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The performance of a pinhole collimator for I-131 SPECT of the head was evaluated. The evaluation included planar and SPECT spatial resolution, sensitivity in air and in water, septal penetration, reconstructed image quality, and ...
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The performance of a pinhole collimator for I-131 SPECT of the head was evaluated. The evaluation included planar and SPECT spatial resolution, sensitivity in air and in water, septal penetration, reconstructed image quality, and activity quantitation within a simple phantom that models tumor uptake in the head. The pinhole collimator was compared to medium and high energy parallel hole collimators. The pinhole collimator demonstrated improved resolution/sensitivity tradeoff compared with the parallel hole collimators over the range of distances relevant to head imaging. In planar point source images the pinhole collimator showed reduced penetration effects although in reconstructed images penetration effects were not apparent for either pinhole or high energy parallel hole collimators. Comparable activity quantitation accuracy was observed with all collimators. The accuracy was dependent on the segmentation threshold and calibration procedure. These results indicate that the pinhole collimator can provide improved performance conventional parallel hole collimators for I-131 imaging in the head.
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Recently, high-resolution inverse synthetic aperture radar (ISAR) imaging with sparse aperture (SA) data has attracted increasing attention. The theory of compressive sensing (CS) suggests that an unknown sparse signal can be accu...
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Recently, high-resolution inverse synthetic aperture radar (ISAR) imaging with sparse aperture (SA) data has attracted increasing attention. The theory of compressive sensing (CS) suggests that an unknown sparse signal can be accurately recovered by takin
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Non-uniform rotational motion of maneuvering targets can result in nonlinear migration through range cells (MTRC) and high order phase term, making final inverse synthetic aperture radar image severely defocused. Therefore, a nove...
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Non-uniform rotational motion of maneuvering targets can result in nonlinear migration through range cells (MTRC) and high order phase term, making final inverse synthetic aperture radar image severely defocused. Therefore, a novel non-uniform rotational motion estimation and compensation method is proposed to achieve the elimination of high order phase term and nonlinear MTRC. Under the constant acceleration model, the estimation of rotational motion parameters is first modeled as an unconstrained optimization problem with the image entropy as the cost function. Particle swarm optimization is utilized to search the global optimal solution making use of its simple structure and high efficiency. Then, resampling is performed to transform the non-uniform rotational motion into linear movement and then residual high order phase term is eliminated by constructing the corresponding compensation term. On this condition, first-order Keystone transform can be applied to correct the MTRC. Focused image can finally be obtained by performing traditional Fourier transform along the cross-range dimension. Experimental results on simulated data, electromagnetic data, and real data are presented to verify the effectiveness and robustness of our proposed algorithm.
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Spatial resolution is a key parameter of all remote sensing satellites and platforms. The nominal spatial resolution of satellites is a well-known characteristic because it is directly related to the area in ground that represents...
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Spatial resolution is a key parameter of all remote sensing satellites and platforms. The nominal spatial resolution of satellites is a well-known characteristic because it is directly related to the area in ground that represents a pixel in the detector. Nevertheless, in practice, the actual resolution of a specific image obtained from a satellite is difficult to know precisely because it depends on many other factors such as atmospheric conditions. However, if one has two or more images of the same region, it is possible to compare their relative resolutions. In this paper, a wavelet-decomposition-based method for the determination of the relative resolution between two remotely sensed images of the same area is proposed. The method can be applied to panchromatic, multispectral, and mixed (one panchromatic and one multispectral) images. As an example, the method was applied to compute the relative resolution between SPOT-3, Landsat-5, and Landsat-7 panchromatic and multispectral images taken under similar as well as under very different conditions. On the other hand, if the true absolute resolution of one of the images of the pair is known, the resolution of the other can be computed. Thus, in the last part of this paper, a spatial calibrator that is designed and constructed to help compute the absolute resolution of a single remotely sensed image is described, and an example of its use is presented.
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The electromagnetic (EM) wave carrying orbital angular momentum (OAM) is usually named vortex EM wave, which has been found great potential to improve the target imaging performance. For conventional ISAR imaging, only 2-D target ...
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The electromagnetic (EM) wave carrying orbital angular momentum (OAM) is usually named vortex EM wave, which has been found great potential to improve the target imaging performance. For conventional ISAR imaging, only 2-D target image can be obtained. In this paper, the OAM-based ISAR technique is developed to achieve 3-D target image with high resolution at terahertz frequencies. First, the imaging model is derived, and the point spread function is analyzed. Subsequently, two imaging algorithms, namely the FFT-based imaging method and the imaging method based on convolution backprojection and power spectrum density estimation, are proposed. Simulation results validate the effectiveness of the proposed methods and indicate that the high-resolution cross-range profile can still be obtained at terahertz frequencies with small rotational angle. This paper can provide a novel manner to realize 3-D imaging of universal targets with high resolution.
