SAR Moving Target Detection and Imaging Based on WVH Transform

Aim To propose a generalized and closed representation of the Wigner Ville Hough transform(WVHT), for the moving target detection and imaging in the design of synthetic aperture radar(SAR). Methods Based on the line integral, the WVH transform was derived by combining the Wigner Ville distribution (WVD) and the Hough transform (HT) together. The new transform was then verified with computer by the simulated SAR echoes. Results and Conclusion The correctness and the validity of the WVH transform were proved by the computer simulation. Compared with the conventional WVD HT method, the new approach based on the WVHT can simplify the processing procedure, it can translate the chirp echoes of multi targets of SAR from the time domain into the parameter space directly, while suppressing the cross terms of WVD and estimating the motion coefficients for the final imaging. It is obvious that the WVH transform can be also used in other cases for the chirp signal detection.

DEVELOPMENT OF MOVING TARGET DETECTION AND IMAGING BY AIRBORNE SAR

The detection and ima ging of moving targets based on airborne synthetic aperture radar (SAR) is a cru cial technique for the modern radar. Firstly, the mathematical model of SAR ech o signal which comes from moving targets is constructed. Based on this model, th e features of moving target imaging are introduced and the effects of target mov ement to SAR imaging are analyzed. Then the development and the status of this t echnique are reviewed in detail. Finally, some frontiers of this field are point ed out.

Research on spatial-variant property of bistatic ISAR imaging plane of space target

The imaging plane of inverse synthetic aperture radar （ISAR） is the projection plane of the target. When taking an image using the range-Doppler theory, the imaging plane may have a spatial-variant property, which causes the change of scatter＇s projection position and results in migration through resolution cells, In this study, we focus on the spatial-variant property of the imaging plane of a three-axis-stabilized space target. The innovative contributions are as follows. 1） The target motion model in orbit is provided based on a two-body model. 2） The instantaneous imaging plane is determined by the method of vector analysis. 3） Three Euler angles are introduced to describe the spatial-variant property of the imaging plane, and the image quality is analyzed. The simulation results confirm the analysis of the spatial-variant property. The research in this study is significant for the selection of the imaging segment, and provides the evidence for the following data processing and compensation algorithm.

Elastic wave imaging of two dimensional targets

Presents a new way of elastic wave imaging which features 1)high inversion accuracy; 2)stable and rapid convergence; 3) high resistance to random noise; 4) little dependence on initial values, and concludes with numerical results that this method has many advantages over all the other imaging methods because our inversion equation following the variation principle reflects the relation between the little variation of scattering field and that of perturbation function.

Targeted prostate biopsy： value of multiparametric magnetic resonance imaging in detection of localized cancer

Prostate cancer is the second most common cancer in men, with 1.1 million new cases worldwide reported by the World Health Organization in one recent year. Transrectal ultrasound （TRUS）-guided biopsy has been used for the diagnosis of prostate cancer for over 2 decades, but the technique is usually blind to cancer location. Moreover, the false negative rate of TRUS biopsy has been reported to be as high as 47%. Multiparametric magnetic resonance imaging （mp-MRI） includes T1- and T2-weighted imaging as well as dynamic contrast-enhanced （DCE） and diffusion-weighted imaging （DWI）. mp-MRI is a major advance in the imaging of prostate cancer, enabling targeted biopsy of suspicious lesions. Evolving targeted biopsy techniquesmincluding direct in-bore biopsy, cognitive fusion and software-based MRI-ultrasound （MRI-US） fusion--have led to a several-fold improvement in cancer detection compared to the earlier method. Importantly, the detection of clinically significant cancers has been greatly facilitated by targeting, compared to systematic biopsy alone. Targeted biopsy via MRI-US fusion may dramatically alter the way prostate cancer is diagnosed and managed.

