Simultaneous multispectral coded excitation for photoacoustic imaging

Currently, there is a demand for real-time photoacoustic imaging to acquire multispectral information for functional images by simultaneous irradiation with a high signal-to-noise ratio (SNR). We propose coded excitation using an m-sequence and related sequences that have good autocorrelation and cross-correlation to satisfy this demand. In this study, we demonstrate the feasibility of our proposal through experiment evaluation. M-sequence family (preferred pairs of m-sequences and related sequences such as Gold codes) are binary sequences having good cross-correlation. We investigated the coded excitation method to separate multispectral components, which are irradiated with coded laser pulses from different laser sources, into separate spectral components. We found that the proposed method can reduce the sending time cost for multispectral information. Its performance increases as the pulse repetition frequency (PRF) and code length increase. Theoretical consideration in previous research has indicated clear SNR improvement compared with averaging. Here, we conducted an experiment to verify the separation of spectral components through two-wave simultaneous sending. We compare the separated signals with the signals acquired by single-wave irradiation using the same codes to examine the reproducibility of separation. Images that demonstrate the separation are formed when a 63-bit preferred pair of m-sequences was used. The PRF in this experiment was 10 kHz because of the performance limitation of our laser system, but a faster laser module would boost the effect. The proposed method can provide an important solution since the demand for multispectral photoacoustic imaging is expected to increase.