4D Flow CMR Research Articles

Left Ventricular Blood Flow Kinetic Energy Assessment by 4D Flow Cardiovascular Magnetic Resonance: A Systematic Review of the Clinical Relevance.

Background: There is an emerging body of evidence that supports the potential clinical value of left ventricular (LV) intracavity blood flow kinetic energy (KE) assessment using four-dimensional flow cardiovascular magnetic resonance imaging (4D flow CMR). The aim of this systematic review is to summarize studies evaluating LV intracavity blood flow KE quantification methods and its potential clinical significance. Methods: A systematic review search was carried out on Medline, Pubmed, EMBASE and CINAHL. Results: Of the 677 articles screened, 16 studies met eligibility. These included six (37%) studies on LV diastolic function, another six (37%) studies on heart failure or cardiomyopathies, three (19%) studies on ischemic heart disease or myocardial infarction and finally, one (6%) study on valvular heart disease, namely, mitral regurgitation. One of the main strengths identified by these studies is high reproducibility of LV blood flow KE hemodynamic assessment (mean coefficient of variability = 6 ± 2%) for the evaluation of LV diastolic function. Conclusions: The evidence gathered in this systematic review suggests that LV blood flow KE has great promise for LV hemodynamic assessment. Studies showed increased diagnostic confidence at no cost of additional time. Results were highly reproducible with low intraobserver variability.

4D flow cardiac magnetic resonance in children and adults with congenital heart disease: Clinical experience in a high volume center

BackgroundCardiac magnetic resonance (CMR) imaging with velocity encoding along all three directions of flow, known as 4DFlow CMR, provides both anatomical and functional information. Few data are available on the usefulness of 4DFlow CMR in everyday practice. Here, our objective was to investigate the usefulness of 4DFlow CMR for assessing congenital heart disease (CHD) in everyday practice. MethodsFrom 2017 to 2019, consecutive patients who underwent 4DFlow CMR were included prospectively at a single high-volume centre. The parameters recommended by an expert's consensus statement for each diagnosis (congenital valvulopathy, septal defect, complex CHD, tetralogy of Fallot, aortic abnormalities) were assessed by two blinded experienced readers. 4DFlow CMRs that provided all recommended parameters were considered successful. Inter-observer and intra-observer agreement were investigated. ResultsWe included 187 adults and 60 children covering broad ranges of weight (4.5–142 kg) and age (0.1–67 years). 4DFlow CMR was always the second-line imaging modality, after inconclusive echocardiography, and was successful in 231/247 (91%) patients, with no significant difference between children and adults (54/60, 90%; and 177/187, 95%; respectively; p = .13). Longer time using 4DFlow CMR at our centre was associated with success; in children, older age was also associated with exam success. There was an about 12-month learning curve in children. The success rate was lowest in neonates. Inter-observer and intra-observer agreement were substantial. ConclusionOur results suggest that 4DFlow CMR usually provides a comprehensive assessment of CHD in adults and children. A learning curve exists for children and the investigation remains challenging in neonates.

Applications of a Specialty Bicuspid Aortic Valve Program: Clinical Continuity and Translational Collaboration

Bicuspid aortic valve (BAV) is a common congenital heart diagnosis and is associated with aortopathy. Current guidelines for aortic resection have been validated but are based on aortic diameter, which is insufficient to predict acute aortic events. Clinical and translational collaboration is necessary to identify biomarkers that can individualize the timing of prophylactic surgery for BAV aortopathy. We describe our multidisciplinary BAV program, including research protocols aimed at biomarker discovery and results from our longitudinal clinical registry. From 2012–2018, 887 patients enrolled in our clinical BAV registry with the option to undergo four dimensional flow cardiovascular magnetic resonance imaging (4D flow CMR) and donate serum plasma or tissue samples. Of 887 patients, 388 (44%) had an elective BAV-related procedure after initial presentation, while 499 (56%) continued with medical management. Of medical patients, 44 (9%) had elective surgery after 2.3 ± 1.4 years. Surgery patients’ biobank donations include 198 (46%) aorta, 374 (86%) aortic valve, and 314 (73%) plasma samples. The 4D flow CMR was completed for 215 (50%) surgery patients and 243 (49%) medical patients. Patients with BAV aortopathy can be safely followed by a multidisciplinary team to detect indications for surgery. Paired tissue and hemodynamic analysis holds opportunity for biomarker development in BAV aortopathy.

Pulmonary artery hemodynamic assessment of blood flow characteristics in repaired tetralogy of Fallot patients versus healthy child volunteers.

