Four-dimensional Flow Magnetic Resonance Imaging Research Articles

Global tendencies and frontier topics in hemodynamics research of intracranial aneurysms: a bibliometric analysis from 1999 to 2022

Background: Hemodynamics plays a crucial role in the initiation, enlargement, and rupture of intracranial aneurysms (IAs). This bibliometric analysis aimed to map the knowledge network of IA hemodynamic research.Methods: Studies on hemodynamics in IAs published from 1999 to 2022 were retrieved from the Web of Science Core Collection (WoSCC). The contributions of countries, institutions, authors, and journals were identified using VOSviewer, Scimago Graphica, and Microsoft Excel. Tendencies, frontier topics, and knowledge networks were analyzed and visualized using VOSviewer and CiteSpace.Results: We identified 2,319 publications on hemodynamics in IAs. The annual number of publications exhibited an overall increasing trend. Among these, the United States, Japan, and China were the three major contributing countries. Capital Medical University, State University of New York (SUNY) Buffalo University, and George Mason University were the three most productive institutions. Meng H ranked first among authors regarding the number of articles and citations, while Cebral JR was first among co-cited authors. The American Journal of Neuroradiology was the top journal in terms of the number of publications, citations, and co-citations. In addition, the research topics can be divided into three clusters: hemodynamics itself, the relationship of hemodynamics with IA rupture, and the relationship of hemodynamics with IA treatment. The frontier directions included flow diverters, complications, morphology, prediction, recanalization, and four-dimensional flow magnetic resonance imaging (4D flow MRI).Conclusion: This study drew a knowledge map of the top countries, institutions, authors, publications, and journals on IA hemodynamics over the past 2 decades. The current and future hotspots of IA hemodynamics mainly include hemodynamics itself (4D flow MRI), its relationship with IA rupture (morphology and prediction), and its relationship with IA treatment (flow diverters, complications, and recanalization).

Hemodynamic predictors of negative false lumen remodeling after frozen elephant trunk for acute aortic dissection.

We evaluated the blood flow within the downstream aortic false lumen after frozen elephant trunk repair for acute aortic dissection and identified hemodynamic predictors of false lumen expansion and negative false lumen remodeling using four-dimensional flow magnetic resonance imaging. Thirty-one patients (Stanford type A, n = 28; Stanford type B, n = 3) with patent false lumen who underwent frozen elephant trunk procedures for acute aortic dissection were included in this observational study. Each patient underwent computed tomography during the follow-up period and four-dimensional flow magnetic resonance imaging within 3 postoperative months. The false lumen volumetric expansion rate was calculated using computed tomography data. The direction and the rate of flow in the lower descending aortic false lumen were analyzed. Negative false lumen remodeling was defined as a volumetric increase of > 10% from the baseline volume. Negative false lumen remodeling had developed in 6 of the 31 patients during the observation period. Most of the false lumen flows were biphasic during systole. The range between peak and nadir flow rates was associated with the false lumen volumetric expansion rate (β coefficient = 6.77; p < 0.01, R2 = 0.43). The range between peak and nadir flow rates may serve as a hemodynamic predictor of negative false lumen remodeling, enabling further treatment for patients at risk of expansion in the downstream aorta.

Abstract 16638: 4D Flow MRI Analysis of the Left Atrial Hemodynamics After Atrial Fibrillation Surgery

Introduction: Postoperative anticoagulation therapy after atrial fibrillation (AF) surgery remains a controversial topic because left atrial (LA) blood flow velocity and pattern remain unclear. This study utilizes four-dimensional (4D) flow magnetic resonance imaging (MRI) to analyze postoperative LA hemodynamics following various atrial fibrillation surgeries. Methods: This retrospective study included nine patients (mean age, 73 ± 8 years; range, 56-83 years) who underwent AF surgeries from August 2021 to June 2022. Maze surgery was performed in 3, pulmonary vein isolation (PVI) and left atrial appendage closure (LAAC) in 3, and the LAAC alone in 3 patients. Postoperative 4D flow MRI scans of the left atrium were performed, and image analysis was conducted. Blood flow velocity in the left atrium was measured, with velocities below 10 cm/s considered flow stasis. The percentage of flow stasis within one systolic-diastolic cycle was evaluated as % stasis. Furthermore, the presence or absence of a physiological vortex flow was assessed from the flow images. Results: Sinus rhythm was postoperatively maintained in 6 patients, and 3 patients were analyzed in AF. The left atrial % stasis was significantly low in the sinus rhythm group (46.0 ± 22.7 in the sinus rhythm group vs. 100 in the AF group, p=0.027). The absence of vortex flow was observed during sinus rhythm in one patient after Maze surgery. Conversely, vortex flow was identified during AF in the patient after LAAC, being accompanied by moderate mitral regurgitation. Conclusions: Any type of AF surgery does not always provide physiological LA blood flow. Further, 4D flow MRI analysis contributes to our understanding of the discrepancy between ideals and reality which may or may not require anticoagulant therapy regardless of postoperative rhythm.

