共查询到20条相似文献,搜索用时 46 毫秒
1.
In this paper, we design a variational model for restoring multiple-coil magnetic resonance images (MRI) corrupted by non-central Chi distributed noise. The energy functional corresponding to the restoration problem is derived using the maximum a posteriori (MAP) estimator. Optimizing this functional yields the solution, which corresponds to the restored version of the image. The non-local total bounded variation prior is being used as the regularization term in the functional derived using the MAP estimation process. Further, the split-Bregman iteration scheme is being followed for fast numerical computation of the model. The results are compared with the state of the art MRI restoration models using visual representations and statistical measures. 相似文献
2.
MR susceptibility misregistration correction 总被引:1,自引:0,他引:1
Sumanaweera TS Glover GH Binford TO Adler JR 《IEEE transactions on medical imaging》1993,12(2):251-259
The authors present a new in vivo method to correct the nonlinear, object-shape-dependent and material-dependent spatial distortion in magnetic resonance (MR) images caused by magnetic susceptibility variations. This distortion across the air/tissue interface before and after the correction is quantified using a phantom. The results are compared to the distortion-free computed tomography (CT) images of the same phantom by fusing CT and MR images using fiducials, with a registration accuracy of better than a millimeter. The distortion at the bone/tissue boundary is negligible compared to the typical MRI (MR imaging) resolution of 1 mm, while that at the air/tissue boundary creates displacements of about 2 mm (for G(x) 3.13 mT/m). This is a significant value if MRI is to provide highly accurate geometric measurements, as in the case of target localization for stereotaxic surgery. The correction scheme provides MR images with accuracy similar to that of CT: 1 mm. A new method to estimate the magnetic susceptibility of materials from MR images is presented. The magnetic susceptibility of cortical bone is measured using a SQUID magnetometer, and is found to be -8.86 ppm (with respect to air), which is quite similar to that of tissue (-9 ppm). 相似文献
3.
《IEEE transactions on bio-medical engineering》2009,56(5):1287-1297
4.
《IEEE transactions on medical imaging》2009,28(6):789-798
5.
Narrowband Magnetic Particle Imaging 总被引:1,自引:0,他引:1
《IEEE transactions on medical imaging》2009,28(8):1231-1237
6.
Eugene Shi Guang Choo Erwin Peng Reshmi Rajendran Prashant Chandrasekharan Chang‐Tong Yang Jun Ding Kai‐Hsiang Chuang Junmin Xue 《Advanced functional materials》2013,23(4):496-505
This study proposes a new method to generate positive contrast in magnetic resonance imaging (MRI) using superparamagnetic contrast agents. Superparamagnetic nanostructures consisting of octahedron manganese ferrite nanoparticles embedded in spherical nanogels are fabricated using a bottom‐up approach. The composite nanoparticles are strongly magnetized in an external magnetic field and produce a unique NMR frequency shift in water protons, which can be demonstrated in MR spectroscopy and imaging to be different from the bulk pool. Moreover, the particles exhibit excellent colloidal stability in aqueous media and good cell biocompatibility. Hence, these particles are potentially useful as biomarkers by taking advantage of the positive contrast effects produced in MRI. 相似文献
7.
《IEEE transactions on medical imaging》2008,27(12):1754-1761
8.
《IEEE transactions on medical imaging》2009,28(12):1974-1985
9.
《IEEE transactions on medical imaging》2010,29(2):365-374
10.
Aijun Shen Xianfu Meng Xiaolong Gao Xiaowen Xu Chulun Shao Zhongmin Tang Yanyan Liu Wenbo Bu Peijun Wang 《Advanced functional materials》2019,29(2)
It is well known that acidic tumor microenvironment (TME) is very important for tumor' growth, metastasis, and drug resistance. In addition, accurate diagnosis of the solid tumors' acidic microenviroment based on the precise location of their site is especially essential for the further treatment and prognostic evaluation of cancer. Although magnetic resonance imaging (MRI) is widely used for clinical cancer diagnosis, there are still enormous challenges left for developing MRI agents which integrate anatomic imaging for tumor site location with functional imaging for pH evaluation, especially for medium or high magnetic field machines. Herein, an innovative strategy is proposed to incorporate anatomic imaging (T1‐weighted imaging, T1WI) with functional imaging (susceptibility weighted imaging, SWI) using one 3.0 T MRI scanner on an adaptable nanoplatform namely, NaGdF4@polydopamine@polyethylene glycol (PEG), which can self‐aggregate under the specific low pH in TME to realize regulatory susceptibility. Moreover, the nanoplatform performs well in tumor accurately location as well as pH sensitively perception. Most importantly, the strategy not only fuses two MRI models on one nanoplatform using one 3.0 T machine to extend the application range but also provides a new insight for the design of other novel imaging agents. 相似文献
11.
