) is a densely myelinated band within layer IVb of the primary visual cortex (V1) and represents the only cortical laminar structure visible macroscopically in vivo. Ultrahigh-field MRI may improve its detection and conspicuity.

PURPOSE: To quantitatively and qualitatively compare the in vivo appearance of the SoG at 3 versus 7 T using matched high-resolution T2-weighted fast spin-echo MRI.

STUDY TYPE: Prospective.

POPULATION: A total of 12 subjects (6 female, 6 male; median age, 17 years; range, 15-24 years) with pediatric-onset epilepsy.

FIELD STRENGTH/SEQUENCE: 3 and 7 T MRI, T2-weighted fast spin-echo, acquired within 1 month of each other.

ASSESSMENT: Cortical line profiles per subject were extracted orthogonally to the calcarine sulcus in V1. Quantitative metrics included peak-valley distance, Δ-signal (peak-valley difference), and contrast ratio (CR). Two blinded neuroradiologists and a radiologist independently rated SoG conspicuity using a 5-point Likert scale.

STATISTICAL TESTS: McNemar's test compared detection rates; paired t-tests or Wilcoxon signed-rank tests compared quantitative metrics; reader preferences were analyzed using Wilcoxon tests; inter-reader agreement was assessed using weighted Cohen's κ. No multiple-comparison correction was applied (α = 0.05).

RESULTS: SoG-consistent valleys were detected in 31% of profiles at 3 T and 65% at 7 T, significantly. Peak-valley distance remained stable across field strengths (0.45 ± 0.06 depth units; p = 0.37). Mean Δ-signal (33.5 vs. 36.1; p = 0.81) and contrast ratio (0.013 vs. 0.000; p = 0.54) did not differ significantly. Both readers demonstrated a strong preference for 7 T images (pseudo-median +1 to +1.5; significant), with fair inter-reader agreement (κ = 0.36).

DATA CONCLUSION: The SoG can be visualized in vivo at both 3 and 7 T, with higher detection frequency and greater subjective conspicuity at 7 T. Quantitative laminar metrics remained stable across field strengths, suggesting that improved detectability at 7 T likely reflects enhanced spatial definition rather than measurable changes in signal contrast.

TECHNICAL EFFICACY: Stage 2.

BACKGROUND AND PURPOSE: The increased SNR at 7T enables higher spatial resolution for neurovascular imaging, yet its application in pediatric MRA remains underexplored. This study systematically evaluates the advantages of 7T TOF-MRA compared with 3T in pediatric patients, hypothesizing that 7T would provide superior vessel contrast and increased vascular volume, given the use of smaller voxels, as well as higher SNR, despite these smaller voxels.

MATERIALS AND METHODS: This Health Insurance Portability and Accountability Act (HIPAA)-compliant, institutional review board-approved retrospective study included pediatric patients (younger than 19 years of age) who underwent 7T TOF-MRA. Controls consisted of either same-subject 3T MRAs within 6 months (when available) or age- and sex-matched 3T MRA subjects. Imaging parameters were optimized for spatial resolution at 7T to achieve 0.3- to 0.4-mm isotropic voxels. Quantitative analysis included contrast ratio and SNR measurements for the ICA, M1 to M4 arterial segments, and the lenticulostriate perforating arteries. Vascular volume was assessed using 3D segmentation. Semiquantitative vessel conspicuity ratings and motion artifact scoring were performed by blinded neuroradiologists.

RESULTS: Fifteen patients (10 with 7T MRA, 5 with matched 3T controls) and 20 MRAs were analyzed. Contrast ratio was significantly higher at 7T for perforators, M3, and M4 branches (P < .05), with the greatest improvement in the M4 branches. Vascular volume was 147% greater at 7T (P = .018), reflecting improved small-vessel depiction and segmentation. Semiquantitative analysis showed significantly better vessel conspicuity at 7T for the M4 branches and lenticulostriate perforators (P < .01). Motion artifact scores were similar between field strengths (P = .118).

