Multi-focus tissue harmonic images obtained with parallel transmit beamforming by means of orthogonal frequency division multiplexing

Parallel beamforming in transmit (PBT) by means of orthogonal frequency division multiplexing (OFDM) was recently applied to increase the frame rate of ultrasound tissue harmonic imaging. OFDM-PBT improves the data acquisition rate by generating, for each transmission event, multiple beams that are allocated to a specific portion of the available transducer bandwidth. Improving the frame rate is however not the only possible application of an increased data acquisition rate. In this paper, OFDM-PBT is exploited to perform multi-focus tissue harmonic imaging for improving the penetration depth and signal to noise ratio (SNR) without affecting the frame rate. Tissue harmonic images of a tissue mimicking phantom were obtained with OFDM-PBT and standard B-mode imaging. Results present improved penetration depth and SNR for OFDM-PBT as compared to standard B-mode. We estimated an improvement of 6 dB of the average SNR, at the expenses of a reduction of the axial resolution (0.7 vs 1.1 mm).