This study aimed to assess the severity of helix and vortex flow in pulmonary artery hemodynamic using 4-dimensional flow cardiac magnetic resonance (4D flow CMR) in patients with repaired tetralogy of Fallot (rTOF) and healthy child volunteers and to explore the relationship between pulmonary hemodynamic changes and right heart function. CMR studies were performed in 25 rTOF patients (15 M/10 F; 8.44±4.52 years) and 10 normal child volunteers (7 M/3 F; 8.2±1.22 years) on 3.0T MR scanners. Cardiac function was calculated in the patient and control groups. Systolic diameter, peak velocity, net flow, and regurgitation was quantified in the main pulmonary artery (MPA) plane, left pulmonary artery (LPA) plane, and right pulmonary artery (RPA) plane. The relationship between the hemodynamic parameters and quantitative flow indices and right ventricular (RV) function were analyzed through simple linear regression analysis using Pearson R-values. We analyzed differences in flow patterns between the 2 groups for the same slice. According to the severity of the helix and vortex flow in the 4D flow CMR, we categorized rTOF patients into the following groups: group 1, severe flow grading; group 2, mild flow grading; group 3, no flow grading; the control cases with no flow grade were included in group 4. We compared RV cardiac function, wall shear stress (WSS), and viscous energy loss (EL) between group 1+2 and group 3+4 using unpaired t-test analysis for normally distributed data and the Mann-Whitney test for non-normally distributed continuous variables. RV end-diastolic volume index (EDVi) (127.8±36.13 vs. 83.11±6.18, respectively; P<0.001), RV end-systolic volume index (ESVi) (65.14±27.02 vs. 36.13±5.95, respectively; P<0.001), and ejection fraction (EF) (49.97±6.39 vs. 56.71±4.56, respectively; P=0.006,) were significantly different between the groups. The rTOF diameters of the MPA and RPA were significantly larger than those of the control group (19.74±4.01 vs. 14.97±2.37 for MPA, P=0.001; 12.04±3.28 vs. 8.99±1.23 for RPA, P=0.004, respectively). There were correlations between peak WSS and pulmonary regurgitation (PR) in the MPA (R=0.48, P=0.014), correlations between peak systolic EL and RVEDV (R=0.51, P=0.008), and between peak systolic EL and RVESV (R=0.51, P=0.009). The peak systole and diastole WSS of group 1+2 were significantly different compared to group 3+4 in the MPA (P<0.05). The peak systole and diastole EL of group 1+2 was significantly different from group 3+4 in the MPA (P<0.05). The peak systole EL of group 1+2 was significantly different from group 3+4 in the RPA (P<0.01). Increased peak WSS and EL were associated with pulmonary hemodynamic changes in the MPA and RPA. There might be an earlier marker of evolving hemodynamic inefficiency than that in traditional parameters. The better understanding of pulmonary artery hemodynamic assessment in rTOF may lead to a greater insight into pulmonary artery (PA)-RV interactions and how they ultimately impact RV function.

4D Flow cardiac magnetic resonance quantification of mitral regurgitation, comparison with transthoracic echocardiography

Mitral valve regurgitation (MR) is primarily assessed by a multiparametric approach with transthoracic echocardiography (TTE) that can be further completed by 2D Cardiac Magnetic Resonance (2D CMR) in case of doubt or poor acoustic window. TTE and 2D CMR have nevertheless imperfect agreement for MR quantification. Time-resolved phase-contrast CMR with flow-encoding in three spatial directions (4D Flow CMR) could help in MR quantification. Compare 4D Flow CMR quantification of MR with TTE using a multiparametric approach. We conducted a prospective study at the Institut Mutualiste Montsouris in Paris between November 2016 and 2017 including patients with chronic primitive MR. MR was evaluated with a multiparametric approach by two cardiologists with TTE and quantitatively by two radiologists with 4D Flow CMR. MR was classified as mild, moderate or severe and evaluated blindly with consensus in case of disagreement. 4D Flow CMR quantified MR regurgitant volume (RV) and MR regurgitant fraction (RF). 4D anterograde mitral flow was compared to left ventricular stroke volume using 2D-cine CMR. Thirty-three patients were included. Inter-observer agreement was good in TTE (kappa = 0.75 95%CI [0.57–0.92]) and excellent in 4D Flow CMR (ICC = 0.94 95%CI [0.79–0.95]). Agreement with TTE was excellent using optimized thresholds (Mild: RV ≤ 20 mL RF ≤ 20%, Moderate: RV = 21–39 mL RF = 21–36%, Severe: RV ≥ 40 mL RF ≥ 37%): kappa = 0.93 95%CI [0.8–1] for RV and kappa = 0.90 95%CI [0.7–0.9] for RF. A validation cohort confirmed that the 4D flow thresholds as determined were accurate for MR grading. Agreement between 4D anterograde mitral flow and 2D-cine CMR left ventricular stroke volume was also excellent (ICC = 0.92 95%CI [0.85–0.96]). 4D Flow CMR is a reliable tool for MR quantification. Providing direct quantitative evaluation of MR with low inter-observer variability, it may therefore be used as a gatekeeper before therapeutic decisions such as surgery.

