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Special Issue "High Field Magnetic Resonance Methods and Materials"

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A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (31 May 2011)

Special Issue Editor

Guest Editor
Prof. Dr. Oliver Speck

Department Biomedical Magnetic Resonance, Faculty of Natural Sciences, Institute for Experimental Physics, Otto-von-Guericke-University Magdeburg, Zenit-Building (House 65), Leipziger Strasse 44,D-39120 Magdeburg, Germany
Fax: +49 391 6117 115

Special Issue Information

Dear Colleagues,

High Field Magnetic Resonance is an ever extending field of technical and methodological development and applications. In particular the advances in magnet design and radio-frequency technology have driven the field and allowed new applications that were not deemed possible in the past. With the installation of almost 40 human 7T MR systems in the world and an even larger number of 9.4T and higher small animal MR systems a new round in the drive for higher sensitivity, resolution, and speed has opened. In this special issue we invite researchers in this field to report on recent progress and the latest developments in hardware and method development for the advancement of high field magnetic resonance.

Prof. Dr. Oliver Speck
Guest Editor

Keywords

  • magnetic resonance imaging
  • high field MR
  • magnetic resonance hardware
  • magnetic resonance methods

Published Papers (7 papers)

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Research

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Open AccessArticle Accurate Measurement of Magnetic Resonance Imaging Gradient Characteristics
Materials 2014, 7(1), 1-15; doi:10.3390/ma7010001
Received: 3 November 2013 / Revised: 13 December 2013 / Accepted: 16 December 2013 / Published: 19 December 2013
Cited by 3 | PDF Full-text (384 KB) | HTML Full-text | XML Full-text
Abstract
Recently, gradient performance and fidelity has become of increasing interest, as the fidelity of the magnetic resonance (MR) image is somewhat dependent on the fidelity of the gradient system. In particular, for high fidelity non-Cartesian imaging, due to non-fidelity of the gradient [...] Read more.
Recently, gradient performance and fidelity has become of increasing interest, as the fidelity of the magnetic resonance (MR) image is somewhat dependent on the fidelity of the gradient system. In particular, for high fidelity non-Cartesian imaging, due to non-fidelity of the gradient system, it becomes necessary to know the actual k-space trajectory as opposed to the requested trajectory. In this work we show that, by considering the gradient system as a linear time-invariant system, the gradient impulse response function (GIRF) can be reliably measured to a relatively high degree of accuracy with a simple setup, using a small phantom and a series of simple experiments. It is shown experimentally that the resulting GIRF is able to predict actual gradient performance with a high degree of accuracy. The method captures not only the frequency response but also gradient timing errors and artifacts due to mechanical vibrations of the gradient system. Some discussion is provided comparing the method presented here with other analogous methods, along with limitations of these methods. Full article
(This article belongs to the Special Issue High Field Magnetic Resonance Methods and Materials)
Open AccessArticle Multi-Echo-Based Echo-Planar Spectroscopic Imaging Using a 3T MRI Scanner
Materials 2011, 4(10), 1818-1834; doi:10.3390/ma4101818
Received: 2 September 2011 / Revised: 6 October 2011 / Accepted: 7 October 2011 / Published: 17 October 2011
Cited by 2 | PDF Full-text (813 KB) | HTML Full-text | XML Full-text
Abstract
The use of spin-echoes has been employed in an Echo-Planar Spectroscopic Imaging (EPSI) sequence to collect multiple phase encoded lines within a single TR in a Multi-Echo-based Echo-Planar Spectroscopic Imaging technique (MEEPSI). Despite the T2 dependence on the amplitude of the [...] Read more.
The use of spin-echoes has been employed in an Echo-Planar Spectroscopic Imaging (EPSI) sequence to collect multiple phase encoded lines within a single TR in a Multi-Echo-based Echo-Planar Spectroscopic Imaging technique (MEEPSI). Despite the T2 dependence on the amplitude of the spin-echoes, the Full Width at Half Maximum (FWHM) of the derived multi-echo Point Spread Function (PSF) is shown to decrease, indicating an improved overall spatial resolution without requiring any additional scan time. The improved spatial resolution is demonstrated in the one-dimensional (1D) spatial profiles of the N-Acetyl Aspartate (NAA) singlet along the phase encode dimension in a gray matter phantom. Although the improved spatial resolution comes at the expense of spectral resolution, it is shown in vivo that peak broadening due to T2* decay is more significant than the loss of resolution from using spin-echoes and therefore does not affect the ability to quantify metabolites using the LCModel fitting algorithm. Full article
(This article belongs to the Special Issue High Field Magnetic Resonance Methods and Materials)
Figures