Design of a Low-Cost, Self-Adaptive and MRI-Compatible Cardiac Gating System.

Cardiac gating, synchronizing medical scans with cardiac activity, is widely used to make quantitative measurements of physiological events and to obtain high-quality scans free of pulsatile artefacts. This can provide important information for disease diagnosis, targeted control of medical microrobots, etc. The current work proposes a low-cost, self-adaptive, MRI-compatible cardiac gating system. The system and its processing algorithm, based on the monitoring and analysis of blood pressure waveforms, are proposed. The system is tested in an in vitro experiment and two living pigs using four-dimensional (4D) flow magnetic resonance imaging (MRI) and two-dimensional phase-contrast (2D-PC) sequences. in vitro and in vivo experiments reveal that the proposed system can provide stable cardiac synchronicity, has good MRI compatibility, and can cope with the fringe magnetic field of the MRI scanner, radiofrequency signals during image acquisition, and heart rate changes. High-resolution 4D flow imaging is successfully acquired both in vivo and in vitro. The difference between the 2D and 4D measurements is ≤ 21%. The incidence of false triggers is 0% in all tests, which is unattainable for other known cardiac gating methods. The system has good MRI compatibility and can provide a stable and accurate trigger signal based on pressure waveform. It opens the door to applications where the previous gating methods were difficult to implement or not applicable.

4D flow MRI-derived energy loss and RV workload in adults with tetralogy of Fallot

PurposeTo assess flow energy loss (EL) pattern inside the pulmonary circulation in adult patients with repaired tetralogy of Fallot (TOF), particularly in TOF with pulmonary stenosis (PS) and pulmonary regurgitation (PR), as a cardiac workload parameter and its relationship to symptoms and major adverse cardiovascular events (MACE). MethodsProspectively, 51 consecutive TOF adults after intracardiac repair, who underwent four-dimensional flow magnetic resonance imaging, were enrolled. All of them had significant PR (PR regurgitant fraction >25 %). TOF patients who had already reached the conventional criteria were excluded. We defined MACE as the following: 1) fatal arrhythmias, 2) sudden cardiac death, 3) surgical pulmonary valvular repair (PVR), 4) right heart failure (HF) needing diuretics and/or hospitalization within 2 years. ResultsA total of 15 patients had MACE; 1) 10 patients underwent PVR within 2 years, 2) 2 patients had ventricular tachycardia, and 3) 6 patients developed right HF (overlapped). Right ventricular (RV) end diastolic volume index (EDVI), RV end systolic volume index (ESVI), average EL/cardiac output (CO), and diastolic EL/CO in patients with MACE were greater than ones without MACE. On a multivariate logistic analysis, the diastolic EL/CO ratio and RVEDVI had the highest odds with MACE in all TOF (odds ratio, 40.7 and 1.15. 95%CI, 1.83–905 and 1.02–13.0; p-value, 0.02 and 0.03). In sub-analysis within 29 patients with moderate PS with PR, and 10 patients with MACE showed higher diastolic EL/CO. Average and diastolic EL/CO negatively correlated with RV ejection fraction (EF) in this sub-analysis. ConclusionsHigh EL, particularly, high diastolic EL/CO, were the important factors for MACE in adult TOF. Higher diastolic EL/CO was also related to lower RV EF and deteriorated RV function in adult TOF with PS and PR. Right-sided EL can be a sensitive marker of excessive cardiac workload which integrates both afterload and preload in adult patients with TOF, beyond the RV size.

