共查询到20条相似文献,搜索用时 12 毫秒
1.
Spin‐echo magnetic resonance spectroscopic imaging at 7 T with frequency‐modulated refocusing pulses
He Zhu Brian J. Soher Ronald Ouwerkerk Michael Schär Peter B. Barker 《Magnetic resonance in medicine》2013,69(5):1217-1225
Two approaches to high‐resolution SENSE‐encoded magnetic resonance spectroscopic imaging (MRSI) of the human brain at 7 Tesla (T) with whole‐slice coverage are described. Both sequences use high‐bandwidth radiofrequency pulses to reduce chemical shift displacement artifacts, SENSE‐encoding to reduce scan time, and dual‐band water and lipid suppression optimized for 7 T. Simultaneous B0 and transmit B1 mapping was also used for both sequences to optimize field homogeneity using high‐order shimming and determine optimum radiofrequency transmit level, respectively. One sequence (“Hahn‐MRSI”) used reduced flip angle (90°) refocusing pulses for lower radiofrequency power deposition, while the other sequence used adiabatic fast passage refocusing pulses for improved sensitivity and reduced signal dependence on the transmit‐B1 level. In four normal subjects, adiabatic fast passage‐MRSI showed a signal‐to‐noise ratio improvement of 3.2 ± 0.5 compared to Hahn‐MRSI at the same spatial resolution, pulse repetition time, echo time, and SENSE‐acceleration factor. An interleaved two‐slice Hahn‐MRSI sequence is also demonstrated to be experimentally feasible. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc. 相似文献
2.
Archie Chu Jeffry R Alger Gregory J Moore Stefan Posse 《Magnetic resonance in medicine》2003,49(5):817-821
A highly effective outer volume suppression (OVS) technique, termed spatially selective echo dephasing (SSED), which employs gradient dephasing of spatially selective spin echoes, is introduced. SSED, which is relatively insensitive to T(1) dispersion among lipid signals and B(1) inhomogeneity, was integrated with very high spatial resolution 2D proton echo-planar spectroscopic imaging (PEPSI) to assess residual lipid bleeding into cortical regions in the human brain. The method was optimized to minimize signal refocusing of secondary spin-echoes in areas of overlapping suppression slices. A comparison of spatial presaturation with single or double SSED, and with combined presaturation and SSED shows that the latter method has superior performance with spatially uniform lipid suppression factors in excess of 70. Metabolite mapping (choline, creatine, and NAA) with a 64 x 64 spatial matrix and 0.3 cm(3) voxels in close proximity to peripheral lipid regions was demonstrated at 1.5 T with a scan time of 32 min using the standard head coil. 相似文献
3.
A novel, noninvasive magnetic resonance imaging-based method for measuring changes in venous cerebral blood volume (CBV(v)) is presented. Venous refocusing for volume estimation (VERVE) exploits the dependency of the spin-spin relaxation rate of deoxygenated blood on the refocusing interval. Interleaved CPMG EPI acquisitions following a train of either tightly or sparsely spaced hard refocusing pulses (every 3.7 or 30 msec, respectively) at matched echo time were used to isolate the blood signal while minimizing the intravascular blood oxygenation level dependent (BOLD) signal contribution. The technique was employed to determine the steady-state increase in the CBV(v) in the visual cortex (VC) in seven healthy adult volunteers during flickering checkerboard photic stimulation. A functional activation model and a set of previously collected in vitro human whole blood relaxometry data were used to evaluate the intravascular BOLD effect on the VERVE signal. The average VC venous blood volume change was estimated to be 16 +/- 2%. This method has the potential to provide efficient and continuous monitoring of venous cerebral blood volume, thereby enabling further exploration of the mechanism underlying BOLD signal changes upon physiologic, pathophysiologic, and pharmacologic perturbations. 相似文献
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Fast method for brain image segmentation: application to proton magnetic resonance spectroscopic imaging. 总被引:1,自引:0,他引:1
David Bonekamp Alena Horská Michael A Jacobs Atilla Arslanoglu Peter B Barker 《Magnetic resonance in medicine》2005,54(5):1268-1272
The interpretation of brain metabolite concentrations measured by quantitative proton magnetic resonance spectroscopic imaging (MRSI) is assisted by knowledge of the percentage of gray matter (GM), white matter (WM), and cerebrospinal fluid (CSF) within each MRSI voxel. Usually, this information is determined from T(1)-weighted magnetic resonance images (MRI) that have a much higher spatial resolution than the MRSI data. While this approach works well, it is time-consuming. In this article, a rapid data acquisition and analysis procedure for image segmentation is described, which is based on collection of several, thick slice, fast spin echo images (FSE) of different contrast. Tissue segmentation is performed with linear "Eigenimage" filtering and normalization. The method was compared to standard segmentation techniques using high-resolution 3D T(1)-weighted MRI in five subjects. Excellent correlation between the two techniques was obtained, with voxel-wise regression analysis giving GM: R2 = 0.893 +/- 0.098, WM: R2 = 0.892 +/- 0.089, ln(CSF): R2 = 0.831 +/- 0.082). Test-retest analysis in one individual yielded an excellent agreement of measurements with R2 higher than 0.926 in all three tissue classes. Application of FSE/EI segmentation to a sample proton MRSI dataset yielded results similar to prior publications. It is concluded that FSE imaging in conjunction with Eigenimage analysis is a rapid and reliable way of segmenting brain tissue for application to proton MRSI. 相似文献
6.
