Keywords: Data Acquisition, Low-Field MRI, MR value

Motivation: Conventional fixed duration acquisitions can result in patient-dependent image quality, leading to either unnecessarily long scan times or insufficient quality across patients.

Goal(s): We propose an inline automatic quality control based on signal-to-noise ratio (SNR) to achieve consistent diagnostic image quality and apply it to 2D phase-contrast flow MRI.

Approach: We designed a closed-loop feedback framework between image reconstruction and data acquisition to automatically stop the acquisition when a target SNR is achieved. Ten healthy volunteers and one patient were imaged at 0.55T.

Results: Deployed inline, the SNR stop threshold saved 53% of the scan duration, with a variation of ±1min across subjects.

Impact: The inline automatic quality control enables a subject-specific optimized scan time while ensuring consistent diagnostic image quality. The distribution of automated stopping times across the population revealed the value of a subject-specific scan time.

Keywords: Flow, Velocity & Flow, Deep-Learning

Motivation: 4D Flow MRI enables comprehensive hemodynamic assessments, but its clinical usage is hindered by long scan times.

Goal(s): To enable a 2-point velocity encoded 4D flow MRI by using deep-learning to estimate the missing two velocity vector-components, reducing scan time by 50%.

Approach: Convolutional neural networks (CNNs) were trained with a single velocity vector-component as input data to generate a 3D velocity vector field (complete 4D flow dataset). CNN performance was evaluated in peak velocity, net and peak flow, and Qp/Qs compared to standard 4D flow MRI.

Results: AI-derived 4D flow MRI showed strong-to-excellent agreement to standard 4D flow MRI across all comparisons.

Impact: This technique enables reduction of 4D flow MRI scan time and data acquired by 50%. Future work will focus on coupling our method with conventional imaging acceleration techniques to achieve greater scan time reductions and/or improvements in temporal resolution.

Keywords: Flow, Low-Field MRI

Motivation: Free-breathing (FB) real-time phase contrast (RT-PC) MR is very useful to resolve the beat-by-beat variations and for patients for whom breath-holding poses a challenge; however its feasibility remains to be tested at low-field. 

Goal(s): To develop a FB RT-PC MR technique on a clinical wide-bore 0.55T MR scanner with reduced gradient performance. 

Approach: FB RT-PC was developed using a dual-density spiral readout with a modified golden-angle rotation strategy and compressed sensing reconstruction. Flow quantifications were compared with the conventional BH segmented PC approach.

Results: Our proposed method yielded flow measurements of comparable accuracy and effectively captured the peak flow dynamics at low-field.

Impact: The proposed RT PC MR technique for low-field systems could enable flow imaging for patients with arrhythmias, critical illnesses, or claustrophobia, potentially making cardiac MRI more accessible and patient-friendly in a variety of clinical settings.

Keywords: Heart Failure, Blood vessels, COPD, Hemodynamics, Heart Failure, 4D Flow

Motivation: Chronic obstructive pulmonary disease (COPD) and emphysema are associated with hemodynamic changes in the pulmonary vasculature, possibly related to increased intra-thoracic pressure during expiration, altering venous return into the thorax.

Goal(s): Assess the association of respiratory dysfunction with hemodynamic parameters of venous return. 

Approach: Velocity, kinetic energy, and stasis in the superior vena cava and inferior vena cava were quantified with 4D Flow MRI in 72 subjects across the COPD spectrum in an ongoing study (SPIROMICS HF).

Results: Our results show an association of impaired (reduced) venous return to the thorax with airway obstruction as assessed by spirometry.

Impact: This study demonstrates impaired venous return in subjects with COPD, which warrant further investigations into the cardiopulmonary interactions of right heart flow in COPD and its potential value as a noninvasive marker of disease progression.

Keywords: Synthetic MR, Velocity & Flow, Simulation

Motivation: Blood flow turbulence and velocity quantification with 4D flow MRI is sensitive to imaging parameters such as V_enc and undersampling factor, but their impact has not been clearly quantified yet.

Goal(s): Use synthetic 4D flow MRI data to determine the impact of encoding directions and strengths for turbulence and velocity quantification.

Approach: Personalized synthetic 4D flow MRI data are simulated for a given set of encoding velocity strengths and directions assuming a fixed scan budget of 15 minutes. 

Results: Turbulent kinetic energy shows large variations depending on the encoding strategy, while velocity magnitudes are marginally affected by the choice.

Impact: Based on the simulations, a 7-point dual- approach represents an efficient approach for  accurate velocity and turbulence quantification. However, the low-V_enc needs to be tuned to be sensitive to the ranges of expected intra-voxel standard deviations.  

