Table 1.

Summary of technical characteristics

	Echo-PIV	VFM	CMR
Data source	Echocardiographic tracking of groups of contrast agent particles	Calculation of laminar and vortical flow components from Colour-Doppler	Influence of flow motion on MR-signal phase: phase contrast
Main advantages	Low cost Wide availability Shorter examination times		Higher spatial resolution with full 3D coverage
Limitations	Inherent to conventional echocardiographic examinations (acoustic shadowing, technically difficult examinations, etc.)		Intracardiac devices not suitable for CMR studies Longer examination times Limited temporal resolution (poor flow characterization in brief phases of cardiac cycle) Flow data are averaged over several cardiac cycles
	Need for the use of contrast agents Requiring frame rates of 60–150 fps for adequate detection of high velocities	Lacking ‘in vivo’ validation study Underestimation of velocities in vortex areas perpendicular to ultrasound beam
Sources of error	Cross-plane migration of contrast agent particles Manual contour detection	Manual de-aliasing Manual definition of endocardial borders	Eddy current effects Maxwell terms Gradient field distortions
Accuracy
High velocities	Limited: affected by frame rate (upper limit of ∼60 cm/s)	Accurate visualization. May require adjustment of Nyquist limit or manual de-aliasing	Accurate visualization, although selectable velocity sensitivity (venc) requires some prior knowledge of the expected velocity values
Low velocities	Accurate visualization	Underestimation. Nyquist limit adjustment and focus on smaller areas may improve the detection but introduces noise through the detection of cardiac wall motion