- 标题
- 摘要
- 关键词
- 实验方案
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Feasible scan timing for 320-row coronary CT angiography generated by the time to peak in the ascending aorta
摘要： Purpose: A 320-row CT scanner can briefly scan the entire heart. Therefore, the feasible scan timing is required. The aim of this study was to propose a refined method for feasible scan timing for coronary CT angiography (CCTA) using a time-density curve of the ascending aorta (AAo). Methods: One-hundred and twenty-nine patients were prospectively enrolled. All patients were performed test-bolus method. For the initial 65 patients, the scan timing was determined as a 3.0 s delay at the peak time in the AAo, which was defined as the conventional protocol (COV-P). For the next 64 patients, a scan timing of 1.0, 3.0, or 5.0 s delay was determined according to the interval from the contrast media arrival to peak time in the AAo, which was defined as the arrival to peak protocol (AP-P). The optimal scan timing was identified by the measurement of CT number in the left atrium, left ventricle, AAo, and descending aorta. The coronary enhancement and heterogeneity were compared between the two protocols. Results: The optimal scan timing was significantly higher in the AP-P than in the COV-P (85.9% vs. 61.5%, p = 0.0017). The CT number in the left circumflex artery (LCX) was significantly higher in the AP-P than the COV-P (344.5 Hounsfield units vs. 316.3 Hounsfield units, p = 0.0484). The heterogeneous index of the LCX was significantly greater for the COV-P than the AP-P (?36.8 vs. –25.8, p = 0.0028). Conclusions: The AP-P can be used to determine the optimal scan timing for CCTA and contributes to stable coronary enhancement.
关键词： Coronary CT angiography,Feasible scan timing,320-row CT
更新于2025-09-19 17:15:36
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Investigation of shutter scan acquisition parameters in a prototype chest digital tomosynthesis system
摘要： A shutter scan acquisition (SSA) method is proposed to reduce patient exposure dose in a chest digital tomosynthesis system. Projections obtained using the SSA constitute a combination of truncated and non-truncated projections. The truncated projections are images in which the lung field is set within a region-of-interest (ROI), and the non-truncated projections are full images in which the ROI is not set at all. We proposed a shutter weighting factor (SWF) as an acquisition parameter for SSA. We call the number of truncated projections divided by the number of non-truncated projections as SWF. We used a prototype CDT system and the LUNGMAN phantom with 8 and 10 mm lung nodules. 81 projections were obtained using SSA in five sets according to the SWFs. The image quality was quantified based on the contrast-to-noise ratio (CNR). We also calculated the figure of merit (FOM) to determine the proper acquisition parameters of the five sets. Both the CNR and FOM values of the 8 mm lung nodule in the selected ROI increased with increases of the SWF. However, the CNR value of the 10 mm lung nodule outside the ROI decreased with increases of the SWF, while the FOM value was maximized when the SWF was 3.05. We investigated the effect of the composition ratio of the truncated and non-truncated projections on the reconstructed images of the SSA based on the FOM values. In conclusion, we determined the proper SSA parameters in a prototype CDT system.
关键词： Digital tomosynthesis,Dose reduction method,Region of interest reconstruction,Shutter scan acquisition
更新于2025-09-19 17:15:36
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Enhanced nonlinear optical properties of ZnS nanoparticles in 1D polymer photonic crystal cavity
摘要： The enhanced nonlinear optical absorption and optical limiting properties of polymeric one dimensional photonic crystal (1DPhC) with ZnS nanoparticles as defect are reported. The 1DPhC was fabricated by spin coating technique, using polystyrene (PS) and cellulose acetate (CA) as high and low refractive index materials. ZnS nanoparticles were synthesized in CA solution by laser ablation technique and the structural, morphological and non linear optical characterizations were done. A microcavity structure with cavity resonance around 532 nm was designed by inserting ZnS NPs/CA defect layer between two Bragg reflectors comprising 10 bilayers of CA/PS. A significant enhancement (4.6 times) in both nonlinear absorption and optical limiting properties of 1DPhC with ZnS defect layer was observed under 532 nm pulse excitation compared to the ZnS reference sample. The enhancement in the observed nonlinear optical properties of the system could be accredited to the confinement of optical field due to the localization of photons in the cavity mode. The current system can play crucial roles in designing practical nonlinear optical devices, such as optical limiters, optical switchers etc.
