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Magnetic Resonance Imaging

Dong Du, Zhibin Pan, Penghui Zhang, Yuxin Li, Weiping Ku
Compressed sensing (CS) has shown to be a successful technique for image recovery. Designing an effective regularization term reflecting the image sparse prior information plays a critical role in this field. Dictionary learning (DL) strategy alleviates the drawback of fixed bases. But the structure information of the image is easy to be blurred in complex regions due to the absence of sparsity in dictionary learning. This paper proposes a novel joint dictionary learning and Shape-Adaptive DCT (SADCT) thresholding method...
September 18, 2018: Magnetic Resonance Imaging
Jiali Li, Lili Liang, Hao Yu, Yaqi Shen, Yao Hu, Daoyu Hu, Hao Tang, Zhen Li
PURPOSE: To evaluate the utility of volumetric histogram analysis of monoexponential and non-Gaussian distribution DWI models for discriminating pancreatic ductal adenocarcinoma (PDAC) and neuroendocrine tumor (pNET). MATERIALS AND METHODS: A total of 340 patients were retrospectively reviewed. Finally, 62 patients with histopathological confirmed PDAC (n = 42) and pNET (n = 20) were enrolled in the study. All the patients accepted magnetic resonance imaging (MRI) at 3 T (including multi-b value DWI, 0-1000 s/mm2 )...
September 18, 2018: Magnetic Resonance Imaging
Patrick Liebig, Robin M Heidemann, Bernhard Hensel, David A Porter
PURPOSE: The standard approach to Echo-Planar Imaging (EPI) is to use trapezoidal readout (RO) gradients with blipped phase-encoding (PE) gradients. Sinusoidal RO gradients with constant PE gradients can reduce acoustic noise. However, this sequence, originally introduced by Mansfield et al., constitutes major challenges for Cartesian parallel imaging techniques. In this study two alternatives to reconstruct a non-blipped EPI are proposed and evaluated. THEORY AND METHODS: The first method separates the acquired k-space data into odd and even echoes and applies Cartesian GRAPPA separately to each partial data set...
September 17, 2018: Magnetic Resonance Imaging
Stefan A Hertel, Daan W de Kort, Isabelle Bush, Andrew J Sederman, Lynn F Gladden, Benjamin Anger, Hilko de Jong, Matthias Appel
Speed of acquisition is paramount for the application of magnetic resonance to flow experiments through porous rocks. One popular method for imaging core floods is the spatially resolved T2 experiment which can separate fluids either by their viscosity contrast or by doping one fluid with a relaxation agent. Existing techniques for spatial-T2 may suffer from long acquisition times and eddy currents due to the pulsing of magnetic field gradients. Here, we propose a constant gradient method for 1d spatially-resolved T2 which embraces the speed of frequency encoding techniques and avoids eddy currents by the absence of any gradient ramps during the radio frequency (r...
September 15, 2018: Magnetic Resonance Imaging
J Ward-Williams, L F Gladden
Fast field cycling, FFC, NMR relaxometry experiments are reported in the frequency range of 10 kHz-40 MHz to characterise the adsorption behaviour of cyclohexane:THF (non-polar:polar) and THF:methanol (polar:polar) binary liquid mixtures adsorbed on a γ-alumina surface of catalytic interest. Laplace inversion of the relaxation rate data is employed to identify the chemical species in the binary mixture. In both systems studied, the more polar molecule preferentially interacts with the surface compared to the co-imbibed species...
September 15, 2018: Magnetic Resonance Imaging
Zhe Sun, Lizhi Xiao, Xueli Hou, Sihui Luo, Guangzhi Liao, Yan Zhang, Wei Liu, Jie Wang, Weiliang Chen, Zhengduo Wang, Lei Li, Yifan Wang, Feixue Gong
In general, only the depth information can be acquired using the centralized downhole NMR tools. The radial profile information is equally important to the depth. Improving the pad tools, also called side-looking tools, is the appropriate direction for solving this problem. The side-looking downhole measurement can provide depth and radially resolved information of the reservoir. In this research a new side-looking tool which includes main magnets and pre-polarized magnets has been designed and built. The pre-polarized magnets in both sides are used to adjust the homogeneity of magnetic field along the length direction of the instrument and polarize the samples when the tool is moving up and down along the borehole with a speed up to 500 m/h...
September 15, 2018: Magnetic Resonance Imaging
Jun Zhang, Dapeng Hao, Feng Duan, Tengbo Yu, Chuanyu Zhang, Junyi Che
PURPOSE: To determine the feasibility of the rotating stretched curved planar reconstruction (CPR) of three-dimensional fast imaging with steady-state acquisition magnetic resonance imaging (3D-FIESTA MRI) for evaluating the anterior cruciate ligament of the knee joint. MATERIALS AND METHODS: MRI of 40 knee joints in healthy volunteers was performed on a 3.0-T MR scanner and a phased-array extremity coil. The protocol consisted of oblique sagittal spin echo (SE) T1WI, coronal FS-PDWI, axial FS-FSE-T2WI, and 3D-FIESTA sequences...
