Autofocus Fourier single-pixel microscopy.

Single-pixel microscopy enables observation of micro samples in invisible wave bands. Finding the focus position is essential to capture a clear image of a sample but could be difficult for single-pixel microscopy particularly in invisible wave bands. It is because the structured patterns projected onto the sample would be invisible and searching for the focus position manually could be exhausting. Here, we report an autofocus method for Fourier single-pixel microscopy. The reported method allows one to find the focus position without recording or reconstructing a complete image. The focus position is determined by the magnitude summation of a small number of Fourier coefficients, which enables fast autofocus. The reported method is experimentally demonstrated in imaging various objects in both visible and near-infrared wave bands. The method adds practicability to a single-pixel microscopy.

Full-resolution, full-field-of-view, and high-quality fast Fourier single-pixel imaging.

Fourier single-pixel imaging (FSI) uses Fourier basis patterns for spatial light modulation to acquire the Fourier spectrum of the object image. The object image can be reconstructed via an inverse Fourier transform. However, the Fourier basis patterns are inherently gray scale, which results in the difficulty that the patterns can hardly be generated at a high speed by using a commonly used spatial light modulator-digital micromirrors device. To tackle this problem, fast FSI, which uses upsampled and dithered Fourier basis patterns to approximate the gray scale patterns, has been reported, but the achievable spatial resolution has to be sacrificed in the pattern upsampling process. Here we propose a method that can achieve not only full-resolution but also full-field-of-view and high-quality FSI. The key to the proposed method is to use a new, to the best of our knowledge, error diffusion dithering algorithm combined with two different scanning strategies to generate two sets of binarized Fourier basis patterns for spatial light modulation. As a result, two images with a sub-pixel shift from each other are reconstructed. It results in the final high-quality reconstruction by synthesizing the two images. We experimentally demonstrate the method can produce a high-quality 1024 × 768-pixel and full resolution image with a digital micromirror device with 1024 × 768 micromirrors.

Image-free active autofocusing with dual modulation and its application to Fourier single-pixel imaging.

Autofocusing is widely used in applications where sharp image acquisition or projection is needed. Here we report an active autofocusing method for sharp image projection. The method works with wide-field structured illumination and single-pixel detection. To find the focus position, the method illuminates the target object with a set of 3-step phase-shifting Fourier basis patterns repeatedly and collects the backscattered light by using a single-pixel detector through a grating. Dual modulation-dynamic modulation by the time-varying structured illumination and static modulation by the grating-embeds the depth information for the target object in the resulting single-pixel measurements. As such, the focus position can be determined by recovering the Fourier coefficients from the single-pixel measurements and searching for the coefficient with the maximum magnitude. High-speed spatial light modulation not only enables rapid autofocusing but also makes the method work even when the lens system is in continuous motion or the focal length of the lens is continuously adjusted. We experimentally validate the reported method in a self-built digital projector and demonstrate the application of the method in Fourier single-pixel imaging.

Ringing-free fast Fourier single-pixel imaging.

Fourier single-pixel imaging (FSI) allows an image to be reconstructed by acquiring the Fourier spectrum of the image using a single-pixel detector. Fast FSI is typically achieved by acquiring a truncated Fourier spectrum, that is, only low-frequency Fourier coefficients are acquired, with the high-frequency coefficients discarded. However, the truncation of the Fourier spectrum leads to undesirable ringing artifacts in the resulting image. Ringing artifacts produce false edges in the image and reduce the image contrast, resulting in image quality degeneration. The artifact is particularly severe in dynamic FSI, where the sampling ratio is generally ultra-low. We propose an effective and fast deringing algorithm to achieve ringing-free fast FSI. The algorithm eliminates ringing artifacts through 2D sub-pixel shifting and preserves image details through image fusion. Both static and dynamic imaging results demonstrate that the proposed method can reconstruct ringing-free images from under-sampled data in FSI. The deringing algorithm not only provides FSI with the capability of fast high-quality single-pixel imaging but also might prove its applicability in other areas, such as Fourier-based data compression algorithms.

[Analysis on the components of rat urinary stone induced by terephthalic acid].

In order to analyze the components of rat urinary stone and to explore the possible mechanism of chemically induced bladder cancer, terephthalic acid (TPA) is orally administrated to rats at the doses of 5000 and 500 mg/kg/BW/everyday for consecutive 90 days and stones in bladder and kidney are collected. Inductive Coupled Plasma Quantomer (ICP), Element Analyzer (EA) and Fourier Transform Infared Spectrometer (FT-IR) are applied for the analysis on the components of stone in bladder and kidney. The results showed that the main components of the stone are calcium, carbon, nitrogen, hydrogen and phosphorus. The FT-IR showed that the stones both in bladder and kidney might contain nitrous, carbonate, ammonium salt, and para-position replaced benzene-ring compounds, but no original TPA is detected. The findings indicate that TPA might have a metabolic turnover inside the rat body, and, at least, might not be completely excreted in its original form.

[Study on the bladder calculi and bladder cancer induced by terephthalic acid in rats].

The carcinogenicity and calculogenesis of terephthalic acid on bladder was investigated. Terephthalic acid at doses of 5000, 500 and 50 mg/kg body weight/d were administrated to SD rats for 90 days consecutively. Control animals received normal feeds. Bladder calculi were induced in 5000 mg/kg (10/17) and 500 mg/kg (2/18) group. Calculi incidence of male rats was higher than that of female rats in 5000 mg/kg dose group. Bladder transitional cell cancer (4/17), atypical hyperplasia (5/17) and single hyperplasia (7/17) could be observed in 5000 mg/kg group. Atypical hyperplasia (10/18) and single hyperplasia (5/18) could be observed in 500 mg/kg group. Single hyperplasia (10/17) could be observed in 50 mg/kg group. The controls were normal except 1 case of single hyperplasia (1/18). There was a positive correlation between pathologic changes and dosage, but no significant correlation between pathologic changes and calculi incidence. Those rats without calculi produced some changes too, but no squamous metaplasia and carcinoma happened. The results suggested that under the study conditions, squamous cell carcinogenicity might be induced by terephthalic acid, and the calculi might not be the major factor inducing cancer.