Multi-level optical angiography for photodynamic therapy.

Blood flow imaging is widely applied in photodynamic therapy (PDT) to provide vascular morphological and statistical parameters. This approach relies on the intensity of time-domain signal differences between blood vessels and background tissues; therefore, it often ignores differences within the vasculature and cannot accommodate abundant structural information. This study proposes a multi-level optical angiography (MOA) method for PDT. It can enhance capillaries and image vessels at different levels by measuring the signal frequency shift associated with red blood cell motion. The experimental results regarding the PDT-induced chorioallantoic membrane model showed that the proposed method could not only perform multi-level angiography but also provide more accurate quantitative information regarding various vascular parameters. This MOA method has potential applications in PDT studies.

Choroidal vascularity index (CVI)-Net-based automatic assessment of diabetic retinopathy severity using CVI in optical coherence tomography images.

A deep learning model called choroidal vascularity index (CVI)-Net is proposed to automatically segment the choroid layer and its vessels in overall optical coherence tomography (OCT) scans. Clinical parameters are then automatically quantified to determine structural and vascular changes in the choroid with the progression of diabetic retinopathy (DR) severity. The study includes 65 eyes consisting of 34 with proliferative DR (PDR), 17 with nonproliferative DR (NPDR), and 14 healthy controls from two OCT systems. On a dataset of 396 OCT B-scan images with manually annotated ground truths, overall Dice coefficients of 96.6 ± 1.5 and 89.1 ± 3.1 are obtained by CVI-Net for the choroid layer and vessel segmentation, respectively. The mean CVI values among the normal, NPDR, and PDR groups are consistent with reported outcomes. Statistical results indicate that CVI shows a significant negative correlation with DR severity level, and this correlation is independent of changes in other physiological parameters.

Heart rate estimation from color video sequences with high SNR.

We propose an absorption intensity heartbeat modulation-averaged shifted histogram (AIHM-ASH) method for estimating human heart rate (HR) using color videos of lip image sequences. When heartbeat occurs, AIHM is generated. Based on the AIHM, HR signals can be demodulated by computing the instantaneous HR modulation depth that presents the relative red blood cell (RBC) concentration from the green channel image of the RGB color video. In addition, the ASH algorithm further suppresses the background tissue and vein signals, and increases the signal-to-noise ratio (SNR). The experimental results for flow phantoms, chicken embryos, and human lips validated the proposed method's optimal estimation conditions and effectiveness, where the accuracy and root mean square error (RMSE) were 99.23% and 0.8 bpm, respectively. The proposed HR estimation method has significant potential to advance health monitoring and disease prevention via conventional color video cameras installed in public places.

Spatiotemporal absorption fluctuation imaging based on U-Net.

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.

Tri-zone flame spatial structure imaging combined with endogenic polarized scattering.

We propose a multi-mode optical imaging method to retrieve the 2D and 3D spatial structures of the preheating, reaction, and recombination zones of an axisymmetric steady flame. In the proposed method, an infrared camera, a visible light monochromatic camera, and a polarization camera are triggered synchronously to capture 2D flame images, and their corresponding 3D images are reconstructed by combining different projection position images. The results of the experiments conducted indicate that the infrared and visible light images represent the flame preheating and flame reaction zones, respectively. The polarized image can be obtained by computing the degree of linear polarization (DOLP) of raw images captured by the polarization camera. We discover that the highlighted regions in the DOLP images lie outside the infrared and visible light zones; they are insensitive to the flame reaction and have different spatial structures for different fuels. We deduce that the combustion product particles cause endogenic polarized scattering, and that the DOLP images represent the flame recombination zone. This study focuses on the combustion mechanisms, such as the formation of combustion products and quantitative flame composition and structure.

Probing Individual Particles in Aquatic Suspensions by Simultaneously Measuring Polarized Light Scattering and Fluorescence.

Suspended particles play a significant role in aquatic systems. However, existing methods to probe suspended particles have several limitations. In this paper, we present a portable prototype to in situ probe individual particles in aquatic suspensions by simultaneously measuring polarized light scattering and fluorescence, aiming to obtain an effective classification of microplastics and microalgae. Results show that the obtained classification accuracy is significantly higher than that for either of these two methods. The setup also successfully measures submicron particles and discriminates two species of Synechococcus. Our study demonstrates the feasibility of simultaneously measuring polarized light scattering and fluorescence, and the promising capability of our method for further aquatic environmental monitoring.