Minimum-norm reconstruction for sensitivity-encoded magnetic resonance spectroscopic imaging. 总被引:1,自引:0,他引:1
Javier Sánchez-González Jeffrey Tsao Ulrike Dydak Manuel Desco Peter Boesiger Klaas Paul Pruessmann 《Magnetic resonance in medicine》2006,55(2):287-295
In this work we propose minimum-norm reconstruction as a means to enhance the spatial response behavior in parallel spectroscopic MRI. By directly optimizing the shape of the spatial response function (SRF), the new method accounts for coil sensitivity variation across individual voxels and their side lobes. In this fashion, it mitigates the signal contamination and side-lobe aliasing, to which previous techniques are susceptible at low resolution. Although the computational burden is higher, minimum-norm reconstruction is shown to be feasible using an iterative algorithm. Benefits in terms of SRF shape and artifact suppression are demonstrated. 相似文献
7.
Manel Martínez‐Ramón Ascensión Gallardo‐Antolín Jesús Cid‐Sueiro Gregory L. Heileman Kaung‐Ti Yung Weili Zheng Chenguang Zhao Stefan Posse 《Magnetic resonance in medicine》2010,63(3):592-600
Spatial suppression of peripheral regions (outer volume suppression) is used in MR spectroscopic imaging to reduce contamination from strong lipid and water signals. The manual placement of outer volume suppression slices requires significant operator interaction, which is time consuming and introduces variability in volume coverage. Placing a large number of outer volume saturation bands for volumetric MR spectroscopic imaging studies is particularly challenging and time consuming and becomes unmanageable as the number of suppression bands increases. In this study, a method is presented that automatically segments a high‐resolution MR image in order to identify the peripheral lipid‐containing regions. This method computes an optimized placement of suppression bands in three dimensions and is based on the maximization of a criterion function. This criterion function maximizes coverage of peripheral lipid‐containing areas and minimizes suppression of cortical brain regions and regions outside of the head. Computer simulation demonstrates automatic placement of 16 suppression slices to form a convex hull that covers peripheral lipid‐containing regions above the base of the brain. In vivo metabolite mapping obtained with short echo time proton‐echo‐planar spectroscopic imaging shows that the automatic method yields a placement of suppression slices that is very similar to that of a skilled human operator in terms of lipid suppression and usable brain voxels. Magn Reson Med 63:592–600, 2010. © 2010 Wiley‐Liss, Inc. 相似文献
8.
Superparamagnetic iron oxide nanoparticles produce changes in the surrounding microscopic magnetic field. A method for generating contrast based on the application of an adiabatic preparation pulse and the failure of the adiabatic condition surrounding the nanoparticles is introduced in this article. Images were obtained in the presence and absence of an adiabatic preparation pulse and the difference was obtained. With the use of an adiabatic full passage pulse, the contrast in the difference image depends linearly on iron concentration up to 1 mM. The use of an adiabatic zero passage pulse resulted in higher sensitivity to nanoparticles compared to the adiabatic full passage, while maintaining linear concentration dependence to 0.1 mM. This technique was shown to be insensitive to magnetization transfer and B(0) inhomogeneity. With its linearity with iron concentration and insensitivity to changes in the main magnetic field, the new method is well suited for quantitative iron oxide nanoparticle imaging. 相似文献
9.
A A Schricker J M Pauly J Kurhanewicz M G Swanson D B Vigneron 《Magnetic resonance in medicine》2001,46(6):1079-1087
Although MR spectroscopic imaging (MRSI) of the prostate has demonstrated clinical utility for the staging and monitoring of cancer extent, current acquisition methods are often inadequate in several aspects. Conventional 180 degrees pulses can suffer from chemical shift misregistration, and have high peak-power requirements that can exceed hardware limits in many prostate MRSI studies. Optimal water and lipid suppression are also critical to obtain interpretable spectra. While complete suppression of the periprostatic lipid resonance is desired, controlled partial suppression of water can provide a valuable phase and frequency reference for data analysis and an assessment of experimental success in cases in which all other resonances are undetectable following treatment. In this study, new spectral-spatial RF pulses were developed to negate chemical shift misregistration errors and to provide dualband excitation with partial excitation of the water resonance and full excitation of the metabolites of interest. Optimal phase modulation was also included in the pulse design to provide 40% reduction in peak RF power. Patient studies using the new pulses demonstrated both feasibility and clear benefits in the reliability and applicability of prostate cancer MRSI. 相似文献
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Flexible proton 3D MR spectroscopic imaging of the prostate with low‐power adiabatic pulses for volume selection and spiral readout
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Isabell K. Steinseifer Bart W.J. Philips Borjan Gagoski Elisabeth Weiland Tom W. J. Scheenen Arend Heerschap 《Magnetic resonance in medicine》2017,77(3):928-935
12.