Reconstruction and Validation of Arterial Geometries for Computational Fluid Dynamics Using Multiple Temporal Frames of 4D Flow-MRI Magnitude Images

PurposeSegmentation and reconstruction of arterial blood vessels is a fundamental step in the translation of computational fluid dynamics (CFD) to the clinical practice. Four-dimensional flow magnetic resonance imaging (4D Flow-MRI) can provide detailed information of blood flow but processing this information to elucidate the underlying anatomical structures is challenging. In this study, we present a novel approach to create high-contrast anatomical images from retrospective 4D Flow-MRI data.MethodsFor healthy and clinical cases, the 3D instantaneous velocities at multiple cardiac time steps were superimposed directly onto the 4D Flow-MRI magnitude images and combined into a single composite frame. This new Composite Phase-Contrast Magnetic Resonance Angiogram (CPC-MRA) resulted in enhanced and uniform contrast within the lumen. These images were subsequently segmented and reconstructed to generate 3D arterial models for CFD. Using the time-dependent, 3D incompressible Reynolds-averaged Navier–Stokes equations, the transient aortic haemodynamics was computed within a rigid wall model of patient geometries.ResultsValidation of these models against the gold standard CT-based approach showed no statistically significant inter-modality difference regarding vessel radius or curvature (p > 0.05), and a similar Dice Similarity Coefficient and Hausdorff Distance. CFD-derived near-wall hemodynamics indicated a significant inter-modality difference (p > 0.05), though these absolute errors were small. When compared to the in vivo data, CFD-derived velocities were qualitatively similar.ConclusionThis proof-of-concept study demonstrated that functional 4D Flow-MRI information can be utilized to retrospectively generate anatomical information for CFD models in the absence of standard imaging datasets and intravenous contrast.

Blood flow analysis with computational fluid dynamics in the left atrium after left atrial plication: a prospective study.

This study aimed to evaluate blood flow stagnation in an enlarged left atrium (LA) and prove that left atrial plication (LAP) could alleviate the stagnation. Five patients with chronic atrial fibrillation who underwent mitral valve surgery followed by LAP for an enlarged LA with a ≥ 60-mm diameter were included. We performed computational fluid dynamics (CFD) analysis using preoperative and postoperative computed tomography and four-dimensional flow magnetic resonance imaging. Additionally, computer graphics were used to create virtual left atrial appendage resection (LAAR) images. We performed CFD analysis to assess blood flow stagnation in the LA for three groups: preoperative, LAAR, and LAP. When the average and constant stagnation volumes were both set to 100 preoperatively, the average stagnation volumes of the LAAR and LAP groups were 67.42 ± 18.64 and 35.88 ± 8.20, respectively. The constant stagnation volumes of these groups reduced to 45.01 ± 7.43 and 21.14 ± 7.70, respectively. The LAP group also had significantly lower average and constant stagnation volumes than those in the LAAR group (p = 0.006 and p = 0.033, respectively). Blood flow stagnation was noted in the LAA and enlarged LA. CFD analysis revealed that LAP for the enlarged LA improved blood flow stagnation more than the virtual LAAR alone. UMIN000049923.

Four-dimensional flow MR imaging for evaluating treatment response after transcatheter arterial chemoembolization in cirrhotic patients with hepatocellular carcinoma.

To prospectively evaluate the potential of four-dimensional (4D) flow magnetic resonance imaging (MRI) in predicting treatment responses after transcatheter arterial chemoembolization (TACE) in cirrhoticpatients with hepatocellular carcinoma (HCC). A total of 195 patients were classified into four groups (A-D): A, cirrhotic patients without HCC (n = 30); B, cirrhotic patients with HCC before TACE (n = 75); C, cirrhotic patients with HCC showing an incomplete response following TACE (n = 56); and D, cirrhotic patients with HCC achieving a complete response (CR) following TACE (n = 34). The patients were subjected to routine laboratory tests and 4D flow MRI using a 3-T MRI system to measure the quantitative parameters of blood flow in the portal vein (PV), splenic vein(SV), and superior mesenteric vein. The data collected by 4D flow MRI were compared among the groups using one-way analysis of variance. A multivariate analysis was performed to verify the association of clinical characteristics and 4D flow parameters with CR after TACE treatment. The average through-plane velocity, peak velocity magnitude, average net flow, peak flow, and net forward volume in the PV and SVwere significantly lower in groups B and C (P < 0.05) compared to those in group A. Moreover, average through-plane velocity and peak velocity magnitude in the PV in groups B and C were significantlylower than those in group D (P < 0.05). The multivariate analysis demonstrated that the average through-plane velocity and peak velocity magnitudein the PV were independently associated with CR in HCC patients after TACE (P < 0.05). The quantitative flow data obtained by 4D flow MRI may be useful for predicting CR after TACE in cirrhotic patients with HCC.

