Four-dimensional Cardiac Magnetic Resonance Research Articles

Left atrial haemodynamic evaluation using 4D flow cardiac magnetic resonance imaging: application to hypertension and hypertrophic cardiomyopathy

Abstract Introduction Changes in left atrial (LA) hemodynamics have been suggested reflective of left ventricular (LV) disease progression. Kinetic energy (KE), viscous energy loss, and vorticity could be promising indices for the assessment of left atrial dynamics by time resolved four-dimensional cardiac magnetic resonance (4D flow CMR). Hypertrophic cardiomyopathy (HCM) patients are at risk of developing mitral regurgitation and left ventricular outflow tract obstruction, with poor outcome (1). Hypertensive myocardial remodelling has been suggested to be due to complex flow and tissue interactions leading to hypertrophy and diastolic dysfunction (2). Early detection of altered LA hemodynamic abnormalities may help non-invasive assessment, improving their long-term outcome (3). Purpose Quantitative and qualitative evaluation of left atrial hemodynamic metrics by 4D flow CMR in a cohort of HCM patients, hypertensive patients, and healthy controls with no known cardiovascular disease. Methods Eighteen HCM patients (50.0 [±18.2] years, 8 females), twenty-one hypertensive patients (55.2 [±6.2] years, 11 females), and seventeen controls (36.7 [±12.8] years, 1 female) underwent 4D flow CMR. Both patient groups had significantly higher LV-indexed mass, end-diastolic volume, and end-systolic volumes (P < 0.05). A semi-automated pipeline was used to segment the LA including pulmonary inflow and mitral outflow tracts using phase contrast magnetic resonance images derived from the 4D flow acquisition's phase and magnitude images. LA KE, viscous energy loss and vorticity were computed throughout the cardiac cycle. Results The HCM and hypertensive groups demonstrated significantly higher average KE integrated across the cardiac cycle (1.58 ± 0.79 and 1.32 ± 0.50 mJ respectively) compared to controls (1.20 ± 0.47 mJ) (P < 0.05), with the systolic curve in HCM showing the highest peak KE. Qualitatively, KE in the diastolic portion of the cardiac cycle appeared less variable between groups (Figure 1). Vorticity in HCM showed different configurations with loss of the central atrial vortex core (Figure 2). Viscous energy loss was also significantly higher in HCM patients confirming the increase in energy loss (Figure 2). Average KE across the cardiac cycle highly correlated with LA volume and pulmonary capillary wedge pressure calculated by a previously published regression method (4) (Pearson correlation: r= 0.76 and 0.71 respectively P < 0.05). There were also significant correlations with cardiac metrics such as indexed end-diastolic and indexed end-systolic volumes (Pearson correlation: r= 0.54 and 0.52 respectively P < 0.05) as well as indexed LV mass (r= 0.59 P < 0.05). Conclusion Hemodynamic metrics derived from 4D flow CMR may be valuable in establishing valuable predictive metrics of ventricular function. Integration of 4D flow MRI in clinical workflows could provide information that may be indicative of pathological onset before abnormal remodelling.Kinetic energy and viscous energy lossParticle pathlines and vorticity

A Segmental Approach from Molecular Profiling to Medical Imaging to Study Bicuspid Aortic Valve Aortopathy.

Bicuspid aortic valve (BAV) patients develop ascending aortic (AAo) dilation. The pathogenesis of BAV aortopathy (genetic vs. haemodynamic) remains unclear. This study aims to identify regional changes around the AAo wall in BAV patients with aortopathy, integrating molecular data and clinical imaging. BAV patients with aortopathy (n = 15) were prospectively recruited to surgically collect aortic tissue and measure molecular markers across the AAo circumference. Dilated (anterior/right) vs. non-dilated (posterior/left) circumferential segments were profiled for whole-genomic microRNAs (next-generation RNA sequencing, miRCURY LNA PCR), protein content (tandem mass spectrometry), and elastin fragmentation and degeneration (histomorphometric analysis). Integrated bioinformatic analyses of RNA sequencing and proteomic datasets identified five microRNAs (miR-128-3p, miR-210-3p, miR-150-5p, miR-199b-5p, and miR-21-5p) differentially expressed across the AAo circumference. Among them, three miRNAs (miR-128-3p, miR-150-5p, and miR-199b-5p) were predicted to have an effect on eight common target genes, whose expression was dysregulated, according to proteomic analyses, and involved in the vascular-endothelial growth-factor signalling, Hippo signalling, and arachidonic acid pathways. Decreased elastic fibre levels and elastic layer thickness were observed in the dilated segments. Additionally, in a subset of patients n = 6/15, a four-dimensional cardiac magnetic resonance (CMR) scan was performed. Interestingly, an increase in wall shear stress (WSS) was observed at the anterior/right wall segments, concomitantly with the differentially expressed miRNAs and decreased elastic fibres. This study identified new miRNAs involved in the BAV aortic wall and revealed the concomitant expressional dysregulation of miRNAs, proteins, and elastic fibres on the anterior/right wall in dilated BAV patients, corresponding to regions of elevated WSS.

