Plane wave contrast imaging: a radiation force point of view

Radiation force is known to produce microbubble axial displacements by an amount that depends on the transmit burst frequency, amplitude and length, as well as the pulse repetition frequency (PRF). In standard focused imaging mode, the actual PRF experienced by each microbubble is low because it is of the order of the frame rate (i.e. usually tens of Hz). In plane-wave imaging mode, however, the actual PRF is considerably higher, as it is equivalent to the transmit PRF (kHz range). Furthermore, the radiation pressure is expected to be almost uniform over the field of view, and typically lower than the peak pressure experienced in focused transmit (TX) mode. We have experimentally investigated the possible effects of radiation force in plane-wave mode. Here we report on preliminary findings that show the acoustic radiation force is negligible only at lower TX levels. At higher TX amplitudes, the bubble displacements due to radiation force are comparable to those obtained for focused waves at the same PRF. In addition, the radiation force is nearly uniform over the field of view and increases as the TX burst central frequency approaches the resonance frequency of size-isolated microbubbles.