Coherent high-resolution sparse aperture imaging testbed

For traditional imaging systems, high imaging quality and system miniaturization are often contradictory. In order to meet the requirements of high imaging quality and system miniaturization, this paper proposes a method to correct the aberration of coherent imaging optical systems. The method is based on the idea of phase recovery and the imaging principle of a coherent imaging system to recover the aberrations at the exit pupil of the system. According to the recovered aberrations, conjugate filters are constructed to correct the image quality in the frequency domain. The imaging quality of the system is improved without changing the original optical path, and the simplicity of the system is guaranteed. To solve the pupil frequency domain aberration more accurately, this paper adopts the dual competition and parallel recombination strategy based on the genetic algorithm and introduces the disaster model. The improved genetic algorithm can effectively restrain the appearance of the “precocity” phenomenon. Finally, the paraxial imaging optical path is simulated and verified by experiments. The results show that, after aberration correction, the image sharpness is improved and the edge information is richer, which verifies the feasibility of the coherent imaging system image quality enhancement method proposed in this paper.

Multiplexed Superresolution CRISPR Imaging of Chromatin in Living Cells

Millimeter-wave interferometric synthetic aperture radiometer (InSAR) imaging has received considerable attention owing to its pure radiation receiving scheme and high resolution. In recent years, compressive sensing (CS) has been applied to InSAR on the assumption that InSAR image could be formulated to a sparse vector. However, the CS-based InSAR ignores the 2-D sparsity of images and its performance degrades while processing large-scale images. Further using the sparsity of InSAR image, a novel InSAR imaging approach referred to as InSAR-matrix completion (MC) is proposed in this letter by adopting the MC techniques, which can recover a low-rank matrix from a small subset of its corrupted entries. Directly representing the target image as a matrix, InSAR-MC formulates the estimation of the visibility function as a 2-D linear transformation and inversely obtains the target image by convex optimization as sparsity of millimeter-wave image and interferometric operation satisfy the low-rank property. Experimental results demonstrate the proposed approach’s validity and better performance of the recovered images with comparison against CS-based InSAR and other traditional approaches.

Designing an optical aerial imaging system with high resolution and large fields of view (FoV) is a longstanding problem in remote sensing, astronomical observation, and geological exploration. In this paper, we propose a light field-guided optical synthetic aperture imaging system on master-slave unmanned aerial vehicles (UAVs). This system consists of single-master UAV and multiple-slave UAVs to capture cross-scale multiview aerial images to stitch an aerial image and even a video with high resolution and large FoV. However, relative poses of UAVs change dynamically during the flight, which causes the inaccuracy of large-FoV image stitching. To address this problem, we convert image stitching as a novel-view synthesis problem on a large-FoV light field. Under this insight, we construct a 5D light field to cover FoVs of all slave UAVs via Gaussian splatting technique. Then we exploit a light field-guided synthetic aperture imaging scheme to generate the high-resolution image. Additionally, this scheme can be extended for large-FoV video generation. Experimental results on real-world scenes show that the proposed imaging system is capable of generating the accurate, large-FoV, high-resolution image sequences. Hence, we believe that this system has great potential in large-FoV high-resolution aerial imaging.

An investigation of scattering mechanisms and dynamics in PMSE using coherent radar imaging

Photoacoustic imaging combines advantages of both ultrasound imaging and optical imaging to provide high ultrasonic resolution and high optical contrast in noninvasive medical images. A photoacoustic computer tomography （PCT） system with a focused digital phased array transducer is proposed. In particular each element of the transducer array has a thin cylindrical ultrasonic lens to select 2D image plane and suppress the out-of-plane signals to realize photoacoustic computed tomography. A fast full-view photoacoustic imaging system for visualizing tissue structures using a linear transducer array with combined scan, whies; detects photoacoustic signals by combined electronic and mechanical scanning. An improved limited-field filtered back projection algorithm with directivity factors was applied to reconstruct the optical absorption distribution and further improve the lateral resolution. In the experiment, the spatial resolution of this imaging system is determined as 0.2mm, and the slice resolution of Z axis is 1.5mm. Mechanical step scanning was performed, leading to a measurement time of 6.4 seconds per position, and a total scan duration of 150 seconds to obtain the two-dimensional photoacoustic image. High spatial resolution of 2D photoacoustic vascular image and quasi-3D photoacoustic CT for breast cancer imaging are achicned. The experimental results demonstrate that this method and imaging system can realize the high resolution photoacoustic tomography wtich can be applied to noninvasive detection of early breast cancer.

