Simultaneous multispectral coded excitation using Gold codes for photoacoustic imaging Gold Code

Photoacoustics (PA) is a new imaging modality based on the generation of ultrasound by laser irradiation [1]. When a nanosecond pulsed laser irradiates biological tissue, thermo-elastic expansion will cause ultrasonic waves that can be used for imaging by mapping the amount of light absorption by using ultrasound transducers. PA imaging is real-time imaging that combines high resolution and relatively high penetration depth of ultrasound imaging compared with light and the high contrast of optical imaging. Furthermore, applying light absorption characteristics using multispectral irradiation enables us to monitor functional information like the blood oxygenation. A problem with PA is that the exciting light will be attenuated because of diffusion with depth. Furthermore, improving the signal-to-noise ratio (SNR) requires repeated irradiation, and it is difficult to maintain simultaneity. In addition, obtaining multispectral information normally takes time corresponding to the number of waves, and further keeps away from real time. Coded excitation can be used to solve this problem by coding the laser pulses. Furthermore, the intensity of the received signal can be enhanced by compressing the coded signals. Using code orthogonality will enable simultaneously distinguishing multispectral photoacoustic signals and facilitating real-time imaging. Previous studies have proposed Orthogonal Golay code for multispectral coded excitation [2]. In this paper, we propose Gold codes that exhibit reasonable aperiodic cross-correlations and off-peak autocorrelations for generating multispectral PA signals simultaneously and more effectively.