用于散射介质内反射模式深光学成像的声光体积选通
Acousto-optic volumetric gating for reflection-mode deep optical imaging within a scattering medium
摘要：
深部组织光学显微镜的成像深度取决于门控操作的性能，门控操作抑制了遮蔽弹道波的多重散射波。虽然基于共焦、时间分辨/相干门控和偏振选择性检测的各种门控操作已被证明是有效的，但每种都有其自身的局限性;某些类型的多重散射波可以绕过门控。在这里，我们提出了一种方法，体积门控，引入超声聚焦共焦反射成像，以抑制多重散射波传播的超声焦体积外。体积选通轴向地抑制传播到比物平面浅的深度的多次散射波，同时抑制在30 ${\times}$ 90 $ μm^2$的超声焦点的横向范围之外穿过物平面传播的较深穿透部分。这些沿轴向和横向的联合选通作用使多重散射波衰减1/1000或更小的因子，从而将成像深度扩展到散射平均自由程的12.1倍，同时保持1.5 $μ$ m的衍射极限分辨率。我们证明了通过其外壁的小鼠结肠和小肠的内部组织成像的成像深度和对比度的增加。我们进一步发展了理论和实验框架来表征散射介质内光轨迹的轴向分布。体积门控将作为一个重要的除了深层组织成像模式和一个有用的工具，研究波在散射介质中的传播。
英文摘要：
The imaging depth of deep-tissue optical microscopy is governed by the performance of the gating operation that suppresses the multiply scattered waves obscuring the ballistic waves. Although various gating operations based on confocal, time-resolved/coherence-gated, and polarization-selective detections have proven to be effective, each has its own limitation; certain types of multiply scattered waves can bypass the gating. Here, we propose a method, volumetric gating, that introduces ultrasound focus to confocal reflectance imaging to suppress the multiply scattered waves traveling outside the ultrasonic focal volume. The volumetric gating axially rejects the multiply scattered wave traveling to a depth shallower than the object plane while suppressing the deeper penetrating portion that travels across the object plane outside the transversal extent of the ultrasonic focus of 30${\times}$90$ μm^2$. These joint gating actions along the axial and lateral directions attenuate the multiply scattered waves by a factor of 1/1000 or smaller, thereby extending the imaging depth to 12.1 times the scattering mean free path while maintaining the diffraction-limited resolution of 1.5 $μ$m. We demonstrated an increase in the imaging depth and contrast for internal tissue imaging of mouse colon and small intestine through their outer walls. We further developed theoretical and experimental frameworks to characterize the axial distribution of light trajectories inside scattering media. The volumetric gating will serve as an important addition to deep-tissue imaging modalities and a useful tool for studying wave propagation in scattering media.
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