4D flow CMR analysis comparing patients with anatomically shaped aortic sinus prostheses, tube prostheses and healthy subjects introducing the wall shear stress gradient: a case control study

BackgroundAnatomically pre-shaped sinus prostheses (SP) were developed to mimic the aortic sinus with the goal to preserve near physiological hemodynamic conditions after valve-sparing aortic root replacement. Although SP have shown more physiological flow patterns, a comparison to straight tube prosthesis and the analysis of derived quantitative parameters is lacking. Hence, this study sought to analyze differences in aortic wall shear stress (WSS) between anatomically pre-shaped SP, conventional straight tube prostheses (TP), and age-matched healthy subjects) using time-resolved 3-dimensional flow cardiovascular magnetic resonance (4D Flow CMR). Moreover, the WSS gradient was introduced and analyzed regarding its sensitivity to detect changes in hemodynamics and its dependency on the expression of secondary flow patterns.MethodsTwelve patients with SP (12 male, 62 ± 9yr), eight patients with TP (6 male, 59 ± 9yr), and twelve healthy subjects (2 male, 55 ± 6yr) were examined at 3 T with a 4D Flow CMR sequence in this case control study. Six analysis planes were placed in the thoracic aorta at reproducible landmarks. The following WSS parameters were recorded: WSSavg (spatially averaged over the contour at peak systole), max. WSSseg (maximum segmental WSS), min. WSSseg (minimum segmental WSS) and the WSS Gradient, calculated as max. WSSseg – min. WSSseg. Kruskal-Wallis- and Mann-Whitney-U-Test were used for statistical comparison of groups. Occurrence and expression of secondary flow patterns were evaluated and correlated to WSS values using Spearman’s correlation coefficient.ResultsIn the planes bordering the prosthesis all WSS values were significantly lower in the SP compared to the TP, approaching the physiological optimum of the healthy subjects. The WSS gradient showed significantly different values in the four proximally localized contours when comparing both prostheses with healthy subjects. Strong correlations between an elevated WSS gradient and secondary flow patterns were found in the ascending aorta and the aortic arch.ConclusionOverall, the SP has a positive impact on WSS, most pronounced at the site and adjacent to the prosthesis. The WSS gradient differed most obviously and the correlation of the WSS gradient with the occurrence of secondary flow patterns provides further evidence for linking disturbed flow, which was markedly increased in patients compared to healthy sub jects, to degenerative remodeling of the vascular wall.

4d cardiac magnetic resonance flow in patients with pulmonary arterial hypertension associated with congenital heart disease

Right heart catheterization is an invasive exam that is currently the gold standard to assess pulmonary hemodynamics for diagnosis and follow-up of pulmonary arterial hypertension (PAH) associated with congenital heart diseases (CHD). Cardiac magnetic resonance 4D flow (4D CMR flow) emerges as a promising non-invasive imaging. We assess the accuracy of 4D CMR flow to measure pulmonary cardiac output (Qp). We prospectively included 28 patients (median age was 42 years old [35–52] with PAH and CHD (pre-tricuspid shunt n = 23, 82.1%, median mean pulmonary artery pressure 46 mmHg [40–58]; median pulmonary vascular resistance 15.0 WU.m 2 [7.5–25.6]). Qp was measured invasively using Fick principle (direct oxygen consumption measure) during a right heart catheterization (QpF) and compared to Qp measured by 2D (Qp2D) and 4D flow CMR (Qp4D) on the same day. 4D CMR flow analysis was feasible in all patients. Qp4D and QpF were strongly correlated (rho = 0.87, P < 0.0001; r 2 = 0.68, P < 0.0001). Using Bland Altman analysis, mean difference was 0.0 ± 1.0 L/min. Mean difference within two observers (interobserver variability) was 0.3 ± 0.4 L/min ( Fig. 1 ). Mean difference within one observer (intra-observer variability) was 0.1 ± 0.3 L/min. Qp2D and QpF were moderately correlated (rho = 0.54, P = 0.008; r 2 = 0.41, P = 0.0007). Using Bland Altman analysis, mean difference was 0.6 ± 2.3 L/min ( Fig. 1 ). Qp measured by 4D CMR flow is well correlated to QpF. Further studies are needed to explore other potential interests of using 4D CMR flow to assess PAH, including the derivation of additional hemodynamic parameters such as pulmonary artery compliance, wall shear stress and pulse wave velocities, which could provide further insights into pulmonary artery remodelling and interactions between pulmonary arterial stiffening and right ventricular dysfunction.

