Coprime dual-velocity encoding for extended velocity dynamic range in 4D flow magnetic resonance imaging

Background: The assessment of left ventricular (LV) mechanical synchrony using phase analysis (PA) provides incremental diagnostic value over conventional indicators and is widely used in clinical practice. Four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) has emerged as an imaging technique to visualize blood flow dynamics. Intra-LV kinetic energy (KE) obtained from 4D-CMR is a novel parameter refers to the quantification of the energy associated with the motion of blood within LV. This study aimed to simultaneously investigate the relationship between LV mechanical synchrony and intra-LV blood flow energy in patients with ischemic heart disease (IHD), using hybrid PET/MR system. Methods: Sixty-six patients (mean age 67 years, male 54) who underwent rest-pharmacological stress 13 N ammonia PET and 4D flow CMR at our hospital between January 2022 and February 2024 were included. Left ventricular ejection fraction (LVEF), PA parameters including histogram bandwidth (BW), phase standard deviation (PSD), and entropy were obtained from rest and stress gated PET. Perfusion defect was assessed as summed defect score from rest and stress static PET images. Intra-LV 4D flow MR acquisition was simultaneously performed for rest and stress. Intra-LV blood flow KE indexed with end-diastolic volume (KEi mJ/mL) was obtained from dynamic 4D flow curve. Results: BW[KF1] was 24.6 ± 17.9 and 24.4 ± 15.4%, PSD was 6.2 ± 3.7 and 6.2 ± 3.5, entropy was 61.6 ± 7.9 and 60.3 ± 9.3 for rest and stress, respectively. Summed defect score was 6.1 ± 7.1 and 11.2 ± 9.4 for rest and stress. KEi[KF2] was 0.018 ± 0.01, and 0.019 ± 0.01 (mJ/mL) for rest and stress. A significant positive correlation was observed between LVEF and KEi at both rest (R=0.30, P=0.014) and stress (R=0.42, P<0.001). Summed defect score was not significantly correlated with KEi at either rest or stress. All PA parameters demonstrated a weak inverse correlation with KEi at rest (BW: R= –0.29, P=0.019; PSD R = –0.27, P=0.026; entropy R = –0.27, P=0.031) and stress (BW: R= –0.28, P=0.023; PSD R = –0.36, P=0.003; entropy R = –0.31, P=0.010). Conclusions: PET-derived PA parameters were significantly associated with intra-LV blood flow KE, suggesting impaired LV mechanical synchrony is linked to intra-LV blood flow energy insufficiency.

BackgroundWe 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.MethodsTen 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.ResultsDobutamine 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).Conclusions4D 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.

To evaluate the intra-cavity left ventricular (LV) blood flow kinetic energy (KE) parameters using four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) in patients with hypertension (HTN). Forty-two HTN patients and twenty age-/gender-matched healthy controls who underwent CMR including cines, pre-/post-T1 mapping, and whole-heart 4D flow imaging were retrospectively evaluated. HTN patients were further divided into two subgroups: with preserved ejection fraction (HTN-pEF) and with reduced ejection fraction (HTN-rEF). KE parameters were indexed to LV end-diastolic volume (EDV) to obtain averaged LV, minimal, systolic, diastolic, peak E-wave, peak A-wave, E-wave, and A-wave KEiEDV, as well as the proportion of in-plane LV KE (%), the time difference (TD). These parameters were compared between the HTN group and healthy controls, also between two subgroups. The correlation of LV blood flow KE parameters with LV function and extracellular volume fraction (ECV) were analyzed in the HTN group using multivariate regression analysis. Peak E-wave KEiEDV in the HTN group was significantly lower (p = 0.01), while in-plane KE and TD were significantly higher (all p < 0.01) than those in healthy controls. Compared to the HTN-pEF subgroup, the proportion of in-plane KE and TD was significantly increased in the HTN-rEF subgroup (all p < 0.01). Only the proportion of in-plane KE demonstrated an independent correlation with ECV (β* = 0.59, p < 0.01). The decreased peak E-wave KEiEDV and the increased proportion of in-plane KE, TD reflected the alterations of LV blood flow in HTN patients, and the proportion of in-plane KE was independently associated with ECV. • 4D flow CMR demonstrated that the peak E-wave KEiEDV was decreased, while the in-plane KE and time difference (TD) were increased in hypertensive (HTN) patients. • The proportion of in-plane KE and TD was further increased in HTN patients with reduced ejection fraction than in HTN patients with preserved ejection fraction, and the proportion of in-plane KE was independently associated with extracellular volume fraction in HTN patients. • 4D flow CMR intra-cavity blood flow KE parameters might reveal the LV hemodynamic status in preclinical HTN patients.