Early clinical outcomes and molecular smooth muscle cell phenotyping using a prophylactic aortic arch replacement strategy in Loeys-Dietz syndrome

ObjectivesPatients with Loeys-Dietz syndrome demonstrate a heightened risk of distal thoracic aortic events after valve-sparing aortic root replacement. This study assesses the clinical risks and hemodynamic consequences of a prophylactic aortic arch replacement strategy in Loeys-Dietz syndrome and characterizes smooth muscle cell phenotype in Loeys-Dietz syndrome aneurysmal and normal-sized downstream aorta. MethodsPatients with genetically confirmed Loeys-Dietz syndrome (n = 8) underwent prophylactic aortic arch replacement during valve-sparing aortic root replacement. Four-dimensional flow magnetic resonance imaging studies were performed in 4 patients with Loeys-Dietz syndrome (valve-sparing aortic root replacement + arch) and compared with patients with contemporary Marfan syndrome (valve-sparing aortic root replacement only, n = 5) and control patients (without aortopathy, n = 5). Aortic tissues from 4 patients with Loeys-Dietz syndrome and 2 organ donors were processed for anatomically segmented single-cell RNA sequencing and histologic assessment. ResultsPatients with Loeys-Dietz syndrome valve-sparing aortic root replacement + arch had no deaths, major morbidity, or aortic events in a median of 2 years follow-up. Four-dimensional magnetic resonance imaging demonstrated altered flow parameters in patients with postoperative aortopathy relative to controls, but no clear deleterious changes due to arch replacement. Integrated analysis of aortic single-cell RNA sequencing data (>49,000 cells) identified a continuum of abnormal smooth muscle cell phenotypic modulation in Loeys-Dietz syndrome defined by reduced contractility and enriched extracellular matrix synthesis, adhesion receptors, and transforming growth factor-beta signaling. These modulated smooth muscle cells populated the Loeys-Dietz syndrome tunica media with gradually reduced density from the overtly aneurysmal root to the nondilated arch. ConclusionsPatients with Loeys-Dietz syndrome demonstrated excellent surgical outcomes without overt downstream flow or shear stress disturbances after concomitant valve-sparing aortic root replacement + arch operations. Abnormal smooth muscle cell–mediated aortic remodeling occurs within the normal diameter, clinically at-risk Loeys-Dietz syndrome arch segment. These initial clinical and pathophysiologic findings support concomitant arch replacement in Loeys-Dietz syndrome.

Graph theory applications in congenital heart disease

Graph theory can be used to address problems with complex network structures. Congenital heart diseases (CHDs) involve complex abnormal connections between chambers, vessels, and organs. We proposed a new method to represent CHDs based on graph theory, wherein vertices were defined as the spaces through which blood flows and edges were defined by the blood flow between the spaces and direction of the blood flow. The CHDs of tetralogy of Fallot (TOF) and transposition of the great arteries (TGA) were selected as examples for constructing directed graphs and binary adjacency matrices. Patients with totally repaired TOF, surgically corrected d-TGA, and Fontan circulation undergoing four-dimensional (4D) flow magnetic resonance imaging (MRI) were included as examples for constructing the weighted adjacency matrices. The directed graphs and binary adjacency matrices of the normal heart, extreme TOF undergoing a right modified Blalock–Taussig shunt, and d-TGA with a ventricular septal defect were constructed. The weighted adjacency matrix of totally repaired TOF was constructed using the peak velocities obtained from 4D flow MRI. The developed method is promising for representing CHDs and may be helpful in developing artificial intelligence and conducting future research on CHD.

Rightward imbalanced pulmonary perfusion predicts better exercise stroke volume in children after Fallot repair

BackgroundResidual lesions following Fallot repair are primarily pulmonary regurgitation and right ventricular outflow tract obstruction. These lesions may impact exercise tolerance, particularly because of a poor increase in left ventricular stroke volume. Pulmonary perfusion imbalance is also common, but its effect on cardiac adaptation to exercise is not known. AimTo assess the association between pulmonary perfusion asymmetry and peak indexed exercise stroke volume (pSVi) in young patients. MethodsWe retrospectively studied 82 consecutive patients with Fallot repair (mean age 15.2±3.8 years) who underwent echocardiography, four-dimensional flow magnetic resonance imaging and cardiopulmonary testing with pSVi measurement by thoracic bioimpedance. Normal pulmonary flow distribution was defined as right pulmonary artery perfusion between 43 and 61%. ResultsNormal, rightward and leftward flow distributions were found in 52 (63%), 26 (32%) and four (5%) patients, respectively. Independent predictors of pSVi were right pulmonary artery perfusion (β=0.368, 95% confidence interval [CI] 0.188 to 0.548; P=0.0003), right ventricular ejection fraction (β=0.205, 95% CI 0.026 to 0.383; P=0.049), pulmonary regurgitation fraction (β=–0.283, 95% CI –0.495 to –0.072; P=0.006) and Fallot variant with pulmonary atresia (β=–0.213, 95% CI –0.416 to –0.009; P=0.041). The pSVi prediction was similar when the categorical variable right pulmonary artery perfusion>61% was used (β=0.210, 95% CI 0.006 to 0.415; P=0.044). ConclusionIn addition to right ventricular ejection fraction, pulmonary regurgitation fraction and Fallot variant with pulmonary atresia, right pulmonary artery perfusion is a predictor of pSVi, in that rightward imbalanced pulmonary perfusion favours greater pSVi.