Accuracy of 4D cardiac magnetic resonance for flow measurement

4D Flow CMR has emerged as an innovative imaging modality providing flow assessment at any selected region of interest. The wide range of dynamic properties and velocity of cardiac flows are a commonly admitted technical limit. We aim to assess if this technique is robust enough to validate the conservation of mass principle applied to vessels and valves of the whole heart. Our working hypothesis was that 4D CMR would prove accurate compared to 2D CMR. Thirty healthy patients underwent both 2D CMR and 4D CMR using a 1.5-T machine. Ventricular volumes were assessed and cardiac output was calculated and used as a reference value. We mapped using 4D Flow analysis (Arterys), cardiac flows from the vena cava to the aorta. The 4D flows through the cardiac valves, and vessels were independently measured by two readers. Agreement between flows measured using 4D CMR and CMR was assessed by linear regression analysis and Bland-Altman plots. Mean net flows were 5.5 ± 1.2 L/min through venae cavae, 5.4 ± 1.1 L/min through the tricuspid valve, 5.5 ± 1.1 L/min through the pulmonary valve, 5.4 ± 1.4 L/min through the pulmonary artery, 5.3 ± 1.1 L/min through the pulmonary veins, 5.5 ± 1.0 L/min through the mitral valve, 5.5 ± 1.4 L/min through the aortic valve and 5.5 ± 1.4 L/min through the aorta compared to 5.6 ± 1.1 with 2D CMR. Correlation coefficients between 4D flows measurements and 2D CMR ranged from 0.60 to 0.86. Agreement was strong between cardiac outputs with a mean bias ranging from 0.01 to 0.33 with no significant bias. Interobserver reproducibility of 4D CMR net flow measurements was good (interclass coefficient ranging from 0.89–0.98; and coefficient of variation of 3.7%–6.3%). 4D CMR flow measurements correlated with cardiac output measured using CMR in healthy volunteers in all valves and vessels, respecting the conservation of mass principle. 4D CMR seems robust enough to obtain precise hemodynamic features of cardiac flow.

Enhancing Magnetic Resonance Imaging With Computational Fluid Dynamics

Abstract The analysis of the blood flow in the great thoracic arteries does provide valuable information about the cardiac function and can diagnose the potential development of vascular diseases. Flow-sensitive four-dimensional flow cardiovascular magnetic resonance imaging (4D flow CMR) is often used to characterize patients' blood flow in the clinical environment. Nevertheless, limited spatial and temporal resolution hinders a detailed assessment of the hemodynamics. Computational fluid dynamics (CFD) could expand this information and, integrated with experimental velocity field, enable to derive the pressure maps. However, the limited resolution of the 4D flow CMR and the simplifications of CFD modeling compromise the accuracy of the computed flow parameters. In this article, a novel approach is proposed, where 4D flow CMR and CFD velocity fields are integrated synergistically to obtain an enhanced MR imaging (EMRI). The approach was first tested on a two-dimensional (2D) portion of a pipe, to understand the behavior of the parameters of the model in this novel framework, and afterwards in vivo, to apply it to the analysis of blood flow in a patient-specific human aorta. The outcomes of EMRI are assessed by comparing the computed velocities with the experimental one. The results demonstrate that EMRI preserves flow structures while correcting for experimental noise. Therefore, it can provide better insights into the hemodynamics of cardiovascular problems, overcoming the limitations of MRI and CFD, even when considering a small region of interest. EMRI confirmed its potential to provide more accurate noninvasive estimation of major cardiovascular risk predictors (e.g., flow patterns, endothelial shear stress) and become a novel diagnostic tool.

P5874D Flow cardiac magnetic resonance quantification of mitral regurgitation, comparison with transthoracic echocardiography

Abstract Background Mitral valve regurgitation (MR) is currently primarily assessed by a multiparametric approach with transthoracic echocardiography (TTE) that can be further completed by 2D Cardiac Magnetic Resonance (2D CMR) in case of doubt or poor acoustic window. TTE and 2D CMR have nevertheless imperfect agreement in terms of MR quantification. Time-resolved phase-contrast cardiac magnetic resonance imaging with flow-encoding in three spatial directions (4D Flow CMR) could help in MR quantification. Purpose Compare 4D Flow CMR quantification of MR with TTE using a multiparametric approach. Methods We conducted a monocentric, prospective study at the Institut Mutualiste Montsouris in Paris between November 2016 and 2017 including patients with chronic primitive MR. MR was evaluated with a multiparametric approach by two cardiologists with TTE and quantitatively by two radiologists with 4D Flow CMR. MR was classified as mild, moderate or severe and evaluated blindly with consensus in case of disagreement. 4D Flow CMR measurements consisted in quantifying MR regurgitant volume (RV) and MR regurgitant fraction (RF). 4D anterograde mitral flow was compared to left ventricular stroke volume using 2D-cine CMR. Results 33 patients were included. Inter-observer agreement was good in TTE (kappa= 0.75 95% CI [0.57- 0.92]) and excellent in 4D Flow CMR (ICC= 0.94 95% CI [0.79–0.95]). Agreement with TTE was excellent using optimized thresholds (Mild: RV≤20mL RF≤20%, Moderate: RV=21–39mL RF=21–36%, Severe: RV≥40mL RF≥37%): kappa= 0.93 95% CI [0.8–1] for RV and kappa= 0.90 95% CI [0.7–0.9] for RF. A validation cohort confirmed that the 4D flow thresholds as determined were accurate for MR grading. Agreement between 4D anterograde mitral flow and 2D-cine CMR left ventricular stroke volume was also excellent (ICC= 0.92 95% CI [0.85–0.96]). Conclusion 4D Flow CMR is a reliable tool for MR quantification. It provides direct quantitative evaluation of MR with low inter-observer variability. It may therefore be used as a gatekeeper before therapeutic decisions such as surgery.

