- 标题
- 摘要
- 关键词
- 实验方案
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Caracterización y simulación de ruido en las imágenes de PET reconstruidas con OSEM: desarrollo de un método para la generación de imágenes sintéticas
摘要： Introduction: The goals of the study are to characterize imaging properties in 2D PET images reconstructed with the iterative algorithm ordered-subset expectation maximization (OSEM) and to propose a new method for the generation of synthetic images. Material and methods: The noise is analyzed in terms of its magnitude, spatial correlation, and spectral distribution through standard deviation, autocorrelation function, and noise power spectrum (NPS), respectively. Their variations with position and activity level are also analyzed. This noise analysis is based on phantom images acquired from 18F uniform distributions. Experimental recovery coefficients of hot spheres in different backgrounds are employed to study the spatial resolution of the system through point spread function (PSF). The NPS and PSF functions provide the baseline for the proposed simulation method: convolution with PSF as kernel and noise addition from NPS. Results: The noise spectral analysis shows that the main contribution is of random nature. It is also proven that attenuation correction does not alter noise texture but it modifies its magnitude. Finally, synthetic images of 2 phantoms, one of them an anatomical brain, are quantitatively compared with experimental images showing a good agreement in terms of pixel values and pixel correlations. Thus, the contrast to noise ratio for the biggest sphere in the NEMA IEC phantom is 10.7 for the synthetic image and 8.8 for the experimental image. Conclusions: The properties of the analyzed OSEM-PET images can be described by NPS and PSF functions. Synthetic images, even anatomical ones, are successfully generated by the proposed method based on the NPS and PSF.
关键词： PET,Autocorrelation function,OSEM,Iterative reconstruction,Noise power spectrum,Point spread function
更新于2025-09-23 15:22:29
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Fast Optical Phased Array Calibration Technique for Random Phase Modulation LiDAR
摘要： Optical phased array (OPA) imaging technique, which uses electro-optic modulation to achieve beam steering rather than mechanical scanning, is a raster scanning imaging method with great potential due to its non-inertia and high-speed. However, fabrication imperfection of an OPA causes pre-designed phase modulations not yielding desired steering angles, and a time-consuming calibration is usually required before practical use. Alternatively, it is possible to obtain images with a random phase modulation OPA. In this work, we propose a fast calibration for the random phase modulation OPA LiDAR. Experimental results demonstrate that, to obtain images of the same quality, the proposed calibration is 3 times faster than the calibration used in raster scanning scheme. In the meantime, the proposed calibration simultaneously retrieves the point spread function of the imaging system during the process, which can be used to remove the image blurring caused by the sidelobes and further improve the image quality.
关键词： calibration,Optical phased array,point spread function,random phase modulation
更新于2025-09-23 15:22:29
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Optimal PSF Estimation for Simple Optical System Using a Wide-Band Sensor Based on PSF Measurement
摘要： Simple optical system imaging is a method to simplify optical systems by removing aberrations using image deconvolution. The point spread function (PSF) used in deconvolution is an important factor that affects the image quality. However, it is difficult to obtain optimal PSFs. The blind estimation of PSFs relies heavily on the information in the image. Measured PSFs are often misused because real sensors are wide-band. We present an optimal PSF estimation method based on PSF measurements. Narrow-band PSF measurements at a single depth are used to calibrate the optical system; these enable the simulation of real lenses. Then, we simulate PSFs in the wavelength pass range of each color channel all over the field. The optimal PSFs are computed according to these simulated PSFs. The results indicated that the use of the optimal PSFs significantly reduces the artifacts caused by misuse of PSFs, and enhances the image quality.
关键词： image restoration,deconvolution,imaging sensors,simple optical system,point spread function
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Quantifying the Relationship Between Higher Photovoltaic Module Efficiency and the Adoption of Distributed Solar
摘要： Some applications of data from the Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometer require the use of the point response function (PRF), which describes the influence of radiance from each point on the measurement. A radiance source for the measurement of the PRF of the CERES instruments was built and installed into the Radiometric Calibration Facility, in which the CERES instruments have been calibrated. The design and application of the PRF source and the computation of the PRF from these measurements are described. In order to compare the PRF based on measurements with the theoretical PRF, it is necessary to account for the finite size of the beam from the source. The use of the PRF source and the analysis of the data are demonstrated by application to the FM-5 instrument. The measured results compare well with theory for the CERES instruments and are presented for FM-5.
