Significance: Full-field optical angiography is critical for vascular disease research and clinical diagnosis. Existing methods struggle to improve the temporal and spatial resolutions simultaneously.
Aim: Spatiotemporal absorption fluctuation imaging (ST-AFI) is proposed to achieve dynamic blood flow imaging with high spatial and temporal resolutions.
Approach: ST-AFI is a dynamic optical angiography based on a low-coherence imaging system and U-Net. The system was used to acquire a series of dynamic red blood cell (RBC) signals and static background tissue signals, and U-Net is used to predict optical absorption properties and spatiotemporal fluctuation information. U-Net was generally used in two-dimensional blood flow segmentation as an image processing algorithm for biomedical imaging. In the proposed approach, the network simultaneously analyzes the spatial absorption coefficient differences and the temporal dynamic absorption fluctuation.
Results: The spatial resolution of ST-AFI is up to 4.33 μm, and the temporal resolution is up to 0.032 s. In vivo experiments on 2.5-day-old chicken embryos were conducted. The results demonstrate that intermittent RBCs flow in capillaries can be resolved, and the blood vessels without blood flow can be suppressed.
Conclusions: Using ST-AFI to achieve convolutional neural network (CNN)-based dynamic angiography is a novel approach that may be useful for several clinical applications. Owing to their strong feature extraction ability, CNNs exhibit the potential to be expanded to other blood flow imaging methods for the prediction of the spatiotemporal optical properties with improved temporal and spatial resolutions.
We propose a logic optical projection tomography (LOPT) method to realize full-view, three-dimensional (3-D) shape parameters measurement and visualization for opaque objects. The main innovation of LOPT is use of a logic process to obtain high-contrast and homogeneous boundary projection signals. According to the reconstructed 2-D cross-section images, the structure characteristic points in each slice are independently extracted and combined to produce a full-view 3-D image. Further, the structural shape parameters of individual parts of object such as the inscribed cylinder, center line, and double threads are obtained and visualized simultaneously. Our experimental results demonstrate that LOPT can be potentially developed as an economical optical measurement and visualization tool for some industrial application.
We propose a full-field optical method for the label-free and quantitative mapping of the velocities of red blood cells (RBCs) in capillaries. It integrates spatiotemporal demodulation and an autocorrelation algorithm, and measures RBC velocity according to the ratio of RBC length to lag time. Conventionally, RBC length is assumed to be a constant and lag time is taken as a variable, while our method treats both of them as variables. We use temporal demodulation and the Butterworth spatial filter to separate RBC signal from background signal, based on which we obtain the RBC length by image segmentation and lag time by autocorrelation analysis. The RBC velocity calculated now is more accurate. The validity of our method is verified by an in vivo experiment on a mouse ear. Owing to its higher image signal-to-noise ratio, our method can be used for mapping RBC velocity in the turbid tissue case.
We present the theory of laser speckle imaging improved with intensity fluctuation modulation, where the dynamic speckle pattern can be isolated from its stationary counterpart. A series of in vivo experiments demonstrate the effectiveness of our method in achieving microangiography and monitoring vascular self-recovering process. All results show the convincing performance of our imaging method in both structural and functional imaging of blood flow, which may have potential applications in biological research and disease diagnosis.
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