Multi-line transmission combined with minimum variance beamforming in medical ultrasound imaging.

Increasing medical ultrasound imaging frame rate is important in several applications such as cardiac diagnostic imaging, where it is desirable to be able to examine the temporal behavior of fast phases in the cardiac cycle. This is particularly true in 3-D imaging, where current frame rate is still much slower than standard 2-D, B-mode imaging. Recently, a method that increases frame rate, labeled multi-line transmission (MLT), was reintroduced and analyzed. In MLT scanning, the transmission is simultaneously focused at several directions. This scan mode introduces artifacts that stem from the overlaps of the receive main lobe with the transmit side lobes of additional transmit directions besides the one of interest. Similar overlaps occur between the transmit main lobe with receive side lobes. These artifacts are known in the signal processing community as cross-talk. Previous studies have concentrated on proper transmit and receive apodization, as well as transmit directions arrangement in the transmit event, to reduce the cross-talk artifacts. This study examines the possibility of using adaptive beamforming, specifically, minimum variance (MV) and linearly constrained minimum variance (LCMV) beamforming, to reduce the cross-talk artifacts, and maintain or even improve image quality characteristics. Simulation results, as well as experimental phantom and in vivo cardiac data, demonstrate the feasibility of reducing cross-talk artifacts with MV beamforming. The MV and LCMV results achieve superior spatial resolution, not only over other MLT methods with data-independent apodization, but even over that of single-line transmission (SLT) without receive apodization. The MV beamformer is shown to be less sensitive to wider transmit profiles required to reduce the transmit crosstalk artifacts. MV beamforming, combined with the wider transmit profiles, can provide a good approach for MLT scanning with reduced cross-talk artifacts, without compromising spatial resolution, and even improving it. We also demonstrate that the MV and LCMV beamformers lead to almost identical results. This is because of their very similar beampatterns, except for the sharp nullifying properties that the LCMV beamformer has around interfering beams.

Multi-line acquisition with minimum variance beamforming in medical ultrasound imaging.

In recent years, multiple-line acquisition (MLA) has been introduced to increase frame rate in cardiac ultrasound medical imaging. However, this method induces blocklike artifacts in the image. One approach suggested, synthetic transmit beamforming (STB), involves overlapping transmit beams which are then interpolated to remove the MLA blocking artifacts. Independently, the application of minimum variance (MV) beamforming has been suggested in the context of MLA. We demonstrate here that each approach is only a partial solution and that combining them provides a better result than applying either approach separately. This is demonstrated by using both simulated and real phantom data, as well as cardiac data. We also show that the STB-compensated MV beamfomer outperforms single-line acquisition (SLA) delay- and-sum in terms of lateral resolution.