Retinal cross-section motion correction in three-dimensional retinal optical coherence tomography.

Motion correction is an important issue in ophthalmic optical coherence tomography (OCT), and can improve the ability of data sets to reflect the physiological structures of tissues and make visualization and subsequent analysis easier. In this study, we present a novel method to correct the cross-sectional motion artifacts in retinal OCT volumes. Motion along the x-direction (fast-scan direction) is corrected through the normalized cross-correlation algorithm, while axial motion compensation is performed using the polynomial fitting method on the inner segment/outer segment (IS/OS) layer segmented by the shortest path faster algorithm (SPFA). The results of volunteers with central serous chorioretinopathy demonstrate that the proposed method effectively corrects motion artifacts in OCT volumes and may have potential application value in the evaluation of ophthalmic diseases such as diabetic retinopathy, glaucoma and age-related macular degeneration.

Full-field optical multi-functional angiography based on endogenous hemodynamic characteristics.

Blood flow functional imaging is widely applied in biological research to provide vascular morphological and statistical parameters. It relies on the absorption difference and is, therefore, easily affected by complex biological structures, and it cannot accommodate abundant functional information. We propose a full-field multi-functional angiography method to classify arteriovenous vessels and to display flow velocity and vascular diameter distribution simultaneously. Unlike previous methods, an under-sampled laser Doppler acquisition mode is used to record the low-coherence speckle, and multi-functional angiography is achieved by modulating the endogenous hemodynamic characteristics from low-coherence speckle. To demonstrate the combination of classified angiography, blood flow velocity measurement, and vascular diameter measurement realized using our method, we performed experiments on the flow phantom and living chicken embryos and generated multi-functional angiograms. The proposed method can be used as a label-free multi-functional angiography technique in which red blood cells provide a strong endogenous source of naturally hemodynamic characteristics.

Enhanced temporal and spatial resolution in super-resolution covariance imaging algorithm with deconvolution optimization.

Based on the numerical analysis that covariance exhibits superior statistical precision than cumulant and variance, a new SOFI algorithm by calculating the n orders covariance for each pixel is presented with an almost 2n -fold resolution improvement, which can be enhanced to 2n via deconvolution. An optimized deconvolution is also proposed by calculating the (n + 1) order SD associated with each n order covariance pixel, and introducing the results into the deconvolution as a damping factor to suppress noise generation. Moreover, a re-deconvolution of the covariance image with the covariance-equivalent point spread function is used to further increase the final resolution by above 2-fold. Simulated and experimental results show that this algorithm can significantly increase the temporal-spatial resolution of SOFI, meanwhile, preserve the sample's structure. Thus, a resolution of 58 nm is achieved for 20 experimental images, and the corresponding acquisition time is 0.8 seconds.

Large-depth-of-field full-field optical angiography.

A large-depth-of-field full-field optical angiography (LD-FFOA) method is developed to expand the depth-of-field (DOF) using a contrast pyramid fusion algorithm (CPFA). The absorption intensity fluctuation modulation effect is utilized to obtain full-field optical angiography (FFOA) images at different focus positions. The CPFA is used to process these FFOA images with different focuses. By selecting high-contrast areas, the CPFA can highlight the characteristics and details of blood vessels to obtain LD-FFOA images. In the optimal case of the proposed method, the DOF for FFOA is more than tripled using 10 differently focused FFOA images. Both the phantom and animal experimental results show that the LD-FFOA resolves FFOA defocusing issues induced by surface and thickness inhomogeneities in biological samples. The proposed method can be potentially applied to practical biological experiments.

Real-time full-field optical angiography utilizing principal component analysis.

We develop a real-time full-field optical angiography method using principal component analysis (PCA). In our approach, an undersampled laser Doppler method is used to record the raw images. Considering the difference in the signal component contributions, PCA is used to separate the dynamic blood flow and static background signals. The principal advantage of the PCA method is that the choice of a high pixel number can aid in efficiently extracting the blood flow signal with finite frame raw images, which can greatly improve the temporal resolution. Our phantom experimental results validate our choice of the optimal frame number for reconstructing an angiographic image. A vascular occlusion test on a rabbit ear demonstrates that global and simultaneous hemodynamic processes of vessels can be monitored.

Wide-field absolute transverse blood flow velocity mapping in vessel centerline.