Guerquin-Kern M Häberlin M Pruessmann KP Unser M 《IEEE transactions on medical imaging》2011,30(9):1649-1660
In this work, we exploit the fact that wavelets can represent magnetic resonance images well, with relatively few coefficients. We use this property to improve magnetic resonance imaging (MRI) reconstructions from undersampled data with arbitrary k-space trajectories. Reconstruction is posed as an optimization problem that could be solved with the iterative shrinkage/thresholding algorithm (ISTA) which, unfortunately, converges slowly. To make the approach more practical, we propose a variant that combines recent improvements in convex optimization and that can be tuned to a given specific k-space trajectory. We present a mathematical analysis that explains the performance of the algorithms. Using simulated and in vivo data, we show that our nonlinear method is fast, as it accelerates ISTA by almost two orders of magnitude. We also show that it remains competitive with TV regularization in terms of image quality. 相似文献
12.
针对应用迭代软阈值(IST)算法对基于低秩稀疏矩 阵(L+S,low rank and sparse)分解模型的动态磁共振成像(MRI)图像 进行重建存在重建精度一般和重建速度慢的问题,提出在矩阵L+S分解模 型的基础上引入全变分(TV)正则项,达到进一步去噪声和去伪影,提高重建精度目的;利用 非精确增广拉 格朗日算法(IALM)达到快速重建的目的。通过对心脏灌注动态MRI成像和心电影MRI成 像的仿真实 验表明:对于L+S低秩稀疏矩阵分解模型的重建,IALM比IS T算法速度更快,精度更高;模型引入TV正则项 后再利用IALM重建,重建速度虽然比之前的IALM有所降低,但依然优于IST算法, 并且重建精 度高于之前的IALM。在L+S分解模型中引入TV正则项 提高了MRI重建精度,运用IALM进行求解加快了重建速度,结合TV正则项和IALM达到了 快速、高精度重建的目的。 相似文献
13.
Shengcai Liu Jiangshe Zhang Junmin Liu Qingyan Yin 《Signal, Image and Video Processing》2016,10(5):861-868
Recently, the design of group sparse regularization has drawn much attention in group sparse signal recovery problem. Two of the most popular group sparsity-inducing regularization models are \(\ell _{1,2}\) and \(\ell _{1,\infty }\) regularization. Nevertheless, they do not promote the intra-group sparsity. For example, Huang and Zhang (Ann Stat 38:1978–2004, 2010) claimed that the \(\ell _{1,2}\) regularization is superior to the \(\ell _1\) regularization only for strongly group sparse signals. This means the sparsity of intra-group is useless for \(\ell _{1,2}\) regularization. Our experiments show that recovering signals with intra-group sparse needs more measurements than those without, by the \(\ell _{1,\infty }\) regularization. In this paper, we propose a novel group sparsity-inducing regularization defined as a mixture of the \(\ell _{1/2}\) norm and the \(\ell _{1}\) norm, referred to as \(\ell _{1/2,1}\) regularization, which can overcome these shortcomings of \(\ell _{1,2}\) and \(\ell _{1,\infty }\) regularization. We define a new null space property for \(\ell _{1/2,1}\) regularization and apply it to establish a recoverability theory for both intra-group and inter-group sparse signals. In addition, we introduce an iteratively reweighted algorithm to solve this model and analyze its convergence. Comprehensive experiments on simulated data show that the proposed \(\ell _{1/2,1}\) regularization is superior to \(\ell _{1,2}\) and \(\ell _{1,\infty }\) regularization. 相似文献
14.
《Solid-State Circuits, IEEE Journal of》2009,44(6):1805-1813
15.
