Fully Automated Valve Segmentation for Blood Flow Assessment From 4D Flow MRI Including Automated Cardiac Valve Tracking and Transvalvular Velocity Mapping.

BACKGROUND: Automated 4D flow MRI valvular flow quantification without time-consuming manual segmentation might improve workflow. PURPOSE: Compare automated valve segmentation (AS) to manual (MS), and manually corrected automated segmentation (AMS), in corrected atrioventricular septum defect (c-AVSD) patients and healthy volunteers, for assessing net forward volume (NFV) and regurgitation fraction (RF). STUDY TYPE: Retrospective. POPULATION: 27 c-AVSD patients (median, 23 years; interquartile range, 16-31 years) and 24 healthy volunteers (25 years; 12.5-36.5 years). FIELD STRENGTH/SEQUENCE: Whole-heart 4D flow MRI and cine steady-state free precession at 3T. ASSESSMENT: After automatic valve tracking, valve annuli were segmented on time-resolved reformatted trans-valvular velocity images by AS, MS, and AMS. NFV was calculated for all valves, and RF for right and left atrioventricular valves (RAVV and LAVV). NFV variation (standard deviation divided by mean NFV) and NFV differences (NFV difference of a valve vs. mean NFV of other valves) expressed internal NFV consistency. STATISTICAL TESTS: Comparisons between methods were assessed by Wilcoxon signed-rank tests, and intra/interobserver variability by intraclass correlation coefficients (ICCs). P < 0.05 was considered statistically significant, with multiple testing correction. RESULTS: AMS mean analysis time was significantly shorter compared with MS (5.3 ± 1.6 minutes vs. 9.1 ± 2.5 minutes). MS NFV variation (6.0%) was significantly smaller compared with AMS (6.3%), and AS (8.2%). Median NFV difference of RAVV, LAVV, PV, and AoV between segmentation methods ranged from -0.7-1.0 mL, -0.5-2.8 mL, -1.1-3.6 mL, and - 3.1--2.1 mL, respectively. Median RAVV and LAVV RF, between 7.1%-7.5% and 3.8%-4.3%, respectively, were not significantly different between methods. Intraobserver/interobserver agreement for AMS and MS was strong-to-excellent for NFV and RF (ICC ≥0.88). DATA CONCLUSION: MS demonstrates strongest internal consistency, followed closely by AMS, and AS. Automated segmentation, with or without manual correction, can be considered for 4D flow MRI valvular flow quantification. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY: Stage 3.

Evaluating a Phase-Specific Approach to Aortic Flow: A 4D Flow MRI Study.

BACKGROUND: Aortic flow parameters can be quantified using 4D flow MRI. However, data are sparse on how different methods of analysis influence these parameters and how these parameters evolve during systole. PURPOSE: To assess multiphase segmentations and multiphase quantification of flow-related parameters in aortic 4D flow MRI. STUDY TYPE: Prospective. POPULATION: 40 healthy volunteers (50% male, 28.9 ± 5.0 years) and 10 patients with thoracic aortic aneurysm (80% male, 54 ± 8 years). FIELD STRENGTH/SEQUENCE: 4D flow MRI with a velocity encoded turbo field echo sequence at 3 T. ASSESSMENT: Phase-specific segmentations were obtained for the aortic root and the ascending aorta. The whole aorta was segmented in peak systole. In all aortic segments, time to peak (TTP; for flow velocity, vorticity, helicity, kinetic energy, and viscous energy loss) and peak and time-averaged values (for velocity and vorticity) were calculated. STATISTICAL TESTS: Static vs. phase-specific models were assessed using Bland-Altman plots. Other analyses were performed using phase-specific segmentations for aortic root and ascending aorta. TTP for all parameters was compared to TTP of flow rate using paired t-tests. Time-averaged and peak values were assessed using Pearson correlation coefficient. P < 0.05 was considered statistically significant. RESULTS: In the combined group, velocity in static vs. phase-specific segmentations differed by 0.8 cm/sec for the aortic root, and 0.1 cm/sec (P = 0.214) for the ascending aorta. Vorticity differed by 167 sec-1 mL-1 (P = 0.468) for the aortic root, and by 59 sec-1 mL-1 (P = 0.481) for the ascending aorta. Vorticity, helicity, and energy loss in the ascending aorta, aortic arch, and descending aorta peaked significantly later than flow rate. Time-averaged velocity and vorticity values correlated significantly in all segments. DATA CONCLUSION: Static 4D flow MRI segmentation yields comparable results as multiphase segmentation for flow-related parameters, eliminating the need for time-consuming multiple segmentations. However, multiphase quantification is necessary for assessing peak values of aortic flow-related parameters. LEVEL OF EVIDENCE: 2 TECHNICAL EFFICACY STAGE: 3.

Particle Tracing Based on 4D Flow Magnetic Resonance Imaging: A Systematic Review into Methods, Applications, and Current Developments.