477Partial fusion of two aortic valve leaflets is related to alterations in ascending aorta flow: 4D flow CMR study

Abstract Introduction Bicuspid aortic valve (BAV) is the most common congenital valve defect. It consists in the fusion of two aortic valve leaflets, and it is associated with a high prevalence of proximal aorta dilation. Dilation is highly prevalent (around 30%) in BAV patient relatives with a tricuspid valve (TAV) identified by echocardiography. However, the presence of partial aortic valve leaflet fusion (also called mini-raphe or forme fruste BAV, see figure 1A) is easily missed by echocardiography. A recent study reported that 44% of patients from a small cohort of BAV patient relatives with aortic dilation followed by CT showed mini-raphe. Purpose We aimed to use 4D flow CMR to assess if the presence of mini-raphe is associated with aortic flow alterations, which may be concurs in the etiology of aortic dilation in BAV patient relatives. Methods Twenty BAV patients first-degree relatives with partial fusion (&lt;50%) of aortic valve leaflets and proximal aorta dilation were identified by CT or cine CMR and prospectively included. One-hundred twenty-five BAV and 95 patients with TAV from our prospective dataset of 4D flow CMR were included for comparison. Propensity score matching was used throughout the study to correct the comparisons between mini-raphe and BAV and mini-raphe and TAV patients for differences in age, maximum aortic diameter, sex, height, weight, proximal aortic pulse wave velocity and, only for BAV, fusion pattern. The hemodynamic parameters previously related to aortic dilation were computed. They were jet angle, normalized flow displacement and systolic flow reversal ratio (SFRR, identifying through-plane vortexes) were computed and compared in the ascending aorta and in the aortic arch. Results The presence of mini-raphe was statistically-significantly associated with increase in jet angle (Figure 1B), flow displacement (Figure 1C) and vortexes (Figure 1D) in most of the ascending aorta and aortic arch when mini-raphe patients were compared with TAV patients. The severity of flow asymmetry found in mini-raphe patients was lower than the one characteristic of BAV patients, but vortexes were even higher in a small region at the distal ascending aorta. Figure 1 Conclusion Partial fusion of the aortic valve leaflets is related to increase in proximal aorta flow eccentricity and vorticity. These flow abnormalities are not as marked as those associated with BAV. Data regarding prevalence of mini-raphe as evaluated with CT or cine CMR are needed, especially in familiar of BAV patients. Acknowledgement/Funding European FP7/People 267128; Spanish Ministry of Economy and Competitiveness RTC-2016-5152-1 and Instituto de Salud Carlos III PI14/0106

P4131Abnormal flow pattern in the main pulmonary artery of Marfan patients is related to local dilation

Abstract Introduction Marfan syndrome (MFS) is a hereditary connective tissue disorder caused by mutation in the FBN1 gene. Main pulmonary artery (MPA) dilation is very prevalent in MFS patients. Indeed, the old Ghent nosology considered main pulmonary artery (MPA) dilation as diagnostic criterion of MFS patients. Although clinical complications related to pulmonary dilation in MFS are rare, this may potentially lead to MPA dissection or be a marker of vascular disease in MFS. Studies regarding potential causes of MPA dilation in MFS patients are very scarce. Purpose Through 4D flow CMR, we aimed to assess whether flow abnormalities exist in the MPA of MFS patients and their relation to local diameter. Methods Fifty-five consecutive Marfan syndrome adults (MFS) and 22 healthy volunteers (HV) were prospectively enrolled. All subjects underwent non-contrast-enhanced 4D flow-MRI, obtaining 4D flow field and a 3D angiography. The MPA was segmented from the 3D angiography, and the segmentation was used to mask 4D velocity data. Four, equidistant analysis planes were placed in the MPA between the pulmonary valve and the pulmonary artery bifurcation. Common descriptors of large arteries hemodynamics were computed at each plane: maximum velocity, systolic flow reversal ratio (a descriptor of the amount of systolic backward flow) and circumferentially-averaged axial and circumferential wall shear stress (WSS). Pulmonary artery diameters were measured on axial images. MPA dilation was defined as a diameter larger than 27 mm in women and 29 mm in men. Systolic (SBP) and diastolic (DBP) systemic blood pressure were measured at the brachial artery with a calibrated cuff immediately after the scan. Results Compared with HV, MFS patients presented similar age, BSA, SBP and maximum blood velocity, but had larger MPA diameter (27.8 vs 25.1 mm, p&lt;0.001) and higher DBP (75.5 vs 66.8 mmHg, p=0.003). According to the used threshold, 45% (27) of MFS patients had MPA dilation. Compared with HV, Marfan patients presented an increased systolic flow reversal ratio in the proximal part of the MPA (Figure 1). In MFS patients axial WSS was reduced in central sections of the MPA, while the circumferential component was not difference with respect to HV. All these flow abnormalities were also present in the subset of 28 MFS patients without pulmonary artery dilation. In multivariable analysis, MPA diameter was independently related to age (B=0.056; p=0.032), sex (B=−2.3; p=0.02) and axial (B=6.4; p=0.039) and circumferential (B=33.9; p&lt;0.001) WSS. Figure 1 Conclusions Dilation of the main pulmonary artery is prevalent in Marfan syndrome patients. Abnormal increase in systolic vortexes and reduction in axial WSS were present in dilated and non-dilated MPA in MFS patients. Axial and circumferential WSS were independently related to MPA diameter. The eventual predictive role of abnormal pulmonary flow pattern in pulmonary artery dilation in MFS patients remain to be established Acknowledgement/Funding Instituto de Salud Carlos III (PI14/0106), La Maratό de TV3 (20151330), CIBERCV and FP7/People (267128)

