共查询到20条相似文献,搜索用时 78 毫秒
1.
Optimized distortion correction of epi-based statistical parametrical maps for stereotactic neurosurgery 总被引:1,自引:0,他引:1
Hunsche S Sauner D Treuer H Hoevels M Hesselmann V Schulte O Lackner K Volker S 《Magnetic resonance imaging》2004,22(2):163-170
A new approach is presented for unwarping geometrical distortions in echo planar imaging (EPI)-based statistical parametrical maps (SPM). With the developed method, a substantial reduction of geometrical distortions in the order of 5-15 mm down to a residue of approximately 1-2 mm was possible, thus allowing reliable activation localization and, hence, interpretation after fusion with undistorted conventional anatomic images. The unwarping procedure is an optimized combination of two distortion correction methods, the "inhomogeneity mapping" and the coregistration approach. Local and global distortions, the first one object-dependent, the second one caused by imperfect gradient waveforms, are reduced. With several examples of patients and volunteers, the applicability for stereotactic neurosurgery is demonstrated. 相似文献
2.
《中国光学快报(英文版)》2019,(9)
A scanning three-dimensional coherent laser radar(ladar) based on the frequency modulated continuous wave(FMCW) is proposed and demonstrated, which can obtain many three-dimensional high-quality images. The system utilizes an electro-optic modulator and an optical filter to output a linear FMCW with a bandwidth of2 GHz. The flexible and variable rotating double prism is used for beam scanning. The images of flight demonstration are formed by attitude compensation correction. The experiment result validates the performance of our system for airborne three-dimensional scanning imaging. 相似文献
3.
An automatic aberration correction method has been implemented in scanning electron microscopes (SEM). Necessity of the automatic aberration correction is discussed. The procedure of the automatic aberration correction is explained in detail, where deconvolution techniques are used in order to extract probe information from SEM images. Due to the precise digitization and the usage of proper combinations of correction fields, linearity has been found between the amplitude of each aberration and the corresponding field strength. Experimental results are shown which demonstrate that the aberrations are corrected automatically by a linear feedback control method. After the automatic aberration correction, the image quality has been improved drastically. 相似文献
4.
Horsfield MA 《Magnetic resonance imaging》1999,17(9):1335-1345
Diffusion-weighted echo-planar magnetic resonance imaging is potentially of great importance as a diagnostic imaging tool; however, the technique currently suffers a number of limitations, including the image distortion caused by the eddy current induced fields when the diffusion-weighting magnetic field gradient pulses are applied. The distortions cause mis-registration between images with different diffusion-weighting, that then results in artifacts in quantitative diffusion images. A method is presented to measure the magnetic fields generated from the eddy currents for each of three orthogonal gradient pulse vectors, and then to use these to ascertain the image distortion that occurs in subsequent diffusion-weighted images with arbitrary gradient pulse vector amplitude and direction, and image plane orientation. The image distortion can then be reversed. Both temporal and spatial dependence of the residual eddy current induced fields are included in the analysis. Image distortion was substantially reduced by the correction scheme, for arbitrary slice position and angulation. This method of correction is unaffected by the changes in image contrast that occur due to diffusion weighting, and does not need any additional scanning time during the patient scan. It is particularly suitable for use with single-shot echo planar imaging. 相似文献
5.
Byoung-Ju Yun Jinhyung Park Seunghae Kim Hyun-Deok Kim Ho-Hyoung Choi 《Optical Review》2013,20(1):65-73
In the image capturing process using a camera, poor illumination has an influence on the image quality, especially in regards to the contrast and details in the dark regions. Generally, high dynamic range (HDR) imaging techniques are used to match the quality between the real scene and the displayed image. However, in images using the multi-exposure technique or regular photography, the images are limited by the veiling glare, which is scene-, exposure-, lens-, aperture-, and camera-dependent. This study mainly addressed images using the multi-exposure technique and developed a color correction scheme that uses a chromatic adaptation method. In the tone mapping using a Gaussian pyramid, the adaptation level is obtained based on a linear Gaussian filter. The resulting image is then processed through the developed tone-mapping function. This allows the chromatic adaptation method to address the mismatches between the real world and the displayed image. The experiment results show that the proposed method yields a better color correction performance compared to conventional methods. 相似文献
6.
平面物体在曲面状态下扫描仪图像的校正理论 总被引:6,自引:5,他引:1
平面物体在曲面状态下经扫描仪扫描后,其图像将发生复杂的畸变。提出将其分类为灰度畸变、投影畸变和成像畸变。通过理论分析,提出了在二元曲面模型下对投影畸变和成像畸变进行数字校正的方法,给出了对灰度畸变进行数字校正的实用方法。 相似文献
7.
A technique is developed to simultaneously acquire ultrasound and photoacoustic (PA) images based on a linear transducer array. The system uses conventional ultrasound for rapid identification of potential targets. After a target is identified, the ultrasound echo and PA signals can be simultaneously obtained with optimized excitation and a signal collection sequence. The corresponding ultrasound impedance and optical absorption images are reconstructed with a phase-controlled algorithm. The approach can effectively reduce the artifacts associated with a conventional filter backprojection algorithm used in PA imaging by linear scanning. The technique provides a new approach for practical applications. 相似文献
8.
