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Background: In patients with bicuspid aortic valve (BAV), 4D flow MRI can quantify regions exposed to abnormal aortic hemodynamics, including high wall shear stress (WSS), a known stimulus for arterial wall dysfunction. However, the long‐term multiscan reproducibility of 4D flow MRI‐derived hemodynamic parameters is unknown. Purpose: To investigate the long‐term stability of 4D flow MRI‐derived peak velocity, WSS, and WSS‐derived heatmaps in patients with BAV undergoing multiyear surveillance imaging. Study Type: Retrospective. Population: 20 BAV patients (mean age 48.4 ± 13.9 years; 14 males) with five 4D flow MRI scans, with intervals of at least 6 months between scans, and 125 controls (mean age: 50.7 ± 15.8 years; 67 males). Field Strength/Sequence: 1.5 and 3.0T, prospectively ECG and respiratory navigator‐gated aortic 4D flow MRI. Assessment: Automated AI‐based 4D flow analysis pipelines were used for data preprocessing, aorta 3D segmentation, and quantification of ascending aorta (AAo) peak velocity, peak systolic WSS, and heatmap‐derived relative area of elevated WSS compared to WSS ranges in age and sex‐matched normative control populations. Growth rate was derived from the maximum AAo diameters measured on the first and fifth MRI scans. Statistical Tests: One‐way repeated measures analysis of variance. P < 0.05 indicated significance. Results: One hundred 4D flow MRI exams (five per patient) were analyzed. The mean total follow‐up duration was 5.5 ± 1.1 years, and the average growth rate was 0.3 ± 0.2 mm/year. Peak velocity, peak systolic WSS, and relative area of elevated WSS did not change significantly over the follow‐up period (P = 0.64, P = 0.69, and P = 0.35, respectively). The patterns and areas of elevated WSS demonstrated good reproducibility on semiquantitative assessment. Conclusion: 4D flow MRI‐derived peak velocity, WSS, and WSS‐derived heatmaps showed good multiyear and multiscan stability in BAV patients with low aortic growth rates. These findings underscore the reliability of these metrics in monitoring BAV patients for potential risk of dilation. Level of Evidence: 3 Technical Efficacy: Stage 1 [ABSTRACT FROM AUTHOR]

Purpose: An automatic method is presented for estimating 4D flow MRI velocity measurement uncertainty in each voxel. The velocity distance (VD) metric, a statistical distance between the measured velocity and local error distribution, is introduced as a novel measure of 4D flow MRI velocity measurement quality. Methods: The method uses mass conservation to assess the local velocity error variance and the standardized difference of means (SDM) velocity to estimate the velocity error correlations. VD is evaluated as the Mahalanobis distance between the local velocity measurement and the local error distribution. The uncertainty model is validated synthetically and tested in vitro under different flow resolutions and noise levels. The VD's application is demonstrated on two in vivo thoracic vasculature 4D flow datasets. Results: Synthetic results show the proposed uncertainty quantification method is sensitive to aliased regions across various velocity‐to‐noise ratios and assesses velocity error correlations in four‐ and six‐point acquisitions with correlation errors at or under 3.2%. In vitro results demonstrate the method's sensitivity to spatial resolution, venc settings, partial volume effects, and phase wrapping error sources. Applying VD to assess in vivo 4D flow MRI in the aorta demonstrates the expected increase in measured velocity quality with contrast administration and systolic flow. Conclusion: The proposed 4D flow MRI uncertainty quantification method assesses velocity measurement error owing to sources including noise, intravoxel phase dispersion, and velocity aliasing. This method enables rigorous comparison of 4D flow MRI datasets obtained in longitudinal studies, across patient populations, and with different MRI systems. [ABSTRACT FROM AUTHOR]

Purpose: To develop a highly‐accelerated, real‐time phase contrast (rtPC) MRI pulse sequence with 40 fps frame rate (25 ms effective temporal resolution). Methods: Highly‐accelerated golden‐angle radial sparse parallel (GRASP) with over regularization may result in temporal blurring, which in turn causes underestimation of peak velocity. Thus, we amplified GRASP performance by synergistically combining view‐sharing (VS) and k‐space weighted image contrast (KWIC) filtering. In 17 pediatric patients with congenital heart disease (CHD), the conventional GRASP and the proposed GRASP amplified by VS and KWIC (or GRASP + VS + KWIC) reconstruction for rtPC MRI were compared with respect to clinical standard PC MRI in measuring hemodynamic parameters (peak velocity, forward volume, backward volume, regurgitant fraction) at four locations (aortic valve, pulmonary valve, left and right pulmonary arteries). Results: The proposed reconstruction method (GRASP + VS + KWIC) achieved better effective spatial resolution (i.e., image sharpness) compared with conventional GRASP, ultimately reducing the underestimation of peak velocity from 17.4% to 6.4%. The hemodynamic metrics (peak velocity, volumes) were not significantly (p > 0.99) different between GRASP + VS + KWIC and clinical PC, whereas peak velocity was significantly (p < 0.007) lower for conventional GRASP. RtPC with GRASP + VS + KWIC also showed the ability to assess beat‐to‐beat variation and detect the highest peak among peaks. Conclusion: The synergistic combination of GRASP, VS, and KWIC achieves 25 ms effective temporal resolution (40 fps frame rate), while minimizing the underestimation of peak velocity compared with conventional GRASP. [ABSTRACT FROM AUTHOR]

The environmental impact of magnetic resonance imaging (MRI) has recently come into focus. This includes its enormous demand for electricity compared to other imaging modalities and contamination of water bodies with anthropogenic gadolinium related to contrast administration. Given the pressing threat of climate change, addressing these challenges to improve the environmental sustainability of MRI is imperative. The purpose of this review is to discuss the challenges, opportunities, and the need for action to reduce the environmental impact of MRI and prepare for the effects of climate change. The approaches outlined are categorized as strategies to reduce greenhouse gas (GHG) emissions from MRI during production and use phases, approaches to reduce the environmental impact of MRI including the preservation of finite resources, and development of adaption plans to prepare for the impact of climate change. Co‐benefits of these strategies are emphasized including lower GHG emission and reduced cost along with improved heath and patient satisfaction. Although MRI is energy‐intensive, there are many steps that can be taken now to improve the environmental sustainability of MRI and prepare for the effects of climate change. On‐going research, technical development, and collaboration with industry partners are needed to achieve further reductions in MRI‐related GHG emissions and to decrease the reliance on finite resources. Level of Evidence: 5 Technical Efficacy: Stage 6 [ABSTRACT FROM AUTHOR]

Background: Chronic graft failure (CGF) in pediatric heart transplant (PHT) is multifactorial and may present with findings of fibrosis and microvessel disease (MVD) on endomyocardial biopsy (EMB). There is no optimal CGF surveillance method. We evaluated associations between cardiac magnetic resonance imaging (CMR) and historical/EMB correlates of CGF to assess CMR's utility as a surveillance method. Methods: Retrospective analysis of PHT undergoing comprehensive CMR between September 2015 and January 2022 was performed. EMB within 6 months was graded for fibrosis (scale 0–5) and MVD (number of capillaries with stenotic wall thickening per field of view). Correlation analysis and logistic regression were performed. Results: Forty‐seven PHT with median age at CMR of 15.7 years (11.6, 19.3) and time from transplant of 6.4 years (4.1, 11.0) were studied. Cardiac allograft vasculopathy (CAV) was present in 11/44 (22.0%) and historical rejection in 14/41 (34.2%). CAV was associated with higher global T2 (49.0 vs. 47.0 ms; p = 0.038) and peak T2 (57.0 vs. 53.0 ms; p = 0.013) on CMR. Historical rejection was associated with higher global T2 (49.0 vs. 47.0 ms; p = 0.007) and peak T2 (57.0 vs. 53.0 ms; p = 0.03) as well as global extracellular volume (31.0 vs. 26.3%; p = 0.03). Higher fibrosis score on EMB correlated with smaller indexed left ventricular mass (rho = −0.34; p = 0.019) and greater degree of MVD with lower indexed left ventricular end‐diastolic volume (rho = −0.35; p = 0.017). Conclusion: Adverse ventricular remodeling and abnormal myocardial characteristics on CMR are present in PHT with CAV, historical rejection, as well as greater fibrosis and MVD on EMB. CMR has the potential use for screening of CGF. [ABSTRACT FROM AUTHOR]

Background: Although radiomics features of the left ventricular wall have been used to assess cardiac diseases, radiomics features of the cardiac blood pool have been relatively ignored. Purpose: To test the hypothesis that cine MRI‐derived radiomics features of the cardiac blood pool are associated with cardiac function and motion. Study Type: Retrospective. Population: A total of 26 healthy volunteers (51.2 ± 15.6 years; 17 males). Field Strength/Sequence: A 1.5 T/balanced steady‐state free precession (bSSFP). Assessment: The radiomics features (107 features in seven classes) of the blood pool of the left/right ventricle/atrium (LV/RV/LA/RA) were extracted on four‐chamber cine images (25 phases). Conventional cardiac function parameters (volumes, ejection fraction [EF] and longitudinal strain) were assessed in each cardiac chamber. Intraobserver‐ and interobserver agreements of radiomics features of all chambers acquired at all phases were assessed, as well as scan–rescan agreement in a subset of 13 volunteers. Statistical Tests: Pearson correlation coefficients (r) were used to assess the associations between peak values of radiomics features and end‐diastolic (or maximal) volume, end‐systolic (or minimal) volume, EF, and longitudinal strain of corresponding chambers. Good intraobserver, interobserver, and scan–rescan agreements for radiomics features acquired were defined as intraclass correlation coefficient (ICC) > 0.7 or coefficient of variation (CoV) < 20%. Results: Most radiomics features of the blood pool varied periodically throughout the cardiac cycle. Peak values of chamber‐specific blood pool radiomics features were correlated with traditional cardiac function and motion indices of corresponding chambers (r: 0.4–0.87). Ninety‐three (87%), 86 (80%), and 73 (68%) radiomics features demonstrated good intraobserver, interobserver, and scan–rescan reproducibility, respectively. Conclusion: Cine MRI‐derived radiomics features within LV/RV/LA/RA are associated with traditional cardiac function and motion indices of corresponding chambers and may have the potential to become novel quantitative imaging biomarkers in cardiovascular medicine. Evidence Level: 3. Technical Efficacy: 1. [ABSTRACT FROM AUTHOR]

Background: Hemodynamic assessment of left atrial (LA) flow using phase contrast MRI provides insight into thromboembolic risk in atrial fibrillation (AF). However, conventional flow imaging techniques are averaged over many heartbeats. Purpose: To evaluate beat‐to‐beat variability and LA hemodynamics in patients with AF using real time phase contrast (RTPC) MRI. Study Type: Prospective. Subjects: Thirty‐five patients with history of AF (68 ± 10 years, nine female), 10 healthy controls (57 ± 19 years, four female). Field Strength/Sequence: 5T, 2D RTPC with through‐plane velocity‐encoded gradient echo sequence and 4D flow MRI with three‐directional velocity‐encoded gradient echo sequence. Assessment: RTPC was continuously acquired for a mid‐LA slice in all subjects. 4D flow data were interpolated at the RTPC location and normally projected for comparison with RTPC. RR intervals extracted from RTPC were used to calculate heart rate variability (HRV = interquartile range over median × 100%). Patients were classified into low (<9.7%) and high (>9.7%) HRV groups. LA peak/mean velocity and stasis (%velocities < 5.8 cm/sec) were calculated from segmented 2D images. Variability in RTPC flow metrics was quantified by coefficient of variation (CV) over all cycles. Statistical Tests: Pearson's correlation coefficient (r), Bland–Altman analysis, Kruskal–Wallis test. A P value < 0.05 was considered statistically significant. Results: RTPC and 4D flow measurements were strongly/significantly correlated for all hemodynamic parameters (R2 = 0.75–0.83) in controls. Twenty‐four patients had low HRV (mean = 4 ± 2%) and 11 patients had high HRV (27 ± 9%). In patients, increased HRV was significantly correlated with CV of peak velocity (r = 0.67), mean velocity (r = 0.51), and stasis (r = 0.41). A stepwise decrease in peak/mean velocity and increase in stasis was observed when comparing controls vs. low HRV vs. high HRV groups. Mean velocity and stasis differences were significant for control vs. high HRV groups. Conclusions: RTPC may be suitable for assessing the impact of HRV on hemodynamics and provide insight for AF management in highly arrhythmic patients. Evidence Level: 1 Technical Efficacy: Stage 2 [ABSTRACT FROM AUTHOR]