Open AccessArticle Single Voxel Proton Spectroscopy for Neurofeedback at 7 Tesla
Materials 2011, 4(9), 1548-1563; doi:10.3390/ma4091548
Received: 21 June 2011 / Revised: 23 August 2011 / Accepted: 5 September 2011 / Published: 15 September 2011
Cited by 4 | PDF Full-text (369 KB) | HTML Full-text | XML Full-text | Correction | Supplementary Files
Abstract
Echo-planar imaging (EPI) in fMRI is regularly used to reveal BOLD activation in presubscribed regions of interest (ROI). The response is mediated by relative changes in T2* which appear as changes in the image pixel intensities. We have proposed an application of [...] Read more.
Echo-planar imaging (EPI) in fMRI is regularly used to reveal BOLD activation in presubscribed regions of interest (ROI). The response is mediated by relative changes in T2* which appear as changes in the image pixel intensities. We have proposed an application of functional single-voxel proton spectroscopy (fSVPS) for real-time studies at ultra-high MR field which can be comparable to the EPI BOLD fMRI technique. A spin-echo SVPS protocol without water suppression was acquired with 310 repetitions on a 7T Siemens MR scanner (TE/TR = 20/1000 ms, flip angle α = 90°, voxel size 10 × 10 × 10 mm3). Transmitter reference voltage was optimized for the voxel location. Spectral processing of the water signal free induction decay (FID) using log-linear regression was used to estimate the T2* change between rest and activation of a functional task. The FID spectrum was filtered with a Gaussian window around the water peak, and log-linear regression was optimized for the particular ROI by adoption of the linearization length. The spectroscopic voxel was positioned on an ROI defined from a real-time fMRI EPI BOLD localizer. Additional online signal processing algorithms performed signal drift removal (exponential moving average), despiking and low-pass filtering (modified Kalman filter) and, finally, the dynamic feedback signal normalization. Two functional tasks were used to estimate the sensitivity of the SVPS method compared to BOLD signal changes, namely the primary motor cortex (PMC, left hand finger tapping) and visual cortex (VC, blinking checkerboard). Four healthy volunteers performed these tasks and an additional session using real-time signal feedback modulating their activation level of the PMC. Results show that single voxel spectroscopy is able to provide a good and reliable estimation of the BOLD signal changes. Small data size and FID signal processing instead of processing entire brain volumes as well as more information revealed from the acquired total water spectrum, i.e., direct estimation of the T2* values and B0 changes, make SVPS proton spectroscopy suitable and advantageous for real-time neurofeedback studies. Particular challenges of ultra-high field spectroscopy due to the non-linearity in the spectral information, e.g., poor main magnetic field homogeneity and the absence of motion correction for the SVPS sequence may lead to the special artifacts in the control signal which still need to be addressed. The contrast to noise ratio (CNR), experimental statistic (t-values) and percent signal change were used as quality parameters to estimate the method performance. The potential and challenges of the spectroscopic approach for fMRI studies needs to be further investigated. Full article
(This article belongs to the Special Issue High Field Magnetic Resonance Methods and Materials)
Open AccessArticle Low and High Field Magnetic Resonance for in Vivo Analysis of Seeds
Materials 2011, 4(8), 1426-1439; doi:10.3390/ma4081426
Received: 7 June 2011 / Revised: 4 August 2011 / Accepted: 4 August 2011 / Published: 16 August 2011
Cited by 7 | PDF Full-text (726 KB) | HTML Full-text | XML Full-text
Abstract
Low field NMR has been successfully used for the evaluation of seed composition and quality, but largely only in crop species. We show here that 1.5T NMR provides a reliable means for analysing the seed lipid fraction present in a wide range [...] Read more.
Low field NMR has been successfully used for the evaluation of seed composition and quality, but largely only in crop species. We show here that 1.5T NMR provides a reliable means for analysing the seed lipid fraction present in a wide range of species, where both the seed size and lipid concentration differed by >10 fold. Little use of high field NMR has been made in seed research to date, even though it potentially offers many opportunities for studying seed development, metabolism and storage. Here we demonstrate how 17.5T and 20T NMR can be applied to image seed structure, and analyse lipid and metabolite distribution. We suggest that further technical developments in NMR/MRI will facilitate significant advances in our understanding of seed biology. Full article
(This article belongs to the Special Issue High Field Magnetic Resonance Methods and Materials)
Open AccessArticle Resonant Mode Reduction in Radiofrequency Volume Coils for Ultrahigh Field Magnetic Resonance Imaging
Materials 2011, 4(8), 1333-1344; doi:10.3390/ma4081333
Received: 13 July 2011 / Revised: 21 July 2011 / Accepted: 25 July 2011 / Published: 28 July 2011
Cited by 6 | PDF Full-text (1167 KB) | HTML Full-text | XML Full-text
Abstract
In a multimodal volume coil, only one mode can generate homogeneous Radiofrequency (RF) field for Magnetic Resonance Imaging. The existence of other modes may increase the volume coil design difficulties and potentially decreases coil performance. In this study, we introduce common-mode resonator [...] Read more.
In a multimodal volume coil, only one mode can generate homogeneous Radiofrequency (RF) field for Magnetic Resonance Imaging. The existence of other modes may increase the volume coil design difficulties and potentially decreases coil performance. In this study, we introduce common-mode resonator technique to high and ultrahigh field volume coil designs to reduce the resonant mode while maintain the homogeneity of the RF field. To investigate the design method, the common-mode resonator was realized by using a microstrip line which was split along the central to become a pair of parallel transmission lines within which common-mode currents exist. Eight common-mode resonators were placed equidistantly along the circumference of a low loss dielectric cylinder to form a volume coil. Theoretical analysis and comparison between the 16-strut common-mode volume coil and a conventional 16-strut volume coil in terms of RF field homogeneity and efficiency was performed using Finite-Difference Time-Domain (FDTD) method at 298.2 MHz. MR imaging experiments were performed by using a prototype of the common-mode volume coil on a whole body 7 Tesla scanner. FDTD simulation results showed the reduced number of resonant modes of the common-mode volume coil over the conventional volume coil, while the RF field homogeneity of the two type volume coils was kept at the same level. MR imaging of a water phantom and a kiwi fruit showing the feasibility of the proposed method for simplifying the volume coil design is also presented. Full article
(This article belongs to the Special Issue High Field Magnetic Resonance Methods and Materials)