BACKGROUND: Particle tracing based on 4D Flow MRI has been applied as a quantitative and qualitative postprocessing technique to study temporally evolving blood flow patterns. PURPOSE: To systematically review the various methods to perform 4D Flow MRI-based particle tracing, as well as the clinical value, clinical applications, and current developments of the technique. STUDY TYPE: The study type is systematic review. SUBJECTS: Patients with cardiovascular disease (such as Marfan, Fontan, Tetralogy of Fallot), healthy controls, and cardiovascular phantoms that received 4D Flow MRI with particle tracing. FIELD STRENGTH/SEQUENCE: Three-dimensional three-directional cine phase-contrast MRI, at 1.5 T and 3 T. ASSESSMENT: Two systematic searches were performed on the PubMed database using Boolean operators and the relevant key terms covering 4D Flow MRI and particle tracing. One systematic search was focused on particle tracing methods, whereas the other on applications. Additional articles from other sources were sought out and included after a similar inspection. Particle tracing methods, clinical applications, clinical value, and current developments were extracted. STATISTICAL TESTS: The main results of the included studies are summarized, without additional statistical analysis. RESULTS: Of 127 unique articles retrieved from the initial search, 56 were included (28 for methods and 54 for applications). Most articles that described particle tracing methods used an adaptive timestep, a fourth order Runge-Kutta integration method, and linear interpolation in the time dimension. Particle tracing was applied in heart chambers, aorta, venae cavae, Fontan circulation, pulmonary arteries, abdominal vasculature, peripheral arteries, carotid arteries, and cerebral vasculature. Applications were grouped as intravascular, intracardiac, flow stasis, and research. DATA CONCLUSIONS: Particle tracing based on 4D Flow MRI gives unique insight into blood flow in several cardiovascular diseases, but the quality depends heavily on the MRI data quality. Further studies are required to evaluate the clinical value of the technique for different cardiovascular diseases. EVIDENCE LEVEL: 5. TECHNICAL EFFICACY: Stage 1.

Age- and sex-specific reference values of biventricular flow components and kinetic energy by 4D flow cardiovascular magnetic resonance in healthy subjects.

BACKGROUND: Advances in four-dimensional flow cardiovascular magnetic resonance (4D flow CMR) have allowed quantification of left ventricular (LV) and right ventricular (RV) blood flow. We aimed to (1) investigate age and sex differences of 4D flow CMR-derived LV and RV relative flow components and kinetic energy (KE) parameters indexed to end-diastolic volume (KEiEDV) in healthy subjects; and (2) assess the effects of age and sex on these parameters. METHODS: We performed 4D flow analysis in 163 healthy participants (42% female; mean age 43 ± 13 years) of a prospective registry study (NCT03217240) who were free of cardiovascular diseases. Relative flow components (direct flow, retained inflow, delayed ejection flow, residual volume) and multiple phasic KEiEDV (global, peak systolic, average systolic, average diastolic, peak E-wave, peak A-wave) for both LV and RV were analysed. RESULTS: Compared with men, women had lower median LV and RV residual volume, and LV peak and average systolic KEiEDV, and higher median values of RV direct flow, RV global KEiEDV, RV average diastolic KEiEDV, and RV peak E-wave KEiEDV. ANOVA analysis found there were no differences in flow components, peak and average systolic, average diastolic and global KEiEDV for both LV and RV across age groups. Peak A-wave KEiEDV increased significantly (r = 0.458 for LV and 0.341 for RV), whereas peak E-wave KEiEDV (r = - 0.355 for LV and - 0.318 for RV), and KEiEDV E/A ratio (r = - 0.475 for LV and - 0.504 for RV) decreased significantly, with age. CONCLUSION: These data using state-of-the-art 4D flow CMR show that biventricular flow components and kinetic energy parameters vary significantly by age and sex. Age and sex trends should be considered in the interpretation of quantitative measures of biventricular flow. Clinical trial registration  https://www. CLINICALTRIALS: gov . Unique identifier: NCT03217240.

Comparison of Four-Dimensional Flow MRI, Two-Dimensional Phase-Contrast MRI and Echocardiography in Transposition of the Great Arteries.

Pulmonary artery (PA) stenosis is a common complication after the arterial switch operation (ASO) for transposition of the great arteries (TGA). Four-dimensional flow (4D flow) CMR provides the ability to quantify flow within an entire volume instead of a single plane. The aim of this study was to compare PA maximum velocities and stroke volumes between 4D flow CMR, two-dimensional phase-contrast (2D PCMR) and echocardiography. A prospective study including TGA patients after ASO was performed between December 2018 and October 2020. All patients underwent echocardiography and CMR, including 2D PCMR and 4D flow CMR. Maximum velocities and stroke volumes were measured in the main, right, and left PA (MPA, LPA, and RPA, respectively). A total of 39 patients aged 20 ± 8 years were included. Maximum velocities in the MPA, LPA, and RPA measured by 4D flow CMR were significantly higher compared to 2D PCMR (p < 0.001 for all). PA assessment by echocardiography was not possible in the majority of patients. 4D flow CMR maximum velocity measurements were consistently higher than those by 2D PCMR with a mean difference of 65 cm/s for the MPA, and 77 cm/s for both the RPA and LPA. Stroke volumes showed good agreement between 4D flow CMR and 2D PCMR. Maximum velocities in the PAs after ASO for TGA are consistently lower by 2D PCMR, while echocardiography only allows for PA assessment in a minority of cases. Stroke volumes showed good agreement between 4D flow CMR and 2D PCMR.

Echo planar imaging-induced errors in intracardiac 4D flow MRI quantification.