Background: In Duchenne muscular dystrophy (DMD), the right ventricle (RV) tends to be relatively well preserved, but characterization remains difficult due to its complex architecture. Tissue phase mapping (TPM) is a phase contrast cine MRI technique that allows for multidirectional assessment of myocardial velocities. Purpose: To use TPM to elucidate relationships between myocardial structure, function, and clinical variables in DMD. Study Type: Retrospective. Subjects: A total of 20 patients with muscular dystrophy (median age: 16 years); 18 age‐matched normal controls (median age: 15 years). Field Strength/Sequence: Three‐directional velocity encoded cine gradient echo sequence (TPM) at 1.5 T, balanced steady‐state free procession (bSSFP), T1 mapping with extracellular volume (ECV), and late gadolinium enhancement (LGE). Assessment: TPM in basal, mid, and apical short‐axis planes was performed as part of a standard MRI study with collection of clinical data. Radial, circumferential, and longitudinal velocities (Vr, Vφ, and Vz, respectively) and corresponding time to peak (TTP) velocities were quantified from TPM and used to calculate RV twist as well as intraventricular and interventricular dyssynchrony. The correlations between TPM velocities, myocardial structure/function, and clinical variables were assessed. Statistical Test: Unpaired t‐test, Wilcoxon rank‐sum test, Bland–Altman analyses were used for comparisons between DMD patients and controls and between DMD subgroups. Pearson's test was used for correlations (r). Significance level: P < 0.05. Results: Compared to controls, DMD patients had preserved RV ejection fraction (RVEF 53% ± 8%) but significantly increased interventricular dyssynchrony (Vφ: 0.49 ± 0.21 vs. 0.72 ± 0.17). Within the DMD cohort, RV dyssynchrony significantly increased with lower LV ejection fraction (intraventricular Vr and Vz: r = −0.49; interventricular Vz: r = 0.48). In addition, RV intraventricular dyssynchrony significantly increased with older age (Vz: r = 0.67). Data Conclusion: RV remodeling in DMD occurs in the context of preserved RVEF. Within DMD, this abnormal RV deformation is associated with older age and decreased LVEF. Evidence Level: 4. Technical Efficacy: Stage 2. [ABSTRACT FROM AUTHOR]

Background: Four‐dimensional (4D) flow MRI allows for the quantification of complex flow patterns; however, its clinical use is limited by its inherently long acquisition time. Compressed sensing (CS) is an acceleration technique that provides substantial reduction in acquisition time. Purpose: To compare intracardiac flow measurements between conventional and CS‐based highly accelerated 4D flow acquisitions. Study Type: Prospective. Subjects: Fifty healthy volunteers (28.0 ± 7.1 years, 24 males). Field Strength/Sequence: Whole heart time‐resolved 3D gradient echo with three‐directional velocity encoding (4D flow) with conventional parallel imaging (factor 3) as well as CS (factor 7.7) acceleration at 3 T. Assessment: 4D flow MRI data were postprocessed by applying a valve tracking algorithm. Acquisition times, flow volumes (mL/cycle) and diastolic function parameters (ratio of early to late diastolic left ventricular peak velocities [E/A] and ratio of early mitral inflow velocity to mitral annular early diastolic velocity [E/e′]) were quantified by two readers. Statistical Tests: Paired‐samples t‐test and Wilcoxon rank sum test to compare measurements. Pearson correlation coefficient (r), Bland–Altman‐analysis (BA) and intraclass correlation coefficient (ICC) to evaluate agreement between techniques and readers. A P value < 0.05 was considered statistically significant. Results: A significant improvement in acquisition time was observed using CS vs. conventional accelerated acquisition (6.7 ± 1.3 vs. 12.0 ± 1.3 min). Net forward flow measurements for all valves showed good correlation (r > 0.81) and agreement (ICCs > 0.89) between conventional and CS acceleration, with 3.3%–8.3% underestimation by the CS technique. Evaluation of diastolic function showed 3.2%–17.6% error: E/A 2.2 [1.9–2.4] (conventional) vs. 2.3 [2.0–2.6] (CS), BA bias 0.08 [−0.81–0.96], ICC 0.82; and E/e′ 4.6 [3.9–5.4] (conventional) vs. 3.8 [3.4–4.3] (CS), BA bias −0.90 [−2.31–0.50], ICC 0.89. Data Conclusion: Analysis of intracardiac flow patterns and evaluation of diastolic function using a highly accelerated 4D flow sequence prototype is feasible, but it shows underestimation of flow measurements by approximately 10%. Evidence Level: 2 Technical Efficacy: Stage 1 [ABSTRACT FROM AUTHOR]

Purpose: To validate a respiratory motion correction method called focused navigation (fNAV) for free‐running radial whole‐heart 4D flow MRI. Methods: Using fNAV, respiratory signals derived from radial readouts are converted into three orthogonal displacements, which are then used to correct respiratory motion in 4D flow datasets. Hundred 4D flow acquisitions were simulated with non‐rigid respiratory motion and used for validation. The difference between generated and fNAV displacement coefficients was calculated. Vessel area and flow measurements from 4D flow reconstructions with (fNAV) and without (uncorrected) motion correction were compared to the motion‐free ground‐truth. In 25 patients, the same measurements were compared between fNAV 4D flow, 2D flow, navigator‐gated Cartesian 4D flow, and uncorrected 4D flow datasets. Results: For simulated data, the average difference between generated and fNAV displacement coefficients was 0.04 ±$$ \pm $$ 0.32 mm and 0.31 ±$$ \pm $$ 0.35 mm in the x and y directions, respectively. In the z direction, this difference was region‐dependent (0.02 ±$$ \pm $$ 0.51 mm up to 5.85 ±$$ \pm $$ 3.41 mm). For all measurements (vessel area, net volume, and peak flow), the average difference from ground truth was higher for uncorrected 4D flow datasets (0.32 ±$$ \pm $$ 0.11 cm2, 11.1 ±$$ \pm $$ 3.5 mL, and 22.3 ±$$ \pm $$ 6.0 mL/s) than for fNAV 4D flow datasets (0.10 ±$$ \pm $$ 0.03 cm2, 2.6 ±$$ \pm $$ 0.7 mL, and 5.1 ±0$$ \pm 0 $$.9 mL/s, p < 0.05). In vivo, average vessel area measurements were 4.92 ±$$ \pm $$ 2.95 cm2, 5.06 ±$$ \pm $$ 2.64 cm2, 4.87 ±$$ \pm $$ 2.57 cm2, 4.87 ±$$ \pm $$ 2.69 cm2, for 2D flow and fNAV, navigator‐gated and uncorrected 4D flow datasets, respectively. In the ascending aorta, all 4D flow datasets except for the fNAV reconstruction had significantly different vessel area measurements from 2D flow. Overall, 2D flow datasets demonstrated the strongest correlation to fNAV 4D flow for both net volume (r2 = 0.92) and peak flow (r2 = 0.94), followed by navigator‐gated 4D flow (r2 = 0.83 and r2 = 0.86, respectively), and uncorrected 4D flow (r2 = 0.69 and r2 = 0.86, respectively). Conclusion: fNAV corrected respiratory motion in vitro and in vivo, resulting in fNAV 4D flow measurements that are comparable to those derived from 2D flow and navigator‐gated Cartesian 4D flow datasets, with improvements over those from uncorrected 4D flow. [ABSTRACT FROM AUTHOR]

Background: 4D Flow MRI is a quantitative imaging technique to evaluate blood flow patterns; however, it is unclear how compressed sensing (CS) acceleration would impact aortic hemodynamic quantification in type B aortic dissection (TBAD). Purpose: To investigate CS‐accelerated 4D Flow MRI performance compared to GRAPP‐accelerated 4D Flow MRI (GRAPPA) to evaluate aortic hemodynamics in TBAD. Study Type: Prospective. Population: Twelve TBAD patients, two volunteers. Field Strength/Sequence: 1.5T, 3D time‐resolved cine phase‐contrast gradient echo sequence. Assessment: GRAPPA (acceleration factor [R] = 2) and two CS‐accelerated (R = 7.7 [CS7.7] and 10.2 [CS10.2]) 4D Flow MRI scans were acquired twice for interscan reproducibility assessment. Voxelwise kinetic energy (KE), peak velocity (PV), forward flow (FF), reverse flow (RF), and stasis were calculated. Plane‐based mid‐lumen flows were quantified. Imaging times were recorded. Tests: Repeated measures analysis of variance, Pearson correlation coefficients (r), intraclass correlation coefficients (ICC). P < 0.05 indicated statistical significance. Results: The KE and FF in true lumen (TL) and PV in false lumen (FL) did not show difference among three acquisition types (P = 0.818, 0.065, 0.284 respectively). The PV and stasis in TL were higher, KE, FF, and RF in FL were lower, and stasis was higher in GRAPPA compared to CS7.7 and CS10.2. The RF was lower in GRAPPA compared to CS10.2. The correlation coefficients were strong in TL (r = [0.781–0.986]), and low to strong in FL (r = [0.347–0.948]). The ICC levels demonstrated moderate to excellent interscan reproducibility (0.732–0.989). The FF and net flow in mid‐descending aorta TL were significantly different between CS7.7 and CS10.2. Conclusion: CS‐accelerated 4D Flow MRI has potential for clinical utilization with shorter scan times in TBAD. Our results suggest similar hemodynamic trends between acceleration types, but CS‐acceleration impacts KE, FF, RF, and stasis more in FL. Evidence Level: 1 Technical Efficacy: Stage 2 [ABSTRACT FROM AUTHOR]

Background: Pulmonary hypertension (PH) contributes to restricted flow through the pulmonary circulation characterized by elevated mean pulmonary artery pressure acquired from invasive right heart catheterization (RHC). MRI may provide a noninvasive alternative for diagnosis and characterization of PH. Purpose: To characterize PH via quantification of regional pulmonary transit times (rPTT). Study Type: Retrospective. Population: A total of 43 patients (58% female); 24 controls (33% female). RHC‐confirmed patients classified as World Health Organization (WHO) subgroups 1–4. Field Strength/Sequence: A 1.5 T/time‐resolved contrast‐enhanced MR Angiography (CE‐MRA). Assessment: CE‐MRA data volumes were combined into a 4D matrix (3D resolution + time). Contrast agent arrival time was defined as the peak in the signal‐intensity curve generated for each voxel. Average arrival times within a vessel region of interest (ROI) were normalized to the main pulmonary artery ROI (t0) for eight regions to define rPTT for all subjects. Subgroup analysis included grouping the four arterial and four venous regions. Intraclass correlation analysis completed for reproducibility. Statistical Tests: Analysis of covariance with age as covariate. A priori Student's t‐tests or Wilcoxon rank‐sum test; α = 0.05. Results compared to controls unless noted. Significant without listing P value. ICC ran as two‐way absolute agreement model with two observers. Results: PH patients demonstrated elevated rPTT in all vascular regions; average rPTT increase in arterial and venous branches was 0.85 ± 0.15 seconds (47.7%) and 1.0 ± 0.18 seconds (16.9%), respectively. Arterial rPTT was increased for all WHO subgroups; venous regions were elevated for subgroups 2 and 4 (group 1, P = 0.86; group 3, P = 0.32). No significant rPTT differences were found between subgroups (P = 0.094–0.94). Individual vessel ICC values ranged from 0.58 to 0.97. Data Conclusion: Noninvasive assessment of PH using standard‐of‐care time‐resolved CE‐MRA can detect increased rPTT in PH patients of varying phenotypes compared to controls. Level of Evidence: 1 Technical Efficacy: Stage 3. [ABSTRACT FROM AUTHOR]

