Bradley D. Allen

A methodology to detect abnormal relative wall shear stress on the full surface of the thoracic aorta using four-dimensional flow MRI

To compute cohort‐averaged wall shear stress (WSS) maps in the thoracic aorta of patients with aortic dilatation or valvular stenosis and to detect abnormal regional WSS.

Efficient method for volumetric assessment of peak blood flow velocity using 4D flow MRI

To test the feasibility and effectiveness of using maximum intensity plots (MIPs) based on 4D flow magnetic resonance imaging (MRI) velocity data to assess systolic peak velocities in a cohort of bicuspid aortic valve (BAV) patients.

Thoracic Aorta 3D Hemodynamics in Pediatric and Young Adult Patients With Bicuspid Aortic Valve

To evaluate the 3D hemodynamics in the thoracic aorta of pediatric and young adult bicuspid aortic valve (BAV) patients.

Evaluation of aortic stenosis severity using 4D flow jet shear layer detection for the measurement of valve effective orifice area.

AIMS The objective of this study was to evaluate the potential of 4D flow MRI to assess valve effective orifice area (EOA) in patients with aortic stenosis as determined by the jet shear layer detection (JSLD) method. METHODS AND RESULTS An in-vitro stenosis phantom was used for validation and in-vivo imaging was performed in 10 healthy controls and 40 patients with aortic stenosis. EOA was calculated by the JSLD method using standard 2D phase contrast MRI (PC-MRI) and 4D flow MRI measurements (EOAJSLD-2D and EOAJSLD-4D, respectively). As a reference standard, the continuity equation was used to calculate EOA (EOACE) with the 2D PC-MRI velocity field and compared to the EOAJSLD measurements. The in-vitro results exhibited excellent agreement between flow theory (EOA=0.78cm(2)) and experimental measurement (EOAJSLD-4D=0.78±0.01cm(2)) for peak velocities ranging from 0.9 to 3.7m/s. In-vivo results showed good correlation and agreement between EOAJSLD-2D and EOACE (r=0.91, p<0.001; bias: -0.01±0.38cm(2); agreement limits: 0.75 to -0.77cm(2)), and between EOAJSLD-4D and EOACE (r=0.95, p<0.001; bias: -0.09±0.26cm(2); limits: 0.43 to -0.62cm(2)). CONCLUSION This study demonstrates the feasibility of measuring EOAJSLD using 4D flow MRI. The technique allows for optimization of the EOA measurement position by visualizing the 3D vena contracta, and avoids potential sources of EOACE measurement variability.

4D flow MRI and T1 -Mapping: Assessment of altered cardiac hemodynamics and extracellular volume fraction in hypertrophic cardiomyopathy.

Hypertrophic cardiomyopathy (HCM) is associated with altered hemodynamics in the left ventricular outflow tract (LVOT) and myocardial tissue abnormalities such as fibrosis. The aim of this study was to quantify changes in LVOT 3D hemodynamics and myocardial extracellular volume fraction (ECV, measure of fibrosis) and to investigate relationships between elevated flow metrics and left ventricular (LV) tissue abnormalities.

4D flow MRI and T 1 -Mapping

Hypertrophic cardiomyopathy (HCM) is associated with altered hemodynamics in the left ventricular outflow tract (LVOT) and myocardial tissue abnormalities such as fibrosis. The aim of this study was to quantify changes in LVOT 3D hemodynamics and myocardial extracellular volume fraction (ECV, measure of fibrosis) and to investigate relationships between elevated flow metrics and left ventricular (LV) tissue abnormalities.

Haemodynamic outcome at four-dimensional flow magnetic resonance imaging following valve-sparing aortic root replacement with tricuspid and bicuspid valve morphology