PURPOSE: To assess errors associated with EPI-accelerated intracardiac 4D flow MRI (4DEPI) with EPI factor 5, compared with non-EPI gradient echo (4DGRE). METHODS: Three 3T MRI experiments were performed comparing 4DEPI to 4DGRE: steady flow through straight tubes, pulsatile flow in a left-ventricle phantom, and intracardiac flow in 10 healthy volunteers. For each experiment, 4DEPI was repeated with readout and blip phase-encoding gradient in different orientations, parallel or perpendicular to the flow direction. In vitro flow rates were compared with timed volumetric collection. In the left-ventricle phantom and in vivo, voxel-based speed and spatio-temporal median speed were compared between sequences, as well as mitral and aortic transvalvular net forward volume. RESULTS: In steady-flow phantoms, the flow rate error was largest (12%) for high velocity (>2 m/s) with 4DEPI readout gradient parallel to the flow. Voxel-based speed and median speed in the left-ventricle phantom were ≤5.5% different between sequences. In vivo, mean net forward volume inconsistency was largest (6.4 ± 8.5%) for 4DEPI with nonblip phase-encoding gradient parallel to the main flow. The difference in median speed for 4DEPI versus 4DGRE was largest (9%) when the 4DEPI readout gradient was parallel to the flow. CONCLUSIONS: Velocity and flow rate are inaccurate for 4DEPI with EPI factor 5 when flow is parallel to the readout or blip phase-encoding gradient. However, mean differences in flow rate, voxel-based speed, and spatio-temporal median speed were acceptable (≤10%) when comparing 4DEPI to 4DGRE for intracardiac flow in healthy volunteers.

Whole-Heart 4D Flow MRI for Evaluation of Normal and Regurgitant Valvular Flow: A Quantitative Comparison Between Pseudo-Spiral Sampling and EPI Readout.

BACKGROUND: Pseudo-spiral Cartesian sampling with compressed sensing reconstruction has facilitated highly accelerated 4D flow magnetic resonance imaging (MRI) in various cardiovascular structures. However, unlike echo planar imaging (EPI)-accelerated 4D flow MRI, it has not been validated in whole-heart applications. HYPOTHESIS: Pseudo-spiral 4D flow MRI (PROUD [PROspective Undersampling in multiple Dimensions]) is comparable to EPI in robustness of valvular flow measurements and remains comparable as the undersampling factor is increased and scan time reduced. STUDY TYPE: Prospective. POPULATION: Twelve healthy subjects and eight patients with valvular regurgitation. FIELD STRENGTH/SEQUENCE: 3.0 T; PROUD and EPI 4D flow sequences, 2D flow and balanced steady-state free precession sequences. ASSESSMENT: Valvular blood flow was quantified using valve tracking. PROUD- and EPI-based measurements of aortic (AV) and pulmonary (PV) flow volumes and left and right ventricular stroke volumes were tested for agreement with 2D MRI-based measurements. PROUD reconstructions with undersampling factors (R) of 9, 14, 28, and 56 were tested for intervalve consistency (per valve, compared to the other valves) and preservation of peak velocities and E/A ratios. STATISTICAL TESTS: We used repeated measures ANOVA, Bland-Altman, Wilcoxon signed rank, and intraclass correlation coefficients. P < 0.05 was considered statistically significant. RESULTS: PROUD and EPI intervalve consistencies were not significantly different both in healthy subjects (valve-averaged mean difference [limits of agreement width]: 3.2 ± 0.8 [8.7 ± 1.1] mL/beat for PROUD, 5.5 ± 2.9 [13.7 ± 2.3] mL/beat for EPI, P = 0.07) and in patients with valvular regurgitation (2.3 ± 1.2 [15.3 ± 5.9] mL/beat for PROUD, 0.6 ± 0.6 [19.3 ± 2.9] mL/beat for EPI, P = 0.47). Agreement between EPI and PROUD was higher than between 4D flow (EPI or PROUD) and 2D MRI for forward flow, stroke volumes, and regurgitant volumes. Up to R = 28 in healthy subjects and R = 14 in patients with valvular regurgitation, PROUD intervalve consistency remained comparable to that of EPI. Peak velocities and E/A ratios were preserved up to R = 9. CONCLUSION: PROUD is comparable to EPI in terms of intervalve consistency and may be used with higher undersampling factors to shorten scan times further. LEVEL OF EVIDENCE: 1 TECHNICAL EFFICACY STAGE: 2.

4D flow cardiovascular magnetic resonance derived energetics in the Fontan circulation correlate with exercise capacity and CMR-derived liver fibrosis/congestion.

