Browsing by Author "Chen, Lei"

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    Characterization of the Foreign Body Response to Common Surgical Biomaterials in a Murine Model.
    (European journal of plastic surgery, 2017-11) Ibrahim, Mohamed; Bond, Jennifer; Medina, Manuel A; Chen, Lei; Quiles, Carlos; Kokosis, George; Bashirov, Latif; Klitzman, Bruce; Levinson, Howard
    BACKGROUND:Implanted biomaterials are subject to a significant reaction from the host, known as the foreign body response (FBR). We quantified the FBR to five materials following subcutaneous implantation in mice. MATERIALS AND METHODS:Polyvinyl alcohol (PVA) and silicone sheets are considered highly biocompatible biomaterials and were cut into 8mm-diameter disks. Expanded PTFE (ePTFE)and polypropylene are also widely used biocompatible biomaterials and were cut into 2cm-long cylinders. Cotton was selected as a negative control material that would invoke an intense FBR, was cut into disks and implanted. The implants were inserted subcutaneously into female C57BL/6 mice. On post-implantation days 14, 30, 60, 90 and 180, implants were retrieved. Cellularity was assessed with DAPI stain, collagen with Masson's trichrome stain. mast cells with toluidine-blue, macrophages with F4/80 immunohistochemical-stain, and capsular thickness and foreign body giant cells with hematoxylin & eosin. RESULTS:DAPI revealed a significantly increased cellularity in both PVA andsilicone, and ePTFE had the lowest cell density. Silicone showed the lowest cellularity at d14 and d90 whereas ePTFE showed the lowest cellularity at days 30, 60, and 180. Masson's trichrome staining demonstrated no apparent difference in collagen. Toluidine blue showed no differences in mast cells. There were, however, fewer macrophages associated with ePTFE. On d14, PVA had highest number of macrophages, whereas polypropylene had the highest number at all time points after d14. Giant cells increased earlier and gradually decreased later. On d90, PVA exhibited a significantly increased number of giant cells compared to polypropylene and silicone. Silicone consistently formed the thinnest capsule throughout all time points. On d14, cotton had formed the thickest capsule. On d30 polypropylenehas formed thickest capsule and on days 60, 90 and 180, PVA had formed thickest capsule. CONCLUSION:These data reveal differences in capsule thickness and cellular response in an implant-related manor, indicating that fibrotic reactions to biomaterials are implant specific and should be carefully considered when performing studies on fibrosis when biomaterials are being used.
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    ItemOpen Access
    Single Image Super Resolution:Perceptual quality & Test-time Optimization
    (2019) Chen, Lei

    Image super resolution is defined as recovering a high-resolution image given a low-resolution image input. It has a wide area of applications in modern digital image processing, producing better results in areas including satellite image processing, medical image processing, microscopy image processing, astrological studies and surveillance area. However, image super resolution is an ill-posed question since there exists non-deterministic answer in the high resolution image space, making it difficult to find the optimal solution.

    In this work, various research directions in the area of single image super resolution are thoroughly studied. Each of the proposed methods' achievements as well as limitations including computational efficiency, perceptual performance limits are compared. The main contribution in this work including implementing a perceptual score predictor and integrating as part of the objective function in the upsampler algorithm. Apart from that, a test-time optimization algorithm is proposed, aiming at further enhance the image quality for the obtained super-resolution image from any upsampler. The proposed methods are implemented and tested using Pytorch. Results are compared on baseline applied datasets including Set5, Set14, Urban100 and DIV2K.

    Results from perceptual score predictor was evaluated on both PSNR precision index and perceptual index, which is a combination of perceptual evaluation Ma score and NIQE score. With new objective function, the upsampler achieved to move along the trade-off curve of precision and perception. The test-time optimization algorithm achieved slightly improvements in both precision and perception index. Note that the proposed test time optimization does not require training of new neural network, thus, is computationally efficient.