Four-Dimensional Flow MRI for the Evaluation of Aortic Endovascular Graft: A Pilot Study.

We aimed to explore the feasibility of 4D flow magnetic resonance imaging (MRI) for patients undergoing thoracic aorta endovascular repair (TEVAR). We retrospectively evaluated ten patients (two female), with a mean (±standard deviation) age of 61 ± 20 years, undergoing MRI for a follow-up after TEVAR. All 4D flow examinations were performed using a 1.5-T system (MAGNETOM Aera, Siemens Healthcare, Erlangen, Germany). In addition to the standard examination protocol, a 4D flow-sensitive 3D spatial-encoding, time-resolved, phase-contrast prototype sequence was acquired. Among our cases, flow evaluation was feasible in all patients, although we observed some artifacts in 3 out of 10 patients. Three individuals displayed a reduced signal within the vessel lumen where the endograft was placed, while others presented with turbulent or increased flow. An aortic endograft did not necessarily hinder the visualization of blood flow through 4D flow sequences, although the graft could generate flow artifacts in some cases. A 4D Flow MRI may represent the ideal tool to follow up on both healthy subjects deemed to be at an increased risk based on their anatomical characteristics or patients submitted to TEVAR for whom a surveillance protocol with computed tomography angiography would be cumbersome and unjustified.

The Use Of 4D Flow MRI in Predicting Clinical Outcomes in SAVR and TAVR

Four-dimensional (4D) flow magnetic resonance imaging (MRI) is a novel imaging technique capable of assessing aortic blood flow and quantifying aortic haemodynamics. Previous studies have reported alterations in aortic wall shear stress distribution and flow eccentricity after both transcatheter aortic valve replacement (TAVR) and surgical aortic valve replacement (SAVR); however, sample size was small, and follow-up limited. Previous studies have demonstrated that changes in the geometry of the AV, such as bicuspid valves, or AVR result in altered blood flow patterns and parameters. Transcatheter aortic valve implantation and AVR with a stented bioprosthesis lead to altered blood flow characteristics in the ascending aorta compared with healthy controls, with more intense flow eccentricity and regional elevation of wall shear stress.

Characterization of baseline hemodynamics after the Fontan procedure: a retrospective cohort study on the comparison of 4D Flow MRI and computational fluid dynamics.

Introduction: The aim of this study was to characterize the hemodynamics of Fontan patients using both four-dimensional flow magnetic resonance imaging (4D Flow MRI) and computational fluid dynamics (CFD). Methods: Twenty-nine patients (3.5 ± 0.5years) who had undergone the Fontan procedure were enrolled, and the superior vena cava (SVC), left pulmonary artery (LPA), right pulmonary artery (RPA), and conduit were segmented based on 4D Flow MRI images. Velocity fields from 4D Flow MRI were used as boundary conditions for CFD simulations. Hemodynamic parameters such as peak velocity (Vmax), pulmonary flow distribution (PFD), kinetic energy (KE), and viscous dissipation (VD) were estimated and compared between the two modalities. Results and discussion: The Vmax, KE, VD, PFDTotal to LPA, and PFDTotal to RPA of the Fontan circulation were 0.61 ± 0.18m/s, 0.15 ± 0.04mJ, 0.14 ± 0.04mW, 41.3 ± 15.7%, and 58.7 ± 15.7% from 4D Flow MRI; and 0.42 ± 0.20m/s, 0.12 ± 0.05mJ, 0.59 ± 0.30mW, 40.2 ± 16.4%, and 59.8 ± 16.4% from CFD, respectively. The overall velocity field, KE, and PFD from the SVC were in agreement between modalities. However, PFD from the conduit and VD showed a large discrepancy between 4D Flow MRI and CFD, most likely due to spatial resolution and data noise. This study highlights the necessity for careful consideration when analyzing hemodynamic data from different modalities in Fontan patients.