Pulmonary arterial hypertension is a severe complication of systemic lupus erythematosus (SLE). Current screening methods often miss early vascular changes. This study aimed to characterize subclinical pulmonary hemodynamic alterations in SLE patients without known pulmonary arterial hypertension using four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) and to investigate their association with left ventricular diastolic function. Twenty-five SLE patients without known pulmonary arterial hypertension and 25 age-matched healthy controls were enrolled. All participants underwent 3-T 4D flow CMR to quantify hemodynamic parameters, including wall shear stress (WSS), flow volume, and relative pressure in the pulmonary arteries. SLE patients were further stratified based on echocardiographic assessment of diastolic function to analyze hemodynamic coupling. Compared to controls, SLE patients exhibited significantly lower maximum WSS in the main pulmonary artery (0.29 versus 0.33 Pa, p = 0.040) and asymmetric flow redistribution, characterized by higher relative pressure in the left pulmonary artery (0.54 versus 0.30 mmHg, p = 0.008) and increased flow rate in the right pulmonary artery (3.51 versus 2.90 L/min, p = 0.015). Qualitative analysis revealed vortical flow patterns in SLE patients. Subgroup analysis demonstrated that the reduction in WSS was primarily driven by patients with diastolic dysfunction (p = 0.006 versus controls). SLE patients without pulmonary arterial hypertension exhibit distinct subclinical pulmonary hemodynamic alterations, including lower WSS and flow asymmetry. These alterations are intimately coupled with left ventricular diastolic dysfunction, suggesting that 4D flow CMR serves as a sensitive noninvasive tool for early risk stratification in this population. 4D flow CMR identifies subclinical pulmonary hemodynamic alterations coupled with diastolic dysfunction in SLE patients, serving as a sensitive noninvasive tool for early risk stratification before irreversible vascular remodeling occurs. SLE patients without known pulmonary arterial hypertension show early pulmonary blood flow changes. 4D flow CMR detected asymmetric pulmonary flow redistribution in SLE patients. SLE patients exhibited altered left atrial function despite normal ventricles. Pulmonary flow changes correlated with left atrial remodeling in SLE. 4D flow CMR detects subclinical pulmonary hemodynamic differences in SLE.

Fully automated on-scanner aortic four-dimensional flow magnetic resonance imaging processing and hemodynamic analysis

