A Phase Recovery Technique Using the Genetic Algorithm for Aberration Correction in a Coherent Imaging System

The optical transfer function (OTF), which correspond to the frequency domain, is of fundamental importance in characterizing imaging ability in optical imaging systems. By using the Collins formula and the optical transfer matrix theory, a simple and unified analytical expression of OTF is presented in any ghost imaging (GI) system. By comparing the spectrum distribution of OTF between different GI systems, one can predict which imaging system can provide better imaging quality when the same imaging object is used. Theoretical and experimental results are also implemented to verify our results.

Optical imaging systems are widely used in various video surveillance sites, which may endure various harsh environmental aging conditions such as salt mist, change of temperature. However, there are few studies on the impact of various environmental tests on the overall imaging performance of the system. In this paper, several common environmental tests are selected to analyze their quantitative impact on the imaging quality of typical imaging systems. The imaging resolution, color revent and gray scale value are selected as the main imaging parameters. The study found that the salt mist test, gas corrosion, damp heat test, high and low temperature shock, and ultraviolet test have a great impact on the optical imaging system. Long-term exposure will cause the imaging quality of the imaging system to decrease significantly, with typical parameters attenuated by more than 10%. High temperature test, low temperature test, vibration test, waterproof test, low air pressure, shock and dust test have little effect on its image quality, the system has good tolerance to it, and the typical parameter attenuation is below 5%. This paper will provide some reference for the rational use of optical imaging systems and the compilation of test standards.

Speckle noise imposes fundamental limitation on image quality in coherent radiation based imaging and optical metrology systems. Speckle noise phenomena are associated with properties of objects to diffusely scatter irradiation and with the fact that in recording the wave field, a number of signal distortions inevitably occur due to technical limitations inherent to hologram sensors. The statistical theory of speckle noise was developed with regard to only limited resolving power of coherent imaging devices. It is valid only asymptotically as much as the central limit theorem of the probability theory can be applied. In applications this assumption is not always applicable. Moreover, in treating speckle noise problem one should also consider other sources of the hologram deterioration. In the paper, statistical properties of speckle due to the limitation of hologram size, dynamic range and hologram signal quantization are studied by Monte-Carlo simulation for holograms recorded in near and far diffraction zones. The simulation experiments have shown that, for limited resolving power of the imaging system, widely accepted opinion that speckle contrast is equal to one holds only for rather severe level of the hologram size limitation. For moderate limitations, speckle contrast changes gradually from zero for no limitation to one for limitation to less than about 20% of hologram size. The results obtained for the limitation of the hologram sensor’s dynamic range and hologram signal quantization reveal that speckle noise due to these hologram signal distortions is not multiplicative and is directly associated with the severity of the limitation and quantization. On the base of the simulation results, analytical models are suggested.

In this paper, we dimension, design, implement and test the performance of a coherent optical imaging system to be embedded in a scleral contact lens. Our system is designed to project monochromatic patterns onto < 1 mm2 at the retinal fovea periphery. For this purpose, we can use an annular guide (ALG), comprising a set of refractive and diffractive periphery to keep the central vision free. Two optical configurations are tested: in-line and folded. We analyze their manufacturability and optical performance in terms of imaging resolution and quality, discuss the importance of key choices such as source characteristics, and suggest some improvements and limitations based on simple engineering rules guiding their encapsulation in contact lenses.

We are developing a method to objectively quantify image quality and applying it to the optimization of fast magnetic resonance imaging methods. In MRI, to capture the details of a dynamic process, it is critical to have both high temporal and spatial resolution. However, there is typically a trade-off between the two, making the sequence engineer choose to optimize imaging speed or spatial resolution. In response to this problem, a number of different fast MRI techniques have been proposed. To evaluate different fast MRI techniques quantitatively, we use a perceptual difference model (PDM) that incorporates various components of the human visual system. The PDM was validated using subjective image quality ratings by naive observers and task-based measures as defined by radiologists. Using the PDM, we investigated the effects of various imaging parameters on image quality and quantified the degradation due to novel imaging techniques including keyhole, keyhole Dixon fat suppression, and spiral imaging. Results have provided significant information about imaging time versus quality tradeoffs aiding the MR sequence engineer. The PDM has been shown to be an objective tool for measuring image quality and can be used to determine the optimal methodology for various imaging applications.

