Multi-transmit beam forming for fast cardiac imaging: Quantitative analysis of the cross-talk between MLT beams

As an alternative to parallel receive beam forming, transmitting multiple beams simultaneously (i.e. multi-line transmit (MLT)) has been proposed to obtain high frame rates when imaging the heart. However, this approach has received less attention likely due to potential artifacts as a result of cross-talk between MLT beams. In this study, the cross-talk level of two MLT beams with different opening angles was quantitatively evaluated by computer simulation. Seven commonly used windowing functions were tested to reduce the cross-talk. Based on the cross-talk analysis, an optimal opening angle of 22.5° and a windowing function scheme of Tukey (α=0.5) - Tukey (α=0.5) was deduced and used to simulate a 4MLT systems. Although some receive cross-talk artifacts were observed within a -55dB dynamic range, the images of the 4MLT system were visually very competitive with images using conventional beam forming but giving a 4 times higher frame rate. The MLT approach can easily be combined with parallel receive beam forming to increase frame rate further. With these methods, a 90° sector image can be generated at approximately 300Hz without significant loss in image quality.