BackgroundAutomated 4D flow MRI valvular flow quantification without time‐consuming manual segmentation might improve workflow.PurposeCompare 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 TypeRetrospective.Population27 c‐AVSD patients (median, 23 years; interquartile range, 16–31 years) and 24 healthy volunteers (25 years; 12.5–36.5 years).Field strength/SequenceWhole‐heart 4D flow MRI and cine steady‐state free precession at 3T.AssessmentAfter 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 TestsComparisons 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.ResultsAMS 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 ConclusionMS 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 Evidence3Technical EfficacyStage 3

Abstract Background It has been demonstrated that the rate of aortic dilatation is influenced by alteration of aortic hemodynamics, such as normalized flow displacement (FDN) and wall shear stress (WSS). However, the effects of ageing on aortic hemodynamics have not yet been described. Case summary 4D-Flow MRI derived aorta hemodynamics were derived in the ascending aorta of a patient with ascending aortic aneurysm (mean ± standard deviation: 46 ± 1 mm) and a healthy volunteer (aortic diameter 30 ± 1 mm) with long-term follow-up of ten and eight years, respectively. At all timepoints, compared to the healthy volunteer, the patient demonstrated higher magnitudes of FDN (7% ± 1% vs. 3% ± 1%) and WSS angle (36° ± 3° vs. 24° ± 6°), and lower WSS magnitude (565 ± 100 mPa vs. 910 ± 115 mPa), axial WSS (426 ± 71 mPa vs. 800 ± 108 mPa) and circumferential WSS (297 ± 64 mPa vs. 340 ± 85 mPa). The patient and healthy volunteer demonstrated different aortic dilatation rates (regression slope ± standard error: 0.2 ± 0.1 vs. 0.1 ± 0.2 mm per year) and trends in FDN (0.1% ± 0.1% vs. 0.1% ± 0.2% per year), WSS magnitude (22 ± 9 vs. 35 ± 13 mPa per year), axial WSS (19 ± 4 vs. 37 ± 7 mPa per year), circumferential WSS (9 ± 8 vs. 5 ± 15 mPa per year), and WSS angle (-0.5° ± 0.4° vs. -0.8° ± 1.0° per year). Discussion Aortic hemodynamic parameters are marginally affected by ageing and the aortic diameter in this case series. Since aortic hemodynamic parameters have been associated with aortic dilation by previous studies, the outcomes of the two subjects suggest that the aortic dilatation rate will remain constant while individuals are ageing and dilating.

Abstract OBJECTIVES Recent evidence suggests that conduits implanted in Fontan patients at the age of 2–4 years become undersized for adulthood. The objective of this study is to use computational fluid dynamic models to evaluate the effect of virtual expansion of the Fontan conduit on haemodynamics and energetics of the total cavopulmonary connection (TCPC) under resting conditions and increased flow conditions. METHODS Patient-specific, magnetic resonance imaging-based simulation models of the TCPC were performed during resting and increased flow conditions. The original 16-mm conduits were virtually enlarged to 3 new sizes. The proposed conduit sizes were defined based on magnetic resonance imaging-derived conduit flow in each patient. Flow efficiency was evaluated based on power loss, pressure drop and resistance and thrombosis risk was based on flow stagnation volume and relative residence time (RRT). RESULTS Models of 5 adult patients with a 16-mm extracardiac Fontan connection were simulated and subsequently virtually expanded to 24–32 mm depending on patient-specific conduit flow. Virtual expansion led to a 40–65% decrease in pressure gradient across the TCPC depending on virtual conduit size. Despite improved energetics of the entire TCPC, the pulmonary arteries remained a significant contributor to energy loss (60–73% of total loss) even after virtual surgery. Flow stagnation volume inside the virtual conduit and surface area in case of elevated RRT (>20/Pa) increased after conduit enlargement but remained negligible (flow stagnation <2% of conduit volume in rest, <0.5% with exercise and elevated RRT <3% in rest, <1% with exercise). CONCLUSIONS Virtual expansion of 16-mm conduits to 24–32 mm, depending on patient-specific conduit flow, in Fontan patients significantly improves TCPC efficiency while thrombosis risk presumably remains low.

