Journals > > Topics > Biophotonics
Biophotonics|27 Article(s)
Method for measuring retinal capillary blood flow velocity by encoded OCTA
Shujiang Chen, Kaixuan Hu, Wei Yi, Fuwang Wu, Yi Wan, Lei Zhang, Jianmei Li, Aiqun Wang, and Weiye Song
The quantification of microvascular blood flow velocity is pivotal in elucidating the characteristics of retinal microcirculation, and it plays a vital role in the early detection of numerous ophthalmic pathologies. However, non-invasive technology with a large field of view for directly measuring retinal capillary blood flow velocity is lacking. In this study, a novel imaging modality called encoding optical coherence tomography angiography (En-OCTA) is presented, utilizing retinal optical coherence tomography angiography (OCTA) encoding to accurately measure the absolute blood flow velocity in retinal capillaries. En-OCTA employs a scanning speed of 250 kHz to capture multiple OCTA images at two different locations on the same unbranched capillary. As red blood cells (RBCs) slowly flow through capillaries in a single file, intermittent light and dark changes can be observed on OCTA images. Analyzing the correlation of light and dark patterns in chronologically coded images of the capillary region allows for the determination of the lag time in RBC movement between two points. Combining this lag time with the distance between scan points allows the absolute blood flow velocity in the capillaries to be accurately calculated. Animal experiments demonstrate that the method can accurately measure capillary blood flow velocity and detect changes in velocity over the duration of anesthesia. The quantification of microvascular blood flow velocity is pivotal in elucidating the characteristics of retinal microcirculation, and it plays a vital role in the early detection of numerous ophthalmic pathologies. However, non-invasive technology with a large field of view for directly measuring retinal capillary blood flow velocity is lacking. In this study, a novel imaging modality called encoding optical coherence tomography angiography (En-OCTA) is presented, utilizing retinal optical coherence tomography angiography (OCTA) encoding to accurately measure the absolute blood flow velocity in retinal capillaries. En-OCTA employs a scanning speed of 250 kHz to capture multiple OCTA images at two different locations on the same unbranched capillary. As red blood cells (RBCs) slowly flow through capillaries in a single file, intermittent light and dark changes can be observed on OCTA images. Analyzing the correlation of light and dark patterns in chronologically coded images of the capillary region allows for the determination of the lag time in RBC movement between two points. Combining this lag time with the distance between scan points allows the absolute blood flow velocity in the capillaries to be accurately calculated. Animal experiments demonstrate that the method can accurately measure capillary blood flow velocity and detect changes in velocity over the duration of anesthesia.
Chinese Optics Letters
- Publication Date: Apr. 23, 2025
- Vol. 23, Issue 4, 041701 (2025)
Label-free cellular imaging of mouse retina with dual-mode full-field optical coherence tomography
Keyi Fei, Bingying Lin, Zhongzhou Luo, Yupei Chen, Jin Yuan, and Peng Xiao
High-resolution label-free dual-mode full-field optical coherence tomography (FFOCT) is developed for simultaneous structural and functional imaging of mouse retinas, achieving both static contrasts gained from structural refractive index gradients and dynamic contrasts induced by endogenous cell motility. Imaging experiments on normal mouse retinas show that static FFOCT images better reveal the relative stationary structures like nerve fibers, vascular walls, and collagens, and dynamic FFOCT images show enhanced contrasts of cells with active intracellular metabolic motions, offering complementary information about major retinal layers. Specifically, dual-mode FFOCT imaging on early ischaemia/reperfusion (I/R) injured mouse retinas highlights the transparent ganglion cells at the cellular level without contrast agent labeling, visualizing their structural and dynamic alterations in early I/R injured retina. High-resolution label-free dual-mode full-field optical coherence tomography (FFOCT) is developed for simultaneous structural and functional imaging of mouse retinas, achieving both static contrasts gained from structural refractive index gradients and dynamic contrasts induced by endogenous cell motility. Imaging experiments on normal mouse retinas show that static FFOCT images better reveal the relative stationary structures like nerve fibers, vascular walls, and collagens, and dynamic FFOCT images show enhanced contrasts of cells with active intracellular metabolic motions, offering complementary information about major retinal layers. Specifically, dual-mode FFOCT imaging on early ischaemia/reperfusion (I/R) injured mouse retinas highlights the transparent ganglion cells at the cellular level without contrast agent labeling, visualizing their structural and dynamic alterations in early I/R injured retina.