CONCLUSIONS: 7T TOF-MRA significantly enhances vascular contrast and improves visualization of small arteries compared with 3T, making it a valuable tool for pediatric cerebrovascular imaging.

BACKGROUND: The posterior fossa undergoes rapid development in utero, yet normative volumetric data are limited, especially during mid-gestation when most fetal MRIs are performed.

OBJECTIVE: This study aimed to develop a segmentation method tailored to the fetal posterior fossa and establish normative growth trajectories for key infratentorial structures between 22 weeks and 32 weeks of gestation.

MATERIALS AND METHODS: Eighty-five pregnant women were prospectively recruited at a single institution. Inclusion criteria were normal singleton pregnancies between 19-40 weeks' gestation and maternal age 18-45 years. Exclusion criteria included fetal abnormalities, MRI contraindications, or significant maternal comorbidities. Eighteen fetuses were excluded, resulting in 67 normal fetuses (43 male, 24 female). Imaging was performed at 3 T using multiplanar T2-weighted sequences, reconstructed into isotropic volumes after motion correction and brain extraction. Segmentation labels were created using age-specific atlases from the Developing Human Connectome Project. Expert annotations defined the midbrain, pons, medulla, vermis, and cerebellar hemispheres. Images were registered to the atlases using the Symmetric Normalization (SyN) algorithm, with labels manually verified by a pediatric neuroradiologist. Volumes were normalized to total brain volume and analyzed using linear regression with gestational age and sex as predictors.

RESULTS: Absolute volumes of all posterior fossa structures significantly increased with gestational age (P<0.001), showing strong linear associations (R2=0.80-0.87). The cerebellum exhibited the steepest growth (β=1,056.01, R2=0.87, P<0.001). Growth was symmetric with no significant left-right differences. Relative volumetric trends varied: the cerebellum increased proportionally (β=0.007, P<0.001), while the midbrain, pons, and medulla decreased relative to total brain volume. The vermis showed no significant association with gestational age but had sex-specific effects; males had smaller relative vermian volumes than females (β=-0.43, P=0.04), despite larger absolute posterior fossa volumes overall.

CONCLUSIONS: This study provides normative volumetric references for fetal posterior fossa structures between 22-32 weeks' gestation using a novel segmentation method. Absolute growth followed linear patterns, while relative measures revealed sex-specific variations in the vermis and cerebellum. These benchmarks may enhance diagnostic accuracy for detecting posterior fossa anomalies in clinical fetal MRI.

Quantitative analysis of pseudo-diffusion in diffusion-weighted magnetic resonance imaging (DWI) data shows potential for assessing fetal lung maturation and generating valuable imaging biomarkers. Yet, the clinical utility of DWI data is hindered by unavoidable fetal motion during acquisition. We present IVIM-morph, a self-supervised deep neural network model for motion-corrected quantitative analysis of DWI data using the Intra-voxel Incoherent Motion (IVIM) model. IVIM-morph combines two sub-networks, a registration sub-network, and an IVIM model fitting sub-network, enabling simultaneous estimation of IVIM model parameters and motion. To promote physically plausible image registration, we introduce a biophysically informed loss function that effectively balances registration and model-fitting quality. We validated the efficacy of IVIM-morph by establishing a correlation between the predicted IVIM model parameters of the lung and gestational age (GA) using fetal DWI data of 39 subjects. Our approach was compared against six baseline methods: 1) no motion compensation, 2) affine registration of all DWI images to the initial image, 3) deformable registration of all DWI images to the initial image, 4) deformable registration of each DWI image to its preceding image in the sequence, 5) iterative deformable motion compensation combined with IVIM model parameter estimation, and 6) self-supervised deep-learning-based deformable registration. IVIM-morph exhibited a notably improved correlation with gestational age (GA) when performing in-vivo quantitative analysis of fetal lung DWI data during the canalicular phase. Specifically, over 2 test groups of cases, it achieved an R f 2 of 0.44 and 0.52, outperforming the values of 0.27 and 0.25, 0.25 and 0.00, 0.00 and 0.00, 0.38 and 0.00, and 0.07 and 0.14 obtained by other methods. IVIM-morph shows potential in developing valuable biomarkers for non-invasive assessment of fetal lung maturity with DWI data. Moreover, its adaptability opens the door to potential applications in other clinical contexts where motion compensation is essential for quantitative DWI analysis. The IVIM-morph code is readily available at:https://github.com/TechnionComputationalMRILab/qDWI-Morph.

