Keywords: Flow, Cardiovascular, Hemodynamics

Motivation: Single-venc 5D flow is useful for measuring the impact of respiration on hemodynamics, however, its single velocity encoding sensitivity (venc) limit its utility in congenital heart disease patients where both venous and arterial measurements are clinically necessary.

Goal(s): We aimed to validate respiratory-resolved dual-venc 5D flow measurements in vivo.

Approach: Nine healthy volunteers underwent CMR studies including dual-venc 5D flow, single-venc 5D flow, and 4D flow. Net flow and peak flow were compared.

Results: We found good agreement of net flow and peak flow with both 4D flow and single-venc 5D flow MRI, with an 85% increase in velocity-to-noise ratio.

Impact: Dual-venc 5D flow increases velocity-to-noise ratio by 85% compared to single-venc 5D flow with good agreement in respiratory-resolved flow measurements. The method may improve simultaneous measurement of venous and arterial flows, which is often necessary in congenital heart disease patients.

Keywords: Flow, Cardiovascular, Data Analysis, Challenges, Flow, Heart, Valves, Velocity & Flow, Validation, 4D-flow, 2D-flow

Motivation: Mitral valve regurgitation (MVR) quantification is crucial for diagnosis and treatment of patients with mitral valve disease. While different MRI based MVR quantification methods exist, their correlation with one another and their reproducibility and reliability remains unknown.

Goal(s): To determine the reproducibility and reliability of four different 2D- and 4D flow MVR volume quantification methods based on CMR.

Approach: The intermethod, inter- and intra-reader agreements between four different methods, 4D-flow_AIM, 2D-PC_standard, 2D-PC_MV, Volumetric, were compared for patients with severe secondary MVR.

Results: Among all techniques, 2D-PC_standard and Volumetric methods were the most reliable ones (ICC>0.99, P-value<0.001).

Impact: 2D-PCstandard and Volumetric methods quantify the MVR volume most consistently and further research with diverse MVR types and larger cohorts is needed to establish reliable conclusions for 2D-PCMV and 4D-flowAIM methods.

Keywords: Flow, Cardiovascular, flow

Motivation: Cardiac force analysis shows promise for non-invasive treatment and diagnosis for patients with heart disease.  

Goal(s): Assessing intracardiac forces as a metric of diagnostics in repaired tetralogy of fallot patients which require lifelong monitoring.

Approach: Intracardiac forces were analyzed using segment in twenty rTOF patients and 20 control patients. These were compared in age and sex-matched groups. 

Results:  Age and sex-matched analysis showed significant differences in intracardiac forces for control and patient groups. Results also indicated that men and women may be affected differently by rTOF, as there were significant differences between the gender groups with rTOF. 

Impact: Evaluation of intracardiac forces shows promise as a biomarker for heart disease in rTOF females and males; also demonstrates potential for other diseases, although more investigations must be conducted. This can be used in clinical settings, for non-invasive diagnoses. 

Keywords: Flow, Velocity & Flow, aorta, aortic dissection, 4D flow MRI

Motivation: In type B aortic dissections (TBAD), surgical outcomes often worsen as the flap stiffens. Earlier intervention (i.e., acute phase) would require prediction of aortic growth to identify high-risk patients, which has not yet been investigated in acute TBADs.

Goal(s): We aimed to identify possible hemodynamic markers of aortic growth from 4D flow MRI data in acute TBAD subjects.

Approach: From the 4D flow data we estimated various hemodynamic metrics.

Results: Peak entry tear velocity, false lumen retrograde flow pre-entry tear, and forward flow post-entry tear were higher in growth cases. We also demonstrate the feasibility of collecting 4D flow MRI from acute patients.

Impact: As the first study focused on in vivo hemodynamics of acute type B aortic dissections (TBAD), we aimed to identify possible metrics for predicting aortic growth. Ultimately, stratifying risk in acute TBAD patients would enable preemptive treatment and improve outcomes.

Keywords: Flow, Validation, 4D PCMR, Flow, Phantom

Motivation: Accurate blood flow measurement is vital for the diagnosis of cardiovascular disorders. Existing phantoms focus primarily on validating flow using phase-contrast MR (PCMR) techniques along the three orthogonal directions. No phantom has been reported for the validation of flow in non-orthogonal orientations.

Goal(s): To validate flow quantification accuracy on a phantom in non-orthogonal directions using 4D flow MRI.

Approach: A multi-directional plexiglass phantom was designed and fabricated to evaluate accuracy of 4D flow PCMR using blood-mimicking flows within tubing controlled by a programmable pump.

Results: The phantom was successfully used to validate flow in orthogonal and non-orthogonal directions simultaneously with 4D flow MRI.

Impact: The flow phantom can be used to validate flow in 5 directions simultaneously with 4D flow MRI. The phantom has the potential to be used to optimize and standardize the 4D flow MR protocol parameters for clinical applications.