Chinese Optics Letters
- Publication Date: Mar. 25, 2025
- Vol. 23, Issue 3, 031701 (2025)
Modified Kelvin-Voigt fractional derivative model for viscoelasticity measurement in optical coherence elastography
Chenming Yang, Zhongliang Li, Nan Nan, Teng Liu, Yaoli Luo, and Xiangzhao Wang
Optical coherence elastography (OCE) can quantitatively obtain the viscoelasticity of tissues using rheological models and is widely applied to the clinical diagnosis of diseases. However, commonly used rheological models in OCE do not account for the distinctive dependence of high-frequency storage and loss moduli on frequency in tissues, which results in the rheological models failing to accurately measure the viscoelastic properties of tissues. In this paper, a modified Kelvin-Voigt fractional derivative model is presented based on the power-law behavior of soft tissues and the dependence of high-frequency complex shear modulus on frequency in living cells. In the rheometer and OCE tests, the modified model can provide the prediction of the power-law relationship between the low-frequency shear viscosity and frequency; compared with the Kelvin-Voigt and Kelvin-Voigt fractional derivative models, the modified model has a higher goodness-of-fit (accuracy >96%) for the high-frequency storage moduli of gelatin phantoms. Furthermore, the proposed model can reduce the root mean square error of fit by approximately 83% for the high-frequency (1–128 kHz) storage modulus of the polydimethylsiloxane phantoms obtained from publicly available data. Overall, the modified model accurately predicts the mechanical properties of biomimetic materials over a wide frequency range, with the potential to more accurately reflect pathological changes in tissues. Optical coherence elastography (OCE) can quantitatively obtain the viscoelasticity of tissues using rheological models and is widely applied to the clinical diagnosis of diseases. However, commonly used rheological models in OCE do not account for the distinctive dependence of high-frequency storage and loss moduli on frequency in tissues, which results in the rheological models failing to accurately measure the viscoelastic properties of tissues. In this paper, a modified Kelvin-Voigt fractional derivative model is presented based on the power-law behavior of soft tissues and the dependence of high-frequency complex shear modulus on frequency in living cells. In the rheometer and OCE tests, the modified model can provide the prediction of the power-law relationship between the low-frequency shear viscosity and frequency; compared with the Kelvin-Voigt and Kelvin-Voigt fractional derivative models, the modified model has a higher goodness-of-fit (accuracy >96%) for the high-frequency storage moduli of gelatin phantoms. Furthermore, the proposed model can reduce the root mean square error of fit by approximately 83% for the high-frequency (1–128 kHz) storage modulus of the polydimethylsiloxane phantoms obtained from publicly available data. Overall, the modified model accurately predicts the mechanical properties of biomimetic materials over a wide frequency range, with the potential to more accurately reflect pathological changes in tissues.