关键词： Aqua,Terra,point spread function,radiometry,National Polar-orbiting Partnership (NPP),Earth radiation budget,point response function (PRF),calibration,Clouds and the Earth’s Radiation Energy System (CERES)
更新于2025-09-23 15:19:57
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The influence of minimal misalignment on the repeatability of PET images examined by the repositioning of point sources
摘要： Objective: We aimed to evaluate the influence of the minimal misalignment of the hot spot on the repeatability of PET images using the repositioning of point sources. Methods: Point sources with an inner-diameter of 1 mm were made with 1μL of 18F solution. Seven point sources were placed on the x-axis in the field-of-view. For fixed position imaging, PET data were acquired for 10 min 5 times serially. For variable position imaging, PET data were acquired for 10 minutes each with the point sources placed at 0 mm, ±0.5 mm, and ±1.0 mm in the x-axis direction. The data were reconstructed using ordered-subsets expectation maximization (OSEM) and OSEM with point-spread function (OSEM+PSF) algorithms. The image matrix was 128×128, 200×200, 256×256, 400×400, and 512×512 pixels. The normalized maximum count (rMax), the variation of rMax (CVmax) and full width at half maximum (FWHM) were analyzed. Results: The hot spots on OSEM images far from the center became faint and broad, while those on the OSEM+PSF images became small and dense. Although the rMax was overestimated at the 5 cm position on OSEM image, those at other positions were overestimated on OSEM+PSF images with a matrix size of ≥256×256. The rMax showed a similar pattern in fixed and variable position images. The CVmax in fixed position OSEM images were <2%, irrespective of the matrix size. In contrast, the CVmax in variable position images were higher in comparison to fixed position images. The CVmax of the OSEM+PSF images were higher in comparison to OSEM images. The FWHM increased at positions far from the center on OSEM image, while that was stable at all positions on OSEM+PSF images. Conclusion: The repeatability of the small hot spot was affected by the minimal misalignment, especially on the OSEM+PSF images. Precise positioning is necessary if PET is to be used as a biomarker. Professions should recognize that the PSF correction deteriorates the repeatability of the small hot spot although it improves the spatial resolution of PET images.
关键词： repositioning,repeatability,point-spread function,PET/CT
更新于2025-09-19 17:15:36
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Comparison of optical quality and distinct macular thickness in femtosecond laser-assisted versus phacoemulsification cataract surgery
摘要： Background: Optical quality and macular thickness changing optical quality is rarely reported after femtosecond laser-assisted cataract surgery (FLACS). In current research, we evaluated optical quality recovery and distinct macular thickness changes after FLACS and phacoemulsification cataract surgery (PCS). Methods: A total of 100 cataract patients (100 eyes) were included (50 eyes for the FLACS group and 50 eyes for the PCS group). Modulation transfer function (MTF), point spread function (PSF) and dysfunctional lens index (DLI) were measured by a ray-tracing aberrometer (iTrace). Uncorrected distance visual acuity (UDVA) and corrected distance visual acuity (CDVA) were also assessed pre-operation,1 week and 1 month after surgery. The MTF values at spatial frequencies of 5, 10, 15, 20, 25 and 30 cycles/degree (c/d) were selected. We used optical coherence tomography (OCT) to assess the macular thickness of different regions pre-operatively and1month after the surgery. Results: In PCS group, we found the statistically significant differences between pre-operation and post-operation in DLI (p < 0.0001), PSF (strehl ratio, SR) (p = 0.027) and MTF (p = 0.028), but not intraocular pressure (IOP) (p = 0.857). The differences between pre-operation and post-operation for DLI (p = 0.031), SR (p = 0.01) and IOP (p = 0.03), but not MTF (p = 0.128) were also found in FLACS group. The differences were statistically significant when the spatial frequencies were at 5, 10 and 25 (p = 0.013, 0.031 and 0.048) between pre-operation and post-operation in PCS group but not FLACS group at 1 month. In PCS group, we found the differences between pre-operation and post-operation in nasal inter macular ring thickness (NIMRT) (p = 0.03), foveal volume (FV) (p = 0.034) and average retinal thickness (ART) (p = 0.025) but not FLACS group at 1 month. Conclusion: FLACS is safe that did not cause significant increase of macular thickness in current study. However, it also cannot produce better optical quality. In contrast, PCS can produce macular thickness changes, but better optical quality recovery. The slightly retinal change may not affect optical quality.