由于存在各种非理想因素,束流在储存环中的闭轨会发生畸变。对束流闭轨畸变进行校正的方法较多,目前合肥光源(HLS)采用奇异值分解(SVD)法进行束流闭轨的全环校正和反馈。针对SVD法不足之处,采用约束线性最小二乘法(CLLS)来改进HLS束流闭轨的全环校正和反馈。介绍了束流闭轨畸变校正的理论,着重介绍应用CLLS对HLS储存环束流闭轨畸变进行全环校正和反馈,并给出运行结果。结果显示,利用CLLS后,HLS敏感实验线站的束流轨道稳定性和重复性得到明显改善。 相似文献
9.
Most of the existing color image watermarking schemes was designed to mark grayscale images or use the color components, which ignore the significant correlation between different color channels. Recently, several approaches were developed to process the color channels intrinsically, but they always cannot counterattack geometric distortions. It is a challenging work to design a robust color image watermarking scheme against geometrical distortions. In this paper, we propose a geometric correction based robust color image watermarking approach using quaternion Exponent moments (QEMs). The novelty of our approach is that (1) the QEMs are derived to deal with the color images in a holistic manner, and (2) the QEMs are exploited for estimating the geometric distortions parameters in order to permit watermark extraction. Experimental results confirm the validity of our approach and its higher robustness against geometrical distortions compared to alternative watermarking methods in the literature. 相似文献
10.
A manual method for higher order Laue zone (HOLZ) line detection with an improved effective high-voltage correction for fast and reliable evaluation of local lattice distortions from convergent-beam electron diffraction (CBED) is presented. It is compared with a high-precision Hough transform method with a dynamic correction for each individual HOLZ line used by Krämer and Mayer. Both methods are applied to unfiltered and filtered experimental CBED patterns. As an example, the local lattice distortions in the γ ? γ′ raft-like structure of a creep-deformed single-crystal nickel-based superalloy (CMSX-6) were measured. The lattice distortions obtained from both methods were analysed and showed good agreement. As a by-product, it was noted that specimen cooling enhanced the contrast of CBED patterns to the extent that the quality of CBED patterns taken at low temperatures without energy filtering was found to be qualitatively similar to that of CBED patterns taken at room temperature with energy filtering. 相似文献
11.
超声显微成像技术广泛应用于工业无损检测领域。相较于闭环、半闭环扫描系统硬件复杂、成本高,开环扫描系统结构简单、成本低,但由于无反馈机制会导致步进电机的非线性运动引起图像像素错位畸变。因此,消除非线性运动带来的错位畸变是采用开环扫描系统实现高质量超声成像的关键。该文提出集最大值投影法、最大类间方差法和中心坐标校正法于一体的MIP-Otsu-C3M方法,对开环扫描系统获得的硬币回波数据采用最大值投影法获取初始灰度图像,采用最大类间方差法获取感兴趣区域的B扫描图像边缘像素位置,并采用中心坐标校正法成功消除像素错位,解决了超声C扫描图像畸变问题。对消除错位畸变的回波数据进行飞行时间法和傅里叶变换法图像重建,直接获得了非畸变的三维图像和透视图像。该新颖算法也验证了最大值投影法可拓展至图像畸变校正应用。 相似文献
12.
A method for determining the near-field image of a semiconductor surface with inhomogenous distribution of carriers has been proposed. This method is based on the linear response theory. As a result, the solution to the self-consistent Lippmann-Schwinger equation is expressed in terms of the effective susceptibility. A calculation is carried out for a semiconductor surface with inhomogenous distribution of electrons under the surface. It is shown that polarizations of both the probe field and the field at the detector in the far zone significantly affect the near-field distribution. The results obtained suggest that the orientation of aggregates (defects) under the semiconductor surface can be determined. The approach developed is universal and can be used for simulation in the scanning near-field microscopy for different types of objects under the surface. 相似文献
13.
平面物体在曲面状态下扫描仪图像的校正实验 总被引:6,自引:5,他引:1
平面物体在曲面状态下经扫描仪扫描后,其图像将发生复杂的畸变。提出了用椭圆柱面加平面模型来描述实际扭曲的情况。基于二元曲面模型的投影畸变和成像畸变数字校正理论,推导了具体的畸变校正公式,并给出了确定成像畸变系数的实用方法。实验结果表明,经校正后投影畸变能够从最大的56%降低到2 5%;成像畸变能够从最大的8 4%降低到0 3%;投影畸变和成像畸变的组合畸变能够从最大的70%降低到3 1%。图像灰度直方图标准偏差的误差可从491%降低到6 5%。 相似文献
14.