Review

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Open AccessReview Advances in High-Field BOLD fMRI
Materials 2011, 4(11), 1941-1955; doi:10.3390/ma4111941
Received: 16 August 2011 / Revised: 7 October 2011 / Accepted: 19 October 2011 / Published: 2 November 2011
Cited by 7 | PDF Full-text (840 KB) | HTML Full-text | XML Full-text
Abstract
This review article examines the current state of BOLD fMRI at a high magnetic field strength of 7 Tesla. The following aspects are covered: a short description of the BOLD contrast, spatial and temporal resolution, BOLD sensitivity, localization and spatial specificity, technical [...] Read more.
This review article examines the current state of BOLD fMRI at a high magnetic field strength of 7 Tesla. The following aspects are covered: a short description of the BOLD contrast, spatial and temporal resolution, BOLD sensitivity, localization and spatial specificity, technical challenges as well as an outlook on future developments are given. It is shown that the main technical challenges of performing BOLD fMRI at high magnetic field strengths—namely development of array coils, imaging sequences and parallel imaging reconstruction—have been solved successfully. The combination of these developments has lead to the availability of high-resolution BOLD fMRI protocols that are able to cover the whole brain with a repetition time (TR) shorter than 3 s. The structural information available from these high-resolution fMRI images itself is already very detailed, which helps to co-localize structure and function. Potential future applications include whole-brain connectivity analysis on a laminar resolution and single subject examinations. Full article
(This article belongs to the Special Issue High Field Magnetic Resonance Methods and Materials)

Other

Jump to: Research, Review

Open AccessCorrection Correction: Koush, Y.; Elliott, M.A. and Mathiak, K. Single Voxel Proton Spectroscopy for Neurofeedback at 7 Tesla. Materials 2011, 4, 1548–1563
Materials 2011, 4(11), 2057-2060; doi:10.3390/ma4112057
Received: 17 November 2011 / Accepted: 24 November 2011 / Published: 24 November 2011
Cited by 1 | PDF Full-text (167 KB) | HTML Full-text | XML Full-text
Abstract
In the published manuscript “Koush, Y.; Elliott, M.A. and Mathiak, K. Single Voxel Proton Spectroscopy for Neurofeedback at 7 Tesla. Materials 2011, 4, 1548-1563”, all estimates of T2* from the single voxel spectroscopy data were overestimated by a factor of [...] Read more.
In the published manuscript “Koush, Y.; Elliott, M.A. and Mathiak, K. Single Voxel Proton Spectroscopy for Neurofeedback at 7 Tesla. Materials 2011, 4, 1548-1563”, all estimates of T2* from the single voxel spectroscopy data were overestimated by a factor of 4. This was due to an incorrectly assumed four-fold lower sampling rate. The focus of the manuscript is on the relative changes in T2* with BOLD activation, and not on the absolute values. Therefore, none of the central claims are affected, but the scaling in most of the figures needs to be adjusted. The authors would like to make the following corrections to their published paper. [...] Full article
(This article belongs to the Special Issue High Field Magnetic Resonance Methods and Materials)

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