ABSTRACTPurposeIdentifying factors associated with left ventricular (LV) remodeling is important for risk stratification of patients with moderate aortic stenosis (AS). The aim of this preliminary study was to explore aortic hemodynamics in these patients and assess their relationships with LV remodeling using four‐dimensional (4D) flow magnetic resonance imaging (MRI).MethodData from 17 patients with moderate AS involving the tricuspid aortic valves and normal LV ejection fraction (EF > 55%) were analyzed. All patients underwent 4D flow MRI of the ascending aorta and cardiac magnetic resonance (CMR) on the same day within 1 month of being diagnosed with moderate AS by transthoracic Doppler echocardiography. 4D flow MRI aortic parameters, including turbulent kinetic energy (TKE), both total and peak; peak wall shear stress (WSS); and the vortex and helix flow severity, were assessed. CMR measures comprised LV structure and function, late gadolinium enhancement (LGE), myocardial native T1 mapping, and extracellular volume fraction.ResultsThe minimum and maximum values of total TKE, peak TKE, and peak WSS were 39.4/160.3 mJ, 876.6/2059.6 J/m3, and 2.0/4.9 Pa, respectively. More than 50% of the patients had vortex and helix flow of Grade 2. Peak TKE significantly correlated with LV end‐diastolic volume index (r = 0.675, p = 0.003), LV end‐systolic volume index (r = 0.666, p = 0.003), and LV mass index (r = 0.653, p = 0.004). LGE was not observed, and peak TKE also showed an inverse correlation with native T1 value (r = −0.571, p = 0.017).ConclusionsAmong patients with moderate AS, 4D flow MRI revealed heterogeneous aortic hemodynamic profiles and peak TKE was a significant hemodynamic parameter related to early LV remodeling. However, these findings need to be confirmed in further studies with larger sample sizes and a long‐term serial follow‐up data.

The article "Assessment of superior mesenteric vascular flow quantitation in children using four-dimensional flow magnetic resonance imaging" suggests to use of four-dimensional (4D) flow magnetic resonance imaging (MRI) which is also to measure the blood flow in the superior mesenteric vein (SMV) in pediatric patients over the traditional method. The study focuses on assessing the potential of SMV and superior mesenteric artery (SMA) flow quantification in children utilizing 4D flow MRI. It included 9 pediatric patients aged 18 years and below where 5 were male and 4 were female patients, on whom magnetic resonance enterorrhaphy (MRE) with 4D flow MRI protocol was used. Statistical analysis was performed using MedCalc. Measurements of SMV and SMA between two readers were calculated using Bland-Altman analysis. The results stated that six patients showed no MRE evidence of active inflammatory bowel disease, two patients showed unmarkable bowel appearance on MRI and one patient showed normal MRE without endoscopy performed at the same timeframe. The study utilized available 4D flow MRI sequences in this study aiming to show the feasibility of 4D flow quantitation of SMA and SMV flow in pediatric patients. The study also discovered good agreement for both peak velocity and peak speed measurements of SMA and SMV.

IntroductionAltered haemodynamic flow patterns in the aorta are linked with increased risk of bicuspid aortic valve (BAV)-associated aortopathy.1–3 Using 4D-flow cardiovascular magnetic resonance (4DF-CMR), we assessed whether our novel 3D...

Our goal was to study both right and left ventricular blood flow in patients with precapillary pulmonary hypertension (pre-PH) with 4-dimensional (4D) flow magnetic resonance imaging (MRI) and to analyze their correlation with cardiac functional metrics on cardiovascular magnetic resonance (CMR) and hemodynamics from right heart catheterization (RHC). 129 patients (64 females, mean age 47 ± 13 y) including 105 patients with pre-PH (54 females, mean age 49 ± 13 y) and 24 patients without PH (10 females, mean age 40 ± 12 y) were retrospectively included. All patients underwent CMR and RHC within 48 hours. 4D flow MRI was acquired using a 3-dimensional retrospectively electrocardiograph-triggered, navigator-gated phase contrast sequence. Right and left ventricular flow components including the percentages of direct flow (PDF), retained inflow (PRI), delayed ejection flow (PDE), and residual volume (PRVo) were respectively quantified. The ventricular flow components between patients with pre-PH and non-PH were compared and correlations of flow components with CMR functional metrics and hemodynamics measured with RHC were analyzed. Biventricular flow components were compared between survivors and deceased patients during the perioperative period. Right ventricular (RV) PDF and PDE significantly correlated with RVEDV and RV ejection fraction. RV PDF negatively correlated with pulmonary arterial pressure (PAP) and pulmonary vascular resistance. When the RV PDF was <11%, the sensitivity and specificity of RV PDF for predicting mean PAP ≥25 mm Hg were 88.6% and 98.7%, respectively, with an area under the curve value of 0.95 ± 0.02. When RV PRVo was more than 42%, the sensitivity and specificity of RV PRVo for predicting mean PAP ≥25 mm Hg were 85.7% and 98.5%, respectively, with an area under the curve value of 0.95 ± 0.01. Nine patients died during the perioperative period. Biventricular PDF, RV PDE, and PRI of survivors were higher than nonsurvivors whereas RV PRVo increased in deceased patients. Biventricular flow analysis with 4D flow MRI provides comprehensive information about the severity and cardiac remodeling of PH and may be a predictor of perioperative death of patients with pre-PH.