4D cardiac magnetic resonance flow in patients with pulmonary hypertension associated with congenital heart disease

Right heart catheterization is an invasive exam that is currently the gold standard to assess pulmonary hemodynamics for diagnosis and follow-up of pulmonary arterial hypertension (PAH) associated with congenital heart diseases (CHD). Cardiac magnetic resonance 4D flow (4D CMR flow) emerges as a promising non-invasive imaging. We assess the accuracy of 4D CMR flow to measure pulmonary cardiac output (Qp). We prospectively included 28 patients with PAH associated with CHD. Qp was measured invasively using Fick principle (direct oxygen consumption measure) during aright heart catheterization (QpF) and compared to Qp measured by 2D (Qp2D) and 4D flow CMR (Qp4D) on the same day. Twenty eight patients was included (median age was 42 years old [35–52]) with PAH and CHD (pre-tricuspid shunt n = 23, 82.1%, median mean pulmonary artery pressure 46 mmHg [40-58]; median pulmonary vascular resistance 15.0 WU.m 2 [7.5–25.6]) 4D CMR flow analysis were feasible in all patients. Qp4D and QpF were strongly correlated (rho = 0.87, P < 0.0001; r 2 = 0.68, P < 0.0001). Using Bland Altman analysis, mean difference was 0.0 ± 1.0 L/min. Mean difference within two observers (interobserver variability) was 0.3 ± 0.4 L/min. Mean difference within one observer (intra-observer variability) was 0.1 ± 0.3 L/min. Qp2D and QpF were moderately correlated (rho = 0.54, P = 0.008; r 2 = 0.41, P = 0.0007). Using Bland Altman analysis, mean difference was 0.6 ± 2.3 L/min ( Fig. 1 ). Qp measured by 4D CMR flow is well correlated to QpF. Further studies are needed to explore other potential interests of using 4D CMR flow to assess PAH, including the derivation of additional hemodynamic parameters such as pulmonary artery compliance, wall shear stress and pulse wave velocities, which could provide further insights into pulmonary artery remodeling and interactions between pulmonary arterial stiffening and right ventricular dysfunction.

520Thoracic aorta flow by 4D flow CMR is altered in patients presenting partial fusion of two aortic valve leaflets

520Thoracic aorta flow by 4D flow CMR is altered in patients presenting partial fusion of two aortic valve leaflets

A Systematic Review of Right Ventricular Diastolic Assessment by 4D Flow CMR.

Background Four-dimensional flow cardiovascular magnetic resonance (4D flow CMR) is a noninvasive novel imaging technology that can be used to visualise and assess right ventricular function. The aim of this systematic review is to summarise the literature available on 4D flow CMR methods used to determine right ventricular diastolic function. Methods A systematic review of current literature was carried out to ascertain what is known about right ventricular assessment by quantification of 4D flow CMR. Structured searches were carried out on Medline and EMBASE in December 2018. PG and NB screened the titles and abstracts for relevance. Results Of the 20 articles screened, 5 studies met eligibility for systematic review. After a further search on pubmed 1 more relevant article was found and added to the review. Conclusions These proposed methods using 4D flow CMR can quantify right ventricular diastolic assessment. The evidence gathered is mainly observational, featuring single-centred studies. Larger, multicentre studies are required to validate the proposed techniques, evaluate reproducibility, and investigate the clinical applicability that 4D flow CMR offers compared to standard practices. PROSPERO registration number is CRD42019121492.