Keywords: Flow, Cardiovascular, Aorta, Aortic Valve, Unicuspid Aortic Valve, Bicuspid Aortic Valve, 4D Flow, 4D Flow MRI

Motivation: Unicuspid Aortic Valve (UAV) is an important subset of Bicuspid Aortic Valve. We identified a need to include wall shear stress in a larger pre- and post-operative cohort of UAV patients.

Goal(s): Our goal was to evaluate the effects of the Ross procedure for UAV patients, specifically evaluating hemodynamic parameters, peak systolic velocity and wall shear stress (WSS), in the ascending aorta (AAo).

Approach: We retrospectively examined these hemodynamic parameters in thirteen patients before and after UAV replacement.

Results: We found that both peak systolic velocity and WSS in the AAo decreased significantly post-operatively, indicating successful restoration of aortic 3D blood flow dynamics.

Impact: Unicuspid Aortic Valve (UAV) is a rare yet important subset of Bicuspid Aortic Valve (BAV). Here, we analyze the hemodynamics of a larger pre- and post-operative UAV cohort with the inclusion of wall shear stress (WSS). 

Keywords: Flow, Cardiovascular, Image Reconstruction

Motivation: 4D Flow MRI is limited by long scan times. Accelerated imaging by compressed sensing leads to long reconstruction times. 

Goal(s): The goal of this work was to evaluate a deep learning-based method (FlowVN) for reconstruction of pseudo-randomly heavily undersampled Cartesian 4D Flow. 

Approach: In this study, we explored FlowVN for the reconstruction of different acceleration factors and did velocity analysis of 4D Flow MRI. 

Results: The results show that FlowVN rapidly reconstructs undersampled 4D Flow images with good accuracy for average and peak velocity in the ascending aorta even at high acceleration factors. 

Impact: High-quality rapid reconstruction of highly undersampled 4D Flow MRI with deep learning has the potential to substantially facilitate the use of 4D Flow MRI in the clinical routine.

Keywords: Flow, Cardiovascular

Motivation:  To survey blood flow alteration after EVAR using 4D Flow MRI.

Goal(s): To reveal how the degree of energy loss occur, and how interact with other parameters. 

Approach: Velocity, volume, reflux ratio, and degree of energy loss at proximal and within the treatment segment were analyzed. Each value gained pre and post EVAR were statistically compared, and the relation between energy loss and pulse wave velocity were evaluated.

Results:  After EVAR, the antegrade velocity and the volume increased at the aneurysmal orifice level, and the degree of energy loss through the treatment segment increased. 

Impact: EVAR facilitates aortic stiffness and increases the antegrade velocity and volume at treatment area. These alterations were considered as the main factors promoting further energy loss, which may concern with cardiac afterload.  

Keywords: Flow, Cardiovascular

Motivation: Background velocity errors caused by eddy currents and mechanical oscillations in PC-MRI are a significant source of measurement error for which prospective corrections remain unavailable.

Goal(s): To prospectively design spoiler gradient waveforms that reduce background velocity errors to levels generally considered irrelevant.

Approach: A gradient optimization toolbox (GrOpt) was used in conjunction with a gradient impulse response to design error-minimizing waveforms.  They were tested in a phantom and in 10 volunteers.

Results: Background velocity errors were reduced by 84±10.4% with the gradient spoiler optimization and to levels below a clinically relevant threshold (0.4% Venc) in 96% of subjects.

Impact: We used a gradient optimization (GrOpt) toolbox and the gradient impulse response function to prospectively design spoiler gradient waveforms that reduce background velocity errors in PC-MRI to levels below a clinically relevant threshold in 96% of subjects.

Keywords: Flow, Cardiovascular, Analysis/Processing, Aortic Stenosis, Blood Vessels, Cardiovascular, Data Analysis, Data Processing, Flow, In Silico, Machine Learning/Artificial Intelligence, Simulations, Velocity

Motivation: Imaging stenotic aortic valves using cine 2D and 4D Flow-MRI is compromised by flow-related image artefacts, making estimation of the effective orifice area challenging.

Goal(s): To estimate aortic valve orifice area and inlet velocity profiles from 2D PC-MRI slices, acquired downstream of the aortic valve.

Approach: Synthetic 2D PC-MRI slices were generated from personalized synthetic flow simulations of pulsatile flow in realistic stenosed aortae.
Two U-Nets were trained to predict valvular orifice and inlet velocity profiles.

Results: This work demonstrates that classification of aortic stenosis and prediction of peak systolic velocities from synthetic 2D PC-MRI slices acquired downstream of the valve is possible.

Impact: Our work indicates that aortic valvular orifice area and inlet velocity profiles can indeed be predicted from a few cine 2D PC-MRI slices acquired downstream of the valve. The approach potentially enables time-efficient standard imaging using a few breathheld scans as available on all clinical MR systems.

Keywords: Flow, Velocity & Flow, Aortic disease

Motivation: Hemodynamics and circulating biomarkers could offer urgently needed improved risk-stratification in individuals with aortic dilation.