Foetal circulation undergoes complex changes in congenital heart disease (CHD) that are challenging to assess with foetal echocardiography. This study aimed to assess clinical feasibility and diagnostic value of 4D flow cardiovascular magnetic resonance (CMR) in foetal CHD. Pregnant women in advanced third trimester pregnancy with foetal CHD were prospectively recruited for foetal CMR between August 2021 and November 2024. CMR protocol included cine and 4D time-resolved PC acquisitions. 4D flow data were evaluated for additional diagnostic information beyond cine imaging. Postnatal examination reports were used to confirm CMR findings. Net flow was quantified in the ascending aorta, distal aortic arch, main pulmonary artery, ductus arteriosus, and descending aorta and normalized to combined ventricular output (CVO). Student's t-test and analysis of variance with Tukey post hoc test were applied. Among 77 participants, 4D flow was of diagnostic quality in 62 (81%) foetuses [11/62 (18%) without CHD, 51/62 (82%) with CHD]. Comparison of net flow distributions revealed significant differences between foetuses without CHD and those with hypoplastic left heart complex (HLHC), dextro-transposition of the great arteries, and coarctation of the aorta. CVO was higher in normal foetal circulation compared with CHD (6.4 ± 1.5 mL vs. 5.1 ± 1.9 mL, P = 0.049). 4D flow provided diagnostic findings beyond cine imaging in 26/51 (51%) foetuses with CHD (e.g. retrograde aortic perfusion in HLHC) that were confirmed postnatally. Foetal 4D flow CMR characterizes flow patterns and provides relevant diagnostic information beyond cine imaging for prenatal CHD assessment.

Interval cross-sectional imaging plays an important role in aortopathy surveillance. Often, cardiac magnetic resonance imaging (MRI) is used over computed tomography (CT) due to the lack of radiation in repeated surveillance and the option of additional hemodynamic assessment. Primarily, assessment includes the orthogonal measurement of aortic dimensions in a three-dimensional (3D) structure. Lately, four-dimensional (4D) flow MRI is becoming more widespread as it can be acquired within 1–5 minutes using advanced techniques. In addition to standard flow quantification, 4D flow MRI offers advanced hemodynamic quantification. This review discusses important advanced imaging biomarkers, including helical flow pattern, wall shear stress (WSS), flow displacement and systolic flow reversal ratio (sFRR). It focuses on those parameters that can be analyzed using commercially available post-processing platforms and are accessible for clinical centers without the need for research setup and collaboration. WSS plays a role in the assessment of bicuspid aortic valve disease. Here it is elevated even without the presence of stenosis. Flow displacement is also of value in bicuspid aortic valve disease and is abnormal in heart failure with preserved ejection fraction (HFpEF) as well as chronic aortic dissection. 4D flow MRI is also useful in understanding and assessing flow changes in aortic valve replacement.

Staged palliation with the creation of a Fontan circulation is the standard surgical approach in patients with a single ventricle. The Fontan circulation is a complex circuit that is associated with various complications that may present early or later in life and can limit life quality and expectancy. In this context, a good understanding of the Fontan physiology is important to improve outcomes for single-ventricle patients. Cardiovascular magnetic resonance (CMR) is recommended for the long-term follow-up of Fontan patients, as it provides functional and haemodynamic information. Four-dimensional (4D) Flow MRI is a time-resolved, three-dimensional, velocity-encoded cardiovascular magnetic resonance technique that is increasingly used in Fontan patients because it not only enables measuring blood flow within a three-dimensional (3D) volume, but also allows for assessing more advanced haemodynamic parameters that may help in understanding the Fontan physiology and pathophysiology. Furthermore, 4D Flow is used for image-based simulations using computational fluid dynamics. In this review, we provide an overview of the use of cardiovascular magnetic resonance flow assessment, with a focus on four-dimensional flow ('4D Flow').

