Acoustic-resolution photoacoustic micro- scopy (AR-PAM) system can provide 3-D images of facial tissues. The lateral resolution of AR-PAM depends on the numerical aperture (NA) of the acoustic lens and the central frequency of the ultrasonic transducer. There is a trade-off between resolution enhancement and imaging depth. The acoustic beam is tight in the acoustic focal plane but expands in the out-of-focus regions, deteriorating the resolution. High-NA AR-PAM has depth-variant resolution. Synthetic aperture focusing technique (SAFT) based on a virtual detector (VD) concept can compensate for the beam shape and improve the lateral resolution via beamforming. Although, beamforming can enhance the resolution but the lateral resolution in the focal plane is still limited by acoustic diffraction. Structured-illumination can shift the spatial spectrum of an image to low frequencies hence high-frequency contents can be reserved to overcome the diffraction limit. Conventional structured-illumination via using a three-phase-shifting method can improve the resolution by two folds. Here, a modified phase-shifting method is used to generate the second harmonic of the fringes and double the spectral shift. In this idea, higher frequency information compared to the three-phase shifting method can fall into the band-limited system response. The modified phase-shifting method expands the spatial bandwidth and increases the lateral resolution by five folds. The mathematical relations and the theory are discussed in the context. Tungsten filament result shows resolution improvement from 44.6 μm\mu \text{m} to 11.3 μm\mu \text{m} by the modified structured illumination. In vivo and ex vivo experimental results validate the system performance.

中文翻译：

---

通过修正相复合的超分辨率光声显微镜


声分辨率光声显微镜（AR-PAM）系统可以提供面部组织的 3D 图像。 AR-PAM 的横向分辨率取决于声透镜的数值孔径 (NA) 和超声换能器的中心频率。分辨率增强和成像深度之间需要权衡。声束在声焦平面中很紧，但在离焦区域中扩展，从而降低了分辨率。高数值孔径 AR-PAM 具有随深度变化的分辨率。基于虚拟探测器（VD）概念的合成孔径聚焦技术（SAFT）可以补偿波束形状并通过波束形成提高横向分辨率。虽然波束形成可以提高分辨率，但焦平面的横向分辨率仍然受到声衍射的限制。结构照明可以将图像的空间光谱转移到低频，因此可以保留高频内容以克服衍射极限。传统的结构照明通过使用三相移方法可以将分辨率提高两倍。这里，使用改进的相移方法来生成条纹的二次谐波并使光谱偏移加倍。在这个想法中，与三相相移方法相比，更高频率的信息可以落入带限系统响应中。改进的相移方法扩大了空间带宽，并将横向分辨率提高了五倍。在上下文中讨论了数学关系和理论。钨丝结果显示，通过改进的结构照明，分辨率从 44.6 μm\mu \text{m} 提高到 11.3 μm\mu \text{m}。体内和离体实验结果验证了系统的性能。