Background: In phase‐contrast (PC) MRI, several dual velocity encoding methods have been proposed to robustly increase velocity‐to‐noise ratio (VNR), including a standard dual‐VENC (SDV), an optimal dual‐VENC (ODV), and bi‐ and triconditional methods. Purpose: To develop a correction method for the ODV approach and to perform a comparison between methods. Study Type: Case–control study. Population: Twenty‐six volunteers. Field Strength/Sequence: 1.5 T phase‐contrast MRI with VENCs of 50, 75, and 150 cm/second. Assessment: Since we acquired single‐VENC protocols, we used the background phase from high‐VENC (VENCH) to reconstruct the low‐VENC (VENCL) phase. We implemented and compared the unwrapping methods for different noise levels and also developed a correction of the ODV method. Statistical Tests: Shapiro–Wilk's normality test, two‐way analysis of variance with homogeneity of variances was performed using Levene's test, and the significance level was adjusted by Tukey's multiple post hoc analysis with Bonferroni (P < 0.05). Results: Statistical analysis revealed no extreme outliers, normally distributed residuals, and homogeneous variances. We found statistically significant interaction between noise levels and the unwrapping methods. This implies that the number of non‐unwrapped pixels increased with the noise level. We found that for β = VENCL/VENCH = 1/2, unwrapping methods were more robust to noise. The post hoc test showed a significant difference between the ODV corrected and the other methods, offering the best results regarding the number of unwrapped pixels. Data Conclusions: All methods performed similarly without noise, but the ODV corrected method was more robust to noise at the price of a higher computational time. Level of Evidence: 4 Technical Efficacy Stage: 1 [ABSTRACT FROM AUTHOR]

Background: Aortopathy is common with bicuspid aortic valve (BAV), and underlying intrinsic tissue abnormalities are believed causative. Valve‐mediated hemodynamics are altered in BAV and may contribute to aortopathy and its progression. The contribution of intrinsic tissue defects versus altered hemodynamics to aortopathy progression is not known. Purpose: To investigate relative contributions of tissue‐innate versus hemodynamics in progression of BAV aortopathy. Study Type: Retrospective. Subjects: Four hundred seventy‐three patients with aortic dilatation (diameter ≥40 mm; comprised of 281 BAV with varied AS severity, 192 tricuspid aortic valve [TAV] without AS) and 124 healthy controls. Subjects were 19–91 years (141/24% female). Field Strength/Sequence: 1.5T, 3T; time‐resolved gradient‐echo 3D phase‐contrast (4D flow) MRI. Assessment: A surrogate measure for global aortic wall stiffness, pulse wave velocity (PWV), was quantified from MRI by standardized, automated technique based on through‐plane flow cross‐correlation maximization. Comparisons were made between BAV patients with aortic dilatation and varying aortic valve stenosis (AS) severity and healthy subjects and aortopathy patients with normal TAV. Statistical Tests: Multivariable regression, analysis of covariance (ANCOVA), Tukey's, student's (t), Mann–Whitney (U) tests, were used with significance levels P < 0.05 or P < 0.01 for post‐hoc Bonferroni‐corrected t/U tests. Bland–Altman and ICC calculations were performed. Results: Multivariable regression showed age with the most significant association for increased PWV in all groups (increase 0.073–0.156 m/sec/year, R2 = 0.30–48). No significant differences in aortic PWV were observed between groups without AS (P = 0.20–0.99), nor were associations between PWV and regurgitation or Sievers type observed (P = 0.60, 0.31 respectively). In contrast, BAV AS patients demonstrated elevated PWV and a significant relationship for AS severity with increased PWV (covariate: age, R2 = 0.48). BAV and TAV patients showed no association between aortic diameter and PWV (P = 0.73). Data Conclusion: No significant PWV differences were observed between BAV patients with normal valve function and control groups. However, AS severity and age in BAV patients were directly associated with PWV increases. Evidence Level: 3 Technical Efficacy: Stage 3 [ABSTRACT FROM AUTHOR]

Background: The hemispherical aortic annuloplasty reconstructive technology (HAART) is an internal geometric annuloplasty ring designed to restore a natural elliptical shape to the aortic annulus as part of aortic valve repair. We present four-dimensional flow hemodynamic analysis before and after implementation of the HAART ring in patients undergoing ascending aortic replacement.Methods: Aortic hemodynamics over the cardiac cycle were visualized using time-resolved three-dimensional pathlines. Velocity streamlines tangent to the time-resolved velocity vector field were used to demonstrate instantaneous aortic hemodynamics. Peak velocities, forward and retrograde flow were calculated at nine planes placed along the midline of the thoracic aorta. Systolic wall shear stress and peak viscous energy loss over the cardiac cycle were calculated.Results: HAART patients displayed similar or improved flow profiles after surgery when compared to a patient undergoing ascending aortic replacement alone.Conclusion: There may be a trend towards improved flow dynamics in patients undergoing HAART ring implantation. [ABSTRACT FROM AUTHOR]

Purpose: Dual‐velocity encoded (dual‐venc or DV) 4D flow MRI achieves wide velocity dynamic range and velocity‐to‐noise ratio (VNR), enabling accurate neurovascular flow characterization. To reduce scan time, we present interleaved dual‐venc 4D Flow with independently prescribed, prospectively undersampled spatial resolution of the high‐venc (HV) acquisition: Variable Spatial Resolution Dual Venc (VSRDV). Methods: A prototype VSRDV sequence was developed based on a Cartesian acquisition with eight‐point phase encoding, combining PEAK‐GRAPPA acceleration with zero‐filling in phase and partition directions for HV. The VSRDV approach was optimized by varying z, the zero‐filling fraction of HV relative to low‐venc, between 0%–80% in vitro (realistic neurovascular model with pulsatile flow) and in vivo (n = 10 volunteers). Antialiasing precision, mean and peak velocity quantification accuracy, and test–retest reproducibility were assessed relative to reference images with equal‐resolution HV and low venc (z = 0%). Results: In vitro results for all z demonstrated an antialiasing true positive rate at least 95% for RPEAK−GRAPPA$$ {R}_{\mathrm{PEAK}-\mathrm{GRAPPA}} $$ = 2 and 5, with no linear relationship to z (p = 0.62 and 0.13, respectively). Bland–Altman analysis for z = 20%, 40%, 60%, or 80% versus z = 0% in vitro and in vivo demonstrated no bias >1% of venc in mean or peak velocity values at any RZF$$ {R}_{\mathrm{ZF}} $$. In vitro mean and peak velocity, and in vivo peak velocity, had limits of agreement within 15%. Conclusion: VSRDV allows up to 34.8% scan time reduction compared to PEAK‐GRAPPA accelerated DV 4D Flow MRI, enabling large spatial coverage and dynamic range while maintaining VNR and velocity measurement accuracy. [ABSTRACT FROM AUTHOR]

Background: Dual‐venc 4D flow MRI, recently introduced for the assessment of intracranial hemodynamics, may provide a promising complementary approach to well‐established tools such as transcranial Doppler ultrasound (TCD) and overcome some of their disadvantages. However, data comparing intracranial flow measures from dual‐venc 4D flow MRI and TCD are lacking. Purpose: To compare cerebral blood flow velocity measures derived from dual‐venc 4D flow MRI and TCD. Study Type: Prospective cohort. Subjects: A total of 25 healthy participants (56 ± 4 years old, 44% female). Field Strength/Sequence: A 3 T/dual‐venc 4D flow MRI using a time‐resolved three‐dimensional phase‐contrast sequence with three‐dimensional velocity encoding. Assessment: Peak velocity measurements in bilateral middle cerebral arteries (MCA) were quantified from dual‐venc 4D flow MRI and TCD. The MRI data were quantified by two independent observers (S.M and Y.M.) and TCD was performed by a trained technician (A.L.M.). We assessed the agreement between 4D flow MRI and TCD measures, and the interobserver agreement of 4D flow MRI measurements. Statistical Tests: Peak velocity from MRI and TCD was compared using Bland–Altman analysis and coefficient of variance. Intraclass correlation coefficient (ICC) was used to assess MRI interobserver agreement. A P value < 0.05 was considered statistically significant. Results: There was excellent interobserver agreement in dual‐venc 4D flow MRI‐based measurements of peak velocity in bilateral MCA (ICC = 0.97 and 0.96 for the left and right MCA, respectively). Dual‐venc 4D flow MRI significantly underestimated peak velocity in the left and right MCA compared to TCD (bias = 0.13 [0.59, −0.33] m/sec and 0.15 [0.47, −0.17] m/sec, respectively). The coefficient of variance between dual‐venc 4D flow MRI and TCD measurements was 26% for the left MCA and 22% for the right MCA. Data Conclusion: There was excellent interobserver agreement for the assessment of MCA peak velocity using dual‐venc 4D flow MRI, and ≤20% under‐estimation compared with TCD. Evidence Level: 3 Technical Efficacy: Stage 2 [ABSTRACT FROM AUTHOR]

Background: Gadobutrol (GB) and gadoterate meglumine (GM) are contrast agents used for contrast‐enhanced magnetic resonance angiography (CEMRA). Supraaortic vasculature (SAV) CEMRAs are used to evaluate stroke risk and neurologic symptoms. There is a need to compare the SAV CEMRA image quality obtained with GB and GM. Purpose: To intra‐individually compare MRA images obtained with equimolar GB and GM at 1.5 T in the SAV. Study Type: Prospective, crossover. Population: Twenty‐eight subjects (54 ± 13 years; 17 female). Field Strength/Sequence: 1.5 T; three‐dimensional (3D) gradient recalled echo. Assessment: Quantitative image quality was measured by normalized signal intensity (SIn) [SIn = SI blood/SD blood] and contrast ratio (CR) [CR = SI blood/SI muscle], determined by an observer (JWC) with 1 year of vascular imaging experience. Three radiologists (AS, PA, and MU) with (5, 5, and 6 years of) vascular imaging experience evaluated image quality by Likert‐scale ratings (of image impression, wall conspicuity, and artifact absence). Statistical Tests: SIn and CR were compared with paired t‐tests or Wilcoxon signed‐rank tests and Bland–Altman plots. Qualitative ratings were compared with Wilcoxon signed‐rank test. Results: No significant difference in SIn was found between GB and GM. CRs with GB were significantly higher than GM at the right common carotid (6.9 ± 2.5 vs. 4.8 ± 1), left internal carotid (7.3 ± 2 vs. 4.4 ± 1.2), right internal carotid (7.7 ± 2.2 vs. 5 ± 1.1), and left vertebral (6.6 ± 2.2 vs. 4.5 ± 1.1) arteries. Bland–Altman plots showed relatively greater differences between GB and GM at higher CRs and SIns. GM showed significantly higher artifact than GB (3.56 ± 0.52 vs. 3.36 ± 0.46) and significantly lower overall image quality (10.73 ± 1.45 vs. 11.26 ± 1.58) at the left vertebral artery. Data Conclusion: At 1.5 T and equimolar demonstration, GB (0.1 mL/kg, i.e., 0.1 mmol/kg) showed higher CRs in the SAV compared to GM (0.2 mL/kg, i.e., 0.1 mmol/kg) at most vessels. Subjective image quality was not significantly different between the two agents for most vessels. Level of Evidence: 2 Technical Efficacy: Stage 2 [ABSTRACT FROM AUTHOR]