关键词： Macular thickness,Femtosecond laser-assisted cataract surgery (FLACS),Point spread function (PSF),Modulation transfer function (MTF),Phacoemulsification cataract surgery (PCS),Dysfunctional lens index (DLI),Optical quality
更新于2025-09-19 17:13:59
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[IEEE 2019 Workshop on Research, Education and Development of Unmanned Aerial Systems (RED UAS) - Cranfield, United Kingdom (2019.11.25-2019.11.27)] 2019 Workshop on Research, Education and Development of Unmanned Aerial Systems (RED UAS) - A multi-UAS system for the inspection of photovoltaic plants based on the ROS-MAGNA framework
摘要： Some applications of data from the Clouds and the Earth’s Radiant Energy System (CERES) scanning radiometer require the use of the point response function (PRF), which describes the in?uence of radiance from each point on the measurement. A radiance source for the measurement of the PRF of the CERES instruments was built and installed into the Radiometric Calibration Facility, in which the CERES instruments have been calibrated. The design and application of the PRF source and the computation of the PRF from these measurements are described. In order to compare the PRF based on measurements with the theoretical PRF, it is necessary to account for the ?nite size of the beam from the source. The use of the PRF source and the analysis of the data are demonstrated by application to the FM-5 instrument. The measured results compare well with theory for the CERES instruments and are presented for FM-5.
关键词： Aqua,Terra,point spread function,radiometry,Earth radiation budget,point response function (PRF),calibration,Clouds and the Earth’s Radiation Energy System (CERES),National Polar-orbiting Partnersship (NPP)
更新于2025-09-16 10:30:52
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[IEEE IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium - Yokohama, Japan (2019.7.28-2019.8.2)] IGARSS 2019 - 2019 IEEE International Geoscience and Remote Sensing Symposium - Improved Vicarious Radiometric Calibration Method Considering Adjacency Effect for High Resolution Optical Sensors
摘要： When using field calibration site to perform on-orbit radiometric calibration for a space-borne remote sensor, the observed signal of the sensor may contain energy from adjacent pixels, due to existence of the earth atmosphere and sensor viewing characteristics. Hence the accuracy of radiometric calibration will be decreased to some extent. When calibration of high-resolution sensor is concerned, the non-uniformity of the ground target will be relatively more obvious. In addition, if the brightness contrast of neighboring targets is not small, the impact of adjacency effect will be more outstanding. How to quantitatively analyze and eliminate the influence of this kind of adjacency effect, becomes an actual demand to reduce the uncertainty of on-orbit radiometric calibration. Aiming at the adjacent effect caused by atmospheric multiple scattering, this paper analyzed radiation transfer mechanism first, then constructed a local atmospheric point spread function model using long time-series satellite-ground synchronous observation data, developed an adjacency effect correction method used in on-orbit vicarious calibration, which considers background reflectance spectral information. Test on Sentinel-2A imagery indicates that the proposed correction method can effectively alleviate the influence of adjacency effect in vicarious calibration.
关键词： Vicarious radiometric calibration,High resolution,Point spread function (PSF),Adjacency effect
更新于2025-09-16 10:30:52
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Point-Spread-Function (PSF) Characterization of a 340 GHz Imaging Radar using Acoustic Levitation
摘要： In this paper, resolution characterization and beam analysis of a 340 GHz imaging radar are demonstrated by means of a point-spread-function imaging an acoustically levitated point-like target. It is shown that at THz frequencies, conventional PSF measurement techniques are limited by the presence of strong scattering response of background objects, such as suspension threads, within the imaging field-of-view (FOV). Using acoustic levitation, it is possible to eliminate secondary objects within the FOV and achieve a pure PSF characterization of the radar. It is shown that the PSF patterns obtained using acoustic levitation exhibit high fidelity and are free from artifacts. We demonstrate this using a small water droplet suspended in air at the focus of the 340 GHz radar. The measured PSF characteristics of the radar are in excellent agreement with physical optics (PO) simulations and analytical results.
关键词： acoustic levitation,submillimeter,antenna,beam,point-spread-function (PSF),Radar,imaging,acoustics
更新于2025-09-11 14:15:04
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - An Adaptation of Cnn for Small Target Detection in the Infrared
摘要： Due to the low signal to noise ratio and limited spatial resolution, small target detection in an infrared image is a challenging task. Existing methods often have high false alarm rates and low probabilities of detection when infrared small targets submerge in the background clutter. In this paper, the Convolutional Neural Network (CNN) is adapted to extract the hidden features of small targets from infrared imagery with a proposed technique for a large amount of training data generation. The Point Spread Function (PSF) is employed to model the small target data and generate positive samples. The random background image patches are selected as the negative samples. In this way, the detection problem is skillfully converted into a problem of pattern classification using CNN. Extensive synthetic and real small targets were tested to evaluate the performance of this novel small target detection framework. The experimental results indicate that the proposed algorithm is simple and effective with satisfactory detection accuracy.
关键词： Infrared image (IR),Convolutional Neural Network (CNN),Point Spread Function (PSF),small target detection
更新于2025-09-10 09:29:36