关键词： 1D Photonic crystal,Nonlinear absorption,Optical limiting,Z-scan
更新于2025-09-19 17:15:36
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Wideband Wide-Scanning Phased Array in Triangular Lattice with Electromagnetic Band-Gap Structures
摘要： A phased array in triangular lattice, with a large element spacing, wide band and wide scan angle, is investigated in this paper. The array is designed based on a connected backed-cavity antenna element. Scan blindness is observed for this triangular lattice array when the beam scans in the E plane due to large element spacing which provides a suitable propagation condition for the leaky surface waves in the array aperture. Therefore, compact electromagnetic band-gap (EBG) structures are loaded in the array element to suppress the leaky surface waves and then remove the E-plane scan blindness for the largest impedance bandwidth. The bandwidths close to the theoretical values are achieved as the beam is scanned in the E and H planes, for the given element spacing. The validity of design is verified by fabricating a 13×5 prototype, the measured results are in good agreements with the full-wave simulations.
关键词： scan blindness,phased arrays,wide scanning,Electromagnetic band-gap (EBG) structures,triangular lattice
更新于2025-09-19 17:15:36
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Multi-parameter optimization of a loose focusing high flux high-harmonic beamline
摘要： We perform a multi-dimensional parameter scan in the generation of high-order harmonics, with the main purpose to find the macroscopic conditions that optimize the harmonic yield in a specific spectral domain, around 40 eV for this particular case. The scanned parameters are the laser pulse energy, gas pressure, interaction cell position relative to focus and the cell length, while the fixed parameters are chosen to model a loose focusing configuration which is used in many existing laboratories. We performed the simulations with a 3D non-adiabatic model complemented by a detailed analysis of the phase matching mechanisms involved in an efficient harmonic generation. Based on the results we identify a range of parameter combinations that lead to a high yield in the specified spectral domain. The method and results presented here can be the framework for the design and construction of high flux high-order harmonic generation beamlines.
关键词： XUV flux,high-order harmonic generation,optimization,multi-dimensional parameter scan,numerical simulation
更新于2025-09-19 17:15:36
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Measuring of nonlinear properties of spatial light modulator with different wavelengths
摘要： The non-linear optical properties of Spatial Light Modulator(SLM) represented by Nonlinear Refractive Index (NLR) and nonlinear Absorption coefficient has been measured in this work using highly sensitive method known as Z-scan technique for different wavelengths (red and green). The capability to do instant measurements of different nonlinear optical parameters lead to consider these techniques as a one of the most desired and effective methods that could apply for different materials. The results showed that the NLR were in the same power for the different wavelengths while the nonlinear absorption is higher in case of green laser.
关键词： Z-scan technique,Nematic Liquid Crystal,SLM
更新于2025-09-19 17:15:36
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The Influence of Quantum Confinement on Third-Order Nonlinearities in Porous Silicon Thin Films
摘要： We present an experimental investigation into the third-order nonlinearity of conventional crystalline (c-Si) and porous (p-Si) silicon with Z-scan technique at 800-nm and 2.4-μm wavelengths. The Gaussian decomposition method is applied to extract the nonlinear refractive index, n2, and the two-photon absorption (TPA) coefficient, β, from the experimental results. The nonlinear refractive index obtained for c-Si is 7 ± 2 × 10?6 cm2/GW and for p-Si is ?9 ± 3 × 10?5 cm2/GW. The TPA coefficient was found to be 2.9 ± 0.9 cm/GW and 1.0 ± 0.3 cm/GW for c-Si and p-Si, respectively. We show an enhancement of the nonlinear refraction and a suppression of TPA in p-Si in comparison to c-Si, and the enhancement gets stronger as the wavelength increases.