Background: Evaluation of aortic stiffness by pulse wave velocity (PWV) across the adult lifespan is needed to better understand normal aging in women and men. Purpose: To characterize PWV in the thoracic aorta using 4D flow MRI in an age‐ and sex‐stratified cohort of healthy adults. Study Type: Retrospective. Population: Ninety nine healthy participants (age: 46 ± 15 [19–79] years, 50% female), divided into young adults (<45 years) (N = 48), midlife (45–65 years) (N = 37), and later life (>65 years) (N = 14) groups. Field Strength/Sequence: 1.5 T or 3 T, 2D cine bSSFP, 4D flow MRI. Assessment: Cardiac functional parameters of end‐diastolic volume (EDV), end‐systolic volume (ESV), stroke volume (SV) and myocardial mass were assessed by 2D cine bSSFP. PWV and aortic blood flow velocity were assessed by 4D flow MRI. Reproducibility of PWV was evaluated in a subset of nine participants. Statistical Tests: Analysis of variance, Pearson's correlation coefficient (r), linear regression, intraclass correlation coefficient (ICC). A P value < 0.05 was considered statistically significant. Results: PWV increased significantly with age (young adults: 5.4 ± 0.9 m/sec, midlife: 7.2 ± 1.1 m/sec, and later life: 9.4 ± 1.8 m/sec) (r = 0.79, slope = 0.09 m/sec/year). PWV did not differ in women and men in entire sample (P = 0.40) or within age groups (young adults: P = 0.83, midlife: P = 0.17, and later life: P = 0.96). PWV was significantly correlated with EDV (r = −0.29), ESV (r = −0.23), SV (r = −0.28), myocardial mass (r = 0.21), and mean aortic blood flow velocity (r = −0.62). In the test–retest subgroup (N = 9), PWV was 6.7 ± 1.5 [4.4–9.3] m/sec and ICC = 0.75. Data Conclusion: 4D flow MRI quantified higher aortic PWV with age, by approximately 1 m/sec per decade, and significant differences between young adults, midlife and later life. Reproducibility analysis showed good test–retest agreement. Increased PWV was associated with decline in cardiac function and reduced aortic blood flow velocity. This study demonstrates the utility of 4D flow MRI‐derived aortic PWV for studying aging. Evidence Level: 2 Technical Efficacy: Stage 2 [ABSTRACT FROM AUTHOR]

Purpose: To develop a convolutional neural network (CNN) for the robust and fast correction of velocity aliasing in 4D‐flow MRI. Methods: This study included 667 adult subjects with aortic 4D‐flow MRI data with existing velocity aliasing (n = 362) and no velocity aliasing (n = 305). Additionally, 10 controls received back‐to‐back 4D‐flow scans with systemically varied velocity‐encoding sensitivity (vencs) at 60, 100, and 175 cm/s. The no‐aliasing data sets were used to simulate velocity aliasing by reducing the venc to 40%–70% of the original, alongside a ground truth locating all aliased voxels (153 training, 152 testing). The 152 simulated and 362 existing aliasing data sets were used for testing and compared with a conventional velocity antialiasing algorithm. Dice scores were calculated to quantify CNN performance. For controls, the venc 175‐cm/s scans were used as the ground truth and compared with the CNN‐corrected venc 60 and 100 cm/s data sets Results: The CNN required 176 ± 30 s to perform compared with 162 ± 14 s for the conventional algorithm. The CNN showed excellent performance for the simulated data compared with the conventional algorithm (median range of Dice scores CNN: [0.89–0.99], conventional algorithm: [0.84–0.94], p < 0.001, across all simulated vencs) and detected more aliased voxels in existing velocity aliasing data sets (median detected CNN: 159 voxels [31–605], conventional algorithm: 65 [7–417], p < 0.001). For controls, the CNN showed Dice scores of 0.98 [0.95–0.99] and 0.96 [0.87–0.99] for venc = 60 cm/s and 100 cm/s, respectively, while flow comparisons showed moderate‐excellent agreement. Conclusion: Deep learning enabled fast and robust velocity anti‐aliasing in 4D‐flow MRI. [ABSTRACT FROM AUTHOR]

Background: Cardiac magnetic resonance imaging (MRI) is becoming an alternative to right heart catheterization (RHC) for evaluating pulmonary hypertension (PH). A need exists to further evaluate cardiac MRI's ability to characterize PH. Purpose: To evaluate the potential for four‐dimensional (4D) flow MRI‐derived pulmonary artery velocities to characterize PH. Study Type: Prospective case–control. Population: Fifty‐four PH patients (56% female); 25 controls (36% female). Field Strength/Sequence: 1.5 T; gradient recalled echo 4D flow and balanced steady‐state free precession cardiac cine. Assessment: RHC was used to derive patients' pulmonary vascular resistance (PVR). 4D flow measured blood velocities at the main, left, and right pulmonary arteries (MPA, LPA, and RPA); cine measured ejection fraction, end diastolic, and end systolic volumes (EF, EDV, and ESV). EDV and ESV were normalized (indexed) to body surface area (ESVI and EDVI). Parameters were evaluated between, and within, PH subgroups: pulmonary arterial hypertension (PAH); PH due to left heart disease (PH‐LHD)/chronic lung disease (PH‐CLD)/or chronic thrombo‐emboli (CTE‐PH). Statistical Tests: Analysis of variance and Kruskal–Wallis tests compared parameters between subgroups. Pearson's r assessed velocity, PVR, and volume correlations. Significance definition: P < 0.05. Results: PAH peak and mean velocities were significantly lower than in controls at the LPA (36 ± 12 cm/second and 20 ± 4 cm/second vs. 59 ± 15 cm/second and 32 ± 9 cm/second). At the RPA, mean velocities were significantly lower in PAH vs. controls (27 ± 6 cm/second vs. 40 ± 9 cm/second). Peak velocities significantly correlated with right ventricular EF at the MPA (r = 0.286), RPA (r = 0.400), and LPA (r = 0.401). Peak velocity significantly correlated with right ventricular ESVI at the RPA (r = −0.355) and LPA (r = −0.316). Significant correlations between peak velocities and PVR were moderate at the LPA in PAH (r = −0.641) and in PH‐LHD (r = −0.606) patients, and at the MPA in PH‐CLD (r = −0.728). CTE‐PH showed non‐significant correlations between peak velocity and PVR at all locations. Data Conclusion: Preliminary findings suggest 4D flow can identify PAH and track PVR changes. Level of Evidence: 1 Technical Efficacy: Stage 5 [ABSTRACT FROM AUTHOR]

Background: Automated segmentation using convolutional neural networks (CNNs) have been developed using four‐dimensional (4D) flow magnetic resonance imaging (MRI). To broaden usability for congenital heart disease (CHD), training with multi‐institution data is necessary. However, the performance impact of heterogeneous multi‐site and multi‐vendor data on CNNs is unclear. Purpose: To investigate multi‐site CNN segmentation of 4D flow MRI for pediatric blood flow measurement. Study Type: Retrospective. Population: A total of 174 subjects across two sites (female: 46%; N = 38 healthy controls, N = 136 CHD patients). Participants from site 1 (N = 100), site 2 (N = 74), and both sites (N = 174) were divided into subgroups to conduct 10‐fold cross validation (10% for testing, 90% for training). Field Strength/Sequence: 3 T/1.5 T; retrospectively gated gradient recalled echo‐based 4D flow MRI. Assessment: Accuracy of the 3D CNN segmentations trained on data from single site (single‐site CNNs) and data across both sites (multi‐site CNN) were evaluated by geometrical similarity (Dice score, human segmentation as ground truth) and net flow quantification at the ascending aorta (Qs), main pulmonary artery (Qp), and their balance (Qp/Qs), between human observers, single‐site and multi‐site CNNs. Statistical Tests: Kruskal–Wallis test, Wilcoxon rank‐sum test, and Bland–Altman analysis. A P‐value <0.05 was considered statistically significant. Results: No difference existed between single‐site and multi‐site CNNs for geometrical similarity in the aorta by Dice score (site 1: 0.916 vs. 0.915, P = 0.55; site 2: 0.906 vs. 0.904, P = 0.69) and for the pulmonary arteries (site 1: 0.894 vs. 0.895, P = 0.64; site 2: 0.870 vs. 0.869, P = 0.96). Qs site‐1 medians were 51.0–51.3 mL/cycle (P = 0.81) and site‐2 medians were 66.7–69.4 mL/cycle (P = 0.84). Qp site‐1 medians were 46.8–48.0 mL/cycle (P = 0.97) and site‐2 medians were 76.0–77.4 mL/cycle (P = 0.98). Qp/Qs site‐1 medians were 0.87–0.88 (P = 0.97) and site‐2 medians were 1.01–1.03 (P = 0.43). Bland–Altman analysis for flow quantification found equivalent performance. Data Conclusion: Multi‐site CNN‐based segmentation and blood flow measurement are feasible for pediatric 4D flow MRI and maintain performance of single‐site CNNs. Level of Evidence: 3 Technical Efficacy: Stage 2 [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this study was to evaluate the accuracy of four‐dimensional (4D) flow MRI for direct assessment of peak velocity, flow volume, and momentum of a mitral regurgitation (MR) flow jets using an in vitro pulsatile jet flow phantom. We systematically investigated the impact of spatial resolution and quantification location along the jet on flow quantities with Doppler ultrasound as a reference for peak velocity. Methods: Four‐dimensional flow MRI data of a pulsatile jet through a circular, elliptical, and 3D‐printed patient‐specific MR orifice model was acquired with varying spatial resolution (1.5–5 mm isotropic voxel). Flow rate and momentum of the jet were quantified at various axial distances (x = 0–50 mm) and integrated over time to calculate Voljet and MTIjet. In vivo assessment of Voljet and MTIjet was performed on 3 MR patients. Results: Peak velocities were comparable to Doppler ultrasound (3% error, 1.5 mm voxel), but underestimated with decreasing spatial resolution (−40% error, 5 mm voxel). Voljet was similar to regurgitant volume (RVol) within 5 mm, and then increased linearly with the axial distance (19%/cm) because of flow entrainment. MTIjet remained steady throughout the jet (2%/cm) as theoretically predicted. Four and 9 voxels across the jet were required to measure flow volume and momentum‐time‐integral within 10% error, respectively. Conclusion: Four‐dimensional flow MRI detected accurate peak velocity, flow rate, and momentum for in vitro MR‐mimicking flow jets. Spatial resolution significantly impacted flow quantitation, which otherwise followed predictions of flow entrainment and momentum conservation. This study provides important preliminary information for accurate in vivo MR assessment using 4D flow MRI. [ABSTRACT FROM AUTHOR]

Purpose: In this work, we integrated the pilot tone (PT) navigation system into a reconstruction framework for respiratory and cardiac motion‐resolved 5D flow. We tested the hypotheses that PT would provide equivalent respiratory curves, cardiac triggers, and corresponding flow measurements to a previously established self‐gating (SG) technique while being independent from changes to the acquisition parameters. Methods: Fifteen volunteers and 9 patients were scanned with a free‐running 5D flow sequence, with PT integrated. Respiratory curves and cardiac triggers from PT and SG were compared across all subjects. Flow measurements from 5D flow reconstructions using both PT and SG were compared to each other and to a reference electrocardiogram‐gated and respiratory triggered 4D flow acquisition. Radial trajectories with variable readouts per interleave were also tested in 1 subject to compare cardiac trigger quality between PT and SG. Results: The correlation between PT and SG respiratory curves were 0.95 ± 0.06 for volunteers and 0.95 ± 0.04 for patients. Heartbeat duration measurements in volunteers and patients showed a bias to electrocardiogram measurements of, respectively, 0.16 ± 64.94 ms and 0.01 ± 39.29 ms for PT versus electrocardiogram and of 0.24 ± 63.68 ms and 0.09 ± 32.79 ms for SG versus electrocardiogram. No significant differences were reported for the flow measurements between 5D flow PT and from 5D flow SG. A decrease in the cardiac triggering quality of SG was observed for increasing readouts per interleave, whereas PT quality remained constant. Conclusion: PT has been successfully integrated in 5D flow MRI and has shown equivalent results to the previously described 5D flow SG technique, while being completely acquisition‐independent. [ABSTRACT FROM AUTHOR]

