GLORIA

GEOMAR Library Ocean Research Information Access

Your email was sent successfully. Check your inbox.

An error occurred while sending the email. Please try again.

Proceed reservation?

Export
Filter
  • Articles  (1,459)
Document type
  • Articles  (1,459)
Source
Publisher
Years
Topic
  • 1
    Publication Date: 2018-07-05
    Description: Publication date: November 2018 Source: Magnetic Resonance Imaging, Volume 53 Author(s): K.A. Smitha, K.M. Arun, P.G. Rajesh, Suresh E. Joel, Ramesh Venkatesan, Bejoy Thomas, Chandrasekharan Kesavadas Background and objectives Ensuring patient comfort and compliance by emphasizing reduced time frame for image acquisition, without compromising image quality is the key aspect with functional MRI examination. Multiband resting state fMRI (MB-rsfMRI) is a fairly new technique that potentially shortens MR image acquisition time by providing increased number of time points. The study aims to compare signal characteristics as well as the functional connectivity using conventional resting-state fMRI (rsfMRI) with that of MB-rsfMRI technique. Materials and methods 9 healthy volunteers have prospectively undergone conventional resting-state fMRI and Multiband rsfMRI scanning technique in a 3T GE scanner (Discovery MR750w™). We compared the temporal SNR (tSNR) of conventional rs-fMRI with that of MB-rsfMRI. We looked at the language network connectivity and small world network characteristics from graph theoretical measures to compare the two techniques. Results We computed the tSNR of conventional resting-state fMRI (rsfMRI) and MB-rsfMRI technique. A strong positive correlation was seen between graph theoretical measures from MB-rsfMRI and conventional rsfMRI (Pearson Correlation, r  = 0.99). Both techniques showed similar small world network characteristics in healthy controls. Conclusion The present study demonstrates negligible differences between the conventional-rsfMRI and MB-rsfMRI acquisitions on the computed graph theoretic measures. Accordingly current analysis proves that MB-rs-fMRI may be used as a time reducing acquisition technique that enables mapping of functional connectivity with similar outcome as conventional rs-fMRI in healthy subjects.
    Print ISSN: 0730-725X
    Electronic ISSN: 1873-5894
    Topics: Medicine
    Published by Elsevier
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 2
    Publication Date: 2018-07-05
    Description: Publication date: Available online 3 July 2018 Source: Magnetic Resonance Imaging Author(s): Florian Siedek, Daniel Giese, Kilian Weiss, Sandra Ekdawi, Sebastian Brinkmann, Wolfgang Schroeder, Christiane Bruns, De-Hua Chang, Thorsten Persigehl, David Maintz, Stefan Haneder Purpose This study aims to assess the feasibility of 4D flow MRI measurements in complex vascular territories; namely, the celiac artery (CA) and superior mesenteric artery (SMA). Materials and methods In this prospective study, 22 healthy volunteers and 10 patients were scanned at 3 T. Blood flow parameters were compared between healthy volunteers and patients with stenosis of the CA and/or SMA as a function of stenosis grade characterized by prior contrast-enhanced computed tomography (CE-CT). The 4D flow MRI acquisition covered the CA, SMA and adjusting parts of the abdominal aorta (AO). Measurements of velocity- (peak velocity [PV], average velocity [AV]) and volume-related parameters (peak flow [PF], stroke volume [SV]) were conducted. Further, stenosis grade and wall shear stress in the CA, SMA and AO were evaluated. Results In patients, prior evaluation by CE-CT revealed 11 low- and 5 mid-grade stenoses of the CA and/or SMA. PV and AV were significantly higher in patients than in healthy volunteers [PV: p 〈 0.0001; AV: p = 0.03, p 〈 0.001]. PF and SV did not differ significantly between healthy volunteers and patients; however, a trend towards lower PF and SV could be detected in patients with mid-grade stenoses. Comparison of 4D flow MRI with CE-CT revealed a strong positive correlation in estimated degree of stenosis (CA: r = 0.86, SMA: r = 0.98). Patients with mid-grade stenoses had a significantly higher average WSS magnitude (AWM) than healthy volunteers (p = 0.02). Conclusion This feasibility study suggests that 4D flow MRI is a viable technique for the evaluation of complex flow characteristics in small vessels such as the CA and SMA. 4D flow MRI approves comparable to the morphologic assessment of complex vascular territories using CE-CT but, in addition, offers the functional evaluation of flow parameters that goes beyond the morphology.