Optical frequency-modulated continuous-wave (FMCW) reflectometry is a ranging technique that allows for high-resolution distance measurements over long ranges. Similarly, swept-source optical coherence tomography (SS-OCT) provides high-resolution depth imaging over typically shorter distances and higher scan speeds. In this work, we demonstrate a low-cost, low-bandwidth 3D imaging system that provides the high axial resolution imaging capability normally associated with SS-OCT over typical FMCW ranging depths. The imaging system combines 12 distributed feedback laser (DFB) elements from a single butterfly module to provide an axial resolution of 27.1 μm over 6 m of depth and up to 14 cubic meters of volume. Active sweep linearization is used, greatly reducing the signal processing overhead. Various sub-surface, OCT-style tomograms of semi-transparent objects are shown, as well as 3D maps of various objects over depths ranging from sub-millimeter to several meters. Such imaging capability would make long-distance, high-resolution surface interrogation possible in a low-cost, compact package.

The primary challenge of a cost-effective and low-complexity near-field millimeter-wave (mmWave) imaging system is to achieve high resolution with a few antenna elements as possible. Multiple-input multiple-output (MIMO) radar using simultaneous operation of spatially diverse transmit and receive antennas is a good candidate to increase the number of available degrees of freedom. On the other hand, higher integration complexity of extremely dense transceiver electronics limits the use of MIMO only solutions within a relatively large imaging aperture. Hybrid concepts combining synthetic aperture radar (SAR) techniques and sparse MIMO arrays present a good compromise to achieve short data acquisition time and low complexity. However, compared with conventional monostatic sampling schemes, image reconstruction methods for MIMO-SAR are more complicated. In this paper, we propose a high-resolution mmWave imaging system combining 2-D MIMO arrays with SAR, along with a novel Fourier-based image reconstruction algorithm using sparsely sampled aperture data. The proposed algorithm is verified by both simulation and processing real data collected with our mmWave imager prototype utilizing commercially available 77-GHz MIMO radar sensors. The experimental results confirm that our complete solution presents a strong potential in high-resolution imaging with a significantly reduced number of antenna elements.

Purpose:Coherent scatter based imaging has shown improved contrast and molecular specificity over conventional digital mammography however the biological risks have not been quantified due to a lack of accurate information on absorbed dose. This study intends to characterize the dose distribution and average glandular dose from coded aperture coherent scatter spectral imaging of the breast. The dose deposited in the breast from this new diagnostic imaging modality has not yet been quantitatively evaluated. Here, various digitized anthropomorphic phantoms are tested in a Monte Carlo simulation to evaluate the absorbed dose distribution and average glandular dose using clinically feasible scan protocols.Methods:Geant4 Monte Carlo radiation transport simulation software is used to replicate the coded aperture coherent scatter spectral imaging system. Energy sensitive, photon counting detectors are used to characterize the x‐ray beam spectra for various imaging protocols. This input spectra is cross‐validated with the results from XSPECT, a commercially available application that yields x‐ray tube specific spectra for the operating parameters employed. XSPECT is also used to determine the appropriate number of photons emitted per mAs of tube current at a given kVp tube potential. With the implementation of the XCAT digital anthropomorphic breast phantom library, a variety of breast sizes with differing anatomical structure are evaluated. Simulations were performed with and without compression of the breast for dose comparison.Results:Through the Monte Carlo evaluation of a diverse population of breast types imaged under real‐world scan conditions, a clinically relevant average glandular dose for this new imaging modality is extrapolated.Conclusion:With access to the physical coherent scatter imaging system used in the simulation, the results of this Monte Carlo study may be used to directly influence the future development of the modality to keep breast dose to a minimum while still maintaining clinically viable image quality.

A Dual Image Sensor Approach for Automated, High Resolution, Region-of-Interest Imaging in a 96-Well Plate

To enable dynamic speech imaging with high spatiotemporal resolution and full-vocal-tract spatial coverage, leveraging recent advances in sparse sampling. An imaging method is developed to enable high-speed dynamic speech imaging exploiting low-rank and sparsity of the dynamic images of articulatory motion during speech. The proposed method includes: (a) a novel data acquisition strategy that collects spiral navigators with high temporal frame rate and (b) an image reconstruction method that derives temporal subspaces from navigators and reconstructs high-resolution images from sparsely sampled data with joint low-rank and sparsity constraints. The proposed method has been systematically evaluated and validated through several dynamic speech experiments. A nominal imaging speed of 102 frames per second (fps) was achieved for a single-slice imaging protocol with a spatial resolution of 2.2 × 2.2 × 6.5 mm(3) . An eight-slice imaging protocol covering the entire vocal tract achieved a nominal imaging speed of 12.8 fps with the identical spatial resolution. The effectiveness of the proposed method and its practical utility was also demonstrated in a phonetic investigation. High spatiotemporal resolution with full-vocal-tract spatial coverage can be achieved for dynamic speech imaging experiments with low-rank and sparsity constraints.