Background: Coarctation of the aorta (CoA) typically requires repair, but re‐interventions and vascular complications occur, particularly with associated defects like bicuspid aortic valve (BAV). Magnetic resonance imaging (MRI) may identify anatomic and hemodynamic factors contributing to clinical complications. Purpose To investigate 4D flow MRI characteristics in pediatric CoA to determine parameters for long‐term clinical surveillance. Study Type: Retrospective. Population: CoA (n = 21), CoA with BAV (n = 24), BAV alone (n = 29), and healthy control (n = 25). Field Strength/Sequence: A 1.5 T, 3D CE IR FLASH MRA, 4D flow MRI using 3D time resolved PC‐MRI with velocity encoding. Assessment Thoracic aorta diameters were measured from 3D CE‐MRA. Peak systolic velocities and wall shear stress were calculated and flow patterns were visualized throughout the thoracic aorta using 4D flow. Repair characteristics, re‐interventions, and need for anti‐hypertensive medications were recorded. Statistics: Descriptive statistics, ANOVA with post hoc t‐testing and Bonferroni correction, Kruskal–Wallis H, intraclass correlation coefficient, Fleiss' kappa. Results: Patients with CoA with or without repair had smaller transverse arch diameters compared to BAV alone and control cohorts (P < 0.05), higher peak systolic flow velocities and wall shear stress compared to controls in the transverse arch and descending aorta (P < 0.05), and flow derangements in the descending aorta. The most common CoA repairs were extended end‐to‐end anastomosis (n = 22/45, 48.9%, age at repair 1 ± 2 years, seven re‐interventions) and stent/interposition graft placement (n = 10/45, 22.2%, age at repair 12 ± 3 years, one re‐intervention). Anti‐hypertensive medications were prescribed to 33.3% (n = 15/45) of CoA and 34.4% of BAV alone patients (n = 10/29). Data Conclusions: Despite repair, CoA alters hemodynamics and flow patterns in the transverse arch and descending aorta. These findings may contribute to vascular remodeling and secondary complications. 4D flow MRI may be valuable in risk stratification, treatment selection and postintervention assessment. Long‐term, prospective studies are warranted to correlate patient and MRI factors with clinical outcomes. Evidence Level 3 Technical Efficacy: Stage 3 [ABSTRACT FROM AUTHOR]

Tissue phase mapping (TPM) is an MRI technique for quantification of regional biventricular myocardial velocities. Despite its potential, clinical use is limited due to the requisite labor‐intensive manual segmentation of cardiac contours for all time frames. The purpose of this study was to develop a deep learning (DL) network for automated segmentation of TPM images, without significant loss in segmentation and myocardial velocity quantification accuracy compared with manual segmentation. We implemented a multi‐channel 3D (three dimensional; 2D + time) dense U‐Net that trained on magnitude and phase images and combined cross‐entropy, Dice, and Hausdorff distance loss terms to improve the segmentation accuracy and suppress unnatural boundaries. The dense U‐Net was trained and tested with 150 multi‐slice, multi‐phase TPM scans (114 scans for training, 36 for testing) from 99 heart transplant patients (44 females, 1‐4 scans/patient), where the magnitude and velocity‐encoded (Vx, Vy, Vz) images were used as input and the corresponding manual segmentation masks were used as reference. The accuracy of DL segmentation was evaluated using quantitative metrics (Dice scores, Hausdorff distance) and linear regression and Bland‐Altman analyses on the resulting peak radial and longitudinal velocities (Vr and Vz). The mean segmentation time was about 2 h per patient for manual and 1.9 ± 0.3 s for DL. Our network produced good accuracy (median Dice = 0.85 for left ventricle (LV), 0.64 for right ventricle (RV), Hausdorff distance = 3.17 pixels) compared with manual segmentation. Peak Vr and Vz measured from manual and DL segmentations were strongly correlated (R ≥ 0.88) and in good agreement with manual analysis (mean difference and limits of agreement for Vz and Vr were −0.05 ± 0.98 cm/s and −0.06 ± 1.18 cm/s for LV, and −0.21 ± 2.33 cm/s and 0.46 ± 4.00 cm/s for RV, respectively). The proposed multi‐channel 3D dense U‐Net was capable of reducing the segmentation time by 3,600‐fold, without significant loss in accuracy in tissue velocity measurements. [ABSTRACT FROM AUTHOR]

Aims: Visceral adipose tissue (AT) promotes inflammation and may be associated with disease progression in heart failure with preserved ejection fraction (HFpEF). We characterized regional AT distribution in HFpEF patients and controls and analysed associations with co‐morbidities and exercise tolerance. Methods and results: Magnetic resonance imaging was performed to quantify epicardial, liver, abdominal, and thigh skeletal muscle AT. We assessed New York Heart Association (NYHA) class, 6 min walk distance, and global well‐being score. Multivariable linear regression models adjusting for body surface area were used. We studied 55 HFpEF patients (41 women, mean age 67 ± 11 years) and 33 controls (21 women, mean age 57 ± 10 years). Epicardial AT (median [interquartile range] 4.6 [2.0] vs. 3.2 [1.4] mm, P < 0.001), thigh intermuscular fat (11.0 [11.5] vs. 5.0 [2.7] cm2, P < 0.001) and liver fat fraction (6.4% [6.1] vs. 4.1% [5.5], P = 0.001) were higher in HFpEF patients than controls. Women with HFpEF had higher abdominal and thigh subcutaneous AT than men. Greater thigh intermuscular fat was associated with higher blood pressure (β [SE] 0.73 [0.17], P < 0.001) and diabetes (odds ratio [95% confidence interval] 1.2 [1.0–1.5], P = 0.03). Greater thigh intramuscular fat was associated with both worse NYHA class (β [SE] 2.7 [1.0], P = 0.01) and shorter 6 min walk distance (β [SE] −4.1 [1.9], P = 0.03), and greater epicardial AT (β [SE] −0.2 [0.1], P < 0.001) and liver fat fraction (β [SE] −0.4 [0.2], P = 0.04) were associated with lower global well‐being score. Conclusions: Heart failure with preserved ejection fraction patients have increased epicardial, liver, and skeletal muscle fat compared with controls out of proportion to their increased body size, and adiposity was associated with worse NYHA class and exercise tolerance in HFpEF. These results provide the basis for further investigation into the effect of interventions to reduce regional AT distribution in relation to HFpEF symptoms and pathophysiology. [ABSTRACT FROM AUTHOR]

Cine magnetic resonance imaging (MRI) is an emerging modality for evaluating left ventricular (LV) motion/deformation patterns, which may have potential to identify LV dysfunctions underlying postcapillary pulmonary hypertension (PH). The aim of this study was to test the hypothesis that cine MRI-derived LV motion/deformation indices can be used to identify an elevated left heart pressure in PH. This was a retrospective study, which included 26 precapillary and 28 postcapillary PH patients (23 males, 58.9 ± 13.5 years old). All patients underwent right heart catheterization (the "reference standard") and cardiac MRI. Balanced steady-state free precession cine sequence acquired at 1.5 T was used. Cine MRI datasets were analyzed by using heart deformation analysis. LV motion/deformation indices were measured through 25 phases within a cardiac cycle. Peak LV displacement, velocity, strain, and strain rates at systole, early and late diastole were compared between the two patient groups using t-tests. The Pearson correlation coefficient (r) was used to investigate the association between cine MRI-derived indices and pulmonary capillary wedge pressure (PCWP). Multivariable linear and logistic regression models were applied to assess the ability of MRI-derived parameters to predict PCWP and postcapillary PH. Compared to 26 precapillary PH patients, the 28 postcapillary PH patients had lower peak late radial diastolic displacement (0.43 ± 0.19 cm vs. 0.64 ± 0.18 cm) and velocity (12.2 ± 5.8 mm/s vs. 18.9 ± 5.6 mm/s) and peak late radial (52.1 ± 32.7%/s vs. 97.1 ± 38%/s) and circumferential (38 ± 19.8%/s vs. 63.1 ± 22.9%/s) strain rates. PCWP was correlated with peak late radial diastolic displacement (r = -0.54) and velocity (r = -0.57) and peak late radial (r = -0.63) and circumferential diastolic (r = -0.63) strain rates. Peak late radial strain rate could predict PCWP (β = -0.09) and postcapillary PH (β = -0.036). All p < 0.05. Cine MRI-derived LV late diastolic motion/deformation properties can be used to estimate elevated left heart pressure in PH. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY STAGE: 1. [ABSTRACT FROM AUTHOR]

Purpose: This study used a 5D flow framework to explore the influence of arrhythmia on thrombogenic hemodynamic parameters in patients with atrial fibrillation (AF). Methods: A fully self‐gated, 3D radial, highly accelerated free‐running 5D flow sequence with interleaved four‐point velocity‐encoding was acquired using an in vitro arrhythmic flow phantom and in 25 patients with a history of AF (68 ± 8 y, 6 female). Self‐gating signals were used to calculate AF burden, bin data, and tag each k‐space line with its RRLength. Data were binned as an RR‐resolved dataset with four RR‐interval bins (RR1‐RR4, short‐to‐long) for compressed sensing reconstruction. AF burden was calculated as interquartile range of all intrascan RR‐intervals divided by median RR‐interval, and left atrial (LA) stasis as the percent of the cardiac cycle where the velocity was <0.1 m/s. Results: In vitro results demonstrated successful recovery of RR‐binned flow curves using RR‐resolved 5D flow compared to a real‐time PC reference standard. In vivo, 5D flow was acquired in 8:48 minutes. AF burden was significantly correlated with 5D flow‐derived peak (PV) and mean (MV) velocity and stasis (|ρ| = 0.54‐0.75, P <.001). Sensitivity analyses determined a threshold for low versus high AF burden at 9.7%. High burden patients had increased LA mean stasis (up to +42%, P <.01), and lower MV and PV (−30%, −40.6%, respectively, P <.01). RR4 deviated furthest from respiratory‐resolved reconstruction (end‐expiration) with increased mean stasis (7.6% ± 14.0%, P =.10) and decreased PV (−12.7 ± 14.2%, P =.09). Conclusions: RR‐resolved 5D flow can capture temporal and RR‐resolved 3D hemodynamics in <10 minutes and offers a novel approach to investigate arrhythmias. [ABSTRACT FROM AUTHOR]

Purpose: To systematically assess the feasibility and performance of a highly accelerated compressed sensing (CS) 4D flow MRI framework at three different acceleration factors (R) for the quantification of aortic flow dynamics and wall shear stress (WSS) in patients with aortic disease. Methods: Twenty patients with aortic disease (58 ± 15 y old; 19 M) underwent four 4D flow scans: one conventional (GRAPPA, R = 2) and three CS 4D flows with R = 5.7, 7.7, and 10.2. All scans were acquired with otherwise equivalent imaging parameters on a 1.5T scanner. Peak‐systolic velocity (Vmax), peak flow (Qmax), and net flow (Qnet) were quantified at the ascending aorta (AAo), arch, and descending aorta (DAo). WSS was calculated at six regions within the AAo and arch. Results: Mean scan times for the conventional and CS 4D flows with R = 5.7, 7.7, and 10.2 were 9:58 ± 2:58 min, 3:40 ± 1:19 min, 2:50 ± 0:56 min, and 2:05 ± 0:42 min, respectively. Vmax, Qmax, and Qnet were significantly underestimated by all CS protocols (underestimation ≤ −7%, −9%, and −10% by CS, R = 5.7, 7.7, and 10.2, respectively). WSS measurements showed the highest underestimation by all CS protocols (underestimation ≤ −9%, −12%, and −14% by CS, R = 5.7, 7.7, and 10.2). Conclusions: Highly accelerated aortic CS 4D flow at R = 5.7, 7.7, and 10.2 showed moderate agreement with the conventional 4D flow, despite systematically underestimating various hemodynamic parameters. The shortened scan time may enable the clinical translation of CS 4D flow, although potential hemodynamic underestimation should be considered when interpreting the results. [ABSTRACT FROM AUTHOR]