Keywords: Flow, Cardiovascular

Motivation: Cardiovascular-related deaths are increasing in athletes, which necessitates a deeper understanding of hemodynamics.

Goal(s): Our goal was to use 4D flow MRI to assess athletes' cardiac and aortic hemodynamics and their links to myocardial fibrosis and cardiac remodeling risks.

Approach: Cardiac MRI was performed on 213 athletes and 32 matched controls. Hemodynamic parameters were measured and analyzed against myocardial fibrosis and cardiac remodeling risks.

Results: Athletes exhibited increased wall shear stress and energy loss. Hemodynamics differed markedly between groups. Our prediction model reliably displayed the potential of 4D flow in assessing cardiac risks.

Impact: Exercise can elevate aortic wall shear stress and energy loss. Four-dimensional flow cardiac MRI may allow predicting myocardial fibrosis or cardiac remodeling risks in athletes, thus informing clinicians of adverse event associations and guiding follow-up adjustments.

Keywords: Flow, Cardiovascular

Motivation: Hepatic fibrosis impacts systemic blood flow.

Goal(s): In this rabbit study, we tracked aortic hemodynamics during fibrosis development. 

Approach: Thirty rabbits underwent biweekly 4D cardiac magnetic resonance (CMR) scans for 14 weeks post-bile duct ligation (BDL). 

Results: Results revealed significant increases in wall shear stress, energy loss, and most aortic parameters at each plane by the 2nd week after bile duct ligation (BDL), peaking at the 6th week (p < 0.05). Liver fibrosis appeared at the 2nd, 4th, and 6th weeks post-BDL, corresponding to grades F2, F3, and F4. Plane 2's relative pressure difference strongly correlated with fibrosis severity (R=0.86).

Impact: The occurrence of liver fibrosis could increase WSS, EL, RPD and other hemodynamic parameters of aorta as early as the second week following BDL, which can be detected by 4D flow MRI.

Keywords: Flow, Heart, Flow, Fat, Whole-heart, Congenital Heart Disease

Motivation: Free-running radial 4D flow has been shown to enable accurate whole-heart quantification and visualization of hemodynamics. However, unsuppressed fat signal can lead to artifacts, which may compromise image quality and cause errors in flow quantification.

Goal(s): Our study therefore aims to reduce fat signal in radial 4D flow MRI.

Approach: We integrated a novel b-splines iteratively optimized water-excitation RF pulse generated with a previously described framework (OptiPulse) into a radial 4D flow sequence to suppress the signal from fat.

Results: We successfully integrated OptiPulse in radial 4D flow to suppress fat signal and demonstrated comparable quantitative flow assessment to non-fat-suppressed 4D flow.

Impact: The integration of b-splines iteratively optimized water-excitation RF pulses (OptiPulse) into a free-running radial whole-heart 4D flow sequence leads to significantly reduced fat-signal in a promising step towards more robust hemodynamic assessment in patients with large amounts of adipose tissue. 

Keywords: Flow, Cardiovascular, Pulmonary Hypertention

Motivation: There is a lack of noninvasive methods to differentiate between different Pulmonary Hypertension Groups/types. Such differentiation is clinically critical because treatments of one group can be harmful to another. 

Goal(s): We investigated a new noninvasive 4D Flow MRI-based method to differentiate between Pulmonary Arterial Hypertension (PAH) and Pulmonary Venous Hypertension (PVH), currently distinguished conclusively only through invasive catheterization.

Approach: Our study focused on analyzing 3D vortex flow and its energetics in the left pulmonary artery (LPA) using  4D Flow MRI. 

Results: We found significant differences in vortex characteristics between PVH and PAH patients, with PVH showing larger vortex cores and higher energetics.

Impact: These findings suggest the potential of LPA vortex flow analysis as a noninvasive diagnostic marker for distinguishing between PAH and PVH and possibly assessing disease severity.

Keywords: Flow, Velocity & Flow, Aorta, Pulse wave velocity, Arterial stiffness

Motivation: To measure 3D pulse wave velocity (PWV) for the investigation of arterial stiffness on a local scale which could benefit patients with aortic disease.

Goal(s): To calculate aortic 3D PWV with the flow-area method and compare with the global method.

Approach: The flow-area method for PWV calculation is applied to 4D flow data combined with automatically-segmented 4D balanced SSFP scans along the thoracic aorta.

Results: This measurement is feasible and shows the expected trend of increasing PWV along the length of the aorta. Averaged values corresponded moderately with the global method.

Impact: Increased arterial stiffness measured by PWV is a well-established risk factor for adverse cardiac events. Development of novel MRI technology to locally map arterial stiffness may allow for improved risk-stratification in cardiovascular disease and ultimately guide therapy.

