Measurement of the three-dimensional flow field inside the cardiac chambers has proven to be a challenging task. This is mainly due to the fact that generalized full-volume velocimetry techniques cannot be easily implemented to the heart chambers. In addition, the rapid pace of the events in the heart does not allow for accurate real-time flow measurements in 3D using imaging modalities such as magnetic resonance imaging, which neglects the transient variations of the flow due to averaging of the flow over multiple heartbeats. In order to overcome these current limitations, we introduce a multi-planar velocity reconstruction approach that can characterize 3D incompressible flows based on the reconstruction of 2D velocity fields. Here, two-dimensional, two-component velocity fields acquired on multiple perpendicular planes are reconstructed into a 3D velocity field through Kriging interpolation and by imposing the incompressibility constraint. Subsequently, the scattered experimental data are projected into a divergence-free vector field space using a fractional step approach. We validate the method in exemplary 3D flows, including the Hill’s spherical vortex and a numerically simulated flow downstream of a 3D orifice. During the process of validation, different signal-to-noise ratios are introduced to the flow field, and the method’s performance is assessed accordingly. The results show that as the signal-to-noise ratio decreases, the corrected velocity field significantly improves. The method is also applied to the experimental flow inside a mock model of the heart’s right ventricle. Taking advantage of the periodicity of the flow, multiple 2D velocity fields in multiple perpendicular planes at different locations of the mock model are measured while being phase-locked for the 3D reconstruction. The results suggest the metamorphosis of the original transvalvular vortex, which forms downstream of the inlet valve during the early filling phase of the right ventricular model, into a streamline single-leg vortex extending toward the outlet.

Various forms of vortex formation in the cardiovascular system convey valuable information regarding the function of heart and great vessels. The vortex ring that forms during systole in the aortic sinus is the first that was recognized and the asymmetric transmitral vortex ring that forms in the left ventricle during diastole has been most commonly used for diagnosis and follow up of heart failure patients. Adverse vortex interaction in the heart can also occur due to valvular regurgitation and may have energetic consequences to the heart. Furthermore, vortices do exist in other chambers such as the right ventricle and may even arise in the great arteries and veins due to congenital heart disease. Here, we summarize diagnostic and prognostic significance of vortices and vortex imaging in the heart, their applications in clinical medicine, and discuss how these flow features can be used to assess functional status of the heart.

Introduction: Although 4D echocardiography is used for many clinical applications, the evolving vortex flow in the right ventricle (RV) is relatively unknown and cannot be characterized with conventional echocardiography. An obstacle is that acquiring high frame rate (>100fps) data in presence of contrast is challenging and has not yet reported. Hypothesis: High frame-rate 4D echocardiographic data in presence of contrast can elucidate RV vortex flow via volumetric Echo-PIV (V-Echo-PIV). Methods: We devised a new transthoracic echocardiography (TTE) protocol using a Philips EPIQ CV9 ultrasound system with a 3D matrix probe (X5-1c) to acquire high frame-rate 4D data for processing with V-Echo-PIV. Apical RV focused view was used for full-volume acquisition by limiting the sector width and imaging depth solely to the entire RV. Visualization of the RV flow and wall dynamics was achieved by IV administration of Optison™ and Normal Saline. VolDICOMs were processed with V-Echo-PIV to obtain RV blood flow velocity field during the full cardiac cycle. Results: We improve the frame rates' scan lines to +30Hz. A 100Hz is achieved by stitching 4 cycles. We show that 4D RV flow can be quantified and characterized at high temporal resolution using V-Echo-PIV. Fig. 1A shows cine blood velocity in a healthy subject with a 51bpm heart rate. For which, V-Echo-PIV acquired 117 three-dimensional vector fields in one cardiac cycle, given the setting of 100Hz acquisition rate. The figure features flow patterns from systole to diastole, from left to right. Fig. 1B depicts the iso-surface of transient tricuspid vortex during diastolic RV filling. Conclusions: Enabled by high speed acquition in presence of contrast, V-Echo-PIV can be used as a viable alternative to 4D Flow MRI to visualize and evaluate real-time intra-cardiac blood flow, as it requires only a very short acquisition time and can be used wherever an echocardiography machine with matrix probes is available.