BackgroundFour dimensional (4D) flow magnetic resonance imaging (MRI) enables both visualisation and quantification of hemodynamics in abdominal aortic aneurysms (AAAs). However, its clinical implementation remains limited due to time-consuming and cumbersome post-processing, as well as a lack of standardisation. While previous work has proposed automated solutions for thoracic and intracranial cases, applications in the abdominal region, particularly for AAAs, remain underexplored. The aim of this study was to develop an automated post-processing pipeline for 4D flow MRI in AAA patients, incorporating aneurysm identification, via automated segmentation, blood flow visualisation and hemodynamic parameter quantification.Methods4D flow MRI and three dimensional (3D) cine balanced steady state free precession (bSSFP) scans were acquired from 16 patients with an AAA in the same field of view and with an isotropic resolution of 1 mm. Using 5-fold cross-validation, an nnU-Net was trained to segment the aorta based on 3D cine bSSFP MRI. The automated post-processing pipeline was built using MATLAB. Wall shear stress (WSS) values were assessed within the extracted aneurysm. nnU-Net performance was assessed with the Dice-similarity coefficient (DSC), 95% percentile Hausdorff distance (HD95) and by calculating the Pearson correlation coefficients between WSS values obtained in the aneurysm based on segmentation with both methods.ResultsThe resulting post-processing pipeline demonstrated robustness to anatomical variability, including tortuosity and intraluminal thrombus (ILT), both characteristic of AAA, and consistently produced output without user-interference. The nnU-Net performance was excellent for lumen segmentation and good for ILT segmentation, with DSCs of 0.93 (0.05) and 0.80 (0.26) respectively. The HD95 was 4.87 (8.59) mm and 6.04 (3.71) mm for respectively lumen and thrombus segmentation. Significant correlations (ρ =0.92 or higher) were found between WSS values derived using the manual and nnU-Net segmentations.ConclusionsAn automated post-processing pipeline was developed specifically for 4D flow MRI in patients with AAA. The pipeline is robust for varying anatomies and may facilitate 4D flow MRI implementation in the clinical workflow.

Hemodynamic evaluation using four-dimensional flow magnetic resonance imaging for a patient with multichanneled aortic dissection

The effectiveness of four-dimensional (4D) flow magnetic resonance imaging (MRI) for assessing hemodynamic changes before and after balloon-occluded retrograde transvenous obliteration (BRTO) remains unclear. To evaluate the feasibility of 4D flow MRI for assessing hemodynamic changes in the portal venous system before and after BRTO. We included 10 patients (7 men, 3 women; mean age = 67 years) with liver cirrhosis who had a high risk of gastric variceal bleeding or hepatic encephalopathy. Non-contrast 4D flow MRI of the upper abdomen was performed before and after BRTO. In addition, we compared the blood flow rates in the portal vein (PV), superior mesenteric vein (SMV), splenic vein (SV), left renal vein, and inferior vena cava before and after BRTO. Moreover, the flow directions of the SMV and SV before and after BRTO were assessed using both portography and 4D flow MRI. There was a significant post-BRTO increase in the blood flow rate in the PV and SV (P < 0.05). There was no significant post-BRTO change in the blood flow rates in the SMV, inferior vena cava, and left renal vein. In four patients, portography confirmed that hepatofugal flow in the SV and SMV changed to hepatopetal flow after BRTO. Moreover, 4D flow MRI correctly assessed the flow directions in the SMV and SV in 70%-100% of the patients. 4D flow MRI can be used to detect hemodynamic changes in the portal venous system before and after BRTO.