Reduced basal macrovascular and microvascular cerebral blood flow in young adults with metabolic syndrome: potential mechanisms.

Ninety-million Americans suffer metabolic syndrome (MetSyn), increasing the risk of diabetes and poor brain outcomes, including neuropathology linked to lower cerebral blood flow (CBF), predominantly in anterior regions. We tested the hypothesis that total and regional CBF is lower in MetSyn more so in the anterior brain and explored three potential mechanisms. Thirty-four controls (25 ± 5 yr) and 19 MetSyn (30 ± 9 yr), with no history of cardiovascular disease/medications, underwent four-dimensional flow magnetic resonance imaging (MRI) to quantify macrovascular CBF, whereas arterial spin labeling quantified brain perfusion in a subset (n = 38/53). Contributions of cyclooxygenase (COX; n = 14), nitric oxide synthase (NOS, n = 17), or endothelin receptor A signaling (n = 13) were tested with indomethacin, NG-monomethyl-L-arginine (L-NMMA), and Ambrisentan, respectively. Total CBF was 20 ± 16% lower in MetSyn (725 ± 116 vs. 582 ± 119 mL/min, P < 0.001). Anterior and posterior brain regions were 17 ± 18% and 30 ± 24% lower in MetSyn; reductions were not different between regions (P = 0.112). Global perfusion was 16 ± 14% lower in MetSyn (44 ± 7 vs. 36 ± 5 mL/100 g/min, P = 0.002) and regionally in frontal, occipital, parietal, and temporal lobes (range 15-22%). The decrease in CBF with L-NMMA (P = 0.004) was not different between groups (P = 0.244, n = 14, 3), and Ambrisentan had no effect on either group (P = 0.165, n = 9, 4). Interestingly, indomethacin reduced CBF more in Controls in the anterior brain (P = 0.041), but CBF decrease in posterior was not different between groups (P = 0.151, n = 8, 6). These data indicate that adults with MetSyn exhibit substantially reduced brain perfusion without regional differences. Moreover, this reduction is not due to loss of NOS or gain of ET-1 signaling but rather a loss of COX vasodilation.NEW & NOTEWORTHY We tested the impact of insulin resistance (IR) on resting cerebral blood flow (CBF) in adults with metabolic syndrome (MetSyn). Using MRI and research pharmaceuticals to study the role of NOS, ET-1, or COX signaling, we found that adults with MetSyn exhibit substantially lower CBF that is not explained by changes in NOS or ET-1 signaling. Interestingly, adults with MetSyn show a loss of COX-mediated vasodilation in the anterior but not posterior circulation.

Calibration of patient-specific boundary conditions for coupled CFD models of the aorta derived from 4D Flow-MRI.

Introduction: Patient-specific computational fluid dynamics (CFD) models permit analysis of complex intra-aortic hemodynamics in patients with aortic dissection (AD), where vessel morphology and disease severity are highly individualized. The simulated blood flow regime within these models is sensitive to the prescribed boundary conditions (BCs), so accurate BC selection is fundamental to achieve clinically relevant results. Methods: This study presents a novel reduced-order computational framework for the iterative flow-based calibration of 3-Element Windkessel Model (3EWM) parameters to generate patient-specific BCs. These parameters were calibrated using time-resolved flow information derived from retrospective four-dimensional flow magnetic resonance imaging (4D Flow-MRI). For a healthy and dissected case, blood flow was then investigated numerically in a fully coupled zero dimensional-three dimensional (0D-3D) numerical framework, where the vessel geometries were reconstructed from medical images. Calibration of the 3EWM parameters was automated and required ~3.5 min per branch. Results: With prescription of the calibrated BCs, the computed near-wall hemodynamics (time-averaged wall shear stress, oscillatory shear index) and perfusion distribution were consistent with clinical measurements and previous literature, yielding physiologically relevant results. BC calibration was particularly important in the AD case, where the complex flow regime was captured only after BC calibration. Discussion: This calibration methodology can therefore be applied in clinical cases where branch flow rates are known, for example, via 4D Flow-MRI or ultrasound, to generate patient-specific BCs for CFD models. It is then possible to elucidate, on a case-by-case basis, the highly individualized hemodynamics which occur due to geometric variations in aortic pathology high spatiotemporal resolution through CFD.

Four-Dimensional Flow Magnetic Resonance Imaging Features of a Platypnea-Orthodeoxia Syndrome Caused by a Patent Foramen Ovale.