Accelerated aortic 4D flow cardiovascular magnetic resonance using compressed sensing: applicability, validation and clinical integration

BackgroundThree-dimensional time-resolved phase-contrast cardiovascular magnetic resonance (4D flow CMR) enables the quantification and visualisation of blood flow, but its clinical applicability remains hampered by its long scan time. The aim of this study was to evaluate the use of compressed sensing (CS) with on-line reconstruction to accelerate the acquisition and reconstruction of 4D flow CMR of the thoracic aorta.Methods4D flow CMR of the thoracic aorta was acquired in 20 healthy subjects using CS with acceleration factors ranging from 4 to 10. As a reference, conventional parallel imaging (SENSE) with acceleration factor 2 was used. Flow curves, net flows, peak flows and peak velocities were extracted from six contours along the aorta. To measure internal data consistency, a quantitative particle trace analysis was performed. Additionally, scan-rescan, inter- and intraobserver reproducibility were assessed. Subsequently, 4D flow CMR with CS factor 6 was acquired in 3 patients with differing aortopathies. The flow patterns resulting from particle trace visualisation were qualitatively analysed.ResultsAll collected data were successfully acquired and reconstructed on-line. The average acquisition time including respiratory navigator efficiency with CS factor 6 was 5:02 ± 2:23 min while reconstruction took approximately 9 min. For CS factors of 8 or less, mean differences in net flow, peak flow and peak velocity as compared to SENSE were below 2.2 ± 7.8 ml/cycle, 4.6 ± 25.2 ml/s and − 7.9 ± 13.0 cm/s, respectively. For a CS factor of 10 differences reached 5.4 ± 8.0 ml/cycle, 14.4 ± 28.3 ml/s and − 4.0 ± 12.2 cm/s. Scan-rescan analysis yielded mean differences in net flow of − 0.7 ± 4.9 ml/cycle for SENSE and − 0.2 ± 8.5 ml/cycle for CS factor of 6.ConclusionsA six- to eightfold acceleration of 4D flow CMR using CS is feasible. Up to a CS acceleration rate of 6, no statistically significant differences in measured flow parameters could be observed with respect to the reference technique. Acquisitions in patients with aortopathies confirm the potential to integrate the proposed method in a clinical routine setting, whereby its main benefits are scan-time savings and direct on-line reconstruction.

Fetal hemodynamics and cardiac streaming assessed by 4D flow cardiovascular magnetic resonance in fetal sheep

BackgroundTo date it has not been possible to obtain a comprehensive 3D assessment of fetal hemodynamics because of the technical challenges inherent in imaging small cardiac structures, movement of the fetus during data acquisition, and the difficulty of fusing data from multiple cardiac cycles when a cardiac gating signal is absent. Here we propose the combination of volumetric velocity-sensitive cardiovascular magnetic resonance imaging (“4D flow” CMR) and a specialized animal preparation (catheters to monitor fetal heart rate, anesthesia to immobilize mother and fetus) to examine fetal sheep cardiac hemodynamics in utero.MethodsTen pregnant Merino sheep underwent surgery to implant arterial catheters in the target fetuses. Anesthetized ewes underwent 4D flow CMR with acquisition at 3 T for fetal whole-heart coverage with 1.2–1.5 mm spatial resolution and 45–62 ms temporal resolution. Flow was measured in the heart and major vessels, and particle traces were used to visualize circulatory patterns in fetal cardiovascular shunts. Conservation of mass was used to test internal 4D flow consistency, and comparison to standard 2D phase contrast (PC) CMR was performed for validation.ResultsStreaming of blood from the ductus venosus through the foramen ovale was visualized. Flow waveforms in the major thoracic vessels and shunts displayed normal arterial and venous patterns. Combined ventricular output (CVO) was 546 mL/min per kg, and the distribution of flows (%CVO) were comparable to values obtained using other methods. Internal 4D flow consistency across 23 measurement locations was established with differences of 14.2 ± 12.1%. Compared with 2D PC CMR, 4D flow showed a strong correlation (R2 = 0.85) but underestimated flow (bias = − 21.88 mL/min per kg, p < 0.05).ConclusionsThe combination of fetal surgical preparation and 4D flow CMR enables characterization and quantification of complex flow patterns in utero. Visualized streaming of blood through normal physiological shunts confirms the complex mechanism of substrate delivery to the fetal heart and brain. Besides offering insight into normal physiology, this technology has the potential to qualitatively characterize complex flow patterns in congenital heart disease phenotypes in a large animal model, which can support the development of new interventions to improve outcomes in this population.

4D flow CMR analysis in repaired tetralogy of Fallot: Where we are and where we are going

