Investigation on phase-coded third harmonic imaging for normal and pathological tissues in transmission mode in vitro

In this paper, a phase-coded pulse technique is proposed to improve the signal-to-noise ratio (SNR) in the 3rd harmonic imaging in transmis-sion mode, where three pulses with initial phases of 0o, 120o and 240o are transmitted and their corre-sponding received signals are linearly summed. By means of simulations and measurements, we show that the 3rd harmonic is enhanced by 9.5 dB, whereas the fundamental or the 2nd harmonic components are suppressed; the axial and lateral beam profiles of the processed 3rd harmonics are superior to those of the fundamental or 2nd harmonic components. In addition, this technique is applied to obtain the 3rd harmonic images for two normal and pathological biological tissues in transmission mode. This technique yields a dramatically cleaner and sharper contrast than the images obtained by the traditional fundamental im-aging and the 2nd harmonic imaging, which helps distinguish the normal and pathological states of tis-sues.