HomeCirculation: Cardiovascular ImagingAhead of PrintFour-Dimensional Flow Magnetic Resonance Imaging Features of a Platypnea-Orthodeoxia Syndrome Caused by a Patent Foramen Ovale No AccessCase ReportRequest AccessAboutView PDFSections ToolsAdd to favoritesDownload citationsTrack citationsPermissionsDownload Articles + Supplements ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toSupplemental MaterialNo AccessCase ReportRequest AccessFour-Dimensional Flow Magnetic Resonance Imaging Features of a Platypnea-Orthodeoxia Syndrome Caused by a Patent Foramen Ovale Samuel Sitbon, Phalla Ou, Caroline Nguyen, Carsten Ehmer, Eric Garbarz, Eric Brochet, Adeline Fuchs, Pierre Aubry and Jeremie Abtan Samuel SitbonSamuel Sitbon https://orcid.org/0000-0003-0639-3557 Département de Cardiologie, Hôpital Bichat, AP-HP (Assistance Publique – Hôpitaux de Paris), Université de Paris, France (S.S., C.N., E.G., E.B., A.F., P.A., J.A.). Search for more papers by this author , Phalla OuPhalla Ou Département de Radiologie, Hôpital Bichat, AP-HP (Assistance Publique – Hôpitaux de Paris), Université de Paris, France (P.O., C.E.). Search for more papers by this author , Caroline NguyenCaroline Nguyen Département de Cardiologie, Hôpital Bichat, AP-HP (Assistance Publique – Hôpitaux de Paris), Université de Paris, France (S.S., C.N., E.G., E.B., A.F., P.A., J.A.). Search for more papers by this author , Carsten EhmerCarsten Ehmer Département de Radiologie, Hôpital Bichat, AP-HP (Assistance Publique – Hôpitaux de Paris), Université de Paris, France (P.O., C.E.). Search for more papers by this author , Eric GarbarzEric Garbarz Département de Cardiologie, Hôpital Bichat, AP-HP (Assistance Publique – Hôpitaux de Paris), Université de Paris, France (S.S., C.N., E.G., E.B., A.F., P.A., J.A.). Search for more papers by this author , Eric BrochetEric Brochet Département de Cardiologie, Hôpital Bichat, AP-HP (Assistance Publique – Hôpitaux de Paris), Université de Paris, France (S.S., C.N., E.G., E.B., A.F., P.A., J.A.). Search for more papers by this author , Adeline FuchsAdeline Fuchs Département de Cardiologie, Hôpital Bichat, AP-HP (Assistance Publique – Hôpitaux de Paris), Université de Paris, France (S.S., C.N., E.G., E.B., A.F., P.A., J.A.). Search for more papers by this author , Pierre AubryPierre Aubry Département de Cardiologie, Hôpital Bichat, AP-HP (Assistance Publique – Hôpitaux de Paris), Université de Paris, France (S.S., C.N., E.G., E.B., A.F., P.A., J.A.). Search for more papers by this author and Jeremie AbtanJeremie Abtan Correspondence to: Jeremie Abtan, MD, PhD, Hôpital Bichat, 46 rue Henri Huchard, 75018 Paris. Email E-mail Address: [email protected] https://orcid.org/0000-0001-8968-6624 Département de Cardiologie, Hôpital Bichat, AP-HP (Assistance Publique – Hôpitaux de Paris), Université de Paris, France (S.S., C.N., E.G., E.B., A.F., P.A., J.A.). FACT (French Alliance for Cardiovascular Clinical Trials), an F-CRIN network, Paris, France (J.A.). Search for more papers by this author Originally published24 Apr 2023https://doi.org/10.1161/CIRCIMAGING.122.014722Circulation: Cardiovascular Imaging. 2023;0:e014722FootnotesSupplemental Material is available at https://www.ahajournals.org/doi/suppl/10.1161/CIRCIMAGING.122.014722.Correspondence to: Jeremie Abtan, MD, PhD, Hôpital Bichat, 46 rue Henri Huchard, 75018 Paris. Email jeremie.[email protected]fr Previous Back to top Next FiguresReferencesRelatedDetails Advertisement Article InformationMetrics © 2023 American Heart Association, Inc.https://doi.org/10.1161/CIRCIMAGING.122.014722PMID: 37092323 Originally publishedApril 24, 2023 Keywordsforamen ovale, patentplatypnea orthodeoxia syndromemagnetic resonance imagingPDF download Advertisement SubjectsDiagnostic TestingEchocardiography

Super-resolution 4D flow MRI to quantify aortic regurgitation using computational fluid dynamics and deep learning