Abstract OBJECTIVES Adequacy of 16–20mm extracardiac conduits for adolescent Fontan patients remains unknown. This study aims to evaluate conduit adequacy using the inferior vena cava (IVC)–conduit velocity mismatch factor along the respiratory cycle. METHODS Real-time 2D flow MRI was prospectively acquired in 50 extracardiac (16–20mm conduits) Fontan patients (mean age 16.9 ± 4.5 years) at the subhepatic IVC, conduit and superior vena cava. Hepatic venous flow was determined by subtracting IVC flow from conduit flow. The cross-sectional area (CSA) was reported for each vessel. Mean flow and velocity was calculated during the average respiratory cycle, inspiration and expiration. The IVC–conduit velocity mismatch factor was determined as follows: Vconduit/VIVC, where V is the mean velocity. RESULTS Median conduit CSA and IVC CSA were 221 mm2 (Q1–Q3 201–255) and 244 mm2 (Q1–Q3 203–265), respectively. From the IVC towards the conduit, flow rates increased significantly due to the entry of hepatic venous flow (IVC 1.9, Q1–Q3 1.5–2.2) versus conduit (3.3, Q1–Q3 2.5–4.0 l/min, P < 0.001). Consequently, mean velocity significantly increased (IVC 12 (Q1–Q3 11–14 cm/s) versus conduit 25 (Q1–Q3 17–31 cm/s), P < 0.001), resulting in a median IVC–conduit velocity mismatch of 1.8 (Q1–Q3 1.5–2.4), further augmenting during inspiration (median 2.3, Q1–Q3 1.8–3.0). IVC–conduit mismatch was inversely related to measured conduit size and positively correlated with conduit flow. The normalized IVC–conduit velocity mismatch factor during expiration and the entire respiratory cycle correlated with peak VO2 (r = –0.37, P = 0.014 and r = –0.31, P = 0.04, respectively). CONCLUSIONS Important blood flow accelerations are observed from the IVC towards the conduit in adolescent Fontan patients, which is related to peak VO2. This study, therefore, raises concerns that implanted 16–20mm conduits have become undersized for older Fontan patients and future studies should clarify its effect on long-term outcome.

(1) Background: Aorta hemodynamics have been associated with aortic remodeling, but the reproducibility of its assessment has been evaluated marginally in patients with thoracic aortic aneurysm (TAA). The current study evaluated intra- and interobserver reproducibility of 4D flow MRI-derived hemodynamic parameters (normalized flow displacement, flow jet angle, wall shear stress (WSS) magnitude, axial WSS, circumferential WSS, WSS angle, vorticity, helicity, and local normalized helicity (LNH)) in TAA patients; (2) Methods: The thoracic aorta of 20 patients was semi-automatically segmented on 4D flow MRI data in 5 systolic phases by 3 different observers. Each time-dependent segmentation was manually improved and partitioned into six anatomical segments. The hemodynamic parameters were quantified per phase and segment. The coefficient of variation (COV) and intraclass correlation coefficient (ICC) were calculated; (3) Results: A total of 2400 lumen segments were analyzed. The mean aneurysm diameter was 50.8 ± 2.7 mm. The intra- and interobserver analysis demonstrated a good reproducibility (COV = 16–30% and ICC = 0.84–0.94) for normalized flow displacement and jet angle, a very good-to-excellent reproducibility (COV = 3–26% and ICC = 0.87–1.00) for all WSS components, helicity and LNH, and an excellent reproducibility (COV = 3–10% and ICC = 0.96–1.00) for vorticity; (4) Conclusion: 4D flow MRI-derived hemodynamic parameters are reproducible within the thoracic aorta in TAA patients.

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. 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). 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. 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. 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.

Abstract OBJECTIVES To date, it is not known if 16–20-mm extracardiac conduits are outgrown during somatic growth from childhood to adolescence. This study aims to determine total cavopulmonary connection (TCPC) haemodynamics in adolescent Fontan patients at rest and during simulated exercise and to assess the relationship between conduit size and haemodynamics. METHODS Patient-specific, magnetic resonance imaging-based computational fluid dynamic models of the TCPC were performed in 51 extracardiac Fontan patients with 16–20-mm conduits. Power loss, pressure gradient and normalized resistance were quantified in rest and during simulated exercise. The cross-sectional area (CSA) (mean and minimum) of the vessels of the TCPC was determined and normalized for flow rate (mm2/l/min). Peak (predicted) oxygen uptake was assessed. RESULTS The median age was 16.2 years (Q1–Q3 14.0–18.2). The normalized mean conduit CSA was 35–73% smaller compared to the inferior and superior vena cava, hepatic veins and left/right pulmonary artery (all P < 0.001). The median TCPC pressure gradient was 0.7 mmHg (Q1–Q3 0.5–0.8) and 2.0 (Q1–Q3 1.4–2.6) during rest and simulated exercise, respectively. A moderate–strong inverse non-linear relationship was present between normalized mean conduit CSA and TCPC haemodynamics in rest and exercise. TCPC pressure gradients of ≥1.0 at rest and ≥3.0 mmHg during simulated exercise were observed in patients with a conduit CSA ≤ 45 mm2/l/min and favourable haemodynamics (<1 mmHg during both rest and exercise) in conduits ≥125 mm2/l/min. Normalized TCPC resistance correlated with (predicted) peak oxygen uptake. CONCLUSIONS Extracardiac conduits of 16–20 mm have become relatively undersized in most adolescent Fontan patients leading to suboptimal haemodynamics.

