Advantages in using multi-frequency driving to enhance ultrasound contrast microbubble non-linearities for optimizing echo particle image velocimetry techniques

Accurate measurement of velocity profile, multiple velocity vectors and local shear stress in arteries is important for a variety of cardiovascular diseases. We have recently developed an ultrasound based velocimetry technique, termed echo particle image velocimetry (Echo-PIV). Preliminary in vitro, animal and clinical studies have shown significant promise of this method for measuring multiple velocity components with good temporal and spatial resolution. However, there is still difficulty in maximizing the non-linearity of bubble backscatter using conventional Gaussian-pulse excitation techniques at modest pressure amplitudes. We present here a potential solution to this problem through the use of multifrequency excitation. Results show that a rectangular wave is effective in improving the visibility of microbubbles. Use of rectangular pulses with 4 and 2 harmonics showed no significant difference in backscatter behavior, indicating that a two-frequency excitation may be sufficient to induce nonlinear behavior of the microbubbles at modest incident pressures.