关键词： Z-scan,third-order nonlinearity,TPA,porous silicon,self-focusing
更新于2025-09-19 17:15:36
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A flexible calibration method for the intrinsic and mechanical parameters of panoramic line-scan cameras
摘要： Panoramic line-scan cameras provide high definition images with a quasi uniform distribution of the sensing elements. Unfortunately, calibration of such devices with classic techniques is not possible making their use, in computer vision field, not straightforward. We propose a flexible and convenient calibration method for the computation of intrinsic and mechanism parameters of such systems by using images of a simple calibration pattern. Unlike existing approaches, the proposed method considers a full geometrical model and does not make any unattainable assumption such as concentricity of images, a priori knowledge about camera poses or coincidence of the rotation axis with the optical center. Using few images taken with free poses, the calibration is performed in two steps. First, the intrinsic parameters are computed using sets of 2D/3D point correspondences that are generated automatically by exploiting the structure of the calibration rig. Then, thanks to the parameterization of the projection of a 3D straight line, the mechanical parameters are computed using points at infinity. For each step, closed form solutions and iterative refinement techniques are presented. The proposed approach is validated with both synthetic and real data collected by our prototype.
关键词： Mechanical parameters,Computer vision,Intrinsic parameters,Panoramic camera,Calibration,Line-scan camera
更新于2025-09-19 17:15:36
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Structure and property relationship of methoxy substituted novel organic crystals for photonic applications
摘要： In the present work, a promising non-centrosymmetric chalcone derivative 3-(2, 4, 6-trimethoxyphenyl)-1-(thiophen-2-yl)-prop-2-en-1-one (2TM) was investigated to define their potential for photonic applications through various characterization techniques. Therefore 2TM has been synthesized and single crystals have been grown using slow evaporation solution growth technique. The UV–Vis-NIR spectrum reveals the transparency of the crystal for the entire visible region. The thermal stability and phase transition of the compound was studied by thermo gravimetric and differential thermal analysis and found to be stable up to 132 °C. For structural conformation, the Fourier transform infrared spectral tests were performed on 2TM. For nonlinear optical studies of the third order, the Z-scan experiment was conducted. The material had reverse saturation absorption and self-defocusing properties and therefore, 2TM showed strong nonlinear absorption coefficients and optical limiting behavior, under continuous wave diode-pumped solid state laser. Second harmonic generation efficiency of 2TM crystal is 1.12 times the urea efficiency. The single crystal x-ray diffraction studies of the crystal showed that the crystal system of 2TM is orthorhombic with space group P n a 21. The structural and property relationship studies are carried out for the methoxy substituted organic crystals. Thus, the reported crystal can be used for photonic applications due to its excellent optical properties.
关键词： Single crystal,Chalcones,Z-scan,Second harmonic generation,Structure–property relationship
更新于2025-09-19 17:13:59
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Near resonant nanosecond laser-driven nonlinear optical response in As <sub/>50</sub> S <sub/>50</sub> thin films
摘要： Nanosecond near resonant excitation in As50S50 thin films leads to strong nonlinear optical response, i.e. nonlinear absorption coefficient up to 4 × 106 cm GW?1 and nonlinear refractive index of 8.5 cm2 GW?1, both of which are the strongest ever reported in amorphous semiconductors. We propose a three-level energy band model to explain this effect, which indicates that the nonlinear process is reverse saturable absorption in nature, mediated by excited-state absorption from slow interband transition between the conduction and valence band. On the other hand, observation of negative nonlinear refractive index reveals the occurrence of self-defocusing effect. Finally, benefitting from the strong nonlinear response, we demonstrate a promising application of As50S50 thin films as an optical limiter for optoelectronic sensors.
关键词： chalcogenide,nonlinear optics,Z-scan,thin films
更新于2025-09-19 17:13:59