Keywords: Valves, Quantitative Imaging, Mitral Valve Regurgitation, Hemodynamic Force, Novel Biomarker

Motivation: This study aims to address shortcomings in assessing mitral regurgitation (MR) by introducing left ventricular hemodynamic force (HDF) as a novel biomarker.

Goal(s): The primary objective of this study is to assess HDF's reliability through 4D flow MRI in distinguishing MR patients from healthy controls and stratifying severity, offering a more precise diagnostic tool.

Approach: This retrospective analysis used 4D flow MRI data to compute HDF in three directions, evaluating its correlation with MR.

Results: MR patients exhibit significantly altered HDF compared to controls. The HDF: peak systolic base-apex, E-wave inferior-anterior, E-wave base-apex, and peak diastolic septal-lateral suggest their potential as mitral biomarkers.

Impact: The introduction of hemodynamic force as a novel biomarker opens new research avenues, potentially reshaping cardiac non-invasive diagnostic techniques. This study may transform the assessment of mitral regurgitation, offering benefits to clinicians for early intervention and proper patient management.

Keywords: Flow, Heart, Athlete; Pulmonary artery; 4D flow

Motivation: Long-term intense training in athletes can lead to pathological cardiac remodeling (CR) and potential myocardial fibrosis (MF), raising cardiovascular risks.

Goal(s): Employ 4D flow MRI to study pulmonary arterial hemodynamics in athletes and explore correlations with CR and MF.

Approach: Scanned 121 athletes and 21 controls using 3 T MRI scanner; 4D flow data analysis on CVI42; built machine learning models for differentiation based on cardiovascular conditions.

Results: Found significant associations between the altered pulmonary arterial hemodynamics parameters and CR and/or MF. Machine learning models identified athletes with cardiac anomalies.

Impact: We indicated that exercise can induce remodeling of the pulmonary circulation in athletes. The evaluation of pulmonary arterial 4D flow hemodynamics parameters can be beneficial for clinical follow-up of athletes.

Keywords: Flow, Cardiovascular, Analysis/Processing, Data Processing, Flow, Heart, In Silico, Modelling, Simulation/Validation, Simulations, Velocity & Flow

Motivation: 4D-Flow CMR allows to analyze 3D blood flow patterns in the left ventricle, however it requires time-consuming acquisitions and complex pre and post-processing.

Goal(s): The objective is to develop a method to analyze blood flow patterns in the left ventricle without these disadvantages. 

Approach: Using Cine-MRI and patient-specific modelling techniques, we introduced a new and semi-automated method to simulate the blood flow inside the left ventricle. Accuracy of the developed method was evaluated by comparing the results to 4D-Flow CMR analysis performed on one healthy subject.

Results: Both techniques showed similar blood flow patterns and comparable hemodynamics parameters.

Impact: This patient-specific model is a relatively simple and time-saving method allowing blood flow analysis in the left ventricle based on Cine-MRI acquisition. It may be used to characterize blood flow in patients with heart disease at rest or under stress.

Keywords: Flow, Data Processing, Image reconstruction

Motivation: Scan times for clinical 4D Flow MRI are still around 5-10 mins, which is too long for ideal integration in clinical practice.

Goal(s): To investigate the possibility to reduce scan time by reconstructing three-directional velocity without the acquisition of reference scan in cardiac applications.

Approach: Training a conditional generative adversarial network (cGAN) to estimate the reference scan from the three-velocity encoded scan segments.

Results: Correlation coefficients for the pulmonary and systemic flow volumes and for maximum velocities were higher than 0.99, showing an excellent agreement between the cGAN-enabled referenceless 4D Flow MRI and conventional 4D flow MRI, thus potentially reducing scan time.

Impact: By reconstructing the three-directional velocity without the reference scan it is possible reduce scan time of 4D Flow MRI, alleviating costs and patient discomfort, which especially is important for elderly and impaired subjects.

Keywords: Flow, Velocity & Flow, COPD, Lung, hemodynamics

Motivation: Previous studies have suggested impaired cardiovascular function in patients with chronic obstructive pulmonary disease (COPD). However, the association between lung disease severity and the degree of cardiac hemodynamic impairment is not well understood. 

Goal(s): We aimed to characterize the hemodynamic changes seen in COPD in order to gain insight into the mechanisms relating COPD and heart failure.

Approach: We analyzed 4D-flow derived hemodynamics in a preliminary sample of 72 participants from the SPIROMICS-HF study.

Results: We found that impaired hemodynamics in the right atrium (blood flow kinetic energy and velocity) and pulmonary artery (flow stasis and velocity) are associated with greater COPD severity.

