Multiwavelength laser doppler holography (MLDH) in spatiotemporal optical coherence tomography (STOC-T)

Spatiotemporal optical coherence tomography (STOC-T) is the novel modality for high-speed, crosstalk- and aberration-free volumetric imaging of biological tissue in vivo. STOC-T extends the Fourier-Domain holographic Optical Coherence Tomography by the spatial phase modulation that enables the reduction of spatial coherence of the tunable laser. By reducing the spatial coherence of the laser, we suppress coherent noise, and, consequently, improve the imaging depth. Furthermore, we remove geometrical aberrations computationally in postprocessing. We recently demonstrated high-speed, high-resolution STOC-T of human retinal imaging in vivo. Here, we show that the dataset produced by STOC-T can be processed differently to reveal blood flow in the human retina in vivo. To render the blood flow, we first pre-process STOC-T holographic data to access the approximated information about the Doppler-shifted optical field backscattered from the sample. Then, we analyze it using methods from the laser Doppler flowmetry, namely, by analyzing the Doppler broadening caused by moving light scatterers (red blood cells). However, contrary to conventional approaches, we use multiple illumination wavelengths. This enables us to render the structural volumetric and blood flow images from the same dataset concurrently. Our method, denoted as multiwavelength laser Doppler holography (MLDH), links laser Doppler flowmetry with multiwavelength holographic detection to enable noninvasive visualization and possible blood flow quantification at different human retina layers at high speeds and high transverse resolution in vivo.

时空光学相干断层扫描（Spatiotemporal Optical Coherence Tomography，STOC-T）是一种新型成像模态，可实现生物组织在体状态下的高速、无串扰、无像差三维体积成像。STOC-T通过空间相位调制技术对傅里叶域全息光学相干断层扫描进行拓展，实现了可调谐激光器空间相干性的降低。通过降低激光器的空间相干性，可有效抑制相干噪声，进而提升成像深度。此外，我们可在后期处理中通过计算方式消除几何像差。我们近期已成功实现人体视网膜在体状态下的高速高分辨率STOC-T成像。本研究表明，针对STOC-T生成的数据集采用差异化处理流程，可实现人体视网膜在体状态下的血流可视化。为实现血流可视化，我们首先对STOC-T全息数据进行预处理，以获取样本背散射的多普勒频移光场的近似信息。随后，我们采用激光多普勒血流仪的相关分析方法，即通过分析由运动光散射体（红细胞）引发的多普勒展宽，对上述信息进行解析。但与传统方法不同的是，本研究采用多照明波长方案。这使得我们可从同一数据集同时获取结构三维图像与血流图像。我们将该方法命名为多波长激光多普勒全息术（Multiwavelength Laser Doppler Holography，MLDH），该技术将激光多普勒血流仪与多波长全息检测技术相结合，可在人体视网膜不同层级实现高速、高横向分辨率的在体无创可视化，并可实现血流定量分析。