Interference illumination of three nonzero-order beams for LCOS-based structured illumination microscopy

To avoid the need for a mask and polarisation-adjusting devices, and to solve the problem of low fringe contrast caused by the reflected light along with 0th-order diffraction beam, this paper presents an illumination method using three nonzero-order diffraction beams in liquid crystal on silicon (LCOS)-based structured illumination microscopy. Here, a LCOS-based spatial light modulator (SLM) is used to diffract the collimated light and a rotating frosted film is used to reduce the spatial coherence of the laser; then, the fringe is produced by adjusting the SLM angle to allow three nonzero-order diffraction beams to interfere on the sample surface. Interference fringes with high contrast in all directions can be obtained without considering polarisation control and the removal of the 0th-order diffraction beam, which demonstrates that the optical setup is simple and easy to control. We carried out experiments on a photolithographic pattern on a silicon chip, and the resolution after reconstruction is 210 nm, reaching the theoretical resolution at our experiment condition and nearly half of the Rayleigh resolution limit (100× objective, NA = 0.8), which is 406 nm. LAY DESCRIPTION: SIM has been widely applied in imaging of biological sample owing to its advantage of super-resolution. Commonly the structured illumination is produced by interfering two or three diffractive beams and the fringe contrast affects the reconstruction result directly. In this study about liquid-crystal-on-silicon based structured illumination microscopy (LCOS-based SIM), we presents an illumination method using three nonzero-order diffractive beams. Our method can avoid the need for a mask and the polarisation-adjusting devices, because three-beam interference can reduce the influence of polarisation on the fringe contrast. Besides, 0th-order beam is not used, because reflected light still exists even the grey level of the picture-pixels uploaded to spatial light modulator are all 0, which means the 0th-order beam will bring obvious noise. Using our method, interference fringe with high contrast in all directions can be obtained at a relatively high utilisation rate of laser intensity without considering the control of polarisation. Our setup is simple and easy to control, because the adjustment of the deflection angle of the spatial light modulator can realise the removal of the zero diffraction order. We have analysed and discussed the reasons why the interference of three nonzero-order beams can avoid the influence of polarisation and amplitude. The experiments carried out on a photolithographic pattern on silicon chip showed that the resolution after reconstruction is 210 nm, reaching the half of the Rayleigh resolution limit (100× objective, NA=0.8), which is 406 nm.

Monochromatic-beam-based dynamic X-ray microtomography based on OSEM-TV algorithm

Monochromatic-beam-based dynamic X-ray computed microtomography (CT) was developed to observe evolution of microstructure inside samples. However, the low flux density results in low efficiency in data collection. To increase efficiency, reducing the number of projections should be a practical solution. However, it has disadvantages of low image reconstruction quality using the traditional filtered back projection (FBP) algorithm. In this study, an iterative reconstruction method using an ordered subset expectation maximization-total variation (OSEM-TV) algorithm was employed to address and solve this problem. The simulated results demonstrated that normalized mean square error of the image slices reconstructed by the OSEM-TV algorithm was about 1/4 of that by FBP. Experimental results also demonstrated that the density resolution of OSEM-TV was high enough to resolve different materials with the number of projections less than 100. As a result, with the introduction of OSEM-TV, the monochromatic-beam-based dynamic X-ray microtomography is potentially practicable for the quantitative and non-destructive analysis to the evolution of microstructure with acceptable efficiency in data collection and reconstructed image quality.

Automated segmentation and enhancement of optical coherence tomography-acquired images of rodent brain

BACKGROUND

Optical coherence tomography (OCT) is a non-invasive optical imaging method that has proven useful in various fields such as ophthalmology, dermatology and neuroscience. In ophthalmology, significant progress has been made in retinal layer segmentation and enhancement of OCT images. There are also segmentation algorithms to separate epidermal and dermal layers in OCT-acquired images of human skin.

NEW METHOD

We describe simple image processing methods that allow automatic segmentation and enhancement of OCT images of rodent brain.

RESULTS

We demonstrate the effectiveness of the proposed methods for OCT-based microangiography (OMAG) and tissue injury mapping (TIM) of mouse cerebral cortex. The results show significant improvement in image contrast, delineation of tissue injury, allowing visualization of different layers of capillary beds.

COMPARISON WITH EXISTING METHODS

Previously reported methods for other applications are yet to be used in neuroscience due to the complexity of tissue anatomy, unique physiology and technical challenges.

CONCLUSIONS

OCT is a promising tool that provides high resolution in vivo microvascular and structural images of rodent brain. By automatically segmenting and enhancing OCT images, structural and microvascular changes in mouse cerebral cortex after stroke can be monitored in vivo with high contrast.

Fast single image haze removal via local atmospheric light veil estimation

In this study, a novel single-image based dehazing framework is proposed to remove haze artifacts from images through local atmospheric light estimation. We use a novel strategy based on a physical model where the extreme intensity of each RGB pixel is used to define an initial atmospheric veil (local atmospheric light veil). Across bilateral filter is applied to each veil to achieve both local smoothness and edge preservation. A transmission map and a reflection component of each RGB channel are constructed from the physical atmospheric scattering model. The proposed approach avoids adverse effects caused by the error in estimating the global atmospheric light. Experimental results on outdoor hazy images demonstrate that the proposed method produces image output with satisfactory visual quality and color fidelity. Our comparative study demonstrates a higher performance of our method over several state-of-the-art methods.

Drift correction for single-molecule imaging by molecular constraint field, a distance minimum metric

Background

The recent developments of far-field optical microscopy (single molecule imaging techniques) have overcome the diffraction barrier of light and improve image resolution by a factor of ten compared with conventional light microscopy. These techniques utilize the stochastic switching of probe molecules to overcome the diffraction limit and determine the precise localizations of molecules, which often requires a long image acquisition time. However, long acquisition times increase the risk of sample drift. In the case of high resolution microscopy, sample drift would decrease the image resolution.

Results

In this paper, we propose a novel metric based on the distance between molecules to solve the drift correction. The proposed metric directly uses the position information of molecules to estimate the frame drift. We also designed an algorithm to implement the metric for the general application of drift correction. There are two advantages of our method: First, because our method does not require space binning of positions of molecules but directly operates on the positions, it is more natural for single molecule imaging techniques. Second, our method can estimate drift with a small number of positions in each temporal bin, which may extend its potential application.

Conclusions

The effectiveness of our method has been demonstrated by both simulated data and experiments on single molecular images.