We propose a wide-field absolute transverse blood flow velocity measurement method in vessel centerline based on absorption intensity fluctuation modulation effect. The difference between the light absorption capacities of red blood cells and background tissue under low-coherence illumination is utilized to realize the instantaneous and average wide-field optical angiography images. The absolute fuzzy connection algorithm is used for vessel centerline extraction from the average wide-field optical angiography. The absolute transverse velocity in the vessel centerline is then measured by a cross-correlation analysis according to instantaneous modulation depth signal. The proposed method promises to contribute to the treatment of diseases, such as those related to anemia or thrombosis.

In vivo full-field functional optical hemocytometer.

We present an in vivo lab-free full-field functional optical hemocytometer (FFOH) for application to the capillaries of a live biological specimen, based on the absorption intensity fluctuation modulation (AIFM) effect. Because of the absorption difference between the red blood cells (RBCs) and background tissue under low-coherence light illumination, an endogenous instantaneous intensity fluctuation is generated by the AIFM effect when RBCs discontinuously traverse the capillary. The AIFM effect is used to highlight the RBC signal relative to the background tissue by computing the real-time modulation depth. FFOH can simultaneously provide a flow video, the flow velocity and the RBC count. Ourexperimental results can potentially be applied to study the physiological mechanisms of the blood circulation systems of near-transparent live biological samples.

Full-field functional optical angiography.

We propose full-field functional optical angiography for a live biological specimen based on the absorption intensity fluctuation modulation (AIFM) effect. Because of the difference in absorption between red blood cells (RBCs) and the background tissue under low-coherence light illumination, the moving RBCs, which discontinuously pass though the capillary vessels, generate an AIFM effect. This effect offers high contrast of absorption imaging and sensitivity of low-coherence interference between RBCs and the background tissue. It is used to distinguish the signal of RBCs from that of the background tissue. The averaged and real-time modulation depths are computed to obtain full-field label-free optical angiography and measure blood flow velocity simultaneously. The AIFM method could potentially be applied to study the physiological mechanisms of blood circulation systems of near-transparent live biologic samples.

High-temporal-resolution, full-field optical angiography based on short-time modulation depth for vascular occlusion tests.

We developed high-temporal-resolution, full-field optical angiography for use in vascular occlusion tests (VOTs). In the proposed method, undersampled signals are acquired by a high-speed digital camera that separates the dynamic and static speckle signals. The two types of speckle signal are used to calculate the short-time modulation depth (STMD) of each of the camera pixels. STMD is then used to realize high-temporal-resolution, full-field optical angiography. Phantom and biological experiments conducted and demonstrated the feasibility of using our proposed method to perform VOTs and to study the reaction kinetics in microfluidic systems.

Full-field velocity imaging of red blood cells in capillaries with spatiotemporal demodulation autocorrelation.

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.

Laser Doppler projection tomography.

We propose a laser Doppler projection tomography (LDPT) method to obtain visualization of three-dimensional (3D) flowing structures. With LDPT, the flowing signal is extracted by a modified laser Doppler method, and the 3D flowing image is reconstructed by the filtered backprojection algorithm. Phantom experiments are performed to demonstrate that LDPT is able to obtain 3D flowing structure with higher signal-to-noise ratio and spatial resolution. Our experiment results display its potentially useful application to develop 3D label-free optical angiography for the circulation system of live small animal models or microfluidic experiments.

In vivo label-free microangiography by laser speckle imaging with intensity fluctuation modulation.

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.

Laser speckle projection tomography.

We propose a laser speckle projection tomography (LSPT) method to obtain a three-dimensional (3D) flowing image. The method combines the advantages of optical projection tomography and laser speckle imaging to reconstruct the visualization of 3D flowing structure. With LSPT, the flowing signal is extracted by laser speckle contrast method and the 3D flowing image is reconstructed by the filtered back-projection algorithm. A phantom experiment is performed to demonstrate that LSPT is able to obtain 3D flowing structure, influenced by concentration and the flow speed.

Laser speckle imaging based on intensity fluctuation modulation.

We present a method, intensity fluctuation modulation (IFM), to obtain a full-field laser speckle microvessel image. Different from laser speckle contrast analysis, IFM imaging is insensitive to flow velocity and can be used to reconstruct microvessel images with higher spatial resolution and SNR. An in vivo animal experiment on a mouse pinna is conducted to demonstrate that IFM imaging is capable of achieving laser speckle microangiography.