Background: Cardiovascular risk factors have been linked with dementia risk in aging adults. However, mechanisms underlying heart‐brain hemodynamic coupling and effects on the brain remain unclear. 4D flow MRI is uniquely poised to systematically evaluate complex hemodynamics along the heart‐brain pathway. Owing to advancements yielding shorter scan times, 4D flow MRI can be acquired in approximately 7 minutes (heart) and 10 minutes (brain). This supports practical add‐on of 4D flow MRI to neuroimaging scans for comprehensive heart‐brain MRI evaluation in under an hour. We aimed to build a heart‐brain MRI acquisition and analysis framework to study relationships between hemodynamics and brain structure with age. Method: 17 healthy participants (age = 53.5±16.3[24‐76] years) underwent heart‐brain MRI at 3T (MAGNETOM Prisma, Siemens, Erlangen, Germany), including a free‐breathing whole‐chest 4D flow MRI research sequence, intracranial dual‐venc 4D flow MRI research sequence, and T1‐ and T2‐weighted structural neuroimaging. Participants were cognitively healthy and screened for history of cardiovascular and cerebrovascular problems that may influence blood flow. 4D flow MRI was used to evaluate blood flow velocities in the aorta and Circle of Willis (Figure 1: left). Mean velocity was determined on a voxel‐wise basis over the entire cardiac cycle. Volumetric and cortical thickness analysis was performed with FreeSurfer (v7.3; Figure 1: right). Left and right hippocampal and amygdala volumes were averaged and corrected for intracranial head size. We examined relationships between hemodynamics, volume and thickness measures, and age using Pearson correlations and multiple regression. Result: Mean aortic velocity was associated with age (r = ‐0.59, p = 0.012), hippocampal volume (r = 0.68, p = 0.003), amygdala volume (r = 0.59, p = 0.012), and inferior temporal thickness (r = 0.49, p = 0.044). Figure 2. Mean velocity in the Circle of Willis (r = ‐0.49, p = 0.048), amygdala volume (r = ‐0.66, p = 0.004) and inferior temporal thickness (r = ‐0.60, p = 0.010) were also associated with age. Using multiple regression, mean aortic velocity was associated with hippocampal volume (p = 0.018) adjusting for age. Conclusion: This study demonstrates capture of comprehensive heart and brain data in a single imaging exam for assessment of age‐related relationships in hemodynamics and brain structure. Heart‐brain MRI is a promising tool for evaluation of hemodynamic coupling along the entire heart‐brain pathway. Grant support: NIH NIA P30AG059988, P30AG072977, K01AG080070; NINDS R21NS122511 [ABSTRACT FROM AUTHOR]

Background: Cardiac MRI is an emerging modality for evaluating left ventricular (LV) diastolic dysfunction (LVDD), a pathological condition that is prevalent in aging populations. However, there is a lack of reports of MRI‐derived LV diastolic properties in late diastole. Purpose: To test the hypothesis that cine MRI‐derived motion/deformation indices can be used to characterize age‐related changes on LV relaxation patterns in late diastole. Study Type: Retrospective. Population: In all, 412 participants (72.5 ± 4.6 years old, range 65–84) without a documented history of cardiovascular diseases. Field Strength/Sequence: Balanced steady‐state free precession(bSSFP) acquired at 1.5T. Assessment: Participants were divided into younger (65–74 years old, n = 275) and older (75–84 years old, n = 137) groups. Status of diabetes mellitus (DM), hypertension (HTN), and lipid disorders were recorded for each participant. Cine MRI datasets were analyzed by using heart deformation analysis (HDA). LV motion/deformation indices (displacement, velocity, strain, and strain rate) were measured through 22 phases within a cardiac cycle. Statistical Tests: The prevalence of traditional cardiovascular risk conditions, LV ejection fraction (LVEF), peak LV regional displacement, velocity, and strain rates at early and late diastole were compared between two participant groups using chi‐square tests or t‐tests. Results: Older participants had a significantly lower peak early radial displacement (0.797 ± 0.249 cm vs. 0.876 ± 0.286 cm), radial velocity (19.3 ± 6.3 mm/s vs. 17.5 ± 5.2 mm/s), and circumferential strain rate (64.6 ± 15.7%/s vs. 70.1 ± 17%/s) but a higher peak late circumferential strain rate (69.8 ± 16.3 %/s vs. 66 ± 15.8 %/s) than their younger counterparts. Data Conclusion: Cine MRI can be used to characterize age‐related LV relaxation patterns in late diastole. Level of Evidence: 3. Technical Efficacy Stage: 1. [ABSTRACT FROM AUTHOR]

Background: Stroke etiology is undetermined in approximately one‐sixth to one‐third of patients. The presence of aortic flow reversal and plaques in the descending aorta (DAo) has been identified as a potential retrograde embolic mechanism. Purpose: To assess the relationships between aortic stiffness, wall thickness, and flow reversal in patients with cryptogenic stroke and healthy controls. Study Type: Prospective. Population: Twenty one patients with cryptogenic stroke and proven DAo plaques (69 ± 9 years, 43% female), 18 age‐matched controls (age: 65 ± 8 years, 61% female), and 14 younger controls (36 ± 9 years, 57% female). Field Strength/Sequence: 1.5T; 4D flow MRI and 3D dark blood T1‐weighted turbo spin echo MRI of the aorta. Assessment: Noncontrast aortic 4D flow MRI to measure 3D flow dynamics and 3D dark blood aortic wall MRI to assess wall thickness. 4D flow MRI analysis included automated quantification of aortic stiffness by pulse wave velocity (PWV) and voxelwise mapping of the flow reversal fraction (FRF). Statistical Tests: Analysis of variance (ANOVA) or Kruskal–Wallis tests, Student's unpaired t‐tests or Wilcoxon rank‐sum tests, regression analysis. Results: Aortic PWV and FRF were statistically higher in patients (8.9 ± 1.7 m/s, 18.4 ± 7.7%) than younger controls (5.3 ± 0.8 m/s, P < 0.0167; 8.5 ± 2.9%, P < 0.0167), but not age‐matched controls (8.2 ± 1.6 m/s, P = 0.22; 15.6 ± 5.8%, P = 0.22). Maximum aortic wall thickness was higher in patients (3.1 ± 0.7 mm) than younger controls (2.2 ± 0.2 mm, P < 0.0167) and age‐matched controls (2.7 ± 0.5 mm) (P < 0.0167). For all subjects, positive relationships were found between PWV and age (R2 = 0.71, P < 0.05), aortic wall thickness (R2 = 0.20, P < 0.05), and FRF (R2 = 0.47, P < 0.05). Patients demonstrated relationships between PWV and FRF in the ascending aorta (R2 = 0.32, P < 0.05) and arch (R2 = 0.24, P < 0.05). Data Conclusion: This study showed the utility of 4D flow MRI for evaluating aortic PWV and voxelwise flow reversal. Positive relationships between aortic PWV, wall thickness, and flow reversal support the hypothesis that aortic stiffness is involved in this retrograde embolic mechanism. Level of Evidence: 2 Technical Efficacy Stage: 1 [ABSTRACT FROM AUTHOR]

Purpose: 4D flow magnetic resonance imaging (4D‐MRI) allows time‐resolved visualization of blood flow patterns, quantification of volumes, velocities, and advanced parameters, such as wall shear stress (WSS). As 4D‐MRI enters the clinical arena, standardization and awareness of confounders are important. Our aim was to evaluate the equivalence of 4D flow‐derived aortic hemodynamics in healthy volunteers using different sequences and field strengths. Methods: 4D‐MRI was acquired in 10 healthy volunteers at 1.5T using three different prototype sequences, at 3T and at 7T (Siemens Healthineers). After evaluation of diagnostic quality in three segments (ascending‐, descending aorta, aortic arch), peak velocity, flow volumes, and WSS were investigated. Equivalence limits for comparison of field strengths/sequences were based on the limits of Bland‐Altman analyses of the intraobserver variability. Results: Non‐diagnostic quality was found in 10/144 segments, 9/10 were obtained at 7T. Apart for the comparison of forward flow between sequence 1 and 3, the differences in measurements between field strengths/sequences exceeded the range of agreement. Significant differences were found between field strengths/sequences for forward flow (1.5T vs. 3T, 3T vs. 7T, sequence 1 vs. 3, 2 vs. 3 [P <.001]), WSS (1.5T vs. 3T [P <.05], sequence 1 vs. 2, 1 vs. 3, 2 vs. 3 [P <.001]), and peak velocity (1.5T vs. 7T, sequence 1 vs. 3 [P >.001]). All parameters at all field strengths/with all sequences correlated moderately to strongly (r ≥ 0.5). Conclusion: Data from all sequences could be acquired and resulting images showed sufficient quality for further analysis. However, the variability of the measurements of peak velocity, flow volumes, and WSS was higher when comparing field strengths/sequences as the equivalence limits defined by the intraobserver assessments. [ABSTRACT FROM AUTHOR]

Highly accelerated real‐time cine MRI using compressed sensing (CS) is a promising approach to achieve high spatio‐temporal resolution and clinically acceptable image quality in patients with arrhythmia and/or dyspnea. However, its lengthy image reconstruction time may hinder its clinical translation. The purpose of this study was to develop a neural network for reconstruction of non‐Cartesian real‐time cine MRI k‐space data faster (<1 min per slice with 80 frames) than graphics processing unit (GPU)‐accelerated CS reconstruction, without significant loss in image quality or accuracy in left ventricular (LV) functional parameters. We introduce a perceptual complex neural network (PCNN) that trains on complex‐valued MRI signal and incorporates a perceptual loss term to suppress incoherent image details. This PCNN was trained and tested with multi‐slice, multi‐phase, cine images from 40 patients (20 for training, 20 for testing), where the zero‐filled images were used as input and the corresponding CS reconstructed images were used as practical ground truth. The resulting images were compared using quantitative metrics (structural similarity index (SSIM) and normalized root mean square error (NRMSE)) and visual scores (conspicuity, temporal fidelity, artifacts, and noise scores), individually graded on a five‐point scale (1, worst; 3, acceptable; 5, best), and LV ejection fraction (LVEF). The mean processing time per slice with 80 frames for PCNN was 23.7 ± 1.9 s for pre‐processing (Step 1, same as CS) and 0.822 ± 0.004 s for dealiasing (Step 2, 166 times faster than CS). Our PCNN produced higher data fidelity metrics (SSIM = 0.88 ± 0.02, NRMSE = 0.014 ± 0.004) compared with CS. While all the visual scores were significantly different (P < 0.05), the median scores were all 4.0 or higher for both CS and PCNN. LVEFs measured from CS and PCNN were strongly correlated (R2 = 0.92) and in good agreement (mean difference = −1.4% [2.3% of mean]; limit of agreement = 10.6% [17.6% of mean]). The proposed PCNN is capable of rapid reconstruction (25 s per slice with 80 frames) of non‐Cartesian real‐time cine MRI k‐space data, without significant loss in image quality or accuracy in LV functional parameters. [ABSTRACT FROM AUTHOR]

Background: Blood flow reversal is a possible mechanism for retrograde embolism in the setting of high-risk atherosclerotic plaques in the descending aorta (DAo). Evidence suggests that pulse wave velocity (PWV) is a determinant of blood flow reversal and can be reduced by the destiffening effect of renin-angiotensin system inhibitors (RASI).Purpose: To evaluate the impact of antihypertensive therapy on in vivo changes in PWV and flow reversal in patients with cryptogenic stroke.Study Type: Prospective.Population: Sixteen patients (69 ± 9 years; 10 males) included after cryptogenic stroke.Field Strength/sequence: 3T. 4D flow sequence (temporal resolution = 19.6 msec) ASSESSMENT: Patients underwent aortic MRI at baseline and at 6-month follow-up. Patients received standard-of-care antihypertensive therapy that were classified as RASI vs. non-RASI medications (ie, destiffening vs. nondestiffening).We compared aortic PWV, flow reversal fraction (FRF), aortic measurements, cardiac function, and other aortic and cardiac measurements in the antihypertensive therapy groups.Statistical Tests: Two-tailed paired or unpaired Student's t-tests (normal distributions) or Wilcoxon tests (nonnormal distribution). Univariate correlations using Pearson correlation coefficients.Results: There was a significant decrease in PWV in the RASI (n = 10) group (9.4 ± 1.6 m/s vs. 8.3 ± 1.9 m/s; P < 0.05), as well as FRF (18.6% ± 4.1% vs. 16.3% ± 4.0%; P < 0.05) between baseline and the 6-month MRI studies. There were no changes in PWV or FRF in the non-RASI (n = 6) group (P = 0.146 and P = 0.32). A decrease in FRF was significantly correlated with a decrease in PWV (r = 0.53; P < 0.05).Data Conclusion: The findings of our study suggest that RASI therapy after cryptogenic stroke resulted in a decrease of blood flow reversal and aortic stiffness.Evidence Level: 1 TECHNICAL EFFICACY STAGE: 4. [ABSTRACT FROM AUTHOR]