To assess errors associated with EPI‐accelerated intracardiac 4D flow MRI (4DEPI) with EPI factor 5, compared with non‐EPI gradient echo (4DGRE).

BACKGROUND:Aortic aneurysm formation is associated with increased risk of aortic dissection. Current diagnostic strategies are focused on diameter growth, the predictive value of aortic morphology and function remains underinvestigated. We aimed to assess the long-term prognostic value of ascending aorta (AA) curvature radius, regional pulse wave velocity (PWV) and flow displacement (FD) on aortic dilatation/elongation and evaluated adverse outcomes (proximal aortic surgery, dissection/rupture, death) in Marfan and non-syndromic thoracic aortic aneurysm (NTAA) patients. METHODS:Long-term magnetic resonance imaging (MRI) and clinical follow-up of two previous studies consisting of 21 Marfan and 40 NTAA patients were collected. Baseline regional PWV, AA curvature radius and normalized FD were assessed as well as diameter and length growth rate at follow-up. Multivariate linear regression was performed to evaluate whether baseline predictors were associated with aortic growth.=. RESULTS:Of the 61 patients, 49 patients were included with MRI follow-up (n = 44) and/or adverse aortic events (n = 7). Six had undergone aortic surgery, no dissection/rupture occurred and one patient died during follow-up. During 8.0 [7.3-10.7] years of follow-up, AA growth rate was 0.40 ± 0.31 mm/year. After correction for confounders, AA curvature radius (p = 0.01), but not FD or PWV, was a predictor of AA dilatation. Only FD was associated with AA elongation (p = 0.01). CONCLUSION:In Marfan and non-syndromic thoracic aortic aneurysm patients, ascending aorta curvature radius and flow displacement are associated with accelerated aortic growth at long-term follow-up. These markers may aid in the risk stratification of ascending aorta elongation and aneurysm formation.

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.

Long scan times prohibit a widespread clinical applicability of 4D flow MRI in Fontan patients. As pulsatility in the Fontan pathway is minimal during the cardiac cycle, acquiring non-ECG gated 3D flow MRI may result in a reduction of scan time while accurately obtaining time-averaged clinical parameters in comparison with 2D and 4D flow MRI. Thirty-two Fontan patients prospectively underwent 2D (reference), 3D and 4D flow MRI of the Fontan pathway. Multiple clinical parameters were assessed from time-averaged flow rates, including the right-to-left pulmonary flow distribution (main endpoint) and systemic-to-pulmonary collateral flow (SPCF). A ten-fold reduction in scan time was achieved [4D flow 15.9 min (SD 2.7 min) and 3D flow 1.6 min (SD 7.8 s), p < 0.001] with a superior signal-to-noise ratio [mean ratio of SNRs 1.7 (0.8), p < 0.001] and vessel sharpness [mean ratio 1.2 (0.4), p = 0.01] with 3D flow. Compared to 2D flow, good–excellent agreement was shown for mean flow rates (ICC 0.82–0.96) and right-to-left pulmonary flow distribution (ICC 0.97). SPCF derived from 3D flow showed good agreement with that from 4D flow (ICC 0.86). 3D flow MRI allows for obtaining time-averaged flow rates and derived clinical parameters in the Fontan pathway with good–excellent agreement with 2D and 4D flow, but with a tenfold reduction in scan time and significantly improved image quality compared to 4D flow.