4D flow cardiovascular magnetic resonance (4D flow CMR) enable time-varying and multidirectional comprehensive retrospective analysis. However, this imaging modality must prove its relevance. After tetralogy of Fallot surgical repair, pulmonary valve function and right ventricle (RV) volumes are carefully followed. We investigate reliability of 4D flow CMR to measure these parameters compared to gold-standard 2D CMR. Twenty patients with rTOF and 5 healthy controls (mean age 29 ± 13 years, mean height 169 ± 7 cm, mean weight 66.2 ± 13.4 kg) underwent RV volumes and pulmonary regurgitation analysis by 2D CMR and 4D flow CMR using a clinical 1.5 T MRI scanner (GE; GE Healthcare, Milwaukee, WI, USA). Mean 4D flow acquisition time was 8.0 ± 1.8 min, whereas conventional 2D CMR was 39 ± 7.2 min ( P < 0.0001). Linear regression analysis shows a good correlation between 2D CMR and 4D flow CMR for RV stroke volume (SV) (r 2 = 0.89, P < 0.0001), end-diastolic RV volume (r 2 = 0.93, P < 0.0001), pulmonary regurgitation volume (r 2 = 0.94, P < 0.0001) and pulmonary regurgitation fraction (r 2 = 0.89, P < 0.0001). Mean bias [−1.96SD; +1.96SD] was 17.5 mL [4.75; 30.15] for RVSV, −8.4 mL [−17.04; 0.16] for end diastolic RV volume, 1.5 mL [−2.17; 5.23] for pulmonary regurgitation volume and 0.7% [−0.8; 2.2] for pulmonary regurgitation fraction by Bland–Altman analysis. Using 4D flow CMR, linear regression analysis showed a good correlation between RV SV and pulmonary valve systolic ejection volume (r 2 = 0.55, P < 0.0001), and between systemic and pulmonary flow (r 2 = 0.90, P < 0.0001). Mean bias was 22.7 mL [6.4; 39.0] for SV, and −0.06 mL [−0.18; 0.06] for systemic and pulmonary flow by Bland–Altman analysis. Vortex in the pulmonary artery trunk were observed in all cases of rTOF patients and limited analysis of pulmonary artery regurgitation flow. 4D flow imaging may be a clinically relevant alternative to 2D CMR in rTOF, providing faster and reliable data.

Impact of Age and Diastolic Function on Novel, 4D flow CMR Biomarkers of Left Ventricular Blood Flow Kinetic Energy

Two-dimensional (2D) methods of assessing mitral inflow velocities are pre-load dependent, limiting their reliability for evaluating diastolic function. Left ventricular (LV) blood flow kinetic energy (KE) derived from four-dimensional flow cardiovascular magnetic resonance imaging (4D flow CMR) may offer improvements. It remains unclear whether 4D LV blood flow KE parameters are associated with physiological factors, such as age when compared to 2D mitral inflow velocities. Fifty-three healthy volunteers underwent standard CMR, plus 4D flow acquisition. LV blood flow KE parameters demonstrated good reproducibility with mean coefficient of variation of 6 ± 2% and an accuracy of 99% with a precision of 97%. The LV blood flow KEiEDV E/A ratio demonstrated good association to the 2D mitral inflow E/A ratio (r = 0.77, P < 0.01), with both decreasing progressively with advancing age (P < 0.01). Furthermore, peak E-wave KEiEDV and A-wave KEiEDV displayed a stronger association to age than the corresponding 2D metrics, peak E-wave and A-wave velocity (r = −0.51 vs −0.17 and r = 0.65 vs 0.46). Peak E-wave KEiEDV decreases whilst peak A-wave KEiEDV increases with advancing age. This study presents values for various LV blood flow KE parameters in health, as well as demonstrating that they show stronger and independent correlations to age than standard diastolic metrics.

4D Flow CMR analysis in repaired Tetralogy of Fallot: Where we are and where we are going

Background 4D flow cardiovascular magnetic resonance (4D Flow CMR) enable time-varying and multidirectional comprehensive retrospective flow quantification in patients after repaired tetralogy of Fallot (TOF). This imaging modality must, however, prove its relevance compared to conventional CMR. Methods 4D flow and 2D flow MRI were acquired using a clinical 1.5T MRI scanner (GE; GE Healthcare, Milwaukee, WI, USA). The 4D flow data were acquired in 18 patients after repair of TOF and in 5 healthy controls during free breathing using retrospectively ECG-gated and navigator-gated three-dimensional, three-directional phase contrast MRI (spatial resolution ∼ 1.4 mm, temporal resolution = 33 ms). Data analysis included the evaluation of haemodynamics in the aorta, the pulmonary trunk (TP), quantitative measurements of flow velocity, right ventricular volumes both by conventional 2D CMR and 4D Flow. Results Eighteen patients with TOF underwent 2D CMR and 4D Flow CMR (mean age 31 ± 13 years, mean size 168 ± 13 cm, mean weight 56.2 ± 13.4 kg). Among them 12 patients had complete evaluation including flow and ventricular volumes. The mean systolic ejection volume was 109 ± 44 mL; the mean right ventricle systolic function was 55 ± 12%. The mean end-diastolic right ventricle volume was respectively 185 ± 66 mL by 2D CMR, and 200 ± 68 mL using 4D Flow. The mean pulmonary regurgitation fraction was respectively 39 ± 18% by 2D CMR, and 32 ± 18% using 4D Flow. Pulmonary regurgitation fraction was almost interchangeable according to the Pearson's coefficient (r2 = 0.9, P Conclusions Based on our experience, 4D Flow imaging can be clinically helpful especially in TOF, compared to 2D CMR. Despite some biases, our results shows good accuracy compared to conventional 2D CMR. Further studies are needed to validate our first conclusions.