Molecular and haemodynamic interplay in bicuspid aortic valve aortopathy: segmental differences across the aortic circumference

Abstract Background Bicuspid aortic valve (BAV) patients develop ascending aortic (AAo) dilation. The pathogenesis of BAV-aortopathy (genetic vs. hemodynamic) remains unclear. Purpose To identify regional changes around the AAo wall in BAV patients with aortopathy integrating clinical imaging and molecular data. Methods BAV patients with aortopathy (n=20) were recruited prospectively to surgically collect aortic tissue and perform four-dimensional cardiac magnetic resonance (CMR) scans. Molecular markers were measured analysing the tissue biopsies (n=15) and wall shear stress (WSS) across the AAo circumference was calculated from the 4D CMR data (n=11 patients, and n=7 additional healthy volunteers for comparison). Dilated (anterior/right) vs. non-dilated (posterior/left) circumferential segments were profiled for whole genomic microRNAs (Next Generation RNA-Sequencing, miRCURY LNA PCR), proteins content (Tandem Mass Spectrometry) and elastin fragmentation and degeneration (histomorphometric analysis). Picture 1 summarises the study approach (including a map of the AAo divided in the following segments: A=anterior, AR=anterior-right, PR=posterior-right, P=posterior, PL=posterior-left, AL=anterior-left). Results Integrated bioinformatic analyses of RNA-sequencing and proteomic datasets identified 5 microRNAs (miR-128-3p, miR-210-3p, miR-150-5p, miR-199b-5p, and miR-21-5p) differentially expressed across the AAo circumference. Among them, three miRNAs (miR-128-3p, miR-150-5p, and miR-199b-5p) were predicted to have an effect on eight common target genes, whose expression was dysregulated according to proteomic analyses and involved in vascular endothelial growth factor signalling, hippo signaling and arachidonic acid pathway. Decreased elastic fibre levels and elastic layer thickness were observed in the dilated segments in the histomorphometric analysis. Increased WSS and flow-velocity, helical streamlines and asymmetrical flow were observed at the anterior/right wall in asymmetrically and symmetrically dilated patients (the latter exhibiting higher WSS), compared to healthy volunteers. Conclusion This study has newly revealed concomitant expressional dysregulation of miRNAs, proteins, and elastic fibres on the anterior/right wall in dilated BAV patients, corresponding to regions of elevated WSS, contributing to advance the understanding of the interplay of genetic and hemodynamic factors underpinning BAV aortopathy. Funding Acknowledgement Type of funding sources: Foundation. Main funding source(s): British Heart Foundation and Above & Beyond

Assessment of flow pattern of right ventricle outflow and pulmonary arteries in surgically corrected tetralogy of Fallot patients by four-dimensional cardiac magnetic resonance flow

BackgroundThe most common post-surgical complication of tetralogy of Fallot (TOF) is pulmonary regurgitation (PR) which can lead to right ventricle (RV) dysfunction/failure. Cardiac magnetic resonance (CMR) is the imaging modality of choice to follow-up a repaired TOF. However, the conventional two-dimensional phase-contrast (2D-PC) flow usually underestimates PR as well as the pulmonary peak systolic velocity (PSV). Recently, four-dimensional (4D) CMR flow is introduced for more accurate quantitative flow assessment. This work aimed to compare between 4D-CMR and 2D-PC flow across the main (MPA), right (RPA), and left (LPA) pulmonary arteries (PAs) in surgically corrected TOF patients.ResultsThis study was conducted on 20 repaired TOF patients (range 3–9 years, 50% males). All patients had CMR exam on 1.5T scanner. 4D-CMR and 2D-PC flows were obtained at the proximal segments of the MPA, RPA, and LPA. The stroke volume index (SVI), regurgitation fraction (RF), and PSV measured by 4D-CMR were compared to 2D-PC flow. The SVI across the PAs was nearly similar between both methods (P = 0.179 for MPA, 0.218 for RPA, and 0.091 for LPA). However, the RF was significantly higher by 4D-CMR in comparison to 2D-PC flow (P = 0.027 for MPA, 0.039 for RPA, and 0.046 for LPA). The PSV as well was significantly higher by 4D-CMR flow (P = 0.003 for MPA, < 0.001 for RPA, and 0.002 for LPA). The Bland-Altman plots showed a good agreement between 4D-CMR and 2D-PC flow for the SVI, RF, and PSV across the pulmonary arteries.ConclusionA good agreement existed between the two studied methods regarding pulmonary flow measurements. Because of its major advantage of performing a comprehensive flow assessment in a shorter time, 4D-CMR flow plays an important role in the assessment of patients with complex CHD especially in the pediatric group.