Magnetic resonance imaging-guided and targeted theranostics of colorectal cancer

Colorectal cancer(CRC)is the most common gastrointestinal tract cancer worldwide and is associated with high morbidity and mortality.The development of nanosized drug delivery systems has provided a new direction in CRC treatment.Among these systems,magnetic nanoparticle(MNP)-based multifunctional platforms provide a novel strategy for magnetic resonance imaging(MRI)-related cancer theranostics.At the beginning o f this original review,the carcinogenesis and treatment status o f CRC are summarized.Then,diversified preparation and functionalization methods of MNPs are systematically analyzed,followed by MRIinvolved theranostic strategies.The latest progress in MRI-mediated multimode diagnosis and image-guided targeted therapy in CRC management is the main focus.Finally,the major challenges in promoting MRI-induced precise theranostics of CRC in clinical practice are discussed.

Optical polarization imaging for underwater target detection with non-scatter background

For conventional optical polarization imaging of underwater target,the polarization degree of backscatter should be pre-measured by averaging the pixel intensities in the no target region of the polarization images,and the polarization property of the target is assumed to be completely depolarized.When the scattering background is unseen in the field of view or the target is polarized,conventional method is helpless in detecting the target.An improvement is to use lots of co-polarization and cross polarization detection components.We propose a polarization subtraction method to estimate depolarization property of the scattering noise and target signal.And experiment in a quartz cuvette container is performed to demonstrate the effectiveness of the proposed method.The results show that the proposed method can work without scattering background reference,and further recover the target along with smooth surface for polarization preserving response.This study promotes the development of optical polarization imaging systems in underwater environments.

Target acquisition performance in the presence of JPEG image compression

This paper presents an investigation on the effect of JPEG compression on the similarity between the target image and the background,where the similarity is further used to determine the degree of clutter in the image.Four new clutter metrics based on image quality assessment are introduced,among which the Haar wavelet-based perceptual similarity index,known as HaarPSI,provides the best target acquisition prediction results.It is shown that the similarity between the target and the background at the boundary between visually lossless and visually lossy compression does not change significantly compared to the case when an uncompressed image is used.In future work,through subjective tests,it is necessary to check whether this presence of compression at the threshold of just noticeable differences will affect the human target acquisition performance.Similarity values are compared with the results of subjective tests of the well-known target Search_2 database,where the degree of agreement between objective and subjective scores,measured through linear correlation,reached a value of 90%.

Improved HHT and its application in narrowband radar imaging for precession cone-shaped targets

Imaging the spatial precession cone-shaped targets with narrowband radar is a new technical approach in mid-course recognition problem. However, most existing time-frequency methods still have some inevitable deficiencies for extracting microDoppler information in practical applications, which leads to blurring of the image. A new narrowband radar imaging algorithm for the precession cone-shaped targets is proposed. The instantaneous frequency of each scattering point is gained by using the improved Hilbert-Huang transform, then the positions of scattering points in the parameter domain are reconstructed. Numerical simulation and experiment results confirm the effectiveness and high precision of the proposed algorithm.

STUDY ON THE SIGNATURE OF GROUND MOVING TARGET FOR AIRBORNE SQUINT SAR IMAGING

Compared with the side-looking Synthetic Aperture Radar (SAR), the flexible beampointing of squint SAR makes great application value. This paper derives the image signature of the ground moving target after the processing of Range-Doppler (RD) algorithm, the SAR signatures of ground moving targets are analyzed, including the geometry correction, the offsets and defocusing in both range and azimuth direction. Finally, computer simulation results validate its effectiveness. The research results are especially significant for moving targets detection and parameters estimation in squint mode SAR.

Micro-motion effect in inverse synthetic aperture radar imaging of ballistic mid-course targets

For ballistic mid-course targets,in addition to constant orbital motion,the target or any structure on the target undergoes micro-motion dynamics,such as spin,precession and tumbling.The micro-motion characteristics of the ballistic mid-course targets were discussed.The target motion model and inverse synthetic aperture radar(ISAR) imaging model for this kind of targets were built.Then,the influence of micro-motion on ISAR imaging based on the established imaging model was presented.The computer simulation to get mid-course target echoes from static darkroom electromagnetic scattering data based on the established target motion model was realized.The imaging results of computer simulation show the validity of ISAR imaging analysis for micro-motion targets.

