Increased SNR in Acousto-Optic Imaging via Coded Ultrasound Transmission

Acousto Optic Imaging (AOI) is a non-invasive hybrid imaging technology that can directly measure the light fluence distribution inside a tissue. In AOI, the tissue is illuminated by a coherent CW laser, leading to the formation of a speckle on the tissue boundary, and an ultrasound pulse is used to modulate the laser light at certain positions within the tissue, effectively modulating the speckle intensity pattern on the boundary. Since the light modulation is proportional to the acoustic power, the measured speckle modulation is indicative of the fluence in the focus of the acoustic beam. We developed a new approach for AOI accordingly instead of a single ultrasound pulse we generate a cyclic coded sequence of acoustic pulses; thus a single measurement represents a set of multiplexed signals from different tissue sections. Comparing the results of single-pulse AOI and our novel multiplexed AOI shows over a 2-fold increase in SNR for the multiplexed approach, in agreement with the theoretical prediction for the used code order of N=19. Due to the increased SNR we are now able to have a deeper view into the tissue from approximately 1cm to 2cm.