AIM: This study explores the relationship between in vivo 4D flow cardiovascular magnetic resonance (CMR) derived blood flow energetics in the total cavopulmonary connection (TCPC), exercise capacity and CMR-derived liver fibrosis/congestion. BACKGROUND: The Fontan circulation, in which both caval veins are directly connected with the pulmonary arteries (i.e. the TCPC) is the palliative approach for single ventricle patients. Blood flow efficiency in the TCPC has been associated with exercise capacity and liver fibrosis using computational fluid dynamic modelling. 4D flow CMR allows for assessment of in vivo blood flow energetics, including kinetic energy (KE) and viscous energy loss rate (EL). METHODS: Fontan patients were prospectively evaluated between 2018 and 2021 using a comprehensive cardiovascular and liver CMR protocol, including 4D flow imaging of the TCPC. Peak oxygen consumption (VO2) was determined using cardiopulmonary exercise testing (CPET). Iron-corrected whole liver T1 (cT1) mapping was performed as a marker of liver fibrosis/congestion. KE and EL in the TCPC were computed from 4D flow CMR and normalized for inflow. Furthermore, blood flow energetics were compared between standardized segments of the TCPC. RESULTS: Sixty-two Fontan patients were included (53% male, 17.3 ± 5.1 years). Maximal effort CPET was obtained in 50 patients (peak VO2 27.1 ± 6.2 ml/kg/min, 56 ± 12% of predicted). Both KE and EL in the entire TCPC (n = 28) were significantly correlated with cT1 (r = 0.50, p = 0.006 and r = 0.39, p = 0.04, respectively), peak VO2 (r = - 0.61, p = 0.003 and r = - 0.54, p = 0.009, respectively) and % predicted peak VO2 (r = - 0.44, p = 0.04 and r = - 0.46, p = 0.03, respectively). Segmental analysis indicated that the most adverse flow energetics were found in the Fontan tunnel and left pulmonary artery. CONCLUSIONS: Adverse 4D flow CMR derived KE and EL in the TCPC correlate with decreased exercise capacity and increased levels of liver fibrosis/congestion. 4D flow CMR is promising as a non-invasive screening tool for identification of patients with adverse TCPC flow efficiency.

Hemodynamic interplay of vorticity, viscous energy loss, and kinetic energy from 4D Flow MRI and link to cardiac function in healthy subjects and Fontan patients.

The purpose of this study was to directly assess (patho)physiology of intraventricular hemodynamic interplay between four-dimensional flow cardiovascular magnetic resonance imaging (4D Flow MRI)-derived vorticity with kinetic energy (KE) and viscous energy loss (EL) over the cardiac cycle and their association to ejection fraction (EF) and stroke volume (SV). Fifteen healthy subjects and thirty Fontan patients underwent whole heart 4D Flow MRI. Ventricular vorticity, KE, and EL were computed over systole (vorticity_volavg systole, KEavg systole, and ELavg systole) and diastole (vorticity_volavg diastole, KEavg diastole, and ELavg diastole). The association between vorticity_vol and KE and EL was tested by Spearman correlation. Fontan patients were grouped to normal and impaired EF groups. A significant correlation was found between SV and vorticity in healthy subjects (systolic: ρ = 0.84, P < 0.001; diastolic: ρ = 0.81, P < 0.001) and in Fontan patients (systolic: ρ = 0.61, P < 0.001; diastolic: ρ = 0.54, P = 0.002). Healthy subjects showed positive correlation between vorticity_vol versus KE (systole: ρ = 0.96, P < 0.001; diastole: ρ = 0.90, P < 0.001) and EL (systole: ρ = 0.85, P < 0.001; diastole: ρ = 0.84, P < 0.001). Fontan patients showed significantly elevated vorticity_vol compared with healthy subjects (vorticity_volavg systole: 3.1 [2.3-3.9] vs. 1.7 [1.3-2.4] L/s, P < 0.001; vorticity_volavg diastole: 3.1 [2.0-3.7] vs. 2.1 [1.6-2.8] L/s, P = 0.002). This elevated vorticity in Fontan patients showed strong association with KE (systole: ρ = 0.91, P < 0.001; diastole: ρ = 0.85, P < 0.001) and EL (systole: ρ = 0.82, P < 0.001; diastole: ρ = 0.89, P < 0.001). Fontan patients with normal EF showed significantly higher vorticity_volavg systole and ELavg systole, but significantly decreased KE avg diastole, in the presence of normal SV, compared with healthy subjects. Healthy subjects show strong physiological hemodynamic interplay between vorticity with KE and EL. Fontan patients demonstrate a pathophysiological hemodynamic interplay characterized by correlation of elevated vorticity with KE and EL in the presence of maintained normal stroke volume. Altered vorticity and energetic hemodynamics are found in the presence of normal EF in Fontan patients.NEW & NOTEWORTHY Physiologic intraventricular hemodynamic interplay/coupling is present in the healthy left ventricle between vorticity versus viscous energy loss and kinetic energy from four-dimensional flow cardiovascular magnetic resonance imaging (4D Flow MRI). Conversely, Fontan patients present compensatory pathophysiologic hemodynamic coupling by an increase in intraventricular vorticity that positively correlates to viscous energy loss and kinetic energy levels in the presence of maintained normal stroke volume. Altered vorticity and energetics are found in the presence of normal ejection fraction in Fontan patients.

Reproducibility of Aorta Segmentation on 4D Flow MRI in Healthy Volunteers.