September 14, 2018: Magnetic Resonance Imaging
Bulat Gizatullin, Carlos Mattea, Siegfried Stapf
Overhauser dynamic nuclear polarization (DNP) is the dominating hyperpolarization technique to increasing the nuclear magnetic resonance signal in liquids and diluted systems. The enhancement obtained depends on the overall mobility of the radical-carrying molecule but also on its specific interaction with the host molecules. Information about the nature of molecular and radical dynamics can be identified from determining the nuclear T1 as a function of Larmor frequency by Fast Field Cycling (FFC) relaxometry...
September 12, 2018: Magnetic Resonance Imaging
Daniel S Weller, Luonan Wang, John P Mugler, Craig H Meyer
Magnetic resonance imaging of patients who find difficulty lying still or holding their breath can be challenging. Unresolved intra-frame motion yields blurring artifacts and limits spatial resolution. To correct for intra-frame non-rigid motion, such as in pediatric body imaging, this paper describes a multi-scale technique for joint estimation of the motion occurring during the acquisition and of the desired uncorrupted image. This technique regularizes the motion coefficients to enforce invertibility and minimize numerical instability...
September 11, 2018: Magnetic Resonance Imaging
Kurt G Schilling, Yurui Gao, Iwona Stepniewska, Vaibhav Janve, Bennett A Landman, Adam W Anderson
For two decades diffusion fiber tractography has been used to probe both the spatial extent of white matter pathways and the region to region connectivity of the brain. In both cases, anatomical accuracy of tractography is critical for sound scientific conclusions. Here we assess and validate the algorithms and tractography implementations that have been most widely used - often because of ease of use, algorithm simplicity, or availability offered in open source software. Comparing forty tractography results to a ground truth defined by histological tracers in the primary motor cortex on the same squirrel monkey brains, we assess tract fidelity on the scale of voxels as well as over larger spatial domains or regional connectivity...
September 10, 2018: Magnetic Resonance Imaging
Rotem Shlomo Lanzman, Alexandra Ljimani, Anja Müller-Lutz, Julia Weller, Julia Stabinska, Gerald Antoch, Hans-Jörg Wittsack
OBJECT: To assess changes diffusion properties of renal cortex over the entire cardiac cycle using electrocardiogram-gated respiratory-triggered dynamic diffusion-weighted imaging (DWI). MATERIALS AND METHODS: 20 healthy volunteers were investigated on a 1.5 T MR scanner. Blood flow velocity within the renal arteries was determined by electrocardiogram-gated phase-contrast measurements. For dynamic renal DWI, an electrocardiogram-gated respiratory-triggered coronal single-slice EPI sequence was acquired at 14 times at 20, 70, 120, 170, …, 570, 620, 720 ms after the R-wave over the cardiac cycle...
September 10, 2018: Magnetic Resonance Imaging
Santiago Aja-Fernández, Tomasz Pieciak, Antonio Tristán-Vega, Gonzalo Vegas-Sánchez-Ferrero, Vicente Molina, Rodrigo de Luis-García
An imaging biomarker is a biologic feature in an image that is relevant to a patient's diagnosis or prognosis. In order to qualify as a biomarker, a measure must be robust and reproducible. However, the usual scalar measures derived from diffusion tensor imaging are known to be highly dependent on the variation of the acquisition parameters, which prevents their possible use as biomarkers. In this work, we propose a new set of quantitative measures based on diffusion magnetic resonance imaging from single-shell acquisitions that are designed to be robust to the variations of several acquisition parameters (number of gradient directions, b-value and SNR) while keeping a high discrimination power on differences in the diffusion characteristics of the tissue...
September 6, 2018: Magnetic Resonance Imaging
Yunyun Yang, Sichun Ruan, Boying Wu
With the wide application of MR images to detect disease in human's brain deeply, the shortcomings of the technology are necessarily waiting to be solved. For example, MR images always show serious intensity inhomogeneity called the bias field, which may prevent to deduce exact analysis of images. To eliminate the distraction, many methods are proposed. Though experimental results already have stood for the advantages of those methods, there are still lots of problems that cannot be neglected, such as bad segmentation, wrong correction and over-correction which has not attracted much attention yet...
September 5, 2018: Magnetic Resonance Imaging
Zidan Yu, Tiejun Zhao, Jakob Assländer, Riccardo Lattanzi, Daniel K Sodickson, Martijn A Cloos
PURPOSE: To explore the motion sensitivity of magnetic resonance fingerprinting (MRF), we performed experiments with different types of motion at various time intervals during multiple scans. Additionally, we investigated the possibility to correct the motion artifacts based on redundancy in MRF data. METHODS: A radial version of the FISP-MRF sequence was used to acquire one transverse slice through the brain. Three subjects were instructed to move in different patterns (in-plane rotation, through-plane wiggle, complex movements, adjust head position, and pretend itch) during different time intervals...
