Intraventricular Vector Flow Mapping
Echocardiographic imaging tools are developed to construct intracardiac velocity vector fields from conventional color Doppler. The original algorithm [IEEE Trans Med Imaging, 2010] has been implemented in Fujifilm Healthcare and Esaote scanners. We recently introduced a new algorithm based on a constrained regularization approach with automatic model selection [Phys Med Biol, 2021].
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Intraventricular Vector Flow Mapping now becomes three-dimensional using triplane color Doppler echocardiography [Phys Med Biol, 2022].
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Ultrafast Echocardiography
We introduced duplex (B-mode + tissue Doppler) 90o-wide echocardiography at >400 frames/s using diverging beams. Motion compensation (MoCo) was integrated in the coherent compounding process to cope with phase delays due to myocardial motion and obtain high-quality high-frame-rate echocardiographic images [IEEE Trans Med Imaging, 2016]. Using MoCo-based echocardiography, we also developed a least-squares framework that combines optical flow and tissue Doppler to provide accurate myocardial velocities at high frame rates [IEEE Trans Med Imaging, 2018].
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Biomechanical modeling
Biomechanical models and/or in vitro experiments are designed in technical and/or clinical studies to develop and/or investigate new imaging tools or diagnostic parameters. For example, we analyzed and validated in patients the effect of aortic stenosis on the coronary flow reserve (CFR) by using a lumped parameter model [J Appl Physiol, 2009]. We also develop advanced modeling such as smoothed particle hydrodynamics (SPH) coupled with acoustic linear weak scattering model to simulate realistic color Doppler and vector flow ultrasound imaging [Phys Med Biol, 2018].
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Clinical studies
Based on hemodynamics principles or new imaging tools, new clinical parameters are proposed for better diagnosis in patients with heart disease (e.g. aortic stenosis, diastolic dysfunction, coronary stenosis). In particular, we introduced the energy loss index to improve the assessment of aortic stenosis [Circulation, 2013]. We are also investigating prospectively whether the CFR-to-FFR ratio can better guide coronary intervention [PLoS ONE, 2019]
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Miscellaneous
- RF signals are generally sampled at a frequency four times the center frequency
- Sub-Nyquist bandpass sampling can be used effectively in color Doppler
- RF undersampling can avoid data overload and reduce data workflow
- See article #53
- Diverging-wave cardiac echo requires signals to be combined coherently
- Neglecting myocardial motion in beamforming cause adverse interferences
- Motion compensation ensures coherent summation and improves image quality
- See articles #41, 50, 52, 54
- SMOOTHN is a fast robust version of a discretized smoothing spline
- This automatic smoother can deal with outlying and missing values
- The Matlab code was selected as "MATLAB Central Pick of the Week"
- See articles #24, 27, 29
- A large blood vortex forms in the left ventricular cavity during diastole
- Its kinematic and dynamic properties likely reflect diastolic filling function
- This vortex can be decipher clinically using color Doppler echocardiography
- See articles #26, 33, 45, 46
- To simulate color Doppler, we used smoothed particle hydrodynamics (SPH)
- The SPH fluid particles directly act as individual ultrasound scatterers
- The mesh-free coupled simulator is 3-D compatible and easily parallelizable
- See article #55
- Speckle tracking echocardiography evaluates regional myocardial function
- The objective was to provide accurate myocardial velocities at high frame rates
- We developed a global framework based on optical flow and tissue Doppler
- See article #52