Impact: This study represents a key step in exploring the cardiopulmonary hemodynamic interaction in chronic obstructive pulmonary disease.

Keywords: Vessel Wall, Cardiovascular, IgG4-related cardiovascular disease, cardiac magnetic resonance, coronary wall contrast enhancement, IgG4-RD responder index

Motivation: The coronary wall involvement in IgG4-related disease (IgG4-RD) is overlooked in conventional imaging, more sensitive approach is needed.

Goal(s): To investigate the feasibility of quantifying contrast enhancement (CE) to detect coronary involvement in IgG4-RD and the influence on disease activity assessment based on the IgG4-RD Responder Index (RI).

Approach: The coronary artery wall images of the IgG4-RD, systemic lupus erythematosus  (SLE) patients and healthy subjects were analyzed and IgG4-RD-RI scores were collected for correlations analysis.

Results:  Coronary artery wall CE can be a direct marker of coronary artery injury and may improve disease activity assessment in IgG4-RD.

Impact: Coronary artery wall CE can serve as an objective indicator of disease activity. Considering coronary artery wall CE in the IgG4-RD-RI scoring has the potential to enhance the comprehensiveness of disease activity assessment and enable more appropriate treatment decisions.

Keywords: Vessel Wall, Cardiovascular, Coronary artery disease

Motivation: Advancements in coronary MR angiography (CMRA) have optimized the visualization of coronary anatomical structures, subsequently enhancing coronary artery stenosis, dilation, and certain anatomical variations^【1-3】.Current meta-analysis shows that coronary MRA has a 79% accuracy rate for detecting obstructive CAD compared with gold-standard ICA

Goal(s): Thus,the combining wall imaging may potentially enhances the diagnosis performance of coronary artery stenosis

Approach: compare diagnostic performance of 3D -non enheanced CMRA with combined wall imaging

Results: Our study suggest that combining these two techniques may improve the accuracy of coronary stenosis.

Impact: CMRA has unique diagnostic in detecting coronary artery stenosis, and the improvement of diagnostic accuracywill further promote its clinical application.

Keywords: Vascular, Machine Learning/Artificial Intelligence

Motivation: To understand how closely aortic morphology is associated with aortic wall properties.

Goal(s): (1) To correlate aortic shape using morphometrics to aortic stiffness indexed by pulse wave velocity
(2) To correlate shape to regional aortic wall shear stress

Approach: We use atlas-based shape analysis (morphometrics) to generate principal modes of shape variation, and then correlate modes of shape variation with pulse wave velocity to check their association. We also generate deep-learning based WSS using aortic shapes defined as point clouds forming the input to the neural network.

Results: Aortic shapes were moderately associated with aortic stiffness as well as regional wall shear stress.

Impact: Studying aortic morphological remodeling patterns may provide key insight into underlying disease processes that involve changes in aortic material wall properties and regional flow characteristics.

Keywords: Vascular, Cardiovascular

Motivation: Abdominal Aortic Aneurysms (AAAs) are common, and rupture has >80% mortality. The standard of care is regular surveillance and repair when maximum diameter thresholds are reached. Many ruptures occur before AAA reach these thresholds at surveillance.

Goal(s): The goal of this prospective study was to determine if AAA wall contrast kinetics using DCE MRI, presumably associated with inflammatory microvasculature, independently predict progression.

Approach: 23 AAA patients were followed over a mean follow-up interval of 14±6 months.

Results: K^trans was significantly associated with progression after controlling for AAA maximum diameter. This suggests that DCE MRI may provide useful information regarding future AAA progression.

Impact: Contrast kinetics in AAA wall tissue assessed by DCE MRI may be useful for improving AAA risk stratification.

Keywords: Vessel Wall, Atherosclerosis

Motivation: Significant atherosclerotic stenosis or occlusion in the distal carotid artery may induce diffuse wall thickening (DWT) in the upstream arterial wall. 

Goal(s): This study aimed to assess the association of atherosclerotic steno-occlusive diseases in the distal internal carotid artery (ICA) with DWT in the upstream ipsilateral ICA.

Approach: Individuals with atherosclerotic stenosis in the distal ICA, detected by carotid MR vessel wall imaging, were enrolled. 

Results: Significant correlations were found between distal ICA stenosis and DWT in the petrous ICA, DWT severity, the longitudinal extent of DWT in the ICA, enhancement in the petrous ICA) and enhancement degree. 

Impact: Diffuse wall thickening is a common secondary change in atherosclerotic steno-occlusive disease in the intracranial carotid. This phenomenon constitutes a confounding factor in the distinction between atherosclerosis and inflammatory vasculopathies, and could be reversed after alleviated atherosclerotic stenosis.