    Print ISSN: 0730-725X
    Electronic ISSN: 1873-5894
    Topics: Medicine
    Published by Elsevier
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 3
    Publication Date: 2018-07-05
    Description: Publication date: November 2018 Source: Magnetic Resonance Imaging, Volume 53 Author(s): Matthias Malzacher, Mathias Davids, Lothar R. Schad, Jorge Chacon-Caldera Specific absorption rate (SAR) simulations are performed for most clinical and research transmit coil configurations. Such simulations allow the determination of limits in transmit power for patient safety. Different human models and coil configurations have been previously investigated using these simulations. However, only a few works have accounted for the effect of the receive (Rx) arrays in the SAR calculations and they have used very specialized setups or simplified detuning modeling of the Rx elements. In this work, we performed electromagnetic simulations using a clinical alike setup for whole-body scans at 3 T and head scans at 7 T. SAR simulations are performed for both setups with and without Rx arrays. A difference below 10% percent was found for max SAR. The maximum difference for the mean SAR values of the 3 T setups remained within 8% and within 15% of the 7 T setup.
    Print ISSN: 0730-725X
    Electronic ISSN: 1873-5894
    Topics: Medicine
    Published by Elsevier
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 4
    Publication Date: 2018-07-02
    Description: Publication date: October 2018 Source: Magnetic Resonance Imaging, Volume 52 Author(s): Alessandro Furlan, Ersin Bayram, Senthur Thangasamy, Dale Barley, Anil Dasyam The aim of this study was to assess changes in acquisition time, image quality and evaluation of pancreatic cysts when applying CS to a 3D MRCP sequence. Thirty subjects (17F; 13M) undergoing MRCP for evaluation of pancreatic cyst(s) were prospectively recruited and underwent 3D MRCP and CS 3D MRCP (CS factor = 2) on a 3T scanner. The acquisition time was recorded. Two experienced radiologists independently recorded quality of the images, presence of artifacts, visualization of the main pancreatic duct, bile ducts and index pancreatic cyst using a five-point scale. Presence of mural nodules and septations in the cyst, size of the cyst and caliber of the main pancreatic duct were also recorded. A paired sample t -test was used to compare the acquisition time of 3D MRCP and CS 3D MRCP. Image quality metrics and visualization of cyst features were compared with Wilcoxon signed-rank test and McNemar test. The mean acquisition time of CS-3D-MRCP (150 ± 63 s) was significantly lower than that of 3D-MRCP (317 ± 104 s; P  〈 0.001). The median score of overall quality (reader 1, 3.7 ± 1.0 vs. 3.4 ± 1.1, P  = 0.11; reader 2, 3.8 ± 1.0 vs. 3.7 ± 1.1, P  = 0.36), artifacts and visualization of the bile ducts were not significantly different between 3D-MRCP and CS-3D-MRCP. There was no significant difference in the visualization score of the index pancreatic cyst (reader 1, 4.2 ± 0.9 vs. 4.1 ± 0.9, P  = 0.42; reader 2, 4.2 ± 0.4 vs. 4.0 ± 0.7, P  = 0.27) and no difference in the assessment of cyst features. Applying CS to 3D-MRCP yields a two-fold reduction in acquisition time with comparable image quality and visualization of key pancreatic cyst features.
