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Multiscale Motion Mapping—In Vitro Results

«Triple-M Imaging» was first applied to synthetic ultrasound data and echocardiograms obtained from physical phantoms for which true motion is known.

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Application to Synthetic Ultrasound Data
The application to synthetic echocardiograms demonstrates the capabilities of Multiscale Motion Mapping in the case of simplified, clearly defined motion. The example shown in Fig. 1(a) simulates an apical short axis view. The applied motion consists of uniform radial expansion/contraction and an underlying rigid translation to the upper right. The estimated motion and deformation is illustrated in Fig. 1(b)-(d): The velocity field (b) reflects the superposition of radial expansion/contraction and global rigid translation. The yellow/red and green/blue color maps (c) indicate uniform outward and inward motion in an intuitive way. The strain rate is superimposed in the form of small ellipses (d) that document myocardial thinning and thickening during diastole and systole, respectively. It is important to note that the strain rate measurements are independent from underlying translation.
a) Original Sequence b) Estimated Velocity Field
c) Color-Coded Radial Velocity d) Estimated Strain Rate
Figure 1: Features of Multiscale Motion Mapping demonstrated on synthetic echocardiogram.
Phantom Experiments
The algorithm’s ability to analyze motion from real ultrasound data was tested by a phantom experiment. A cylinder-shaped, tissue-mimicking phantom was placed inside a tube of water and rotated with constant angular velocity around its longitudinal axis. One acquired B-mode sequence is shown in Fig. 2(a). The corresponding estimated velocity field is superimposed in Fig. 2(b). For comparison, the measured color Doppler signal is shown in Fig. 2(c). The Doppler signal is more difficult to interpret and the central vertical line of zero Doppler velocities clearly demonstrates that motion orthogonal to the beam direction cannot be measured. In contrast, the estimated velocity field (b) represents well the rotational motion and does not suffer from angle dependencies.
a) B-mode echocardiogram b) Estimated velocity field by Multiscale Motion Mapping c) Measured color Doppler signal
Figure 2: Comparison of Multiscale Motion Mapping and color Doppler on phantom data.