OBJECTIVE To provide a more complete characterization of aortic blood flow in patients following valve-sparing aortic root replacement (VSARR) compared with presurgical cohorts matched by tricuspid and bicuspid valve morphology, age and presurgical aorta size. METHODS Four-dimensional (4D) flow magnetic resonance imaging (MRI) was performed to analyse three-dimensional (3D) blood flow in the thoracic aorta of n = 13 patients after VSARR with reimplantation of native tricuspid aortic valve (TAV, n = 6) and bicuspid aortic valve (BAV, n = 7). Results were compared with presurgical age and aortic size-matched control cohorts with TAV (n = 10) and BAV (n = 10). Pre- and post-surgical aortic flow was evaluated using time-resolved 3D pathlines using a blinded grading system (0-2, 0 = small, 1 = moderate and 2 = prominent) analysing ascending aortic (AAo) helical flow. Systolic flow profile uniformity in the aortic root, proximal and mid-AAo was evaluated using a four-quadrant model. Further analysis in nine analysis planes distributed along the thoracic aorta quantified peak systolic velocity, retrograde fraction and peak systolic flow acceleration. RESULTS Pronounced AAo helical flow in presurgical control subjects (both BAV and TAV: helix grading = 1.8 ± 0.4) was significantly reduced (0.2 ± 0.4, P < 0.001) in cohorts after VSARR independent of aortic valve morphology. Presurgical AAo flow was highly eccentric for BAV patients but more uniform for TAV. VSARR resulted in less eccentric flow profiles. Systolic peak velocities were significantly (P < 0.05) increased in post-root repair BAV patients throughout the aorta (six of nine analysis planes) and to a lesser extent in TAV patients (three of nine analysis planes). BAV reimplantation resulted in significantly increased peak velocities in the proximal AAo compared with root repair with TAV (2.3 ± 0.6 vs 1.6 ± 0.4 m/s, P = 0.017). Post-surgical patients showed a non-significant trend towards higher systolic flow acceleration as a surrogate measure of reduced aortic compliance. CONCLUSIONS VSARR restored a cohesive flow pattern independent of native valve morphology but resulted in increased peak velocities throughout the aorta. 4D flow MRI methods can assess the clinical implications of altered aortic flow dynamics in patients undergoing VSARR.

Three-dimensional haemodynamics in patients with obstructive and non-obstructive hypertrophic cardiomyopathy assessed by cardiac magnetic resonance

AIMS The left ventricular outflow tract (LVOT) peak pressure gradient is an important haemodynamic descriptor in patients with hypertrophic cardiomyopathy (HCM); however, secondary alterations in aortic blood flow have not been well described in these patients. Aortic flow derangement is not easily assessed by traditional imaging methods, but may provide unique characterization of this disease. In this study, we demonstrated how four-dimensional (4D) flow MRI can assess LVOT peak pressure gradients in HCM patients and also evaluated the ascending aorta (AAo) haemodynamic derangement associated with HCM. METHODS AND RESULTS Obstructive (n = 12) and non-obstructive (n = 18) HCM patients were included in the study along with 10 normal volunteers. 4D flow MRI was used to visualize three-dimensional (3D) blood flow patterns within the LVOT and AAo, which were graded for the presence of helical flow as a marker of flow derangement (absent = 0, mild/moderate = 1, and severe = 2). MRI-estimated pressure gradient (ΔPMRI) was calculated from the peak systolic 3D blood velocity profile within the LVOT. There was higher grade helical flow in obstructive HCM patients compared with non-obstructive patients (P = 0.04) and volunteers (P < 0.001). Non-obstructive patients also had higher helix grade than volunteers (P = 0.002). There was a significant correlation between helical grade and increasing ΔPMRI (rS = 0.69, P < 0.001). Systolic anterior motion (SAM) of the mitral valve was associated with both increasing helix grade (P < 0.001) and ΔPMRI (P = 0.006). CONCLUSIONS Ascending aorta flow derangement occurs in both obstructive and non-obstructive HCM patients and can be identified using 4D flow MRI. The degree of flow derangement correlates with LVOT gradient, SAM, and outflow tract geometry.

Influence of documented history of coronary artery disease on outcomes in patients admitted for worsening heart failure with reduced ejection fraction in the EVEREST trial.

Data on the prognosis of heart failure (HF) patients with coronary artery disease (CAD) have been conflicting. We describe the clinical characteristics and mode‐specific outcomes of HF patients with reduced ejection fraction (EF) and documented CAD in a large randomized trial.

Time-resolved three-dimensional phase contrast MRI evaluation of bicuspid aortic valve and coarctation of the aorta

A 41-year-old man with a bicuspid aortic valve (BAV) and coarctation of the aorta, as visualized by 2D phase contrast cardiovascular magnetic resonance imaging (CMR) ( Figure 1D , Supplementary data online, Videos S1 ) and contrast enhanced MR angiography ( Figure 1A ), was referred for evaluation by time-resolved 3D phase contrast (4D flow) CMR to assess the flow velocity through the coarctation and provide aortic flow characterization. Findings of the comprehensive examination demonstrate the complex haemodynamic patterns that emerge throughout the aorta secondary …