Safety of fast cardiac imaging using multiple transmit beams: Experimental verification

High frame rate (HFR) echocardiography may be of benefit for functional analysis of the heart. It has recently been demonstrated that multiple-line transmit (MLT), i.e. the simultaneous transmission of multiple focused beams into different directions, increases the frame rate without significantly compromising the resolution or SNR. In MLT mode, the excitation pulse applied on a given element is equivalent to the sum of pulses that would be individually applied to generate single line transmit (SLT) beams along the selected MLT directions. Since a non-standard excitation is involved and an increased number of beams yields an increased energy transfer to the human body, the possible bio-effects must be taken into consideration. In this paper, the thermal (TI) and mechanical (MI) indexes of MLT are experimentally evaluated and compared with those of SLT.