PurposeTo assess the impact of prostate MRI image quality by means of the Prostate Imaging Quality (PI-QUAL) score, on the identification of extraprostatic extension of disease (EPE), predicted using the EPE Grade Score, Likert Scale Score (LSS) and a clinical nomogram (MSKCCn). MethodsWe retrospectively included 105 patients with multiparametric prostate MRI prior to prostatectomy. Two radiologists evaluated image quality using PI-QUAL (≥4 was considered high quality) in consensus. All cases were also scored using the EPE Grade, the LSS, and the MSKCCn (dichotomized). Inter-rater reproducibility for each score was also assessed. Accuracy was calculated for the entire population and by image quality, considering two thresholds for EPE Grade (≥2 and = 3) and LSS (≥3 and ≥ 4) and using McNemar’s test for comparison. ResultsOverall, 66 scans achieved high quality. The accuracy of EPE Grade ranged from 0.695 to 0.743, while LSS achieved values between 0.705 and 0.733. Overall sensitivity for the radiological scores (range = 0.235–0.529) was low irrespective of the PI-QUAL score, while specificity was higher (0.775–0.986). The MSKCCn achieved an AUC of 0.76, outperforming EPE Grade (=3 threshold) in studies with suboptimal image quality (0.821 vs 0.564, p = 0.016). EPE Grade (=3 threshold) accuracy was also better in high image quality studies (0.849 vs 0.564, p = 0.001). Reproducibility was good to excellent overall (95 % Confidence Interval range = 0.782–0.924). ConclusionAssessing image quality by means of PI-QUAL is helpful in the evaluation of EPE, as a scan of low quality makes its performance drop compared to clinical staging tools.

Blind super-resolution for handheld ultrasound image: Two-stage degradation based unpaired deep learning.

Coherent field imaging is based on the assumption of equal transmitting apertures spacing and equal spectrum of laser, and high-resolution image is reconstructed by iteratively computing the frequency spectrum. However, the inevitable transmitting aperture spacing error of laser is a key factor to affect the coherent field imaging quality in the application. Aiming at the problem of degrading imaging quality caused by the transmitting aperture spacing error, we discuss the mechanism of influence of aperture spacing error on imaging quality and propose a novel method of improving imaging quality from the perspective of suppressing the influence of transmitting aperture spacing error. Firstly, the mechanism of the influence of aperture spacing error on imaging quality and laser echo spectrum is analyzed in detail. Then we derive a frequency spectrum error propagation model. Based on the model, the iterative effect of frequency spectrum error is investigated and the trend of variation in imaging quality with frequency spectrum error is given. We propose a theoretical equation, in which the transmitting aperture spacing error has no influence on frequency spectrum nor imaging quality. To solve the above equation, an optimized method of linear programming is proposed and the optimized matrix of aperture spacing error is obtained. In practice, the influence of aperture spacing error on imaging quality can be largely counteracted by reasonably allocating aperture spacing error according to the optimized spacing error matrix. The correctness and validity of the theoretical model are verified by a simulation experiment. The results show that the Strehl ratio of imaging quality index can be improved by about 100% through using the proposed method, the greater the aperture spacing error, the higher the Strehl ratio of imaging quality index obtained by the method will be. In addition, the method is easy to use practically and less costly as well. Finally, it is concluded that the proposed method can easily and effectively counteract the degrading effect of aperture spacing error on imaging quality. The research can provide a theoretical basis for improving imaging quality and reasonably assigning transmitter aperture spacing accuracy of coherent field imaging telescope.

In response to the practical demands for a wide field of view (FOV), long exit pupil distance, and high image quality in head-mounted displays, an initial structure was built based on the principles of catadioptric lenses in a folded optical path (pancake optics) and the field curvature correction formula. Subsequently, using even-order aspheric surfaces, a VR optical system was developed with a FOV of 2w=110∘, an exit pupil distance of 15 mm, and an exit pupil diameter of 8 mm. Compared to traditional designs, a human eye model was introduced as the image plane to construct a VR-human eye optical system analysis model, allowing for direct analysis of the retinal image quality under different states of the human eye. After that, based on medical statistical data, the impact of different light intensity conditions on the retinal image quality of the VR optical system was explored. Experimental results showed that changes in light intensity affect the pupil diameter, which, in turn, influences the final image quality of the system. To solve the issues, two solutions were proposed: adjusting the screen distance and changing the lens spacing. Both methods significantly improved the imaging quality on the human retina, with an increase of over 30% in the average MTF value. A comparison of these methods was conducted, providing valuable references for future VR optical system designs.