Chinese Optics Letters
- Publication Date: Feb. 11, 2025
- Vol. 23, Issue 1, 011701 (2025)
Flat-top beam illumination for polarization-sensitive second-harmonic generation microscopy
Bing Wang, Xiang Li, Wenhui Yu, Binglin Shen, Rui Hu, Junle Qu, and Liwei Liu
Wide-field second-harmonic generation (SHG) was used to obtain the second-harmonic signal from the entire image area for rapid imaging, despite the fact that conventional Gaussian beam illumination has low energy utilization efficiency, which makes it easy to overexpose the intensity of the image center area. However, flat-top beam illumination has uniform spatial distribution, thereby improving the photon excitation efficiency in the entire image region and reducing laser damage and thermal effect. By combining flat-top beam illumination and wide-field SHG polarization measurement, we can calculate more myosin fibril symmetrical axis orientations through polarization analysis of 16 images at a fast imaging speed while expanding the field of view. More importantly, the application of a flat-top beam can further improve the capability of polarization measurement in SHG microscopy. Wide-field second-harmonic generation (SHG) was used to obtain the second-harmonic signal from the entire image area for rapid imaging, despite the fact that conventional Gaussian beam illumination has low energy utilization efficiency, which makes it easy to overexpose the intensity of the image center area. However, flat-top beam illumination has uniform spatial distribution, thereby improving the photon excitation efficiency in the entire image region and reducing laser damage and thermal effect. By combining flat-top beam illumination and wide-field SHG polarization measurement, we can calculate more myosin fibril symmetrical axis orientations through polarization analysis of 16 images at a fast imaging speed while expanding the field of view. More importantly, the application of a flat-top beam can further improve the capability of polarization measurement in SHG microscopy.
Chinese Optics Letters
- Publication Date: Jun. 07, 2024
- Vol. 22, Issue 6, 061701 (2024)
Multi-focus non-periodic scanning method for femtosecond lasers based on DMD and galvanometer scanners [Invited]|Editors' Pick
Huaming Li, Yu Wang, Qinglei Hu, Zhuoyu Zhang, Xiaohua Lü, and Shaoqun Zeng
Multi-focus parallel scanning can effectively increase laser fabrication throughput. However, the conventional approach of using a spatial light modulator (SLM) to generate multi-foci and scan this fixed number of foci with galvanometer scanners can only achieve a periodic scanning trajectory due to the low switching speed of the SLM. Here we demonstrate a multi-focus non-periodic scanning method for femtosecond lasers by using, instead, a fast-switching digital micromirror device (DMD) to generate a dynamic number of foci. The number of effective foci is quickly switched by introducing aberration to the undesired focus. In this way, the intensity allocated to each focus will not be affected by the number of foci, and a uniformity of 98% with different numbers of foci is achieved without adjusting the total laser energy. Finally, we validate the effectiveness of this scanning method by demonstrating corneal flap fabrication of porcine cornea in vitro. Multi-focus parallel scanning can effectively increase laser fabrication throughput. However, the conventional approach of using a spatial light modulator (SLM) to generate multi-foci and scan this fixed number of foci with galvanometer scanners can only achieve a periodic scanning trajectory due to the low switching speed of the SLM. Here we demonstrate a multi-focus non-periodic scanning method for femtosecond lasers by using, instead, a fast-switching digital micromirror device (DMD) to generate a dynamic number of foci. The number of effective foci is quickly switched by introducing aberration to the undesired focus. In this way, the intensity allocated to each focus will not be affected by the number of foci, and a uniformity of 98% with different numbers of foci is achieved without adjusting the total laser energy. Finally, we validate the effectiveness of this scanning method by demonstrating corneal flap fabrication of porcine cornea in vitro.
Chinese Optics Letters
- Publication Date: May. 17, 2024
- Vol. 22, Issue 5, 051701 (2024)
Iterative multi-photon adaptive compensation technique for deep tissue two-photon fluorescence lifetime imaging
Kexin Wang, Wenhui Yu, Junle Qu, Changrui Liao, Yiping Wang, Jun He, and Liwei Liu
Fluorescence lifetime imaging can reveal the high-resolution structure of various biophysical and chemical parameters in a microenvironment quantitatively. However, the depth of imaging is generally limited to hundreds of micrometers due to aberration and light scattering in biological tissues. This paper introduces an iterative multi-photon adaptive compensation technique (IMPACT) into a two-photon fluorescence lifetime microscopy system to successfully overcome aberrations and multiple scattering problems in deep tissues. It shows that 400 correction modes can be achieved within 5 min, which was mainly limited by the frame rate of a spatial light modulator. This system was used for high-resolution imaging of mice brain tissue and live zebrafish, further verifying its superior performance in imaging quality and photon accumulation speed. Fluorescence lifetime imaging can reveal the high-resolution structure of various biophysical and chemical parameters in a microenvironment quantitatively. However, the depth of imaging is generally limited to hundreds of micrometers due to aberration and light scattering in biological tissues. This paper introduces an iterative multi-photon adaptive compensation technique (IMPACT) into a two-photon fluorescence lifetime microscopy system to successfully overcome aberrations and multiple scattering problems in deep tissues. It shows that 400 correction modes can be achieved within 5 min, which was mainly limited by the frame rate of a spatial light modulator. This system was used for high-resolution imaging of mice brain tissue and live zebrafish, further verifying its superior performance in imaging quality and photon accumulation speed.