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A super-resolution computational imaging method, called post random modulation radar imaging, based on single-input multiple-output radar detection system is proposed in this letter. In the proposed method, the target is detected ...
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A super-resolution computational imaging method, called post random modulation radar imaging, based on single-input multiple-output radar detection system is proposed in this letter. In the proposed method, the target is detected in coherent mode using the multilinear frequency modulation signal. The echoes received by the radar elements of the receiving array are recorded, respectively. Then, random modulations of the directional pattern factor of the receiving radar array, which are nonlinear processes, are optimized according to the position and the size of the target that are estimated roughly using the traditional method. Finally, the super-resolution radar imaging is obtained to solve the equation group formed by the data from the nonlinear post random modulation process. The resolution of the proposed imaging method can break the diffraction limit corresponding to the aperture of the receiving radar array. The anti-interference ability of the proposed approach is improved significantly compared with the incoherent imaging method using a multiple-input single-output structure. Experiments are carried out to validate the proposed approach.
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The authors have developed a laser imaging system that: 1) depicts potential distribution with high spatial and temporal resolution; 2) can image large areas; 3) does not require filtering for signal or image enhancement; 4) is fl...
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The authors have developed a laser imaging system that: 1) depicts potential distribution with high spatial and temporal resolution; 2) can image large areas; 3) does not require filtering for signal or image enhancement; 4) is flexible, allowing for the acquisition of images of programmable size and shape at varying frame rates; and 5) has a large depth of field, thus minimizing the loss of focus when simultaneously imaging areas of the heart at different distances from the prime focal plane. The high duality of the images obtained with this technique allows quantitative measurements to be made of both the potential distribution and the change in this distribution over time. Here, the authors discuss the components of the system and the present their experimental results.
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A volume imaging positron emission tomography (PET) scanner with a large acceptance angle, such as the PENN-PET, offers fine spatial sampling and resolution in three dimensions, and a high sensitivity because of the inclusion of a...
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A volume imaging positron emission tomography (PET) scanner with a large acceptance angle, such as the PENN-PET, offers fine spatial sampling and resolution in three dimensions, and a high sensitivity because of the inclusion of all cross-plane rays. The signal-to-noise ratio (SNR) is used to evaluate image quality for different scanning conditions of the PENN-PET using an activated cylindrical phantom with cold spheres of various sizes. Raising the energy threshold to 400 keV improves the SNR by lowering the scatter fraction, though it also reduces the sensitivity. Increasing the axial acceptance angle from +or-1.3 degrees to +or-6.5 degrees improves the SNR by increasing the sensitivity, even with a two-dimensional reconstruction algorithm, which compromises spatial resolution in the axial direction for points at the edge of the radial field of view. Initial results show that a three-dimensional reconstruction offers an improved SNR over a two-dimensional reconstruction that does not use all cross-plane rays.
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In this paper, a new method of image upscaling along with de-blocking of compressed images has been presented. In the case of highly compressed images, there is a high probability that these images may contain the noise in the for...
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In this paper, a new method of image upscaling along with de-blocking of compressed images has been presented. In the case of highly compressed images, there is a high probability that these images may contain the noise in the form of blocking artifacts. In this presented work, a spatial domain-based approach has been suggested with two roles, one of which is to process the image for reduction of compression-based blocking artifacts and other is to upscale the low-resolution image to high-resolution image. Image upscaling is one of the implementation techniques of image super-resolution (SR). It is a type of SR where only a single image-based SR is being implemented. In the proposed technique, image de-blocking along with interpolation based super resolution has been developed in the spatial domain, therefore it is a practical and realistic method. The results of the proposed method in the form of quality metrics like PSNR, MSE and MSSIM have been compared with other methods of interpolation along with de-blocking method.
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Random stepped-frequency radar without delay–Doppler coupling can suppress the range ambiguity and become less sensitive to electronic countermeasures. Considering its inherent randomness, this paper focuses on sidelobe reduction...
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Random stepped-frequency radar without delay–Doppler coupling can suppress the range ambiguity and become less sensitive to electronic countermeasures. Considering its inherent randomness, this paper focuses on sidelobe reduction in inverse synthetic aperture radar imaging for sparse target scenes based on the compressed sensing (CS) theory. First, precise motion compensation and a high-resolution range profile (HRRP) with a low sidelobe are simultaneously achieved by the CS scheme for each train containing fewer pulses. Then, we analyze the disadvantages of conventional cross-range compression algorithms, which cannot guarantee high-quality focusing performance because there may be some false HRRPs caused by the uncertainty of the CS theory or some other factors. Finally, the modified correlation coefficient is defined to discard a large percentage of those uncorrelated HRRPs and the cross-range resolution is achieved by using the CS theory again. The validity of this decoupled imaging algorithm is demonstrated by some simulation and experimental results, which indicate that the approach is capable of precise estimation of scattering centers and effective suppression of a high sidelobe.
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