Jan Weis Anders Ericsson Hans C.:Son Silander Anders Hemmingsson 《Magnetic resonance imaging》1998,16(10):1265-1272
We present a method for the quantification and correction of geometrical/intensity distortions of magnetic resonance images predominantly caused by bulk magnetic susceptibility shifts due to susceptibility heterogeneities of measured biologic tissues and shape of the object under investigation. The method includes precise and fast measurements of the static magnetic-field distribution inside the measured object and automated data processing. Magnetic-field deviations in the range −2.4; 2.6 ppm were found in the human brain at B0 = 1.5 T. For routinely used imaging parameters, with a read gradient strength of about 1 mT/m, the magnetic-field perturbations in the human brain can cause geometrical distortions up to ±4 mm and intensity changes up to ±50%. MR images corrected by the described method are suitable for planning high precision applications in neurosurgery. 相似文献
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16.
Nondestructive methods aim at detecting, locating and identifying defects. Inversion of ultrasonic measurements obtained by inspecting a steel component of regular geometry with an immersed transducer leads to accurate location of defects. When the component is cladded, the irregular geometry of the surface and the anisotropic nature of the cladding material lead to aberrations of the radiated field (e.g., beam distortions, splitting and defocusing, these varying with the transducer scanning position). As a consequence, defect location may be inaccurate and defects (e.g., cracks) sizing impossible. In the present paper, a model-based inverse method is developed to solve this problem. It relies on the time-dependent simulation of ultrasonic propagation in this material of complex geometry and structure, in order to determine a set of probable positions for the defect at the origin of the measured ultrasonic echo-structure. The most probable position is determined by minimizing a cost-function of likeness between the simulated and measured ultrasonic images. The overall scheme shall generally apply to inverse measured ultrasonic echo-structures as soon as the simulation of the forward problem is tractable. To validate the method, examples of application are given dealing with actual measurements obtained in the real configuration of pressure vessel inspection. 相似文献
17.
Jung-Hwan Kim Sung-Won Yoon Jeong-Ho Lee Woo-Jung Ahn Heui-Jae Pahk 《Optics and Lasers in Engineering》2008,46(2):140-148
White-light phase shifting interferometry (WLPSI) is frequently used for the precision measurement of 3D patterns in various fields. Phase error is one of the most dominant errors in WLPSI, and it is mainly generated by the scanner positioning error and mechanical vibrations. In this paper, phase error detection method by image analysis is proposed, and the numerical correction method for minimizing the phase error is also proposed. The image reconstruction method (IRM), iterative IRM (IIRM) as pre-processors, partial IRM (PIRM), least squares method (LSM) as a main processor, and surface compensation method (SCM) as a post-processor were developed for correcting phase errors. The five methods are implemented and simulated, and the pros and cons of each method are explained.Mirau type interferometry and the phase error generator using a PZT stage were used, and the measurements by WLPSI were done under various vibration conditions. The captured images were analyzed by the five correction methods, and the results were compared. Phase error was effectively minimized by the correction methods, and repeatability of 0.2 nm was obtained in the case of the specimen of 500 nm in height. Repeatability of 10 nm was obtained by conventional WLPSI algorithms for the same specimen. 相似文献
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19.
We have developed a superresolution vibrational imaging method by simultaneous detection of Raman and hyper-Raman scattering. Raman and hyper-Raman images obtained with the same laser spot carry independent information on the sample spatial distribution, owing to different signal dependence (linear in Raman and quadratic in hyper-Raman) on the incident light intensity. This information can be quantitatively analyzed to recover the incident light intensity distribution at the focal plane. A superresolution vibrational image is then derived by the constrained deconvolution of the images by the obtained incident light intensity distribution. This method has been applied to a TiO? nanostructure and the obtained superresolution image was compared with a scanning electron microscopy image. The spatial resolution achieved by the present method is evaluated to be 160 nm, which is more than twice better than the diffraction limited resolution. 相似文献
20.
Susceptibility artifacts from magnetic resonance (MR)-compatible cryoprobes can distort MR images of iceballs. In this work, we investigate the ability of view angle tilting (VAT) to correct susceptibility induced distortions in MR images of cryosurgery. The efficacy of VAT was tested in an ex vivo bovine liver model of cryosurgery using MR-compatible cryoprobes. Artifacts on high bandwidth fast spin echo images of freezing obtained with and without VAT were compared with photographs of the actual iceball shape and size. In vivo imaging with VAT was demonstrated during percutaneous MR-guided cryosurgery of pig liver and brain. VAT was most successful in reducing probe and iceball distortions when the imaging plane was normal to the cryoprobe, and the cryoprobe was perpendicular to the main magnetic field of the scanner. VAT had the greatest benefit when used to correct MR images of freezing when the surface of the iceball was relatively near to the cryoprobe. For large iceballs, the artifact was small so the VAT correction was less important. We conclude that VAT significantly reduced distortions in the shape of the signal void corresponding to the extent of freezing visualized during MR-guided cryosurgery. This improved ability to visualize the exact location of the cryoprobe, as well as the precise shape of the iceball, particularly during initial freezing when the iceball is small, has potential to significantly improve the accuracy of MR-guided cryosurgery of small lesions, and the accuracy of MR-assisted temperature calculations that are based on precise imaging of the probe location, and boundary geometry of the iceball. 相似文献