    Print ISSN: 0730-725X
    Electronic ISSN: 1873-5894
    Topics: Medicine
    Published by Elsevier
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 5
    Publication Date: 2018-06-30
    Description: Publication date: October 2018 Source: Magnetic Resonance Imaging, Volume 52 Author(s): Daniel S. Weller, Michael Salerno, Craig H. Meyer This paper describes an adaptive approach to regularizing model-based reconstructions in magnetic resonance imaging to account for local structure or image content. In conjunction with common models like wavelet and total variation sparsity, this content-aware regularization avoids oversmoothing or compromising image features while suppressing noise and incoherent aliasing from accelerated imaging. To evaluate this regularization approach, the experiments reconstruct images from single- and multi-channel, Cartesian and non-Cartesian, brain and cardiac data. These reconstructions combine common analysis-form regularizers and autocalibrating parallel imaging (when applicable). In most cases, the results show widespread improvement in structural similarity and peak-signal-to-error ratio relative to the fully sampled images. These results suggest that this content-aware regularization can preserve local image structures such as edges while providing denoising power superior to sparsity-promoting or sparsity-reweighted regularization.
    Print ISSN: 0730-725X
    Electronic ISSN: 1873-5894
    Topics: Medicine
    Published by Elsevier
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 6
    Publication Date: 2018-06-30
    Description: Publication date: October 2018 Source: Magnetic Resonance Imaging, Volume 52 Author(s): Nima Yaghoobi, Reza P.R. Hasanzadeh De-noising is a crucial topic in Magnetic Resonance Imaging (MRI) which focuses on less loss of Magnetic Resonance (MR) image information and details preservation during the noise suppression. Nowadays multiple-coil MRI system is preferred to single one due to its acceleration in the imaging process. Due to the fact that the model of noise in single-coil and multiple-coil MRI systems are different, the de-noising methods that mostly are adapted to single-coil MRI systems, do not work appropriately with multiple-coil one. The model of noise in single-coil MRI systems is Rician while in multiple-coil one (if no subsampling occurs in k -space or GRAPPA reconstruction process is being done in the coils), it obeys noncentral Chi (nc-χ). In this paper, a new filtering method based on the Linear Minimum Mean Square Error (LMMSE) estimator is proposed for multiple-coil MR Images ruined by nc-χ noise. In the presented method, to have an optimum similarity selection of voxels, the Bayesian Mean Square Error (BMSE) criterion is used and proved for nc-χ noise model and also a nonlocal voxel selection methodology is proposed for nc-χ distribution. The results illustrate robust and accurate performance compared to the related state-of-the-art methods, either on ideal nc-χ images or GRAPPA reconstructed ones.
    Print ISSN: 0730-725X
    Electronic ISSN: 1873-5894
    Topics: Medicine
    Published by Elsevier
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 7
    Publication Date: 2018-06-29
    Description: Publication date: October 2018 Source: Magnetic Resonance Imaging, Volume 52 Author(s): Gregory Simchick, Amelia Yin, Hang Yin, Qun Zhao Purpose To explore, at a high field strength of 7T, the performance of various fat spectral models on the quantification of triglyceride composition and proton density fat fraction ( PDFF ) using chemical-shift encoded MRI (CSE-MRI). Methods MR data was acquired from CSE-MRI experiments for various fatty materials, including oil and butter samples and in vivo brown and white adipose mouse tissues. Triglyceride composition and PDFF were estimated using various a priori 6- or 9-peak fat spectral models. To serve as references, NMR spectroscopy experiments were conducted to obtain material specific fat spectral models and triglyceride composition estimates for the same fatty materials. Results obtained using the spectroscopy derived material specific models were compared to results obtained using various published fat spectral models. Results Using a 6-peak fat spectral model to quantify triglyceride composition may lead to large biases at high field strengths. When using a 9-peak model, triglyceride composition estimations vary greatly depending on the relative amplitudes of the chosen a priori spectral model, while PDFF estimations show small variations across spectral models. Material specific spectroscopy derived spectral models produce estimations that better correlate with NMR spectroscopy estimations in comparison to those obtained using non-material specific models. Conclusion At a high field strength of 7T, a material specific 9-peak fat spectral model, opposed to a widely accepted or generic human liver model, is necessary to accurately quantify triglyceride composition when using CSE-MRI estimation methods that assume the spectral model to be known as a priori information. CSE-MRI allows for the quantification of the spatial distribution of triglyceride composition for certain in vivo applications. Additionally, PDFF quantification is shown to be independent of the chosen a priori spectral model, which agrees with previously reported results obtained at lower field strengths (e.g. 3T). Graphical abstract
