In this letter, we reported a high-resolution photoacoustic microscopy (PAM) to image erythrocytes and blood vessels. The developed system had the ability to provide a lateral resolution of 1.0 μm at the wavelength of 532 nm with a × 10 objective. First, we used a sharp edge to measure the lateral resolution of the PAM and testified the stability with carbon fibers. Then, using this system, in vivo blood vessels and capillaries of a mouse ear, even a single erythrocyte can be clearly imaged. There was a pair of accompanying venule and arteriole, whose detailed and further complicated branches can be clearly identified. And likely red blood cells (RBCs) arrayed one by one in microvasculature was also shown. The experimental results demonstrate that the high-resolution PAM has potential clinical applications for imaging of erythrocytes and blood vessels.
Polarization-sensitive optical coherence tomography (PS-OCT) enables depth-resolved mapping of sample polarization information, such as phase-retardation and optical axis orientation, which is particularly useful when the nano-scale organization of tissue that are difficult to be observed in the intensity images of a regular optical coherence tomography (OCT). In this review, we survey two types of methods and systems of PS-OCT. The first type is PS-OCT with single input polarization state, which contain bulk optics or polarization maintaining fiber (PMF) based systems and single-mode fiber (SMF) based systems. The second type is PS-OCT with two different input polarization states, which contain SMF based systems and PMF based systems, through either time, frequency, or depth multiplexing. In addition, representative biomedical applications using PS-OCT, such as retinal imaging, skin cancer detection, and brain mapping, are demonstrated.
The applications of two-photon microscopy (TPM) on pre-clinical and clinical study of human cancer and diseases are reviewed in this paper. First, the principle of two-photon excitation (TPE) is introduced. The resulting advantages of TPM for imaging studies of animal models and human samples are then elaborated. Subsequently, the applications of TPM on various aspects of tumor studies, including tumor angiogenesis, invasion and metastasis, tumor microenvironment and metabolism are introduced. Furthermore, studies of TPM on clinical human skin biopsy and the development of two-photon microendoscopy are reviewed. Finally, potential future directions are discussed.
Point spread function (PSF) engineering-based methods to enhance resolution and contrast of optical microscopes have experienced great achievements in the last decades. These techniques include: stimulated emission depletion (STED), time-gated STED (g-STED), ground-state depletion microscopy (GSD), difference confocal microscopy, fluorescence emission difference microscopy (FED), switching laser mode (SLAM), virtual adaptable aperture system (VAAS), etc. Each affords unique strengths in resolution, contrast, speed and expenses. We explored how PSF engineering generally could be used to break the diffraction limitation, and concluded that the common target of PSF engineering-based methods is to get a sharper PSF. According to their common or distinctive principles to reshape the PSF, we divided all these methods into three categories, nonlinear PSF engineering, linear PSF engineering, and linear-based nonlinear PSF engineering and expounded these methods in classification. Nonlinear effect and linear subtraction is the core techniques described in this paper from the perspective of PSF reconstruction. By comparison, we emphasized each method’s strengths, weaknesses and biologic applications. In the end, we promote an expectation of prospective developing trend for PSF engineering.
The depth ranges of typical implementations of Fourier domain optical coherence tomography (FDOCT), including spectral domain OCT (SDOCT) and swept source OCT (SSOCT), are limited to several millimeters. To extend the depth range of current OCT systems, two novel systems with ultralong depth range were developed in this study. One is the orthogonal dispersive SDOCT (OD-SDOCT), and the other is the recirculated swept source (R-SS) interferometer/OCT. No compromise between depth range and depth resolution is required in both systems. The developed OD-SDOCT system realized the longest depth range (over 100 mm) ever achieved by SDOCT, which is ready to be modified for depth-encoded parallel imaging on multiple sites. The developed R-SS interferometer achieved submicron precision within a depth range of 30 mm, holding potential in real-time contact-free on-axis metrology of complex optical systems.
Doppler optical coherence tomography or optical Doppler tomography (ODT) has been demonstrated to spatially localize flow velocity mapping as well as to obtain images of microstructure of samples simultaneously. In recent decades, spectral domain Doppler optical coherence tomography (OCT) has been applied to observe three-dimensional (3D) vascular distribution. In this study, we developed a spectral domain optical coherence tomography system (SD-OCT) using super luminescent diode (SLD) as light source. The center wavelength of SLD is 835 nm with a 45-nm bandwidth. Theoretically, the transverse resolution, axial resolution and penetration depth of this SD-OCT system are 6.13 μm, 6.84 μm and 3.62 mm, respectively. By imaging mouse model with dorsal skin window chamber, we obtained a series of real-time OCT images and reconstructed 3D images of the specific area inside the dorsal skin window chamber by Amira. As a result, we can obtain the clear and complex distribution images of blood vessels of mouse model.