BACKGROUND: Hemodynamic aorta parameters can be derived from 4D flow MRI, but this requires lumen segmentation. In both commercially available and research 4D flow MRI software tools, lumen segmentation is mostly (semi-)automatically performed and subsequently manually improved by an observer. Since the segmentation variability, together with 4D flow MRI data and image processing algorithms, will contribute to the reproducibility of patient-specific flow properties, the observer's lumen segmentation reproducibility and repeatability needs to be assessed. PURPOSE: To determine the interexamination, interobserver reproducibility, and intraobserver repeatability of aortic lumen segmentation on 4D flow MRI. STUDY TYPE: Prospective and retrospective. POPULATION: A healthy volunteer cohort of 10 subjects who underwent 4D flow MRI twice. Also, a clinical cohort of six subjects who underwent 4D flow MRI once. FIELD STRENGTH/SEQUENCE: 3T; time-resolved three-directional and 3D velocity-encoded sequence (4D flow MRI). ASSESSMENT: The thoracic aorta was segmented on the 4D flow MRI in five systolic phases. By positioning six planes perpendicular to a segmentation's centerline, the aorta was divided into five segments. The volume, surface area, centerline length, maximal diameter, and curvature radius were determined for each segment. STATISTICAL TESTS: To assess the reproducibility, the coefficient of variation (COV), Pearson correlation coefficient (r), and intraclass correlation coefficient (ICC) were calculated. RESULTS: The interexamination and interobserver reproducibility and intraobserver repeatability were comparable for each parameter. For both cohorts there was very good reproducibility and repeatability for volume, surface area, and centerline length (COV = 10-32%, r = 0.54-0.95 and ICC = 0.65-0.99), excellent reproducibility and repeatability for maximal diameter (COV = 3-11%, r = 0.94-0.99, ICC = 0.94-0.99), and good reproducibility and repeatability for curvature radius (COV = 25-62%, r = 0.73-0.95, ICC = 0.84-0.97). DATA CONCLUSION: This study demonstrated no major reproducibility and repeatability limitations for 4D flow MRI aortic lumen segmentation. LEVEL OF EVIDENCE: 3 TECHNICAL EFFICACY STAGE: 2.

Associations between left ventricular function, vascular function and measures of cerebral small vessel disease: a cross-sectional magnetic resonance imaging study of the UK Biobank.

OBJECTIVES: Impaired cardiovascular function has been associated with cognitive deterioration; however, to what extent cardiovascular dysfunction plays a role in structural cerebral changes remains unclear. We studied whether vascular and left ventricular (LV) functions are associated with measures of cerebral small vessel disease (cSVD) in the middle-aged general population. METHODS: In this cross-sectional analysis of the UK Biobank, 4366 participants (54% female, mean age 61 years) underwent magnetic resonance imaging to assess LV function (ejection fraction [EF] and cardiac index [CI]) and cSVD measures (total brain volume, grey and white matter volumes, hippocampal volume and white matter hyperintensities [WMH]). Augmentation index (AIx) was used as a measure of arterial stiffness. Linear and non-linear associations were evaluated using cardiovascular function measures as determinants and cSVD measures as outcomes. RESULTS: EF was non-linearly associated with total brain volume and grey matter volume, with the largest brain volume for an EF between 55 and 60% (both p < 0.001). EF showed a negative linear association with WMH (- 0.23% [- 0.44; - 0.02], p = 0.03), yet no associations were found with white matter or hippocampal volume. CI showed a positive linear association with white matter (ß 3194 mm3 [760; 5627], p = 0.01) and hippocampal volume (ß 72.5 mm3 [23.0; 122.0], p = 0.004). No associations were found for CI with total brain volume, grey matter volume or WMH. No significant associations were found between AIx and cSVD measures. CONCLUSIONS: This study provides novel insights into the complex associations between the heart and the brain, which could potentially guide early interventions aimed at improving cardiovascular function and the prevention of cSVD. KEY POINTS: • Ejection fraction is non-linearly and cardiac index is linearly associated with MRI-derived measures of cerebral small vessel disease. • No associations were found for arterial stiffness with cSVD measures.

Normal and reference values for cardiovascular magnetic resonance-based pulse wave velocity in the middle-aged general population.

BACKGROUND: Aortic stiffness, assessed through pulse wave velocity (PWV), is an independent predictor for cardiovascular disease risk. However, the scarce availability of normal and reference values for cardiovascular magnetic resonance imaging (CMR) based PWV is limiting clinical implementation. The aim of this study was to determine normal and reference values for CMR assessed PWV in the general population. METHODS: From the 2,484 participants of the Netherlands Epidemiology of Obesity (NEO) study that have available CMR-PWV data, 1,394 participants free from cardiovasculard disease, smokers or treatment for diabetes, hypertension or dyslipidaemia were selected (45-65 years, 51% female). Participants were divided into sex, age and blood pressure (BP) subgroups. Normal values were specified for participants with a BP < 130/80 mmHg and reference values for elevated BP subgroups (≥ 130/80 and < 140/90 mmHg; and ≥ 140/90 mmHg). Differences between groups were tested with independent samples t-test or ANOVA. Due to an oversampling of obese individuals in this study, PWV values are based on a weighted analysis making them representative of the general population. RESULTS: Normal mean PWV was 6.0 m/s [95% CI 5.8-6.1]. PWV increased with advancing age and BP categories (both p < 0.001). There was no difference between sex in normal PWV, however in the BP > 140/90 mmHg women had a higher PWV (p = 0.005). The interpercentile ranges were smaller for participants < 55 years old compared to participants ≥ 55 years, indicating an increasing variability of PWV with age. PWV upper limits were particularly elevated in participants ≥ 55 years old in the high blood pressure subgroups. CONCLUSION: This study provides normal and reference values for CMR-assessed PWV per sex, age and blood pressure category in the general population.