Aortic aneurysm is associated with aberrant blood flow and wall shear stress (WSS). This can be studied by coupling magnetic resonance imaging (MRI) with computational fluid dynamics (CFD). For patient-specific simulations, extra attention should be given to the variation in segmentation of the MRI data-set and its effect on WSS. We performed CFD simulations of blood flow in the aorta for ten different volunteers and provided corresponding WSS distributions. The aorta of each volunteer was segmented four times. The same inlet and outlet boundary conditions were applied for all segmentation variations of each volunteer. Steady-state CFD simulations were performed with inlet flow based on phase-contrast MRI during peak systole. We show that the commonly used comparison of mean and maximal values of WSS, based on CFD in the different segments of the thoracic aorta, yields good to excellent correlation (0.78-0.95) for rescan and moderate to excellent correlation (0.64-1.00) for intra- and interobserver reproducibility. However, the effect of geometrical variations is higher for the voxel-to-voxel comparison of WSS. With this analysis method, the correlation for different segments of the whole aorta is poor to moderate (0.43-0.66) for rescan and poor to good (0.48-0.73) for intra- and interobserver reproducibility. Therefore, we advise being critical about the CFD results based on the MRI segmentations to avoid possible misinterpretation. While the global values of WSS are similar for different modalities, the variation of results is high when considering the local distributions.

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.

Coarctation patients before curative reconstruction are exposed to abnormal flow patterns which potentially could cause wall deterioration. This study evaluated the effect of age at correction on the pulse wave velocity (PWV) and peak wall shear stress (WSS) in adolescent patients with corrected coarctation. Effects of valve morphology and presence of reobstruction were also evaluated. Twenty-one patients aged 13.7 ± 2.6 years (mean ± standard deviation) were included (bicuspid aortic valve, n = 14; reobstruction, n = 9). Mean age at correction was 1.0 ± 1.8 years. PWV was determined from two high-temporal through-plane phase-contrast magnetic resonance imaging (MRI) acquisitions, for two segments: ascending aorta plus aortic arch and descending aorta. WSS was determined from four-dimensional flow MRI. Peak WSS over five systolic phases was determined for ascending aorta, aortic arch, and descending aorta. Patients with tricuspid aortic valve showed a significant correlation between the age at correction and descending aorta PWV (rs = 0.80, p = 0.010). Significant differences were found between patients without and with reobstruction for peak WSS in the aortic arch (3.9 ± 1.3 Pa versus 6.5 ± 2.2 Pa, respectively; p = 0.003) and descending aorta (5.0 ± 1.3 Pa versus 6.7 ± 1.1 Pa, respectively; p = 0.005). A prolonged period of abnormal haemodynamic exposure may result in increased aortic wall stiffening. The increased peak WSS as results of a reobstruction possibly promotes different disease progression, which endorse longitudinal follow-up examination of corrected coarctation patients.

Abstract Aim: In patients after atrioventricular septal defect correction, altered geometry leads to a changed position and subsequent flow over the left ventricular outflow tract. We hypothesised that this altered flow may influence haemodynamics in the ascending aorta. Methods: In total, 30 patients after atrioventricular septal defect correction (age 27.6 ± 12.8 years) and 28 healthy volunteers (age 24.8 ± 13.7 years) underwent 4D flow cardiovascular magnetic resonance. Left ventricular ejection fraction and mean and peak wall shear stress calculated at ascending aortic peak systole were obtained from cardiovascular magnetic resonance. Left ventricular outflow tract data including velocity and diameter were obtained from echocardiography. Results: Patients showed a higher mean (911 ± 173 versus 703 ± 154 mPa, p = 0.001) and peak ascending aortic wall shear stress (1264 ± 302 versus 1009 ± 240 mPa, p = 0.001) compared to healthy volunteers. Increased blood flow velocities over the left ventricular outflow tract (1.49 ± 0.30 m/s versus 1.22 ± 0.20 m/s, p < 0.001) correlated well with mean and peak ascending aortic wall shear stress (r = 0.67, p < 0.001 and r = 0.77, p < 0.001). Conclusion: After atrioventricular septal defect correction, increased wall shear stress was observed, which correlated to velocities over the left ventricular outflow tract. These findings imply that altered outflow tract geometry contributes to changed aortic haemodynamics.