Purpose: To develop a reliable, consistent, and reproducible reference phantom for error quantification of phase‐contrast MRI so it can be used for validation and quality control. Methods: An air‐driven rotation phantom consisting of a steadily rotating cylinder surrounded by a static ring both filled with agarose gel was developed. Rotational speed was measured and controlled in real time using an optical counter and a closed‐loop controller. Consistency of the phantom was assessed by recording variations in rotational speed. The phantom was imaged with 2D phase‐contrast MRI, and the velocity at each point was compared with analytically predicted velocity. Additionally, to examine reproducibility, the phantom was run with the same rotational speed on 2 different days and imaged using the same phase‐contrast MRI protocol. Results: The rotation phantom provided consistent rotational speed with 2 revolutions per minute SD from the set value for 20 min. Comparison between predicted and measured velocities demonstrated excellent agreement (intraclass correlation coefficient of 0.99). The RMS error in velocity components were less than 1% of maximum value. The scan–rescan experiment showed that the phantom can reproduce the same velocity distributions (intraclass correlation coefficient of 0.99) using the same rotational speed and MRI settings. Conclusion: The developed rotation phantom provided well‐defined and reproducible linear velocity distributions, which can be used for systematic and quantitative error analysis of phase‐contrast MRI for a range of known velocities. [ABSTRACT FROM AUTHOR]

Purpose: To generate fully automated and fast 4D‐flow MRI‐based 3D segmentations of the aorta using deep learning for reproducible quantification of aortic flow, peak velocity, and dimensions. Methods: A total of 1018 subjects with aortic 4D‐flow MRI (528 with bicuspid aortic valve, 376 with tricuspid aortic valve and aortic dilation, 114 healthy controls) comprised the data set. A convolutional neural network was trained to generate 3D aortic segmentations from 4D‐flow data. Manual segmentations served as the ground truth (N = 499 training, N = 101 validation, N = 418 testing). Dice scores, Hausdorff distance, and average symmetrical surface distance were calculated to assess performance. Aortic flow, peak velocity, and lumen dimensions were quantified at the ascending, arch, and descending aorta and compared using Bland‐Altman analysis. Interobserver variability of manual analysis was assessed on a subset of 40. Results: Convolutional neural network segmentation required 0.438 ± 0.355 seconds versus 630 ± 254 seconds for manual analysis and demonstrated excellent performance with a median Dice score of 0.951 (0.930‐0.966), Hausdorff distance of 2.80 (2.13‐4.35), and average symmetrical surface distance of 0.176 (0.119‐0.290). Excellent agreement was found for flow, peak velocity, and dimensions with low bias and limits of agreement less than 10% difference versus manual analysis. For aortic volume, limits of agreement were moderate within 16.3%. Interobserver variability (median Dice score: 0.950; Hausdorff distance: 2.45; and average symmetrical surface distance: 0.145) and convolutional neural network–based analysis (median Dice score: 0.953‐0.959; Hausdorff distance: 2.24‐2.91; and average symmetrical surface distance: 0.145‐1.98 to observers) demonstrated similar reproducibility. Conclusions: Deep learning enabled fast and automated 3D aortic segmentation from 4D‐flow MRI, demonstrating its potential for efficient clinical workflows. Future studies should investigate its utility for other vasculature and multivendor applications. [ABSTRACT FROM AUTHOR]

Purpose: To examine the effects of age, sex, and left ventricular global function on velocity, helicity, and 3D wall shear stress (3D‐WSS) in the aorta of N = 100 healthy controls. Methods: Fifty female and 50 male volunteers with no history of cardiovascular disease, with 10 volunteers per age group (18‐30, 31‐40, 41‐50, 51‐60, and 61‐80 years) underwent aortic 4D‐flow MRI. Quantification of systolic aortic peak velocity, helicity, and 3D‐WSS distribution and the calculation of age group–averaged peak systolic velocity and 3D‐WSS maps ("atlases") were computed. Age‐related and sex‐related changes in peak velocity, helicity, and 3D‐WSS were computed and correlated with standard metrics of left ventricular function derived from short‐axis cine MRI. Results: No significant differences were found in peak systolic velocity or 3D‐WSS based on sex except for the 18‐ to 30‐year‐old group (males 8% higher velocity volume and 3D‐WSS surface area). Between successively older groups, systolic velocity decreased (13%, <1%, 7%, and 55% of the aorta volume) and 3D‐WSS decreased (21%, 2%, 30%, and 62% of the aorta surface area). Mean velocity, mean 3D‐3D‐WSS, and median helicity increased with cardiac output (r = 0.27‐0.43, all P <.01), and mean velocity and 3D‐WSS decreased with increasing diameter (r > 0.35, P <.001). Arch and descending aorta systolic mean velocity, mean 3D‐WSS, and median helicity increased with normalized left ventricular volumes: end diastolic volume (r = 0.31‐0.37, P <.01), end systolic volume (r = 0.27‐0.35, P <.01), and stroke volume (r = 0.28‐0.35, P <.01). Conclusion: Healthy aortic hemodynamics are dependent on subject age, and correlate with vessel diameter and cardiac function. [ABSTRACT FROM AUTHOR]

Background: Doxorubicin and doxorubicin‐trastuzumab combination chemotherapy have been associated with cardiotoxicity that eventually leads to heart failure and may limit dose‐effective cancer treatment. Current diagnostic strategies rely on decreased ejection fraction (EF) to diagnose cardiotoxicity. Purpose The aim of this study is to explore the potential of cardiac MR (CMR) imaging to identify imaging biomarkers in a mouse model of chemotherapy‐induced cardiotoxicity. Methods: A cumulative dose of 25 mg/kg doxorubicin was administered over three weeks using subcutaneous pellets (n = 9, Dox). Another group (n = 9) received same dose of Dox and a total of 10 mg/kg trastuzumab (DT). Mice were imaged at baseline, 5/6 weeks and 10 weeks post‐treatment on a 7T MRI system. The protocol included short‐axis cine MRI covering the left ventricle (LV) and mid‐ventricular short‐axis tissue phase mapping (TPM), pre‐ and post‐contrast T1 mapping, T2 mapping and Displacement Encoding with Stimulated Echoes (DENSE) strain encoded MRI. EF, peak myocardial velocities, native T1, T2, extracellular volume (ECV), and myocardial strain were quantified. N = 7 mice were sacrificed for histopathologic assessment of apoptosis at 5/6 weeks. Results: Global peak systolic longitudinal velocity was reduced at 5/6 weeks in Dox (0.6 ± 0.3 vs 0.9 ± 0.3, p = 0.02). In the Dox group, native T1 was reduced at 5/6 weeks (1.3 ± 0.2 ms vs 1.6 ± 0.2 ms, p = 0.02), and relatively normalized at week 10 (1.4 ± 0.1 ms vs 1.6 ± 0.2 ms, p > 0.99). There was no change in EF and other MRI parameters and histopathologic results demonstrated minimal apoptosis in all mice (~1–2 apoptotic cell/high power field), suggesting early‐stage cardiotoxicity. Conclusions: In a mouse model of chemotherapy‐induced cardiotoxicity using doxorubicin and trastuzumab, advanced CMR shows promise in identifying treatment‐related decrease in myocardial velocity and native T1 prior to the onset of cardiomyocyte apoptosis and reduction of EF. [ABSTRACT FROM AUTHOR]

Background: Magnetic resonance tissue phase mapping (TPM) measures three-directional myocardial velocities of the left and right ventricle (LV, RV). This noninvasive technique may supplement endomyocardial biopsy (EMB) in monitoring grafts post-heart transplantation (HTx).Purpose: To assess biventricular myocardial velocity alterations in grafts and investigate the relationship between velocities and acute cellular rejection (ACR) episodes.Study Type: Prospective.Subjects: Twenty-seven patients within 1 year post-HTx (49 ± 13 years, 19 M) and 18 age-matched controls (49 ± 15 years, 12 M).Field Strength/sequence: 1.5T, 2D balanced steady-state free precession, and TPM.Assessment: Ventricular function: end-diastolic and end-systolic volumes, stroke volumes, ejection fraction (EF), and myocardial mass. TPM velocities: peak-systolic and peak-diastolic velocities, cardiac twist, and interventricular dyssynchrony. ACR rejection episodes: International Society for Heart and Lung Transplantation grading of EMB specimens.Statistical Tests: The Lilliefors test for normality, unpaired t-tests, and Wilcoxon rank-sum tests for normally and nonnormally distributed data, respectively, were used, as well as multivariate regression for confounding variables and Pearson's correlation for associations between TPM velocities and global function.Results: Compared to controls, HTx patients demonstrated reduced biventricular systolic longitudinal velocities (LV: 5.2 ± 2.1 vs. 4.0 ± 1.5 cm/s, P < 0.05; RV: 4.2 ± 1.3 vs. 3.1 ± 1.2 cm/s, P < 0.01). Correlation analysis revealed significant positive relationships for biventricular EF with radial peak velocities of the same ventricle in both systole and diastole (LV systole: r = 0.48, P < 0.01; LV diastole: r = 0.28, P < 0.05; RV systole: r = 0.35, P < 0.01; RV diastole: r = 0.36, P < 0.01). Segmentally, longitudinal velocities were impaired in 7/16 LV segments and 5/10 RV segments in systole and 7/10 RV segments in diastole. TPM analysis in studies with >4 preceding ACR episodes showed globally reduced RV and LV systolic radial velocity, and segmentally reduced radial and longitudinal systolic velocities.Data Conclusion: Biventricular global and segmental velocities were reduced in HTx patients. Patients with >4 rejection episodes showed reduced myocardial velocities. The TPM sequence may add functional information for monitoring graft dysfunction.Level Of Evidence: 2 TECHNICAL EFFICACY STAGE: 2 J. Magn. Reson. Imaging 2020;52:920-929. [ABSTRACT FROM AUTHOR]

Retrospective electrocardiogram‐gated, 2D phase‐contrast (PC) flow MRI is routinely used in clinical evaluation of valvular/vascular disease in pediatric patients with congenital heart disease (CHD). In patients not requiring general anesthesia, clinical standard PC is conducted with free breathing for several minutes per slice with averaging. In younger patients under general anesthesia, clinical standard PC is conducted with breath‐holding. One approach to overcome this limitation is using either navigator gating or self‐navigation of respiratory motion, at the expense of lengthening scan times. An alternative approach is using highly accelerated, free‐breathing, real‐time PC (rt‐PC) MRI, which to date has not been evaluated in CHD patients. The purpose of this study was to develop a 38.4‐fold accelerated 2D rt‐PC pulse sequence using radial k‐space sampling and compressed sensing with 1.5 × 1.5 × 6.0 mm3 nominal spatial resolution and 40 ms nominal temporal resolution, and evaluate whether it is capable of accurately measuring flow in 17 pediatric patients (aortic valve, pulmonary valve, right and left pulmonary arteries) compared with clinical standard 2D PC (either breath‐hold or free breathing). For clinical translation, we implemented an integrated reconstruction pipeline capable of producing DICOMs of the order of 2 min per time series (46 frames). In terms of association, forward volume, backward volume, regurgitant fraction, and peak velocity at peak systole measured with standard PC and rt‐PC were strongly correlated (R2 > 0.76; P < 0.001). Compared with clinical standard PC, in terms of agreement, forward volume (mean difference = 1.4% (3.0% of mean)) and regurgitant fraction (mean difference = −2.5%) were in good agreement, whereas backward volume (mean difference = −1.1 mL (28.2% of mean)) and peak‐velocity at peak systole (mean difference = −21.3 cm/s (17.2% of mean)) were underestimated by rt‐PC. This study demonstrates that the proposed rt‐PC with the said spatial resolution and temporal resolution produces relatively accurate forward volumes and regurgitant fractions but underestimates backward volumes and peak velocities at peak systole in pediatric patients with CHD. [ABSTRACT FROM AUTHOR]