Assessment of turbulent blood flow and wall shear stress in aortic coarctation using image-based simulations.

In this study, we analyzed turbulent flows through a phantom (a 180[Formula: see text] bend with narrowing) at peak systole and a patient-specific coarctation of the aorta (CoA), with a pulsating flow, using magnetic resonance imaging (MRI) and computational fluid dynamics (CFD). For MRI, a 4D-flow MRI is performed using a 3T scanner. For CFD, the standard [Formula: see text], shear stress transport [Formula: see text], and Reynolds stress (RSM) models are applied. A good agreement between measured and simulated velocity is obtained for the phantom, especially for CFD with RSM. The wall shear stress (WSS) shows significant differences between CFD and MRI in absolute values, due to the limited near-wall resolution of MRI. However, normalized WSS shows qualitatively very similar distributions of the local values between MRI and CFD. Finally, a direct comparison between in vivo 4D-flow MRI and CFD with the RSM turbulence model is performed in the CoA. MRI can properly identify regions with locally elevated or suppressed WSS. If the exact values of the WSS are necessary, CFD is the preferred method. For future applications, we recommend the use of the combined MRI/CFD method for analysis and evaluation of the local flow patterns and WSS in the aorta.

Clinical assessment of aortic valve stenosis: Comparison between 4D flow MRI and transthoracic echocardiography.

BACKGROUND: The prevalence of valvular aortic stenosis (AS) increases as the population ages. Echocardiographic measurements of peak jet velocity (Vpeak ), mean pressure gradient (Pmean ), and aortic valve area (AVA) determine AS severity and play a pivotal role in the stratification towards valvular replacement. A multimodality imaging approach might be needed in cases of uncertainty about the actual severity of the stenosis. PURPOSE: To compare four-dimensional phase-contrast magnetic resonance (4D PC-MR), two-dimensional (2D) PC-MR, and transthoracic echocardiography (TTE) for quantification of AS. STUDY TYPE: Prospective. POPULATION: Twenty patients with various degrees of AS (69.3 ± 5.0 years). FIELD STRENGTH/SEQUENCES: 4D PC-MR and 2D PC-MR at 3T. ASSESSMENT: We compared Vpeak , Pmean , and AVA between TTE, 4D PC-MR, and 2D PC-MR. Flow eccentricity was quantified by means of normalized flow displacement, and its influence on the accuracy of TTE measurements was investigated. STATISTICAL TESTS: Pearson's correlation, Bland-Altman analysis, paired t-test, and intraclass correlation coefficient. RESULTS: 4D PC-MR measured higher Vpeak (r = 0.95, mean difference + 16.4 ± 10.7%, P <0.001), and Pmean (r = 0.92, mean difference + 14.9 ± 16.0%, P = 0.013), but a less critical AVA (r = 0.80, mean difference + 19.9 ± 20.6%, P = 0.002) than TTE. In contrast, unidirectional 2D PC-MR substantially underestimated AS severity when compared with TTE. Differences in Vpeak between 4D PC-MR and TTE showed to be strongly correlated with the eccentricity of the flow jet (r = 0.89, P <0.001). Use of 4D PC-MR improved the concordance between Vpeak and AVA (from 0.68 to 0.87), and between PGmean and AVA (from 0.68 to 0.86). DATA CONCLUSION: 4D PC-MR improves the concordance between the different AS parameters and could serve as an additional imaging technique next to TTE. Future studies should address the potential value of 4D PC-MR in patients with discordant echocardiographic parameters. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:472-480.

Altered Ascending Aorta Hemodynamics in Patients After Arterial Switch Operation for Transposition of the Great Arteries.

BACKGROUND: Patients with transposition of the great arteries (TGA) have an altered aortic geometry after an arterial switch operation (ASO), with neo-aortic root dilatation as an important complication. Geometry-related aortic hemodynamics have been assumed to contribute to pathology of the ascending aorta (AAo). PURPOSE: To evaluate aortic flow displacement (FD) and regional wall shear stress (WSS) in relation to ascending neo-aortic geometry in children after ASO. STUDY TYPE: Prospective. POPULATION: Twenty-eight TGA patients after ASO and 10 healthy volunteers. FIELD STRENGTH/SEQUENCE: 3.0T/4D flow (segmented fast-spoiled echo pulse), noncontrast-enhanced MR angiography (Dixon), and anatomic images (SSFP). ASSESSMENT: Aortic diameters and body surface area-indexed aortic dimensions (Z-scores), normalized FD and planar ascending aortic WSS. STATISTICAL TESTS: Mann-Whitney and chi-square tests for differences in FD magnitude, WSS, and FD directionality between groups, respectively. Spearman rank correlation to assess the degree of association between aortic geometry, FD and WSS parameters. Shapiro-Wilk test to evaluate distribution normality on the absolute differences in octant location between FD and WSS. RESULTS: TGA patients showed a significantly dilated proximal AAo and relatively small mid-AAo dimensions at the level of the pulmonary arteries (Z-scores neo-aortic root: 4.38 ± 1.96 vs. 1.52 ± 0.70, P < 0.001; sinotubular junction: 3.48 ± 2.67 vs. 1.38 ± 1.30, P = 0.010; mid-AAo: 0.32 ± 3.06 vs. 1.69 ± 1.24, P = 0.001). FD magnitude was higher in TGA patients (neo-aortic root: 0.048 ± 0.027 vs. 0.021 ± 0.006, P < 0.001; sinotubular junction: 0.054 ± 0.037 vs. 0.029 ± 0.013, P < 0.05) and was related to the neo-aortic Z-score. Clear areas of higher WSS at the right and anterior aortic wall regions along the distal AAo were detected in TGA patients, most pronounced in those with relatively smaller mid-AAo diameters. DATA CONCLUSION: TGA-specific geometry related to the ASO, evidenced by neo-aortic root dilatation and a sudden change in vessel diameter at mid-AAo level, leads to more aortic flow asymmetry in the proximal AAo and WSS distribution with higher WSS at the right and anterior aortic wall regions along the distal AAo. LEVEL OF EVIDENCE: 1 Technical Efficacy Stage: 3 J. Magn. Reson. Imaging 2020;51:1105-1116.