Compressive spectral imaging (CSI) enables the acquisition of spectral and spatial information of a scene using fewer projected measurements than traditional scanning approaches. Recently, research efforts have focused on obtaining high-resolution spectral images via expensive detectors and sophisticated CSI devices. Alternatively, high-resolution spectral images can be obtained using side information or fusion of compressed measurements, without significantly increasing acquisition costs. Indeed, these approaches retrieve improved resolution images applying iterative and computationally expensive algorithms. This paper proposes the fusion of compressed measurements obtained from two state-of-the-art CSI systems, the single-pixel camera (SPC) and the three-dimensional coded aperture snapshot imaging system (3D-CASSI), such that high-resolution images can be obtained by exploiting detailed spectra provided by the SPC and high spatial resolution of the 3D-CASSI. Specifically, a noniterative reconstruction algorithm is proposed, based on the fact that the spatial-spectral data lie in a low-dimensional subspace. In contrast to related works, the proposed approach relies on implementable CSI systems. Simulations and experimental results show the effectiveness of the proposed method compared to similar approaches, both in reconstruction quality and complexity. Specifically, the proposed method is up to 5.6 times faster than its counterparts and provides comparable quality of attained reconstructions.

Imaging of the cervical spine in functional positions has so far been limited to conventional X-ray examinations or the scarcely available open magnetic resonance imaging (MRI). An MRI compatible positioning device allows MRI examinations in various positions and even in motion. In combination with high-resolution T2-weighted MRI it allows detailed functional imaging of the cervical spine and nerve roots. To evaluate the utility of this method a population of patients from a clinical study was examined 5 years after anterior cervical discectomy and fusion (ACDF). A total of 32 patients (median age 51.5 years, 15 female, 17 male) were examined after a median interval of 64.3 months from ACDF including 16 patients with a titanium cage and 16 with autologous bone graft. The prototype of an MR compatible positioning device (NeuroSwing) was used for MRI of the cervical spine in functional positions on a 1.5 T MRI unit (Siemens Avanto). A real-time true fast imaging with steady-state precession (FISP) sequence [6 mm, TR 704, TE 1.3 ms, matrix 256 x 207, field of view (FoV) 22 cm] was used for monitoring of flexion up to 45° and extension up to 40° or until patient discomfort. A sagittal T2 sampling perfection with application optimized contrast using different flip angle evolution sequence (SPACE sequence, 0.9 mm isotropic voxels, TR 1770, TE 186 ms, matrix 320 x 318, FoV 28 cm) and an axial true FISP sequence (3 mm slices, TR 194, TE 1.9 ms, matrix 256 x 256, FoV 22 cm) were used for imaging in the end positions. Using the motorized positioning device and a real-time true FISP sequence, imaging of the cervical spine in flexion and extension motion was possible in a quality suitable to observe changes in the alignment of vertebral bodies, the width of the spinal canal and the spinal cord itself. The 3D T2-weighted SPACE sequence yielded high quality and resolution images in the maximum flexion and extension positions. Compared to primary axial T2 true FISP slices, axial reconstructions of the T2 SPACE sequence were found to be clearly less affected by metal artifacts with the additional benefit of multiplanar and transforaminal reconstructions. The combination of a mechanical positioning device and a high-resolution 3D T2-weighted sequence (SPACE) on a conventional 1.5 T MRI allows kinematic imaging of the cervical spine as well as high-resolution imaging in the end positions, even in the presence of metal implants. In this proof of concept study a good visualization of narrowing of the spinal canal in functional positions could be achieved, showing the potential of MRI in functional positions for clinical and research applications.

Investigation of water management in polymer electrolyte membrane fuel cells (PEMFCs) is a fundamental and important issue for their implementation. Consequently, it is necessary to investigate water content distribution in PEMs under typical fuel cell operating conditions. Our research group has therefore investigated transversal water content distribution in PEMs under fuel cell operating conditions using a magnetic resonance imaging (MRI) system. However, the spatial resolution limitations impeded our prior studies to elucidate the distribution of water contents in a thin membrane. We investigated water content distribution in a thin membrane using a high spatial resolution magnetic resonance imaging (MRI) system to overcome spatial resolution limitations in a thin membrane in this study. Transversal water content distribution in PEM (e.g. Nafion 115) was investigated at room temperature and ambient pressure using a high spatial resolution (e.g. < 10 micrometer) MR imaging system.

High-resolution imaging using Hadamard Encoding