September 5, 2018: Magnetic Resonance Imaging
Hans Jonas Meyer, Leonard Leifels, Gordian Hamerla, Anne Kathrin Höhn, Alexey Surov
OBJECTIVE: Apparent diffusion coefficient (ADC) values derived from Diffusion-weighted images are able to reflect tumor microstructure, such as cellularity, extracellular matrix or proliferation potential. This present study sought to correlate prognostic relevant histopathologic parameters with ADC values derived from a whole lesion measurement in head and neck squamous cell carcinoma (HNSCC). MATERIALS AND METHODS: Thirty-four patients with histological proven primary HNSCC were prospectively acquired...
September 4, 2018: Magnetic Resonance Imaging
Antonietta Canna, Sara Ponticorvo, Andrea G Russo, Renzo Manara, Francesco Di Salle, Renato Saponiero, Martina F Callaghan, Nikolaus Weiskopf, Fabrizio Esposito
Quantitative MRI (qMRI) provides surrogate brain maps of myelin and iron content. After spatial normalization to a common standard brain space, these may be used to detect altered myelination and iron accumulation in clinical populations. Here, volumetric and combined volumetric and surface-based (CVS) normalization were compared to identify which procedure would afford the greatest sensitivity to inter-regional differences (contrast), and the lowest inter-subject variability (under normal conditions), of myelin- and iron-related qMRI parameters, in whole-brain group-level studies...
September 1, 2018: Magnetic Resonance Imaging
Yousef Mazaheri, Amita Shukla-Dave, Debra A Goldman, Chaya S Moskowitz, Toshikazu Takeda, Victor E Reuter, Oguz Akin, Hedvig Hricak
PURPOSE: To retrospectively measure metabolic ratios and apparent diffusion coefficient (ADC) values from 3-Tesla MR spectroscopic imaging (MRSI) and diffusion-weighted imaging (DWI) in benign and malignant peripheral zone (PZ) prostate tissue, assess the parameters' associations with malignancy, and develop and test rules for classifying benign and malignant PZ tissue using whole-mount step-section pathology as the reference standard. METHODS: This HIPAA-compliant, IRB-approved study included 67 men (median age, 61 years; range, 41-74 years) with biopsy-proven prostate cancer who underwent preoperative 3 T endorectal multiparametric MRI and had ≥1 PZ lesion >0...
August 31, 2018: Magnetic Resonance Imaging
Megha Maria Cheriyan, Prawin Angel Michael, Anil Kumar
The development of automated segmentation approaches, which do not suffer from excessive computational burden and intra- and inter-observer variability, is the holy grail of multispectral MR image classification. A new segmentation approach to the data set of MR brain images using a combination of Independent Component Analysis (ICA) with a generalized version of the popular Gaussian Mixture Model (GMM) for unsupervised classification is proposed to be superior to conventional methods in this paper. We propose to optimize the parameters of the mixture model using a meta-heuristic approach like the Particle Swarm Optimization (PSO) to escape the problem of local traps (maxima or minima)...
August 31, 2018: Magnetic Resonance Imaging
Paaladinesh Thavendiranathan, Christoph Guetter, Juliana Serafim da Silveira, Xiaoguang Lu, Debbie Scandling, Hui Xue, Marie-Pierre Jolly, Subha V Raman, Orlando P Simonetti
BACKGROUND: Doppler based mitral annular velocities are an integral part of echocardiographic left ventricular diastolic function assessment. Although these measurements can be obtained by phase contrast cardiac magnetic resonance imaging (PC-CMR), this approach has limitations. The aims of this study were to assess the accuracy and reproducibility of a high temporal resolution steady-state free precession (SSFP) cine acquisition coupled with semi-automated mitral annular tracking to measure tissue velocity, and compare to echocardiography as the reference method...
August 30, 2018: Magnetic Resonance Imaging
Shi Su, Na Lu, Lin Jia, Xiaojing Long, Chunxiang Jiang, Hang Zhang, Ye Li, Kaibao Sun, Rong Xue, Lijuan Zhang, Xin Liu, Guoxi Xie
We introduce an accelerated gradient echo (GRE) sequence combining simultaneous multislice excitation (SMS) with echo-shifting technique for high spatial resolution blood oxygen level dependent (BOLD) functional MRI (fMRI). The simulation was conducted to optimize scan parameters. To validate the feasibility of the proposed technique, the visual and motor task experiments were performed at 7.0 Tesla (T). The single-shot EPI sequence was also applied in comparison with the proposed technique. The simulation results showed that an optimized flip angle of 9° provided maximal BOLD contrast for our scanning scheme, allowing low power deposition and SMS acceleration factor of 5...
August 30, 2018: Magnetic Resonance Imaging
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