Chinese Optics Letters
- Publication Date: Apr. 26, 2024
- Vol. 22, Issue 4, 041702 (2024)
Noncontact ultrasound sensing based on Mach–Zehnder homodyne interferometer for photoacoustic imaging
Xing Long, Yicheng Hu, Yibing Wang, and Changhui Li
We present a novel noncontact ultrasound (US) and photoacoustic imaging (PAI) system, overcoming the limitations of traditional coupling media. Using a long coherent length laser, we employ a homodyne free-space Mach–Zehnder setup with zero-crossing triggering, achieving a noise equivalent pressure of 703 Pa at 5 MHz and a -6 dB bandwidth of 1 to 8.54 MHz. We address the phase uncertainty inherent in the homodyne method. Scanning the noncontact US probe enables photoacoustic computed tomography (PACT). Phantom studies demonstrate imaging performance and system stability, underscoring the potential of our system for noncontact US sensing and PAI. We present a novel noncontact ultrasound (US) and photoacoustic imaging (PAI) system, overcoming the limitations of traditional coupling media. Using a long coherent length laser, we employ a homodyne free-space Mach–Zehnder setup with zero-crossing triggering, achieving a noise equivalent pressure of 703 Pa at 5 MHz and a -6 dB bandwidth of 1 to 8.54 MHz. We address the phase uncertainty inherent in the homodyne method. Scanning the noncontact US probe enables photoacoustic computed tomography (PACT). Phantom studies demonstrate imaging performance and system stability, underscoring the potential of our system for noncontact US sensing and PAI.
Chinese Optics Letters
- Publication Date: Mar. 28, 2024
- Vol. 22, Issue 3, 031702 (2024)
Stimulated emission–depletion-based point-scanning structured illumination microscopy
Lei Wang, Meiting Wang, Luwei Wang, Xiaomin Zheng, Jiajie Chen, Wenshuai Wu, Wei Yan, Bin Yu, Junle Qu, Bruce Zhi Gao, and Yonghong Shao
Wide-field linear structured illumination microscopy (LSIM) extends resolution beyond the diffraction limit by moving unresolvable high-frequency information into the passband of the microscopy in the form of moiré fringes. However, due to the diffraction limit, the spatial frequency of the structured illumination pattern cannot be larger than the microscopy cutoff frequency, which results in a twofold resolution improvement over wide-field microscopes. This Letter presents a novel approach in point-scanning LSIM, aimed at achieving higher-resolution improvement by combining stimulated emission depletion (STED) with point-scanning structured illumination microscopy (psSIM) (STED-psSIM). The according structured illumination pattern whose frequency exceeds the microscopy cutoff frequency is produced by scanning the focus of the sinusoidally modulated excitation beam of STED microscopy. The experimental results showed a 1.58-fold resolution improvement over conventional STED microscopy with the same depletion laser power. Wide-field linear structured illumination microscopy (LSIM) extends resolution beyond the diffraction limit by moving unresolvable high-frequency information into the passband of the microscopy in the form of moiré fringes. However, due to the diffraction limit, the spatial frequency of the structured illumination pattern cannot be larger than the microscopy cutoff frequency, which results in a twofold resolution improvement over wide-field microscopes. This Letter presents a novel approach in point-scanning LSIM, aimed at achieving higher-resolution improvement by combining stimulated emission depletion (STED) with point-scanning structured illumination microscopy (psSIM) (STED-psSIM). The according structured illumination pattern whose frequency exceeds the microscopy cutoff frequency is produced by scanning the focus of the sinusoidally modulated excitation beam of STED microscopy. The experimental results showed a 1.58-fold resolution improvement over conventional STED microscopy with the same depletion laser power.