Rotational parameters estimation of maneuvering target in ISAR imaging

The rotational parameters estimation of maneuvering target is the key of cross-range scaling of ISAR （inverse synthetic aperture radar）, which can be used in the target feature extraction. The cross-range signal model of rotating target with fixed acceleration is presented and the weighted linear least squares estimation of rotational parameters with fixed velocity or acceleration is proposed via the relationship of cross-range FM （frequency modulation） parameter, scatterers coordinates and rotational parameters. The FM parameter is calculated via RWT （Radon-Wigner transform）. The ISAR imaging and cross-range scaling based on scaled RWT imaging method are implemented after obtaining rotational parameters. The rotational parameters estimation and cross-range scaling are validated by the ISAR processing of experimental radar data, and the method presents good application foreground to the ISAR imaging and scaling of maneuvering target.

Fluorescence imaging of drug target proteins using chemical probes

Fluorescence imaging can provide valuable information on the expression,distribution,and activity of drug target proteins.Chemical probes are useful small-molecule tools for fluorescence imaging with high structural flexibility and biocompatibility.In this review,we briefly introduce two classes of fluorescent probes for the visualization of drug target proteins.Enzymatically activatable probes make use of the specific enzymatic transformations that generally produce a fluorogenic response upon reacting with target enzymes.Alternatively,specific imaging can be conferred with a ligand that drives the probes to target proteins,where the labeling relies on noncovalent binding,covalent inhibition,or traceless labeling by ligand-directed chemistry.

Cardiac hybrid imaging: novel tracers for novel targets

Non-invasive cardiac imaging has explored enormous advances in the last few decades.In particular,hybrid imaging represents the fusion of information from multiple imaging modalities,allowing to provide a more comprehensive dataset compared to traditional imaging techniques in patients with cardiovascular diseases.The complementary anatomical,functional and molecular information provided by hybrid systems are able to simplify the evaluation procedure of various pathologies in a routine clinical setting.The diagnostic capability of hybrid imaging modalities can be further enhanced by introducing novel and specific imaging biomarkers.The aim of this review is to cover the most recent advancements in radiotracers development for SPECT/CT,PET/CT,and PET/MRI for cardiovascular diseases.

Usefulness of Magnetic Particle Imaging for Monitoring the Effect of Magnetic Targeting

Purpose: Magnetic targeting refers to the attachment of therapeutic agents to magnetizable particles such as magnetic nanoparticles (MNPs) and then applying magnetic fields to concentrate them to the targeted region such as solid tumors. The purpose of this study was to investigate the usefulness of magnetic particle imaging (MPI) for monitoring the effect of magnetic targeting using tumor-bearing mice. Materials and Methods: Colon-26 cells (1 × 106 cells) were implanted into the backs of eight-week-old male BALB/c mice. When the tumor volume reached approximately 100 mm3, the mice were divided into treated (n = 8) and untreated groups (n = 8). The tumors in the treated group were directly injected with MNPs (Resovist?, 250 mM) and a neodymium magnet was attached to the tumor surface, whereas the magnet was not attached to the tumor in the untreated group. The mice were imaged using our MPI scanner and the average and maximum MPI values were obtained by drawing a region of interest (ROI) on the tumor, with the threshold value for extracting the contour of the tumor being taken as 40% of the maximum MPI value in the ROI. The relative tumor volume growth (RTVG) was calculated from (V ? V0)/V0, where V0 and V represented the tumor volume immediately before and after the injection of MNPs, respectively. Results: The average and maximum MPI values in the treated group were significantly higher than those in the untreated group 3 days after the injection of MNPs, suggesting the effectiveness of magnetic targeting. There were no significant differences in RTVG between the two groups. Conclusion: Our preliminary results suggest that MPI is useful for monitoring the effect of magnetic targeting.