    Print ISSN: 0730-725X
    Electronic ISSN: 1873-5894
    Topics: Medicine
    Published by Elsevier
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 8
    Publication Date: 2018-06-29
    Description: Publication date: October 2018 Source: Magnetic Resonance Imaging, Volume 52 Author(s): Hirohito Kan, Nobuyuki Arai, Masahiro Takizawa, Kazuyoshi Omori, Harumasa Kasai, Hiroshi Kunitomo, Yasujiro Hirose, Yuta Shibamoto Purpose We developed a non-regularized, variable kernel, sophisticated harmonic artifact reduction for phase data (NR-VSHARP) method to accurately estimate local tissue fields without regularization for quantitative susceptibility mapping (QSM). We then used a digital brain phantom to evaluate the accuracy of the NR-VSHARP method, and compared it with the VSHARP and iterative spherical mean value (iSMV) methods through in vivo human brain experiments. Materials and methods Our proposed NR-VSHARP method, which uses variable spherical mean value (SMV) kernels, minimizes L2 norms only within the volume of interest to reduce phase errors and save cortical information without regularization. In a numerical phantom study, relative local field and susceptibility map errors were determined using NR-VSHARP, VSHARP, and iSMV. Additionally, various background field elimination methods were used to image the human brain. Results In a numerical phantom study, the use of NR-VSHARP considerably reduced the relative local field and susceptibility map errors throughout a digital whole brain phantom, compared with VSHARP and iSMV. In the in vivo experiment, the NR-VSHARP-estimated local field could sufficiently achieve minimal boundary losses and phase error suppression throughout the brain. Moreover, the susceptibility map generated using NR-VSHARP minimized the occurrence of streaking artifacts caused by insufficient background field removal. Conclusion Our proposed NR-VSHARP method yields minimal boundary losses and highly precise phase data. Our results suggest that this technique may facilitate high-quality QSM.
    Print ISSN: 0730-725X
    Electronic ISSN: 1873-5894
    Topics: Medicine
    Published by Elsevier
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 9
    facet.materialart.
    Unknown
    Elsevier
    Publication Date: 2018-06-21
    Description: Publication date: September 2018 Source: Magnetic Resonance Imaging, Volume 51
    Print ISSN: 0730-725X
    Electronic ISSN: 1873-5894
    Topics: Medicine
    Published by Elsevier
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
  • 10
    Publication Date: 2018-06-16
    Description: Publication date: October 2018 Source: Magnetic Resonance Imaging, Volume 52 Author(s): Guopeng Huang, Hongbing Ji, Wenbo Zhang It is difficult to segment images in the presence of intensity inhomogeneity due to the overlap of the intensity ranges between different object regions. To deal with this problem, this paper presents a novel level set method to segment inhomogeneous images. Based on the inhomogeneous image model, an optimal segmentation plane is derived in image domain to provide the optimal partition for every pixel. With the plane, a new region-based pressure force function is proposed and used to define an energy functional in the level set formulation on the whole image region. By minimizing the energy functional, the proposed method can segment the inhomogeneous image and estimate the bias field at the same time. Besides, a new bias field initialization is introduced to improve the robustness to the initial contour. In addition, a novel adaptive scale parameter is designed for the kernel function in order to estimate the bias field accurately. The proposed method is first presented as a two-phase level set formulation and then extended to a multi-phase one. Finally, the experimental results on both synthetic and real images demonstrate the superiority of the proposed method in terms of accuracy, efficiency and robustness.
    Print ISSN: 0730-725X
    Electronic ISSN: 1873-5894
    Topics: Medicine
    Published by Elsevier
    Location Call Number Limitation Availability
    BibTip Others were also interested in ...
Close ⊗
This website uses cookies and the analysis tool Matomo. More information can be found here...