With the rapid development of life sciences, there is an increasing demand for intravital fluorescence imaging of small animals. However, large dimensions and limited working distances of objective lenses in traditional fluorescence microscopes have limited their imaging applications mostly to superficial tissues. To overcome these disadvantages, researchers have developed the graded-index (GRIN) probes with small diameters for imaging internal organs of small animals in a minimally invasive fashion. However, dynamic imaging based on GRIN lens has not been studied extensively. Here, this paper presented a fluorescence endoscopic imaging system based on GRIN lenses using one-photon and two-photon excitation. GRIN lenses with 1.15 mm diameter and 7.65 mm length were used in the system. The images were acquired by a compact laser scanning imaging system with a resonant galvo-mirror system to scan the laser beam and a photomultiplier tube (PMT) to detect fluorescence signals. Experimental results showed that this system using two-photon excitation could implement dynamic fluorescence microendoscopic imaging and monitor the movement of blood flow beneath the skin in anesthetized mice while producing images with higher contrast and signal to noise ratio (SNR) than those using one photon excitation. It would be a useful tool for studying biological processes of small animals or plants in vivo.
Accurate diagnosis of different bronchopulmonary diseases is important in clinical practice. This study involved 20 healthy volunteers and 77 patients with bronchopulmonary diseases, including chronic obstructive pulmonary disease (COPD), bronchial asthma, pulmonary tuberculosis, and community-acquired pneumonia. The absorption spectrum of exhaled air samples was recorded on an intra-cavity photo-acoustic gas analyzer (ILPA-1, Special Technologies, Ltd., Russia) with photo-acoustic detectors and CO2 laser with a tuning range from 9.2 to 10.8 μm. In conclusion, analysis of the Mahalanobis distance-based absorption spectral profiles of breath air from bronchopulmonary patients and healthy volunteers allows the formulation of a preliminary diagnosis.
Laser speckle contrast imaging (LSCI) is a powerful tool for blood flow mapping. In this paper, we described a simple algorithm based on histogram analysis of laser speckle contrast image to provide rapid differentiation between macro- and microcirculations. The algorithm was successfully verified by the study of blood flow in rat cortex under functional activation.
Aiming at solving the problem of low resolution and visual blur in infrared imaging, a super-resolution infrared image reconstruction method using human vision processing mechanism (HVPM) was proposed. This method combined a mechanism of vision lateral inhibition with an algorithm projection onto convex sets (POCS) reconstruction, the improved vision lateral inhibition network was utilized to enhance the contrast between object and background of low-resolution image sequences, then POCS algorithm was adopted to reconstruct super-resolution image. Experimental results showed that the proposed method can significantly improve the visual effect of image, whose contrast and information entropy of reconstructed infrared images were improved by approximately 5 times and 1.6 times compared with traditional POCS reconstruction algorithm, respectively.
Integrating sphere technique is widely used to measure the total reflectance and transmittance of turbid sample, but the unavoidable light loss induces some measuring error. It has never been reported whether the error depends on the shape and size of light beam. In this paper, a convolution for computing the responses to rectangular incident light beam based on the Monte Carlo method was presented. The effects of light beam shape and size, and optical properties of sample on the measurements were addressed. The results show that the light loss with rectangular incident light beam is larger than that with circular one with the same area. The more the area of light beam, the more the light loss. And the light loss induced by the optical properties of sample is much more significant than that by the shape and size of the incident light beam.
In this study, the interaction between diode laser radiation and chicken soft tissue was studied in vitro by a high-speed digital video camera. We used a diode laser with a wavelength of (980 ± 10) nm and average power of 10 W. The diode laser was operated in continuous wave (CW) and pulsed modes. In CW mode, the average laser radiation power was 10 W; in pulsed mode, the average laser radiation power was 10 W and the peak power was 20 W. Diode laser radiation was delivered to soft tissue (chicken meat) using a quartz optical fiber with either a clear distal end (clear tip) or a distal end containing an optothermal converter (hot tip). Application of the diode laser in pulsed mode resulted in crater depths and areas of collateral damage in soft tissue about 1.6 times greater than those observed in CW mode at treatment with the clear tip. Significant differences in the crater depth and collateral damage width of chicken meat were not found after hot-tip treatment with the diode laser in CW and pulsed modes. Soft tissue treated with the hot tip showed crater depths about 3.4 times greater than those observed after treatment with the clear tip. Hot tip treatment further resulted in collateral damage widths about 2.7 times lower than those obtained after treatment with the clear tip.
Close packed ZnO nanoparticles on carbon cloth were synthesized by repeating a facile hydrothermal route in this study. After characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), the obtained ZnO cloth was further studied for the applications in lithium (Li)-ion batteries (LIBs) and dye-sensitized solar cells (DSSCs). When ZnO cloth annealed at 400°C for 2 h were used as anodes of LIBs, it exhibited high capacity of 600 mAh/g and outstanding cycling capability without significant fading after 130 cycles. Moreover, it was also found that our electrodes displayed good stabilities under various humidity and temperature. Furthermore, the obtained composites were calcined at higher temperature (800°C) to remove carbon and white pure ZnO cloth was formed. We transferred the as-formed ZnO cloth to?fluorine-doped tin oxide (FTO) substrate to make DSSCs, exhibiting an improved efficiency of around 0.38% assisted by TiCl4 treatment.