Photoacoustic imaging creates light-induced ultrasonic signals to provide valuable information on internal body structures and tissue morphology non-invasively. A multi-aperture photoacoustic imaging (MP-PAI) system is an improvement over conventional photoacoustic imaging (PAI) systems in terms of resolution, contrast, and field of view. Previously, a prototype MP-PAI system was introduced based on multiple capacitive micromachined ultrasound transducers (CMUTs) with shared channels, such that each element in a CMUT shares its channel with its counterpart in other CMUTs. The system uses the biasing voltages of the CMUTs to switch between them and multiplex the received signals in time. Notwithstanding all the enhancements, the signal-to-noise ratio (SNR) remains limited in PAI. To address this issue, we are proposing a multi-aperture encoding scheme (MAES) to further increase the SNR in a multi-aperture PAI system. The proposed method involves receiving signals with multiple CMUTs simultaneously based on an encoding matrix, instead of switching between individual CMUTs. As a result, shared channels contain a superposition of signals, which are later recovered by applying a decoding matrix. Here, an analytical model for computing SNR with an arbitrary encoding sequence is presented, and the method is validated through numerical simulations and in an experimental study. Bipolar and unipolar encoding sequences were considered for the experiments. The numerical results show, in comparison to conventional MP-PAI, that MAES will obtain an SNR gain of 5.8 and 8.8 dB for S-sequence and truncated Hadamard encodings, respectively, when using 15 transducers. In experiments, three transducers are encoded by S-sequences and show 1.5 dB improvement in SNR over conventional MP-PAI method, which aligns well with the analytical model.

中文翻译：

---

一种提高光声成像信噪比的多孔径编码方案

光声成像产生光感应超声波信号，以非侵入性方式提供有关身体内部结构和组织形态的有价值的信息。多孔径光声成像（MP-PAI）系统在分辨率、对比度和视场方面比传统光声成像（PAI）系统有所改进。此前，基于具有共享通道的多个电容式微机械超声换能器 (CMUT) 推出了原型 MP-PAI 系统，使得 CMUT 中的每个元件与其他 CMUT 中的对应元件共享其通道。该系统使用 CMUT 的偏置电压在它们之间切换并及时复用接收到的信号。尽管进行了所有增强，PAI 中的信噪比 (SNR) 仍然有限。为了解决这个问题，我们提出了一种多孔径编码方案（MAES），以进一步提高多孔径 PAI 系统中的 SNR。所提出的方法涉及基于编码矩阵同时使用多个 CMUT 接收信号，而不是在各个 CMUT 之间切换。因此，共享通道包含信号的叠加，随后通过应用解码矩阵来恢复这些信号。这里提出了一种计算任意编码序列的信噪比的分析模型，并通过数值模拟和实验研究对该方法进行了验证。实验考虑了双极和单极编码序列。数值结果表明，与传统的 MP-PAI 相比，当使用 15 个换能器时，MAES 对于 S 序列和截断 Hadamard 编码将分别获得 5.8 和 8.8 dB 的 SNR 增益。在实验中，三个换能器由 S 序列编码，与传统 MP-PAI 方法相比，SNR 提高了 1.5 dB，这与分析模型非常吻合。