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Thu-Thao Le - Top 30 Publications

Importance of Sex-Specific Regression Models to Estimate Synthetic Hematocrit and Extracellular Volume Fraction.

Cardiac magnetic resonance T1 and extracellular volume mapping with motion correction and co-registration based on fast elastic image registration.

Our aim was to investigate the technical feasibility of a novel motion compensation method for cardiac magntic resonance (MR) T1 and extracellular volume fraction (ECV) mapping.

Fractal analysis of left ventricular trabeculations is associated with impaired myocardial deformation in healthy Chinese.

Left ventricular (LV) non-compaction (LVNC) is defined by extreme LV trabeculation, but is measured variably. Here we examined the relationship between quantitative measurement in LV trabeculation and myocardial deformation in health and disease and determined the clinical utility of semi-automated assessment of LV trabeculations.

Novel Index of Maladaptive Myocardial Remodeling in Hypertension.

Hypertensive left ventricular hypertrophy (HTN-LVH) is a leading cause of heart failure. Conventional patterns of cardiac geometry do not adequately risk-stratify patients with HTN-LVH. Using cardiovascular magnetic resonance, we developed a novel Remodeling Index (RI) that was designed to detect an exaggerated hypertrophic response to hypertension and tested its potential to risk-stratify hypertensive patients.

Computational medical imaging and hemodynamics framework for functional analysis and assessment of cardiovascular structures.

Cardiac dysfunction constitutes common cardiovascular health issues in the society, and has been an investigation topic of strong focus by researchers in the medical imaging community. Diagnostic modalities based on echocardiography, magnetic resonance imaging, chest radiography and computed tomography are common techniques that provide cardiovascular structural information to diagnose heart defects. However, functional information of cardiovascular flow, which can in fact be used to support the diagnosis of many cardiovascular diseases with a myriad of hemodynamics performance indicators, remains unexplored to its full potential. Some of these indicators constitute important cardiac functional parameters affecting the cardiovascular abnormalities. With the advancement of computer technology that facilitates high speed computational fluid dynamics, the realization of a support diagnostic platform of hemodynamics quantification and analysis can be achieved. This article reviews the state-of-the-art medical imaging and high fidelity multi-physics computational analyses that together enable reconstruction of cardiovascular structures and hemodynamic flow patterns within them, such as of the left ventricle (LV) and carotid bifurcations. The combined medical imaging and hemodynamic analysis enables us to study the mechanisms of cardiovascular disease-causing dysfunctions, such as how (1) cardiomyopathy causes left ventricular remodeling and loss of contractility leading to heart failure, and (2) modeling of LV construction and simulation of intra-LV hemodynamics can enable us to determine the optimum procedure of surgical ventriculation to restore its contractility and health This combined medical imaging and hemodynamics framework can potentially extend medical knowledge of cardiovascular defects and associated hemodynamic behavior and their surgical restoration, by means of an integrated medical image diagnostics and hemodynamic performance analysis framework.

Stress cardiovascular magnetic resonance imaging: current and future perspectives.

Vasodilator and dobutamine are the main pharmacological agents used in current stress cardiovascular magnetic resonance (CMR). Exercise stress has well-established advantages and it is commonly used in other stress imaging, but the technical considerations have limited its use in stress CMR. In this review, we will describe the diagnostic performance, prognostic value, strengths and challenges of current stress CMR techniques. We will also discuss future perspectives of exercise stress CMR. Areas covered: Despite notable mechanistic differences, vasodilator and dobutamine stress CMR offer similar diagnostic and prognostic value in coronary artery disease. Combined perfusion and wall motion assessment has been explored with dobutamine stress CMR: diagnostic sensitivity improved at the expense of reduced specificity. However, a combined assessment may provide additional prognostic value in selected patients. There is emerging interest and promising data in exercise stress CMR because of the availability of CMR-compatible stress equipment and development of novel real-time sequences that allow imaging during exercise with adequate spatiotemporal resolution. Expert commentary: Exercise stress CMR is able to assess wall motion abnormalities, perfusion defects, exercise capacity and viability in a single examination. This holds important clinical potential in a variety of cardiovascular conditions.

Assessing exercise cardiac reserve using real-time cardiovascular magnetic resonance.

Exercise cardiovascular magnetic resonance (ExCMR) has great potential for clinical use but its development has been limited by a lack of compatible equipment and robust real-time imaging techniques. We developed an exCMR protocol using an in-scanner cycle ergometer and assessed its performance in differentiating athletes from non-athletes.

Cardiovascular magnetic resonance reference ranges for the heart and aorta in Chinese at 3T.

Cardiovascular magnetic resonance (CMR) reference ranges have not been well established in Chinese. Here we determined normal cardiac and aortic reference ranges in healthy Singaporean Chinese and investigated how these data might affect clinical interpretation of CMR scans.

Left ventricular diastolic function assessment using time differences between mitral annular velocities and transmitral inflow velocities in patients with heart failure.

Evaluation of left ventricular (LV) diastolic function is important in clinical echocardiography. The relationship between mitral annular velocities and transmitral inflow velocities provide additional information about LV filling and diastolic function. This study evaluates the relationships of time intervals between peaks E of mitral inflow velocities and E' of mitral annular velocities, and peaks A and A' in patients with heart failure (HF).