High resolution inverse synthetic aperture radar imaging of three-axis-stabilized space target by exploiting orbital and sparse priors

The development of inverse synthetic aperture radar （ISAR） imaging techniques is of notable significance for moni- toring, tracking and identifying space targets in orbit. Usually, a well-focused ISAR image of a space target can be obtained in a deliberately selected imaging segment in which the target moves with only uniform planar rotation. However, in some imaging segments, the nonlinear range migration through resolution cells （MTRCs） and time-varying Doppler caused by the three-dimensional rotation of the target would degrade the ISAR imaging performance, and it is troublesome to realize accurate motion compensation with conventional methods. Especially in the case of low signal-to-noise ratio （SNR）, the estimation of motion parameters is more difficult. In this paper, a novel algorithm for high-resolution ISAR imaging of a space target by using its precise ephemeris and orbital motion model is proposed. The innovative contributions are as follows. 1） The change of a scatterer projection position is described with the spatial-variant angles of imaging plane calculated based on the orbital motion model of the three-axis-stabilized space target. 2） A correction method of MTRC in slant- and cross-range dimensions for arbitrarily imaging segment is proposed. 3） Coarse compensation for translational motion using the precise ephemeris and the fine compensation for residual phase errors by using sparsity-driven autofo- cus method are introduced to achieve a high-resolution ISAR image. Simulation results confirm the effectiveness of the proposed method.

Recent advances in targeted endoscopic imaging:Early detection of gastrointestinal neoplasms

Molecular imaging has emerged as a new discipline in gastrointestinal endoscopy.This technology encompasses modalities that can visualize disease-specific morphological or functional tissue changes based on the molecular signature of individual cells.Molecular imaging has several advantages including minimal damage to tissues,repetitive visualization,and utility for conducting quantitative analyses.Advancements in basic science coupled with endoscopy have made early detection of gastrointestinal cancer possible.Molecular imaging during gastrointestinal endoscopy requires thedevelopment of safe biomarkers and exogenous probes to detect molecular changes in cells with high specificity anda high signal-to-background ratio.Additionally,a high-resolution endoscope with an accurate wide-field viewing capability must be developed.Targeted endoscopic imaging is expected to improve early diagnosis and individual therapy of gastrointestinal cancer.

Evaluation of Trajectory Error Effects in BP Based Space Target ISAR Imaging

The space target imaging is important in the development of space technology.Due to the availability of trajectory information of the space targets and the arising of rapid parallel processing hardware,the back projection (BP) method has been applied to synthetic aperture radar (SAR) imaging and shows a number of advantages as compared with conventional Fourier-domain imaging algorithms.However,the practical processing shows that the insufficient accuracy of the trajectory information results in the degrading of the imaging results.On the other hand,the autofocusing algorithms for BP imaging are not well developed,which is a bottleneck for the application of BP imaging.Here,an analysis of the effect of trajectory errors on the space target imaging using microlocal technology is presented.Our analysis provides an explicit quantitative relationship between the trajectory errors of the space target and the positioning errors in the reconstructed images.The explicit form of the position errors for some typical trajectory errors is also presented.Numerical simulations demonstrate our theoretical findings.The measured position errors obtained from the reconstructed images are consistent with the analytic errors calculated by using the derived formulas.Our results will be used in the development of effective autofocusing methods for BP imaging.

Target rotation parameter estimation for ISAR imaging via frame processing

Frame processing method offers a model-based approach to Inverse Synthetic Aperture Radar(ISAR) imaging. It also provides a way to estimate the rotation rate of a non-cooperative target from radar returns via the frame operator properties. In this paper, the relationship between the best achievable ISAR image and the reconstructed image from radar returns was derived in the framework of Finite Frame Processing theory. We show that image defocusing caused by the use of an incorrect target rotation rate is interpreted under the FP method as a frame operator mismatch problem which causes energy dispersion. The unknown target rotation rate may be computed by optimizing the frame operator via a prominent point. Consequently, a prominent intensity maximization method in FP framework was proposed to estimate the underlying target rotation rate from radar returns. In addition, an image filtering technique was implemented to assist searching for a prominent point in practice. The proposed method is justified via a simulation analysis on the performance of FP imaging versus target rotation rate error.Effectiveness of the proposed method is also confirmed from real ISAR data experiments.

A PARAMETER ESTIMATION FOR DETECTION AND IMAGING OF MOVING TARGETS WITH SAR BY WVD

Based on a joint time-frequency two dimensional processing, this paper proposes a method for the detection and imaging of moving targets SAR by using Wigner-Ville Distribution (WVD). It is a parameter estimation method to generate a high resolution image. The problem of WVD in dealing with multi-point targets and extended targets are also discussed. The computer simulation results illustrate its availability.