Background: Systematic evaluation of complex flow in the true lumen and false lumen (TL, FL) is needed to better understand which patients with chronic descending aortic dissection (DAD) are predisposed to complications.Purpose: To develop quantitative hemodynamic maps from 4D flow MRI for evaluating TL and FL flow characteristics.Study Type: Retrospective.Population: In all, 20 DAD patients (age = 60 ± 11 years; 12 male) (six medically managed type B AD [TBAD], 14 repaired type A AD [rTAAD] now with ascending aortic graft [AAo] or elephant trunk [ET1] repair) and 21 age-matched controls (age = 59 ± 10 years; 13 male) were included.Field Strength/sequence: 1.5T, 3T, 4D flow MRI.Assessment: 4D flow MRI was acquired in all subjects. Data analysis included 3D segmentation of TL and FL and voxelwise calculation of forward flow, reverse flow, flow stasis, and kinetic energy as quantitative hemodynamics maps.Statistical Tests: Analysis of variance (ANOVA) or Kruskal-Wallis tests were performed for comparing subject groups. Correlation and Bland-Altman analysis was performed for the interobserver study.Results: Patients with rTAAD presented with elevated TL reverse flow (AAo repair: P = 0.004, ET1: P = 0.018) and increased TL kinetic energy (AAo repair: P = 0.0002, ET1: P = 0.011) compared to controls. In addition, TL kinetic energy was increased vs. patients with TBAD (AAo repair: P = 0.021, ET1: P = 0.048). rTAAD was associated with higher FL kinetic energy and lower FL stasis compared to patients with TBAD (AAo repair: P = 0.002, ET1: P = 0.024 and AAo repair: P = 0.003, ET1: P = 0.048, respectively).Data Conclusion: Quantitative maps from 4D flow MRI demonstrated global and regional hemodynamic differences between DAD patients and controls. Patients with rTAAD vs. TBAD had significantly altered regional TL and FL hemodynamics. These findings indicate the potential of 4D flow MRI-derived hemodynamic maps to help better evaluate patients with DAD.Level Of Evidence: 3 Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2020;51:1357-1368. [ABSTRACT FROM AUTHOR]

Background: Endomyocardial biopsy (EMB) is the standard method for detecting allograft rejection in pediatric heart transplants (Htx). As EMB is invasive and carries a risk of complications, there is a need for a noninvasive alternative for allograft monitoring.Purpose: To quantify left and right ventricular (LV & RV) peak velocities, velocity twist, and intra-/interventricular dyssynchrony using tissue phase mapping (TPM) in pediatric Htx compared with controls, and to explore the relationship between global cardiac function parameters and the number of rejection episodes to these velocities and intra-/interventricular dyssynchrony.Study Type: Prospective.Subjects: Twenty Htx patients (age: 16.0 ± 3.1 years, 11 males) and 18 age- and sex-matched controls (age: 15.5 ± 4.3 years, nine males).Field Strength/sequence: 5T; 2D balanced cine steady-state free-precession (bSSFP), TPM (2D cine phase contrast with three-directional velocity encoding).Assessment: LV and RV circumferential, radial, and long-axis velocity-time curves, global and segmental peak velocities were measured using TPM. Short-axis bSSFP images were used to measure global LV and RV function parameters.Statistical Tests: A normality test (Lilliefors test) was performed on all data. For comparisons, a t-test was used for normally distributed data or a Wilcoxon rank-sum test otherwise. Correlations were determined by a Pearson correlation.Results: Htx patients had significantly reduced LV (P < 0.05-0.001) and RV (P < 0.05-0.001) systolic and diastolic global and segmental long-axis velocities, reduced RV diastolic peak twist (P < 0.01), and presented with higher interventricular dyssynchrony for long-axis and circumferential motions (P < 0.05-0.001). LV diastolic long-axis dyssynchrony (r = 0.48, P = 0.03) and RV diastolic peak twist (r = -0.64, P = 0.004) significantly correlated with the total number of rejection episodes.Data Conclusion: TPM detected differences in biventricular myocardial velocities in pediatric Htx patients compared with controls and indicated a relationship between Htx myocardial velocities and rejection history.Level Of Evidence: 2 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2020;51:1212-1222. [ABSTRACT FROM AUTHOR]

Purpose: To evaluate the utility of an efficient triple velocity‐encoding (VENC) 4D flow MRI implementation to improve velocity unwrapping of 4D flow MRI data with the same scan time as an interleaved dual‐VENC acquisition. Methods: A balanced 7‐point acquisition was used to derive 3 sets of 4D flow images corresponding to 3 different VENCs. These 3 datasets were then used to unwrap the aliased lowest VENC into a minimally aliased, triple‐VENC dataset. Triple‐VENC MRI was evaluated and compared with dual‐VENC MRI over 3 different VENC ranges (50‐150, 60‐150, and 60‐180 cm/s) in vitro in a steadily rotating phantom as well as in a pulsatile flow phantom. In vivo, triple‐VENC data of the thoracic aorta were also evaluated in 3 healthy volunteers (2 males, 26‐44 years old) with VENC = 50/75/150 cm/s. Two triple‐VENC (triconditional and biconditional) and 1 dual‐VENC unwrapping algorithms were quantitatively assessed through comparison to a reference, unaliased, single‐VENC scan. Results: Triple‐VENC 4D flow constant rotation phantom results showed high correlation with the analytical solution (intraclass correlation coefficient = 0.984‐0.995, P <.001) and up to a 61% reduction in velocity noise compared with the corresponding single‐VENC scans (VENC = 150, 180 cm/s). Pulsatile flow phantom experiments demonstrated good agreement between triple‐VENC and single‐VENC acquisitions (peak flow < 0.8% difference; peak velocity < 11.7% difference). Triconditional triple‐VENC unwrapping consistently outperformed dual‐VENC unwrapping, correctly unwrapping more than 83% and 46%‐66% more voxels in vitro and in vivo, respectively. Conclusion: Triple‐VENC 4D flow MRI adds no additional scan time to dual‐VENC MRI and has the potential for improved unwrapping to extend the velocity dynamic range beyond dual‐VENC methods. [ABSTRACT FROM AUTHOR]

Background: The effect of different expressions of aortic valve disease on 3D aortic hemodynamics is unclear.Purpose: To investigate changes in aortic hemodynamics in patients with dilated ascending aorta (AAo) but different severity of aortic valve stenosis (AS) and/or regurgitation (AR).Study Type: Retrospective.Population: A total of 111 subjects (86 patients with AAo diameter ≥ 40 mm and 25 healthy controls, all with trileaflet aortic valve [TAV]). Patients were further stratified by TAV dysfunction: n = 9 with combined moderate or severe AS and AR (ASR, 56 ± 13 years), n = 14 with moderate or severe AS (AS, 64 ± 14 years), n = 33 with moderate or severe AR (AR, 62 ± 14 years), n = 30 with neither AS nor AR (no AS/AR, 63 ± 9 years).Field Strength/sequence: 4D flow MRI on 1.5/3T systems for the in vivo analysis of aortic blood flow dynamics.Assessment: Data analysis included grading of 3D AAo vortex/helix flow and AAo flow eccentricity as well as quantification of systolic peak velocities and wall shear stress (WSS).Statistical Tests: Continuous variables were compared by one-way analysis of variance or Kruskal-Wallis, followed by a pairwise Tukey or Dunn test if there was a significant difference.Results: All patients demonstrated markedly elevated vortex and helix flow compared with controls (P < 0.05). Peak velocities were significantly elevated in ASR, AS, and AR patients compared with controls (P < 0.05). Increased flow eccentricity was observed in entire AAo for AR, at the mid and distal AAo for ASR and AS, and at the proximal AAo for no AS/AR. Compared with controls, WSS in the AAo was significantly elevated in ASR and AS patients (P < 0.05) and reduced in no AS/AR patients (P < 0.05).Data Conclusion: The presence of TAV dysfunction is associated with aberrant hemodynamics and altered WSS, which may play a role in the development of aortopathy.Level Of Evidence: 3 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2020;51:481-491. [ABSTRACT FROM AUTHOR]

Aims: While right ventricular (RV) dysfunction is associated with worse prognosis in co‐morbid pulmonary hypertension and heart failure with preserved ejection fraction (PH‐HFpEF), the mechanisms driving RV dysfunction are unclear. We evaluated the extent and clinical correlates of diffuse RV myocardial fibrosis in PH‐HFpEF, as measured by cardiovascular magnetic resonance‐derived extracellular volume (ECV). Methods and results: We prospectively enrolled participants with PH‐HFpEF (n = 14), pulmonary arterial hypertension (PAH; n = 13), and controls (n = 8). All participants underwent high‐resolution cardiovascular magnetic resonance, and case subjects (PH‐HFpEF and PAH) additionally underwent right heart catheterization. T1 mapping was performed using high‐resolution modified look‐locker inversion recovery with a 1 × 1 mm2 in‐plane resolution. RV free wall T1 values were quantified, and ECV was calculated. Participants with PH‐HFpEF were older and carried higher rates of hypertension and obstructive sleep apnoea than those with PAH. While RV ECV was similar between PH‐HFpEF and PAH (33.1 ± 8.0 vs. 34.0 ± 4.5%; P = 0.57), total pulmonary resistance was lower in PH‐HFpEF compared with PAH [PH‐HFpEF: 5.68 WU (4.70, 7.66 WU) vs. PAH: 8.59 WU (8.14, 12.57 WU); P = 0.01]. RV ECV in PH‐HFpEF was associated with worse indices of RV structure (RV end‐diastolic volume: r = 0.67, P = 0.01) and RV function (RV free wall strain: r = 0.59, P = 0.03) but was not associated with RV afterload (total pulmonary resistance: r = 0.08, P = 0.79). Conversely, there was a strong correlation between RV ECV and RV afterload in PAH (r = 0.57, P = 0.04). Conclusions: Diffuse RV fibrosis, as measured by ECV, is present in PH‐HFpEF and is associated with adverse RV structural and functional remodelling but not degree of pulmonary vasculopathy. In PH‐HFpEF, diffuse RV fibrosis may occur out of proportion to the degree of RV afterload. [ABSTRACT FROM AUTHOR]

Aortic valve replacement (AVR) is a common treatment for severe aortic valve disease, which can adversely affect blood flow in the aorta. Seismocardiography (SCG) measures physical vibrations at the exterior of the chest, which can be sensitive to altered cardiac function and flow dynamics. Magnetic resonance imaging (MRI) can image blood movement, and it can provide depiction and quantification of aortic flow. Here we present SCG and MRI measurements from before and after AVR and ascending aorta replacement, in the case of a woman with bicuspid aortic valve disease and a dilated ascending aorta. SCG measurements show elevated energy during systole indicating stenotic flow before surgery and lowered systolic energy levels after replacement with a prosthetic valve. MRI shows jetting, helical flow before surgery, and cohesive flow after. [ABSTRACT FROM AUTHOR]

Background: Cerebral arteriovenous malformations (AVMs) are pathological connections between arteries and veins. Dual-venc 4D flow MRI, an extended 4D flow MRI method with improved velocity dynamic range, provides time-resolved 3D cerebral hemodynamics.Purpose: To optimize dual-venc 4D flow imaging parameters for AVM; to assess the relationship between spatial resolution, acceleration, and flow quantification accuracy; and to introduce and apply the flow distribution network graph (FDNG) paradigm for storing and analyzing complex neurovascular 4D flow data.Study Type: Retrospective cohort study.Subjects/phantom: Scans were performed in a specialized flow phantom: 26 healthy subjects (age 41 ± 17 years) and five AVM patients (age 27-68 years).Field Strength/sequence: Dual-venc 4D flow with varying spatial resolution and acceleration factors were performed at 3T field strength.Assessment: Quantification accuracy was assessed in vitro by direct comparison to measured flow. FDNGs were used to quantify and compare flow, peak velocity (PV), and pulsatility index (PI) between healthy controls with various Circle of Willis (CoW) anatomy and AVM patients.Statistical Tests: In vitro measurements were compared to ground truth with Student's t-test. In vivo groups were compared with Wilcoxon rank-sum test and Kruskal-Wallis test.Results: Flow was overestimated in all in vitro experiments, by an average 7.1 ± 1.4% for all measurement conditions. Error in flow measurement was significantly correlated with number of voxels across the channel (P = 3.11 × 10-28 ) but not with acceleration factor (P = 0.74). For the venous-arterial PV and PI ratios, a significant difference was found between AVM nidal and extranidal circulation (P = 0.008 and 0.05, respectively), and between AVM nidal and healthy control circulation (P = 0.005 and 0.003, respectively).Data Conclusion: Dual-venc 4D flow MRI and standardized FDNG analysis might be feasible in clinical applications. Venous-arterial ratios of PV and PI are proposed as network-based biomarkers characterizing AVM nidal hemodynamics.Level Of Evidence: 3 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;50:1718-1730. [ABSTRACT FROM AUTHOR]