Goal(s): To explore correlations between hemodynamics markers measured with 4D Flow MRI and circulating biomarkers in aortic dilation individuals with tricuspid aortic valves.

Approach: Wall shear stress (WSS) parameters were assessed from 4D flow MRI in cases with dilation and controls. Blood plasma samples were used to quantify the inflammation biomarker IL-6 and several extracellular matrix biomarkers including collagen type I α1 chain (COL1α1).

Results: IL-6 correlated to time-averaged WSS (r=0.54, p<0.001), whereas COL1α1 correlated to the oscillatory shear index (r=0.61, p<0.001).

Impact: The observed correlations between 4D Flow MRI-derived wall shear stress and circulating biomarkers of inflammation and collagen synthesis raises the intriguing possibility that altered aortic hemodynamics causes biomarker leakage from the aortic tissue into the circulation.

Keywords: Flow, Velocity & Flow, 4D flow MRI, Advance flow biomarkers, Aortic valve

Motivation: Congenital bicuspid aortic valve (BAV) effects and its associated lesions on hemodynamic alterations, leading to aortic root dilation as the most severe form of aortopathy, remains unexplored. 

Goal(s): We aimed to examine the relationship between BAV phenotypes, considering various regurgitation severities, and aortic root dilation by analyzing abnormal wall shear stress (WSS) and normalized flow displacement (NFD) related to retrograde and anterograde flow jets. 

Approach: We utilized time-resolved three-dimensional phase contrast MRI to measure these velocity-derived flow biomarkers in healthy and BAV cohorts. 

Results: WSS proved a more sensitive and reliable metric than NFD in distinguishing BAV from healthy controls. 

Impact: Validating and quantifying advanced flow biomarkers in the aortic root due to its different biomechanical properties could enhance risk assessment, prognosis, and prevention of clinical complications in BAV patients with secondary valvular insufficiency.

Keywords: Flow, Cardiovascular

Motivation: Phase-contrast (PC) MRI evaluates blood flow in cardiovascular disease. However, the prolonged scan times limit its efficiency.

Goal(s): We sought to develop a highly accelerated PC technique based on omitting high-frequency k-space regions along the phase encoding direction.

Approach: A deep learning k-space restoration and enhancement strategy for training (KREST) was developed to improve resolution while maintaining phase information. KREST was trained and tested with PC images from 1600 patients.

Results: In a prospective study of 16 patients, KREST reduced breath-hold time relative to parallel imaging (19 vs 6 s).

Impact: Our k-space restoration and enhancement strategy enables resolution-enhancement while providing k-space data consistency. Deep learning accelerated phase-contrast imaging showed similarly accurate quantification of peak mean velocity to a standardized parallel imaging method. 

Keywords: Flow, Valves, regurgitation

Motivation: MRI is not capable of measuring tricuspid regurgitant jets, required for diastolic function evaluation.

Goal(s): Using a dynamic slice plane which tracked the tricuspid valve, we studied patients with suspected tricuspid regurgitation. 

Approach: The valve-tracking phase-contrast sequence used deep learning to automatically prescribe a phase-dependent slice plane. 

Results: Tricuspid regurgitation was measured and tricuspid regurgitant jets could be visualized in patients.

Impact: A new automated 2D valve-tracking phase-contrast approach permits visualization of tricuspid regurgitant jets.  This will enable evaluation of diastolic function by MRI.

Keywords: Flow, Cardiovascular, 4D flow MRI, rotational flow, vorticity

Motivation: Rotational flow within the aorta has been associated with cardiovascular disease and ventricular-vascular coupling, but no study has investigated its direct correlation with LV function.

Goal(s): This study aims to explore whether the assessment of rotational flow can effectively identify left ventricle dysfunction between youth and adult type 2 diabetes (T2D) subjects.  

Approach: Correlation between global function and strain changes by CMR and rotational flow indices and pulse wave velocity by 4D flow MRI were evaluated.

Results: Adult T2D had significant decrease in vorticity indices with CMR biomarkers, while showing less significance in CMR biomarkers compared to youth T2D.

Impact: Vorticity indices are potential biomarkers to assess LV dysfunction and understand ventricular-vascular coupling even in the absence of geometric anomalies within the aorta. A comprehensive examination of rotational flow and LV function is required.

Keywords: Flow, Quantitative Imaging

Motivation: To establish accurate measures in predicting prognosis in patients with sigmoid HCM from their 4D-flow-derived hemodynamics.

Goal(s): We explored the association between aortic stiffness and sigmoid HCM through measuring peak wall shear stress in the three ascending aorta segments: proximal, mid, and descending.

Approach: We recruited 40 subjects and divided them into control and affected groups and then compared ascending aorta 4D flow hemodynamics.

Results: Maximum diameters and peak flow velocity of ascending aorta were higher in the affected group.

Impact: Assessing aortic hemodynamics with 4D Flow CMR in patients with hypertrophic cardiomyopathy will help us understand the relationship between aortic stiffness and left ventricular hypertrophy, which is associated with outcomes in hypertrophic cardiomyopathy patients.