Erratum to: Decreased Diastolic Ventricular Kinetic Energy in Young Patients with Fontan Circulation Demonstrated by Four-Dimensional Cardiac Magnetic Resonance Imaging.

Erratum to: Decreased Diastolic Ventricular Kinetic Energy in Young Patients with Fontan Circulation Demonstrated by Four-Dimensional Cardiac Magnetic Resonance Imaging.

Decreased Diastolic Ventricular Kinetic Energy in Young Patients with Fontan Circulation Demonstrated by Four-Dimensional Cardiac Magnetic Resonance Imaging

Four-dimensional (4D) flow magnetic resonance imaging (MRI) enables quantification of kinetic energy (KE) in intraventricular blood flow. This provides a novel way to understand the cardiovascular physiology of the Fontan circulation. In this study, we aimed to quantify the KE in functional single ventricles. 4D flow MRI was acquired in eleven patients with Fontan circulation (median age 12 years, range 3–29) and eight healthy volunteers (median age 26 years, range 23–36). Follow-up MRI after surgical or percutaneous intervention was performed in 3 patients. Intraventricular KE was calculated throughout the cardiac cycle and indexed to stroke volume (SV). The systolic/diastolic ratio of KE in Fontan patients was similar to the ratio of the controls’ left ventricle (LV) or right ventricle (RV) depending on the patients’ ventricular morphology (Cohen´s κ = 1.0). Peak systolic KE/SV did not differ in patients compared to the LV in controls (0.016 ± 0.006 mJ/ml vs 0.020 ± 0.004 mJ/ml, p = 0.09). Peak diastolic KE/SV in Fontan patients was lower than in the LV of the control group (0.028 ± 0.010 mJ/ml vs 0.057 ± 0.011 mJ/ml, p < 0.0001). The KE during diastole showed a plateau in patients with aortopulmonary collaterals. This is to our knowledge the first study that quantifies the intraventricular KE of Fontan patients. KE is dependent on the morphology of the ventricle, and diastolic KE indexed to SV in patients is decreased compared to controls. The lower KE in Fontan patients may be a result of impaired ventricular filling.

Application of hyperelastic-based active mesh model in cardiac motion recovery

Considering the nonlinear hyperelastic or viscoelastic nature of soft tissues has an important effect on modeling results. In medical applications, accounting nonlinearity begets an ill posed problem, due to absence of external force. Myocardium can be considered as a hyperelastic material, and variational approaches are proposed to estimate stiffness matrix, which take into account the linear and nonlinear properties of myocardium. By displacement estimation of some points in the four-dimensional cardiac magnetic resonance imaging series, using a similarity criterion, the elementary deformations are estimated, then using the Moore-Penrose inverse matrix approach, all point deformations are obtained. Using this process, the cardiac wall motion is quantized to mechanically determine local parameters to investigate the cardiac wall functionality. This process was implemented and tested over 10 healthy and 20 patients with myocardial infarction. In all patients, the process was able to precisely determine the affected region. The proposed approach was also compared with linear one and the results demonstrated its superiority respect to the linear model.

Knowledge-based system for boundary detection of four-dimensional cardiac magnetic resonance image sequences

A strategy for a knowledge-based system to detect the interior and exterior boundaries of the left ventricle from time-varying cross-sectional images obtained by ECG-gated magnetic resonance imaging (MRI) is discussed. The system uses both fuzzy set theory and Dempster and Shafer theory to manage the knowledge and to control the flow of system information for more efficient use of limited computational resources and memory space. The key to the approach is that it performs edge detection on images through integration and unification of knowledge and information from edge candidates on all the slices and phases of the acquired cardiac MRI dataset. The analysis system does not base decisions on individual measurements, but on consensus opinions by combining many knowledge sources, some of which may not be completely accurate.