PURPOSE: To develop a rapid, high-resolution and distortion-free technique for simultaneous water-fat separation, R 2 * and B 0 mapping of the fetal brain at 3T.

METHODS: A 2D multi-echo radial FLASH sequence with blip gradients is adapted for data acquisition during maternal free breathing. A calibrationless model-based reconstruction with sparsity constraints is developed to jointly estimate water, fat, R 2 * and B 0 field maps directly from k-space. This approach was validated and compared to reference methods using numerical and NIST phantoms and data from nine fetuses between 26 and 36 weeks of gestation age.

RESULTS: Both numerical and experimental phantom studies confirm good accuracy and precision. In fetal studies, model-based reconstruction yields quantitative R 2 * values in close agreement with those from a parallel imaging compressed sensing (PICS) technique using Graph Cut (intra-class correlation coefficient [ICC] = 0.9601), while providing enhanced image detail. Repeated scans confirm good reproducibility (ICC = 0.9213). Compared to multi-echo EPI, the proposed radial technique produces higher-resolution (1.1 × 1.1 × 3 mm3 vs. 2-3 × 2-3 × 3 mm3) R 2 * maps with reduced distortion. Despite of differences in motion, resolution and distortion, R 2 * values are comparable between the two acquisition strategies (ICC = 0.8049). Additionally, the proposed approach enables synthesis of high-resolution and distortion-free R 2 * -weighted images.

CONCLUSION: This study demonstrates the feasibility of using multi-echo radial FLASH combined with calibrationless model-based reconstruction for motion-robust, distortion-free R 2 * mapping of the fetal brain at 3T, achieving a nominal resolution of 1.1 × 1.1 × 3 mm3 within 2 seconds per slice.

BACKGROUND: T2*-weighted imaging at 7 T offers detailed visualization of brain structures, but image quality and artifacts depend on echo time (TE) adjustments. Optimizing TE is crucial for tissue contrast and artifact minimization.

OBJECTIVE: To evaluate the impact of TE on tissue contrast and image quality in T2*-weighted sequences at 7 T in adolescents and young adults.

MATERIALS AND METHODS: Ten adolescent and young adult patients underwent 7-T MRI with multi-echo T2*-weighted sequences. Six TEs (8.1 ms to 36 ms) were acquired. Signal contrast ratios (CR) for seven brain regions-caudate nuclei, corpus callosum genu, frontal cortex, cortical veins, globi pallidi, medullary veins, and left optic radiation-were analyzed. Two blinded neuroradiologists assessed image quality and artifact severity using a 4-point Likert scale (IQS). Statistical trends were analyzed using the Jonckheere-Terpstra test. A P-value < 0.05 was considered statistically significant.

RESULTS: The study cohort consisted of 4 male and 6 females; the median age of the patients was 16 years (range 15-23 years). CR increased significantly with higher TEs for most regions except the caudate, where CR decreased (P < 0.05). Longer TEs led to greater artifact severity in the brainstem, temporal, occipital, and frontal lobes (P < 0.02), but not in parietal lobes (P > 0.05). Kappa agreement for IQS was 0.76.

CONCLUSION: TE significantly affects contrast and artifacts in 7-T T2*-weighted imaging. TEs between 20 and 30 ms offer the best balance between tissue contrast and artifact severity, optimizing image quality for clinical and research applications.