Changes in cardiovascular hemodynamics are closely related to the development of aortic regurgitation (AR), a type of valvular heart disease. Metrics derived from blood flows are used to indicate AR onset and evaluate its severity. These metrics can be non-invasively obtained using four-dimensional (4D) flow magnetic resonance imaging (MRI), where accuracy is primarily dependent on spatial resolution. However, insufficient resolution often results from limitations in 4D flow MRI and complex aortic regurgitation hemodynamics. To address this, computational fluid dynamics simulations were transformed into synthetic 4D flow MRI data and used to train a variety of neural networks. These networks generated super-resolution, full-field phase images with an upsample factor of 4. Results showed decreased velocity error, high structural similarity scores, and improved learning capabilities from previous work. Further validation was performed on two sets of in vivo 4D flow MRI data and demonstrated success in de-noising flow images. This approach presents an opportunity to comprehensively analyse AR hemodynamics in a non-invasive manner.

Wall Shear Stress Associated with Stroke Occurrence and Mechanisms in Middle Cerebral Artery Atherosclerosis.

Various mechanisms are involved in the etiology of stroke caused by atherosclerosis of the middle cerebral artery (MCA). Here, we compared differences in plaque nature and hemodynamic parameters according to stroke mechanism in patients with MCA atherosclerosis. Consecutive patients with asymptomatic and symptomatic MCA atherosclerosis (≥50% stenosis) were enrolled. MCA plaque characteristics (location and plaque enhancement) and wall shear stress (WSS) were measured using high-resolution vessel wall and four-dimensional flow magnetic resonance imaging, respectively, at five points (initial, upstream, minimal lumen, downstream, and terminal). These parameters were compared between patients with asymptomatic and symptomatic MCA atherosclerosis with infarctions of different mechanisms (artery-to-artery embolism vs. local branch occlusion). In total, 110 patients (46 asymptomatic, 32 artery-to-artery embolisms, and 32 local branch occlusions) were investigated. Plaques were evenly distributed in the MCA of patients with asymptomatic MCA atherosclerosis, more commonly observed in the distal MCA of patients with artery-to-artery embolism, and in the middle MCA of patients with local branch occlusion. Maximum WSS and plaque enhancement were more prominent in the minimum lumen area of patients with asymptomatic MCA atherosclerosis or those with local branch occlusion, and were more prominent in the upstream area in those with artery-to-artery embolism. The elevated variability in the maximum WSS was related to stroke caused by artery-to-artery embolism. Stroke caused by artery-to-artery embolism was related to plaque enhancement and the highest maximum WSS at the upstream point of the plaque, and was associated with elevated variability of maximum WSS.

Liver cirrhosis: relationship between fibrosis-associated hepatic morphological changes and portal hemodynamics using four-dimensional flow magnetic resonance imaging

PurposeThe mechanisms underlying the morphological changes in liver cirrhosis remain unknown. This study aimed to clarify the relationship between fibrotic hepatic morphology and portal hemodynamic changes using four-dimensional flow magnetic resonance imaging (MRI).Materials and methodsOverall, 100 patients with suspected liver disease who underwent 3-T MRI were evaluated in this retrospective study. Liver fibrosis was assessed using a combination of visual assessment of the hepatic morphology and quantitative measures, including the fibrosis-4 index and aspartate transaminase-to-platelet ratio. It was classified into three groups according to the severity of fibrosis as follows: A (normal), B (mild-to-moderate), and C (severe). Quantitative indices, including area (mm2), net flow (mL/s), and average velocity (cm/s), were measured in the right portal vein (RPV) and left portal vein (LPV), and were compared across the groups using the Kruskal–Wallis and Mann–Whitney U tests.ResultsAmong the 100 patients (69.1 ± 12.1 years; 59 men), 45, 35, and 20 were categorized into groups A, B, and C, respectively. The RPV area significantly differed among the groups (from p < 0.001 to p = 0.001), showing a gradual decrease with fibrosis progression. Moreover, the net flow significantly differed between groups A and B and between groups A and C (p < 0.001 and p < 0.001, respectively), showing a decrease during the early stage of fibrosis. In the LPV, the net flow significantly differed among the groups (from p = 0.001 to p = 0.030), revealing a gradual increase with fibrosis progression.ConclusionThe atrophy–hypertrophy complex, which is a characteristic imaging finding in advanced cirrhosis, was closely associated with decreased RPV flow in the early stage of fibrosis and a gradual increase in LPV flow across all stages of fibrosis progression.