Effect of Liraglutide on Cardiovascular Function and Myocardial Tissue Characteristics in Type 2 Diabetes Patients of South Asian Descent Living in the Netherlands: A Double-Blind, Randomized, Placebo-Controlled Trial.

BACKGROUND: The glucagon-like peptide-1 (GLP-1) receptor agonist liraglutide may be beneficial in the regression of diabetic cardiomyopathy. South Asian ethnic groups in particular are at risk of developing type 2 diabetes. PURPOSE: To assess the effects of liraglutide on left ventricular (LV) diastolic and systolic function in South Asian type 2 diabetes patients. STUDY TYPE: Prospective, double-blind, randomized, placebo-controlled trial. POPULATION: Forty-seven type 2 diabetes patients of South Asian ancestry living in the Netherlands, with or without ischemic heart disease, who were randomly assigned to 26-week treatment with liraglutide (1.8 mg/day) or placebo. FIELD STRENGTH/SEQUENCE: 3T (balanced steady-state free precession cine MRI, 2D and 4D velocity-encoded MRI, 1 H-MRS, T1 mapping). ASSESSMENT: Primary endpoints were changes in LV diastolic function (early deceleration peak [Edec], ratio of early and late peak filling rate [E/A], estimated LV filling pressure [E/Ea]) and LV systolic function (ejection fraction). Secondary endpoints were changes in aortic stiffness (aortic pulse wave velocity [PWV]), myocardial steatosis (myocardial triglyceride content), and diffuse fibrosis (extracellular volume [ECV]). STATISTICAL TESTS: Data were analyzed according to intention-to-treat. Between-group differences were reported as mean (95% confidence interval [CI]) and were assessed using analysis of covariance (ANCOVA). RESULTS: Liraglutide (n = 22) compared with placebo (n = 25) did not change Edec (+0.2 mL/s2 × 10-3 (-0.3;0.6)), E/A (-0.09 (-0.23;0.05)), E/Ea (+0.1 (-1.2;1.3)) and ejection fraction (0% (-3;2)), but decreased stroke volume (-9 mL (-14;-5)) and increased heart rate (+10 bpm (4;15)). Aortic PWV (+0.5 m/s (-0.6;1.6)), myocardial triglyceride content (+0.21% (-0.09;0.51)), and ECV (-0.2% (-1.4;1.0)) were unaltered. DATA CONCLUSION: Liraglutide did not affect LV diastolic and systolic function, aortic stiffness, myocardial triglyceride content, or extracellular volume in Dutch South Asian type 2 diabetes patients with or without coronary artery disease. LEVEL OF EVIDENCE: 1 Technical Efficacy Stage: 4 J. Magn. Reson. Imaging 2020;51:1679-1688.

Energetics of Blood Flow in Cardiovascular Disease: Concept and Clinical Implications of Adverse Energetics in Patients With a Fontan Circulation.

Visualization and quantification of the adverse effects of distorted blood flow are important emerging fields in cardiology. Abnormal blood flow patterns can be seen in various cardiovascular diseases and are associated with increased energy loss. These adverse energetics can be measured and quantified using 3-dimensional blood flow data, derived from computational fluid dynamics and 4-dimensional flow magnetic resonance imaging, and provide new, promising hemodynamic markers. In patients with palliated single-ventricular heart defects, the Fontan circulation passively directs systemic venous return to the pulmonary circulation in the absence of a functional subpulmonary ventricle. Therefore, the Fontan circulation is highly dependent on favorable flow and energetics, and minimal energy loss is of great importance. A focus on reducing energy loss led to the introduction of the total cavopulmonary connection (TCPC) as an alternative to the classical Fontan connection. Subsequently, many studies have investigated energy loss in the TCPC, and energy-saving geometric factors have been implemented in clinical care. Great advances have been made in computational fluid dynamics modeling and can now be done in 3-dimensional patient-specific models with increasingly accurate boundary conditions. Furthermore, the implementation of 4-dimensional flow magnetic resonance imaging is promising and can be of complementary value to these models. Recently, correlations between energy loss in the TCPC and cardiac parameters and exercise intolerance have been reported. Furthermore, efficiency of blood flow through the TCPC is highly variable, and inefficient blood flow is of clinical importance by reducing cardiac output and increasing central venous pressure, thereby increasing the risk of experiencing the well-known Fontan complications. Energy loss in the TCPC will be an important new hemodynamic parameter in addition to other well-known risk factors such as pulmonary vascular resistance and can possibly be improved by patient-specific surgical design. This article describes the theoretical background of mechanical energy of blood flow in the cardiovascular system and the methods of calculating energy loss, and it gives an overview of geometric factors associated with energy efficiency in the TCPC and its implications on clinical outcome. Furthermore, the role of 4-dimensional flow magnetic resonance imaging and areas of future research are discussed.

