Multidimensional flow mapping can measure the paths, compartmentalization and kinetic energy changes of blood flowing into the LV, demonstrating differences of KE loss between compartments, and potentially between the flows in normal and dilated left ventricles.

Purpose: To determine the difference in flow patterns between healthy volunteers and ascending aortic aneurysm patients using time-resolved three-dimensional (3D) phase contrast magnetic resonance velocity (4D-flow) profiling. Materials and Methods:4D-flow was performed on 19 healthy volunteers and 13 patients with ascending aortic aneurysms. Vector fields placed on 2D planes were visually graded to analyze helical and retrograde flow patterns along the aortic arch. Quantitative analysis of the pulsatile flow was carried out on manually segmented planes. Results:In volunteers, flow progressed as follows: an initial jet of blood skewed toward the anterior right wall of the ascending aorta is reflected posterolaterally toward the inner curvature creating opposing helices, a right-handed helix along the left wall and a left-handed helix along the right wall; retrograde flow occurred in all volunteers along the inner curvature between the location of the two helices. In the aneurysm patients, the helices were larger; retrograde flow occurred earlier and lasted longer. The average velocity decreased between the ascending aorta and the transverse aorta in volunteers (47.9 mm/second decrease, P ϭ 0.023), while in aneurysm patients the velocity increased (145 mm/second increase, P Ͻ 0.001). Conclusion:Dilation of the ascending aorta skews normal flow in the ascending aorta, changing retrograde and helical flow patterns.

The flow patterns in the human heart are complex and difficult to visualize using conventional two‐dimensional (2D) modalities, whether they depict a single velocity component (Doppler echocardiography) or all three components in a few slices (2D phase contrast MRI). To avoid these shortcomings, a temporally resolved 3D phase contrast technique was used to derive data describing the intracardiac velocity fields in normal volunteers. The MRI data were corrected for phase shifts caused by eddy currents and concomitant gradient fields, with improvement in the accuracy of subsequent flow visualizations. Pathlines describing the blood pathways through the heart were generated from the temporally resolved velocity data, starting from user‐specified locations and time frames. Flow trajectories were displayed as 3D particle traces, with simultaneous demonstration of morphologic 2D slices. This type of visualization is intuitive and interactive and may extend our understanding of dynamic and previously unrecognized patterns of intracardiac flow. Magn Reson Med 41:793–799, 1999. © 1999 Wiley‐Liss, Inc.

A conventional 3D phase contrast acquisition generates images with good spatial resolution, but often gives rise to artifacts due to pulsatile flow. 2D cine phase contrast, on the other hand, can register dynamic flow, but has a poor spatial resolution perpendicular to the imaging plane. A combination of both high spatial and temporal resolution may be advantageous in some cases, both in quantitative flow measurements and in MR angiography. The described 3D cine phase contrast pulse sequence creates a temporally resolved series of 3D data sets with velocity encoded data.

Background-Abnormal flow patterns in the left atrium in atrial fibrillation or mitral stenosis are associated with an increased risk of thrombosis and systemic embolisation; the characteristics of normal atrial flow that avoid stasis have not been well defined.Objectives-To present a three dimensional particle trace visualisation of normal left atrial flow in vivo, constructed from flow velocities in three dimensional space. Methods-Particle trace visualisation of time resolved three dimensional magnetic resonance imaging velocity measurements was used to provide a display of intracardiac flow without the limitations of angle sensitivity or restriction to imaging planes. Global flow patterns of the left atrium were studied in 11 healthy volunteers. Results-In all subjects vortical flow was observed in the atrium during systole and diastolic diastasis (mean (SD) duration of systolic vortex, 280 (77) ms; and of diastolic vortex, 256 (118) ms). The volume incorporated and recirculated within the vortices originated predominantly from the left pulmonary veins. Inflow from the right veins passed along the vortex periphery, constrained between the vortex and the atrial wall. Conclusions-Global left atrial flow in the normal human heart comprises consistent patterns specific to the phase of the cardiac cycle. Separate paths of left and right pulmonary venous inflow and vortex formation may have beneficial eVects in avoiding left atrial stasis in the normal subject in sinus rhythm. (Heart 2001;86:448-455)

Changes in supravalvular flow accompany loss of sinus architecture. Whether the presence, size, and velocity of supravalvular vortices affects the function or durability of the preserved aortic valve remains to be studied.

Accurate, easy-to-use, noninvasive cardiovascular pressure registration would be an important addition to the diagnostic armamentarium for assessment of cardiac function. A novel noninvasive and three-dimensional (3D) technique for estimation of relative cardiovascular pressures is presented. The relative pressure is calculated using the Navier-Stokes equations along user-defined lines placed within a time-resolved 3D phase contrast MRI dataset. The lines may be either straight or curved to follow an actual streamline. Cardiac pressure estimation is critical in the evaluation of many cardiovascular disorders. The pressure drop that occurs over constrictions is the basis for evaluating the severity of valvular and vascular stenoses. Changes in the filling pressure of the heart have profound effects on both systolic and diastolic efficiency. Catheter measurements have been the basis for our understanding of these important pressure dynamics, but are expensive, not readily repeatable, and associated with the risks of radiation and vascular invasion.Noninvasive methods for estimation of pressure differences have been developed based on both ultrasound and magnetic resonance imaging techniques. Hatle et al. (1) estimated the transvalvular pressure difference across stenotic mitral valves by applying the simplified Bernoulli equation to Doppler ultrasound velocity measurements. This method is accurate under conditions of severe stenosis at the time of peak flow and has become the clinical standard for noninvasive evaluation of mitral stenosis. Color M-mode ultrasound has been proposed as another method for noninvasive transmitral pressure registration (2), but may be significantly limited by Doppler's sensitivity to insonation angle and by imprecise alignment with true inflow directions. The Navier-Stokes equations describe the relation between the velocity field and the pressure gradient field. A least-squares approximation of the relative pressure field can be obtained from the pressure gradient field using the pressure Poisson equation (3). These pressure estimation techniques based on MRI velocity data (4,5), however, demand accurate segmentation in order to set the boundary conditions. Segmentation is difficult to perform with the magnitude images of 3D phase contrast due to the minimal contrast between blood and myocardium.A different approach for evaluating pressure differences can be based on guidance by 3D visualization of cardiovascular flow. Time-resolved 3D phase contrast MR allows measurement of velocity throughout the 3D volume of the entire heart (6). This large amount of velocity data can be visualized intuitively by particle traces, which simulate the path taken by imaginary particles released in the velocity field. Particle trace can be calculated and visualized in two ways: pathlines and streamlines. Pathlines follow the trajectory of particles as they move through space over time. Streamlines are the tangent to the velocity vector field and demonstrate a snapshot of the flow field at a given instan...

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