Lawrence BG Crozier S Cowin G Yau DD 《IEEE transactions on bio-medical engineering》2002,49(9):1024-1030
Radio-frequency (RF) coils are a necessary component of magnetic resonance imaging (MRI) systems. When used in transmit operation, they act to generate a homogeneous RF magnetic field within a volume of interest and when in receive operation, they act to receive the nuclear magnetic resonance signal from the RF-excited specimen. This paper outlines a procedure for the design of open RF coils using the time-harmonic inverse method. This method entails the calculation of an ideal current density on a multipaned planar surface that would generate a specified magnetic field within the volume of interest. Because of the averaging effect of the regularization technique in the matrix solution, the specified magnetic field is shaped within an iterative procedure until the generated magnetic field matches the desired magnetic field. The stream-function technique is used to ascertain conductor positions and a method of moments package is then used to finalize the design. An open head/neck coil was designed to operate in a clinical 2T MRI system and the presented results prove the efficacy of this design methodology. 相似文献
16.
S. I. Kasatkin A. M. Murav’jev N. V. Plotnikova F. A. Pudonin L. A. Azhaeva Z. N. Sergeeva V. D. Khodzhaev 《Russian Microelectronics》2005,34(1):47-53
Magnetic properties of nanoscale magnetic-layer systems using FeNi, Co, FeMn, Al2O3, and SiC layers are studied experimentally. The dependence of magnetic behavior on the system geometry and parameters is addressed. Ferromagnet-semiconductor exchange coupling subject to the amplitude of an applied magnetic field is revealed. It is found that the magnetic behavior of the nanostructures varies in a nonlinear manner with applied magnetic field. Spin-tunneling magnetoresistance is observed in magnetic-layer junctions containing an Al2O3 spacer. In-plane-conduction magnetic-field sensors using an Al2O3 or a SiC spacer are fabricated and tested.Translated from Mikroelektronika, Vol. 34, No. 1, 2005, pp. 56–64.Original Russian Text Copyright © 2005 by Kasatkin, Muravjev, Plotnikova, Pudonin, Azhaeva, Sergeeva, Khodzhaev. 相似文献
17.
Magnetic resonance image (MRI) reconstruction using SENSitivity Encoding (SENSE) requires regularization to suppress noise and aliasing effects. Edge-preserving and sparsity-based regularization criteria can improve image quality, but they demand computation-intensive nonlinear optimization. In this paper, we present novel methods for regularized MRI reconstruction from undersampled sensitivity encoded data--SENSE-reconstruction--using the augmented Lagrangian (AL) framework for solving large-scale constrained optimization problems. We first formulate regularized SENSE-reconstruction as an unconstrained optimization task and then convert it to a set of (equivalent) constrained problems using variable splitting. We then attack these constrained versions in an AL framework using an alternating minimization method, leading to algorithms that can be implemented easily. The proposed methods are applicable to a general class of regularizers that includes popular edge-preserving (e.g., total-variation) and sparsity-promoting (e.g., l(1)-norm of wavelet coefficients) criteria and combinations thereof. Numerical experiments with synthetic and in vivo human data illustrate that the proposed AL algorithms converge faster than both general-purpose optimization algorithms such as nonlinear conjugate gradient (NCG) and state-of-the-art MFISTA. 相似文献
18.
Magnetic nanoparticles can be caused to oscillate under the influence of an incident ultrasonic wave. If the particles are momentarily aligned with a magnetizing pulse creating a macroscopic magnetization, this oscillation will result in a time-varying magnetic moment which should be detectable as an induced voltage in a nearby pickup coil. In this way, focused ultrasound can be used to map, or image, the spatial distribution of the magnetic particles after these particles have been introduced into the body. The magnetic particles could be antibody-labeled to target tumor cells or used as a cardiovascular contrast agent, among other applications. The magnitude of the induced signal is estimated for one micron particles with a Fe/tissue volume fraction of 10(-6), which is about the limit of detectability for MRI superparamagnetic contrast agents consisting of single domain iron-oxide particles. One advantage of this method compared to conventional MRI is potentially greater sensitivity due to the absence of a large background signal. 相似文献
19.
《IEEE transactions on medical imaging》2009,28(7):1093-1104
20.
Lousberg G. P. Fagnard J.-F. Ausloos M. Vanderbemden P. Vanderheyden B. 《Applied Superconductivity, IEEE Transactions on》2010,20(1):33-41