Automated Cardiac Valve Tracking for Flow Quantification with Four-dimensional Flow MRI.

Purpose To compare four-dimensional flow MRI with automated valve tracking to manual valve tracking in patients with acquired or congenital heart disease and healthy volunteers. Materials and Methods In this retrospective study, data were collected from 114 patients and 46 volunteers who underwent four-dimensional flow MRI at 1.5 T or 3.0 T from 2006 through 2017. Among the 114 patients, 33 had acquired and 81 had congenital heart disease (median age, 17 years; interquartile range [IQR], 13-49 years), 51 (45%) were women, and 63 (55%) were men. Among the 46 volunteers (median age, 28 years; IQR, 22-36 years), there were 19 (41%) women and 27 (59%) men. Two orthogonal cine views of each valve were used for valve tracking. Wilcoxon signed-rank test was used to compare analysis times, net forward volumes (NFVs), and regurgitant fractions. Intra- and interobserver variability was tested by using intraclass correlation coefficients (ICCs). Results Analysis time was shorter for automated versus manual tracking (all patients, 14 minutes [IQR, 12-15 minutes] vs 25 minutes [IQR, 20-25 minutes]; P < .001). Although overall differences in NFV and regurgitant fraction were comparable between both methods, NFV variation over four valves was smaller for automated versus manual tracking (all patients, 4.9% [IQR, 3.3%-6.7%] vs 9.8% [IQR, 5.1%-14.7%], respectively; P < .001). Regurgitation severity was discordant for seven pulmonary valves, 22 mitral valves, and 21 tricuspid valves. Intra- and interobserver agreement for automated tracking was excellent for NFV assessment (intra- and interobserver, ICC ≥ 0.99) and strong to excellent for regurgitant fraction assessment (intraobserver, ICC ≥ 0.94; interobserver, ICC ≥ 0.89). Conclusion Automated valve tracking reduces analysis time and improves reliability of valvular flow quantification with four-dimensional flow MRI in patients with acquired or congenital heart disease and in healthy volunteers. © RSNA, 2018 Online supplemental material is available for this article. See also the editorial by François in this issue.

Correction to: Effect of liraglutide on cardiac function in patients with type 2 diabetes mellitus: randomized placebo-controlled trial.

Following publication of the original article [1], the authors reported an error in Fig. 3. The bars in the upper right panel that represent heart rate in placebo treated patients is not correct.

Effect of liraglutide on cardiac function in patients with type 2 diabetes mellitus: randomized placebo-controlled trial.

BACKGROUND: Liraglutide is an antidiabetic agent with cardioprotective effect. The purpose of this study is to test efficacy of liraglutide to improve diabetic cardiomyopathy in patients with diabetes mellitus type 2 (DM2) without cardiovascular disease. METHODS: Patients with DM2 were randomly assigned to receive liraglutide 1.8 mg/day or placebo in this double-blind trial of 26 weeks. Primary outcome measures were LV diastolic function (early (E) and late (A) transmitral peak flow rate, E/A ratio, early deceleration peak (Edec), early peak mitral annular septal tissue velocity (Ea) and estimated LV filling pressure (E/Ea), and systolic function (stroke volume, ejection fraction, cardiac output, cardiac index and peak ejection rate) assessed with CMR. Intention-to-treat analysis of between-group differences was performed using ANCOVA. Mean estimated treatment differences (95% confidence intervals) are reported. RESULTS: 23 patients were randomized to liraglutide and 26 to placebo. As compared with placebo, liraglutide significantly reduced E (- 56 mL/s (- 91 to - 21)), E/A ratio (- 0.17 (- 0.27 to - 0.06)), Edec (- 0.9 mL/s2 * 10-3 (- 1.3 to - 0.2)) and E/Ea (- 1.8 (- 3.0 to - 0.6)), without affecting A (3 mL/s (- 35 to 41)) and Ea (0.4 cm/s (- 0.9 to 1.4)). Liraglutide reduced stroke volume (- 9 mL (- 16 to - 2)) and ejection fraction (- 3% (- 6 to - 0.1)), but did not change cardiac output (- 0.4 L/min (- 0.9 to 0.2)), cardiac index (- 0.1 L/min/m2 (- 0.4 to 0.1)) and peak ejection rate (- 46 mL/s (- 95 to 3)). CONCLUSIONS: Liraglutide reduced early LV diastolic filling and LV filling pressure, thereby unloading the left ventricle. LV systolic function reduced and remained within normal range. Future studies are needed to investigate if liraglutide-induced left ventricular unloading slows progression of diabetic cardiomyopathy into symptomatic stages. Trial registration ClinicalTrials.gov: NCT01761318.