Background Changes in brain stiffness can be an important biomarker for neurological disease. Magnetic resonance elastography (MRE) quantifies tissue stiffness, but the results vary between acquisition and reconstruction methods. Purpose To measure MRE repeatability and estimate the effect of different reconstruction methods and varying data quality on estimated brain stiffness. Study Type Prospective. Subjects Fifteen healthy subjects. Field Strength/Sequence 3T MRI, gradient‐echo elastography sequence with a 50 Hz vibration frequency. Assessment Imaging was performed twice in each subject. Images were reconstructed using a curl‐based and a finite‐element‐model (FEM)‐based method. Stiffness was measured in the whole brain, in white matter, and in four cortical and four deep gray matter regions. Repeatability coefficients (RC), intraclass correlation coefficients (ICC), and coefficients of variation (CV) were calculated. MRE data quality was quantified by the ratio between shear waves and compressional waves. Statistical Tests Median values with range are presented. Reconstruction methods were compared using paired Wilcoxon signed‐rank tests, and Spearman's rank correlation was calculated between MRE data quality and stiffness. Holm–Bonferroni corrections were employed to adjust for multiple comparisons. Results In the whole brain, CV was 4.3% and 3.8% for the curl and the FEM reconstruction, respectively, with 4.0–12.8% for subregions. Whole‐brain ICC was 0.60–0.74, ranging from 0.20 to 0.89 in different regions. RC for the whole brain was 0.14 kPa and 0.17 kPa for the curl and FEM methods, respectively. FEM reconstruction resulted in 39% higher stiffness than the curl reconstruction (P < 0.05). MRE data quality, defined as shear‐compression wave ratio, was higher in peripheral regions than in central regions of the brain (P < 0.05). No significant correlations were observed between MRE data quality and stiffness estimates. Data Conclusion MRE of the human brain is a robust technique in terms of repeatability. Caution is warranted when comparing stiffness values obtained with different techniques. Level of Evidence 1 Technical Efficacy Stage 1

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Atrial fibrillation (AF) diminishes left atrial (LA) mechanical function and impairs blood flow. The latter can lead to blood stasis and increased risk of thrombus formation and stroke. We investigate this risk by studying the effects of LA flow in sinus rhythm (SR) and AF on blood coagulation dynamics.Patient-specific computational fluid dynamics (CFD) simulations were coupled with the reaction-diffusionconvection equation for thrombin. Patient LA wall motions driving the flow were reconstructed from Cine MRI data during SR and AF. 15 cardiac cycles were simulated for each patient to evaluate the likelihood of thrombus formation in the critical left atrial appendage (LAA) and right inferior pulmonary vein (RIPV) regions.The simulations showed that mean blood flow velocity in the LA cavity was substantially decreased (47%) during AF compared to SR. Specifically in LAA, mean flow velocities decreased from 0.06m/s in SR to 0.035m/s in AF, leading to enhanced thrombin generation. In the RIPV, higher mean flow velocities (0.16m/s) enabled thrombin washout through the mitral valve irrespective of SR or AF.This study proposes a novel modelling approach for quantifying the likelihood of AF-related thrombogenesis within LA and demonstrates increased risk of thrombus formation in the LAA when compared with the RIPV.

ObjectivesThree-dimensional (3D) magnetic resonance elastography (MRE) measures liver fibrosis and inflammation but requires several breath-holds that hamper clinical acceptance. The aim of this study was to evaluate the technical and clinical feasibility of a single breath-hold 3D MRE sequence as a means of measuring liver fibrosis and inflammation in obese patients.MethodsFrom November 2020 to December 2021, subjects were prospectively enrolled and divided into 2 groups. Group 1 included healthy volunteers (n = 10) who served as controls to compare the single breath-hold 3D MRE sequence with a multiple–breath-hold 3D MRE sequence. Group 2 included liver patients (n = 10) who served as participants to evaluate the clinical feasibility of the single breath-hold 3D MRE sequence in measuring liver fibrosis and inflammation. Controls and participants were scanned at 60 Hz mechanical excitation with the single breath-hold 3D MRE sequence to retrieve the magnitude of the complex-valued shear modulus (|G*| [kPa]), the shear wave speed (Cs [m/s]), and the loss modulus (G" [kPa]). The controls were also scanned with a multiple–breath-hold 3D MRE sequence for comparison, and the participants had histopathology (Ishak scores) for correlation with Cs and G".ResultsFor the 10 controls, 5 were female, and the mean age and body mass index were 33.1 ± 9.5 years and 23.0 ± 2.1 kg/m2, respectively. For the 10 participants, 8 were female, and the mean age and body mass index were 45.1 ± 16.5 years and 33.1 ± 4.0 kg/m2 (obese range), respectively. All participants were suspected of having nonalcoholic fatty liver disease. Bland-Altman analysis of the comparison in controls shows there are nonsignificant differences in |G*|, Cs, and G" below 6.5%, suggesting good consensus between the 2 sequences. For the participants, Cs and G" correlated significantly with Ishak fibrosis and inflammation grades, respectively (ρ = 0.95, P < 0.001, and ρ = 0.84, P = 0.002).ConclusionThe single breath-hold 3D MRE sequence may be effective in measuring liver fibrosis and inflammation in obese patients.