Assessment of left ventricular preload by cardiac magnetic resonance imaging predicts exercise capacity in adult operated tetralogy of Fallot: a retrospective study.

The optimal timing of pulmonary homograft valve replacement (PVR) is uncertain. Cardiopulmonary exercise testing (CPET) and cardiac magnetic resonance (CMR) are often used to guide the clinical decision for PVR in operated tetralogy of Fallot (TOF) patients with significant pulmonary regurgitation (PR). We aim to study the relationship between exercise capacity and CMR in these patients.

Assessment of arterial elastance and ventricular-arterial coupling in patients with systemic lupus erythematosus.

Endothelial function is associated with myocardial diastolic function in women with systemic lupus erythematosus.

Endothelial dysfunction is associated with traditional and systemic lupus erythematosus (SLE)-specific risk factors, and early data suggest reversibility of endothelial dysfunction with therapy. The clinical relevance of endothelial function assessment has been limited by the lack of studies, demonstrating its prognostic significance and impact on early myocardial function. Therefore, we aimed to determine the association between endothelial and myocardial diastolic function in SLE women. Women with SLE and no coronary artery disease were prospectively recruited and underwent radionuclide myocardial perfusion imaging (MPI) (Jetstream, Philips, the Netherlands) to exclude subclinical myocardial ischemia. Cardiac and vascular functions were assessed in all patients (Alpha 10, Aloka, Tokyo). Diastolic function was assessed using pulse wave early (E) and late mitral blood inflow and myocardial tissue Doppler (mean of medial and lateral annulus e') velocities. Endothelial function was measured using brachial artery flow-mediated vasodilatation (FMD%). Univariate and multivariate linear regressions were used to assess the association between FMD% and myocardial diastolic function, adjusting for potential confounders. Thirty-eight patients without detectable myocardial ischemia on MPI were studied (mean age 44 ± 10 years; mean disease duration 14 ± 6 years). About 61 % of patients had normal diastolic function (E/e' ≤ 8), and 5 % of patients had definite diastolic dysfunction with E/e' > 13 (mean 7.1 ± 2.9). FMD% was associated with E/e' (regression coefficient β = -0.35; 95 % CI -0.62 to -0.08; p = 0.01) independent of systolic blood pressure, age, and SLICC/ACR Damage Index.

Fragmented QRS complexes predict right ventricular dysfunction and outflow tract aneurysms in patients with repaired tetralogy of Fallot.

Fragmented QRS complexes (fQRS) correlate with myocardial scar, and may predict arrhythmias in patients with repaired tetralogy of Fallot (TOF). We investigated the relationship between fQRS in operated TOF patients with right ventricular (RV) dysfunction and RV outflow tract (RVOT) aneurysm.

Attenuation of stress-based ventricular contractility in patients with heart failure and normal ejection fraction.

The maximal rate of change of pressure-normalised wall stress dσ*/dtmax has been proposed as cardiac index of left ventricular (LV) contractility. In this study, we assessed the capacity of dσ*/dtmax to diagnose heart failure with normal ejection fraction (HFNEF).

Effects of surgical ventricular restoration on left ventricular contractility assessed by a novel contractility index in patients with ischemic cardiomyopathy.

A pressure-normalized left ventricular (LV) wall stress (dsigma*/dt(max)) was recently reported as a load-independent index of LV contractility. We hypothesized that this novel contractility index might demonstrate improvement in LV contractile function after surgical ventricular restoration (SVR) using magnetic resonance imaging. A retrospective analysis of magnetic resonance imaging data of 40 patients with ischemic cardiomyopathy who had undergone coronary artery bypass grafting with SVR was performed. LV volumes, ejection fraction, global systolic and diastolic sphericity, and dsigma*/dt(max) were calculated. After SVR, a decrease was found in end-diastolic and end-systolic volume indexes, whereas LV ejection fraction increased from 26% +/- 7% to 31% +/- 10% (p <0.001). LV mass index and peak normalized wall stress were decreased, whereas the sphericity index (SI) at end-diastole increased, indicating that the left ventricle became more spherical after SVR. LV contractility index dsigma*/dt(max) improvement (from 2.69 +/- 0.74 to 3.23 +/- 0.73 s(-1), p <0.001) was associated with shape change as evaluated by the difference in SI between diastole and systole (r = 0.32, p <0.001, preoperative; r = 0.23, p <0.001, postoperative), but not with baseline LV SI. In conclusion, SVR excludes akinetic LV segments and decreases LV wall stress. Despite an increase in sphericity, LV contractility, as determined by dsigma*/dt(max), actually improves. A complex interaction of LV maximal flow rate and LV mass may explain the improvement in LV contractility after SVR. Because dsigma*/dt(max) can be estimated from simple noninvasive measurements, this underscores its clinical utility for assessment of contractile function with therapeutic intervention.

Regional assessment of left ventricular surface shape from magnetic resonance imaging.

Left ventricular functional abnormalities are postulated to be associated with regional modification of surface curvature. This study describes the computation of the differential properties of the LV surface via an analytic approach using local surface fitting. Quantification was implemented with cine magnetic resonance imaging (MRI), which was used as the source to derive 3D wire-frame models and the related shape descriptors. Based on these shape descriptors, the shape of LV could be represented in both static and dynamic manners. These may have implications for diverse cardiac diseases.