Aims To non-invasively assess intraventricular viscous energy loss (EL) and proportionality to kinetic energy (KE) in Fontan patients using 4D flow magnetic resonance imaging (MRI) and compare to healthy controls. Methods and results Thirty Fontan patients and 15 controls underwent 4D flow MRI. Ventricular EL was computed and normalized by end-diastolic volume (EDV). EL over the cardiac cycle (ELcycle) relative to the average kinetic energy (KEcycle) was quantified using a dimensionless index, ELindex (ELcycle/KEcycle). EL was significantly elevated in Fontan patients compared to controls (ELcycle/EDV: 3.7 vs. 2.6J/m(3), P=0.001). Fontan patients with inflow of blood entering a ventricle, which leaves that ventricle through a ventricular septal defect to the aorta, defined as discordant inflow-to-outflow showed significantly higher EL compared to patients with inflow of blood into the same ventricle from which the blood is ejected into the aorta, defined as concordant inflow-to-outflow (ELcycle/EDV: 6.8 vs. 3.2J/m(3), P=0.001). EL was not significantly different in Fontan patients with a systemic left vs. a systemic right ventricle (ELcycle/EDV: 3.5 vs. 3.6J/m(3), P=0.91). ELindex was significantly elevated in Fontan patients compared to controls (ELindex: 0.4 vs. 0.2, P<0.001). Highest ELindex was found in Fontan patients with discordant inflow-to-outflow compared to concordant inflow-to-outflow (0.5 vs. 0.3, P=0.01). Conclusion Fontan patients show disproportionate intraventricular EL relative to KE. Intraventricular EL is elevated in these patients compared to healthy controls, and highest EL is found in patients with discordant inflow-to-outflow.

We hypothesize that dobutamine-induced stress impacts intracardiac hemodynamic parameters and that this may be linked to decreased exercise capacity in Fontan patients. Therefore, the purpose of this study was to assess the effect of pharmacologic stress on intraventricular kinetic energy (KE), viscous energy loss (EL) and vorticity from four-dimensional (4D) Flow cardiovascular magnetic resonance (CMR) imaging in Fontan patients and to study the association between stress response and exercise capacity. Ten Fontan patients underwent whole-heart 4D flow CMR before and during 7.5 μg/kg/min dobutamine infusion and cardiopulmonary exercise testing (CPET) on the same day. Average ventricular KE, EL and vorticity were computed over systole, diastole and the total cardiac cycle (vorticity_volavg cycle, KEavg cycle, ELavg cycle). The relation to maximum oxygen uptake (VO2 max) from CPET was tested by Pearson’s correlation or Spearman’s rank correlation in case of non-normality of the data. Dobutamine stress caused a significant 88 ± 52% increase in KE (KEavg cycle: 1.8 ± 0.5 vs 3.3 ± 0.9 mJ, P < 0.001), a significant 108 ± 49% increase in EL (ELavg cycle: 0.9 ± 0.4 vs 1.9 ± 0.9 mW, P < 0.001) and a significant 27 ± 19% increase in vorticity (vorticity_volavg cycle: 3441 ± 899 vs 4394 ± 1322 mL/s, P = 0.002). All rest-stress differences (%) were negatively correlated to VO2 max (KEavg cycle: r = − 0.83, P = 0.003; ELavg cycle: r = − 0.80, P = 0.006; vorticity_volavg cycle: r = − 0.64, P = 0.047). 4D flow CMR-derived intraventricular kinetic energy, viscous energy loss and vorticity in Fontan patients increase during pharmacologic stress and show a negative correlation with exercise capacity measured by VO2 max.

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.

The aim of the current study was to assess the scan–rescan reproducibility of left ventricular (LV) kinetic energy (KE), viscous energy loss (EL) and vorticity during diastole from four-dimensional flow magnetic resonance imaging (4D flow MRI) in healthy subjects. Twelve volunteers (age 27 ± 3 years) underwent whole-heart 4D flow MRI twice in one session. In-scan consistency was evaluated by correlation between KE and EL. ELindex was computed to measure the amount of EL relative to KE over diastole. Scan–rescan analysis was performed to test reproducibility of volumetric measurements of KE, EL, ELindex and vorticity in the LV over early (E) and late (A) diastolic filling. In-scan consistency between KE and EL was strong-excellent (E-filling scan1: r = 0.92, P < 0.001; scan2: ρ = 0.96, P < 0.001 and A-filling scan1: ρ = 0.87, P < 0.001; scan2: r = 0.99, P < 0.001). For the majority of subjects (10 out of 12), KE and EL measures showed good to strong reproducibility. However, with a wide range of agreement [intraclass correlation (ICC): 0.64–0.95] and coefficients of variation (CV) ≤ 25%. ELindex showed strong reproducibility for all 12 subjects with a strong ICC (0.94, P < 0.001) and a CV of 9%. Scan–rescan reproducibility of volumetric vorticity showed good–excellent ICCs (0.83–0.95) with CVs ≤ 11%. In conclusion, the current study shows strong–excellent in-scan consistency and overall good agreement between scans for 4D flow MRI assessment of left ventricular kinetic energy, energy loss and vorticity over diastole. However, substantial differences between the scans were also found in some parameters in two out of twelve subjects. Strong reproducibility was found in the dimensionless ELindex, which measures the amount of viscous energy loss relative to the average kinetic energy over diastole.