Chinese Optics Letters
- Publication Date: Mar. 13, 2024
- Vol. 22, Issue 3, 031701 (2024)
Laser speckle contrast imaging based on uniting spatiotemporal Fourier transform
Linjun Zhai, Yongzhao Du, Xunxun Wu, Yong Diao, and Yuqing Fu
We propose a laser speckle contrast imaging method based on uniting spatiotemporal Fourier transform. First, the raw speckle images are entirely transformed to the spatiotemporal frequency domain with a three-dimensional (3D) fast Fourier transform. Second, the dynamic and static speckle components are extracted by applying 3D low-pass and high-pass filtering in the spatiotemporal frequency domain and inverse 3D Fourier transform. Third, we calculate the time-averaged modulation depth with the average of both components to map the two-dimensional blood flow distribution. The experiments demonstrate that the proposed method could effectively improve computational efficiency and imaging quality. We propose a laser speckle contrast imaging method based on uniting spatiotemporal Fourier transform. First, the raw speckle images are entirely transformed to the spatiotemporal frequency domain with a three-dimensional (3D) fast Fourier transform. Second, the dynamic and static speckle components are extracted by applying 3D low-pass and high-pass filtering in the spatiotemporal frequency domain and inverse 3D Fourier transform. Third, we calculate the time-averaged modulation depth with the average of both components to map the two-dimensional blood flow distribution. The experiments demonstrate that the proposed method could effectively improve computational efficiency and imaging quality.
Chinese Optics Letters
- Publication Date: Jan. 08, 2024
- Vol. 22, Issue 1, 011701 (2024)
Aberration correction for multiphoton microscopy using covariance matrix adaptation evolution strategy
Ke Wang, Lei Zheng, Mengyuan Qin, Wanjian Zhang, Xiangquan Deng, Shen Tong, Hui Cheng, Jie Huang, Jincheng Zhong, Yingxian Zhang, and Ping Qiu
Multiphoton microscopy is the enabling tool for biomedical research, but the aberrations of biological tissues have limited its imaging performance. Adaptive optics (AO) has been developed to partially overcome aberration to restore imaging performance. For indirect AO, algorithm is the key to its successful implementation. Here, based on the fact that indirect AO has an analogy to the black-box optimization problem, we successfully apply the covariance matrix adaptation evolution strategy (CMA-ES) used in the latter, to indirect AO in multiphoton microscopy (MPM). Compared with the traditional genetic algorithm (GA), our algorithm has a greater improvement in convergence speed and convergence accuracy, which provides the possibility of realizing real-time dynamic aberration correction for deep in vivo biological tissues. Multiphoton microscopy is the enabling tool for biomedical research, but the aberrations of biological tissues have limited its imaging performance. Adaptive optics (AO) has been developed to partially overcome aberration to restore imaging performance. For indirect AO, algorithm is the key to its successful implementation. Here, based on the fact that indirect AO has an analogy to the black-box optimization problem, we successfully apply the covariance matrix adaptation evolution strategy (CMA-ES) used in the latter, to indirect AO in multiphoton microscopy (MPM). Compared with the traditional genetic algorithm (GA), our algorithm has a greater improvement in convergence speed and convergence accuracy, which provides the possibility of realizing real-time dynamic aberration correction for deep in vivo biological tissues.
Chinese Optics Letters
- Publication Date: Apr. 12, 2023
- Vol. 21, Issue 5, 051701 (2023)
Topics
© Copyright 2018-2021 | Chinese Laser Press. All Rights Reserved 沪ICP备15018463号-20