Magnetic particle imaging (MPI) is a relatively new method to image the spatial distribution of magnetic nanoparticle (MNP) tracers administered to the body with high spatial and temporal resolution using an inhomogeneous magnetic field. The spatial information of the MNP's is encoded using a field free point (FFP), or a field free line (FFL), in which the magnetic field vanishes at a point, or on a line, respectively. FFL scanning has the advantage of improved sensitivity compared to FFP scanning as a result of higher signal-to-noise ratio. The trajectory traversed by the FFL or FFP is an important parameter of the MPI system and should be selected to achieve the best imaging quality in minimum scan time, while considering hardware constraints and patient safety. In this study, we analyzed the image quality of different FFL trajectories for a large field of view (FOV) using simulations, to provide a baseline information for FFL scanning MPI system design. We simulated a human-sized FFL scanning MPI configuration to image a circular FOV with 160mm diameter, and compared Radial, Spiral, Uniform Spiral, Flower, and Lissajous trajectories with different trajectory densities scanned by the FFL for constant scan time. We analyzed the system matrices of the trajectories in terms of mutual coherence and homogeneity of the spatial sensitivity. We calculated the maximum electric fields induced on a homogeneous conductive body by the selection field (SF) and the focus field (FF) to compare the trajectories based on the nerve stimulation threshold. The images were obtained using the system matrix reconstruction approach with two different image reconstruction methods. In the first one, we used the conventional image reconstruction method, algebraic reconstruction technique (ART), which gives a regularized least-squares solution. In the second one, we used the state-of-the-art alternating direction method of multipliers (ADMM), which minimizes a weighted sum of the l1 -norm and the total variation (TV) of the images. The Radial and Spiral trajectories resulted in a poor imaging performance at low trajectory densities due to relatively high coherency and poor sensitivity of the measurements, respectively. For ART reconstruction, the highest image quality with the lowest trajectory density was achieved with the Uniform Spiral trajectory. Uniform Spiral, Flower, and Lissajous trajectories yielded comparable performance with ADMM reconstruction. The rotating SF induced higher electric field amplitude compared to the FF. Consequently, maximum allowable gradient at the same trajectory density was greater for the Radial trajectory compared to the other trajectories. For a large FOV coverage, the Uniform Spiral trajectory offers a good compromise between image quality and imaging time, taking safety and hardware limitations into account. The Radial trajectory, especially using l1 -norm and TV priors in the reconstruction, may be favorable in case the SF induced electric field is higher than that of the FF at the same frequency (e.g., relatively small FOV coverage). In general, ADMM reconstruction resulted in higher contrast and resolution compared to ART, leading to lighter requirements on the density of the trajectory.

Aim:An image-guided radiotherapy capable linear accelerator was installed at our hospital which is equipped with an X-ray volumetric imaging (XVI) system. The aim of this study was to describe the results of acceptance tests which were carried out on the XVI facility to verify the manufacturer’s specification.Materials and methods:The commissioning test had six elements: system safety, geometric accuracy, image quality, registration and correction accuracy, X-ray tube and generator performance, and quality assurance (QA) procedures.Results:We had satisfactory results for all the tests. The system passed the safety testes, and the agreement of isocentres was found to be within the tolerance limit. Imaging quality was acceptable. Registration and correction accuracy was tasted with indigenously developed phantom and positioned accurately at isocentre. X-ray tube and generator test results showed that the tube was performing properly.Findings:The described tests represent that the performance of the system is maintained at acceptable levels.

A pupil modulator is a useful tool to improve the resolution of an optical imaging system beyond the classical diffraction limit. However, when this technology is used in a large-aperture telescopic imaging system, the field of view (FOV) with good superresolution (SR) imaging quality is significantly smaller than the designed FOV of the baseline optical system. In this paper, we investigate the influence of various aberrations on the SR properties of a telescopic system using a low sidelobe five-ring pure phase pupil modulator. On this basis, we propose an optimal design method for a wide FOV and a large-aperture telescopic baseline optical system with uniform image quality and a particular residue of symmetric aberration. The design results show that when the optimized 4 m aperture baseline optical system and the modulator are combined as the imaging system, the imaging system has a round and very similar point spread function in the FOV range of 0.28°; the SR gain ratio is 1.234-1.254; and the highest sidelobe intensity is less than 0.1; thus, the system maintains a high resolution ratio and a low sidelobe energy throughout the entire FOV. Finally, a reasonable tolerance model of the baseline optical system is established. The central symmetry tolerances are observed to be loose in this model, thereby reducing the cost and manufacturing difficulty of the system.

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.

The American College of Radiology's (ACR) Nuclear Medicine and PET Accreditation Programs evaluate qualifications of personnel, equipment, image quality, and quality control measures. It is believed that these are primary factors that impact the quality of patient imaging. The ACR accreditation allows facilities to critique and improve their practices as part of their preparation for the accreditation evaluation process. The goals of the ACR Nuclear Medicine and PET Accreditation Programs are improvement in the quality of imaging, provision of educational information by raising awareness of imaging issues, and the recognition of imaging facilities which meet program objectives. This presentation will outline the program requirements, highlighting some of the common pitfalls that may cause deficiencies in both the clinical and phantom submissions.This presentation will provide participants with:1. General information describing the ACR Accreditation Programs2. Information about the Diagnostic Modality Accreditation Programs3. Specific information about the ACR Nuclear Medicine and PET Accreditation Program, to include the application process, clinical images submission and quality control requirements.

Coherent high resolution imaging of distant targets is a challenging problem whose complexity involves understanding of diffractive properties of the optical imaging system, speckle properties of target, statistical properties of the atmospheric refractive index variations, coherence properties of the light source and noise limtations of the detector array to mention a few major issues. In a coherent laser radar imaging system, the target is illuminated with a laser beam, and the scattered light wave from the target light wave is mixed with a local oscillator wave from the same source. The system is referred to as spatial heterodyne imaging system. The sparse aperture imaging approach is based on reducing the total irradiance collection area using smaller sub-apertures, while the resulting resolution of the sparse aperture imaging array is equivalent to an aperture larger than the subapertures. The Ladar and Optical Communications Institute (LOCI) currently has a prototype of the high resolution sparse aperture imaging testbed with an indoor and outdoor range capability. In collaboration with industry partners, academic institutions, and the government this testbed is becoming an innovative research tool in the field of high resolution coherent ladar imaging.