Christine I. Haupt Andreas P. Kiefer Andrew A. Maudsley 《Magnetic resonance in medicine》1998,39(5):749-753
A motion-detection method is described that is specifically suited for MR spectroscopic imaging (MRSI) studies. Information on in-plane rotation and translation of the subject was obtained using external spatial reference markers that are uniquely identified via their chemical shift. The marker locations were obtained directly from the acquired data at each encoding step, and no additional data acquisition was required. This method was applied to brain 1H MRSI studies that include subcutaneous lipid signals, which otherwise result in enhanced sensitivity to subject motion. 相似文献
13.
Improved volume selective 1H MR spectroscopic imaging of the prostate with gradient offset independent adiabaticity pulses at 3 tesla
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Isabell K. Steinseifer Jack J.A. van Asten Elisabeth Weiland Tom W.J. Scheenen Marnix C. Maas Arend Heerschap 《Magnetic resonance in medicine》2015,74(4):915-924
14.
Andrew A. Maudsley G. B. Matson J. W. Hugg M. W. Weiner 《Magnetic resonance in medicine》1994,31(6):645-651
The effect of different spatial-encoding (k-space) sampling distributions are evaluated for magnetic resonance spectroscopic imaging (MRSI) using Fourier reconstruction. Previously, most MRSI studies have used square or cubic k-space functions, symmetrically distributed. These studies examine the conventional k-space distribution with spherical distribution, and 1/2 k-space acquisition, using computer simulation studies of the MRSI acquisition for three spatial dimensions and experimental results. Results compare the spatial response function, Gibbs ringing effects, and signal contamination for different spatial-encoding distribution functions. Results indicate that spherical encoding, in comparison with cubic encoding, results in a modest improvement of the re sponse function with approximately equivalent spatial resolution for the same acquisition time. For spin-echo acquired data, reduced acquisition times can readily be obtained using 1/2 k-space methods, with a concomitant reduction in signal to noise ratio. 相似文献
15.
Spiral k-space magnetic resonance spectroscopic imaging (MRSI) requires high performance from gradient hardware systems. During the readout phase, oscillating gradients are continuously played out, which can cause undesired effects. These effects on the quality of SI data are non-intuitive because of their time-varying nature. In this work we describe the effects of undesirable gradient performance on SI. Measurements of the true readout trajectories were performed and the results were then used in the reconstruction process. The effects of these imperfections resulted in a spatially and spectrally varying amplitude and frequency modulation. The use of the measured trajectories in the reconstruction process yielded an up to 20% increase in signal amplitude recovery. 相似文献
16.
A new method for the simultaneous suppression of water and lipid resonances using a series of dual‐band frequency‐selective radiofrequency (RF) pulses with associated dephasing gradients is presented. By optimizing the nutation angles of the individual pulses, the water and lipid suppression is made insensitive to a range of both T1‐relaxation times and B1 inhomogeneities. The method consists only of preparatory RF pulses and thus can be combined with a wide variety of MRSI schemes including both long and short TE studies. Simulations yield suppression factors, in the presence of ±20% B1 inhomogeneity, on the order of 100 for lipid peaks with three different T1s (300 ms, 310 ms, and 360 ms), and water peaks with T1s ranging from 0.8 s to 4 s. Excellent in vivo study performance is demonstrated using a 3 Tesla volumetric proton spectroscopic imaging (1H‐MRSI) sequence for measuring the primary brain metabolites peaks of choline (Cho), creatine (Cr), and N‐acetyl aspartate (NAA). Magn Reson Med 61:462–466, 2009. © 2009 Wiley‐Liss, Inc. 相似文献
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Charles H Cunningham Daniel B Vigneron Albert P Chen Duan Xu Sarah J Nelson Ralph E Hurd Douglas A Kelley John M Pauly 《Magnetic resonance in medicine》2005,54(5):1286-1289
The spatial resolution of conventional magnetic resonance spectroscopic imaging-(MRSI) is typically coarse, mainly due to SNR limitations. The increased signal available with higher field scanners and new array coils now permits higher spatial resolution, but conventional chemical shift imaging (phase encoding) limits the spatial coverage possible in a patient-acceptable acquisition time. The "flyback" echo-planar trajectory is particularly insensitive to errors and provides data that are simple to process. In this study, high-efficiency gradient waveforms for flyback echo-planar MRSI were designed and implemented. Normal volunteer studies at 3 T showed the feasibility of acquiring high spatial resolution with large coverage in a short scan time (2048 voxels in 2.3 min and 4096 voxels in 8.5 min). The trajectories were insensitive to errors in timing and require only a modest (10 to 30%) penalty in SNR relative to conventional phase encoding using the same acquisition time. 相似文献
19.
Unaliasing lipid contamination for MR spectroscopic imaging of gliomas at 3T using sensitivity encoding (SENSE). 总被引:1,自引:0,他引:1
Esin Ozturk-Isik Jason C Crane Soonmee Cha Susan M Chang Mitchel S Berger Sarah J Nelson 《Magnetic resonance in medicine》2006,55(5):1164-1169
3D magnetic resonance spectroscopic imaging (MRSI) has been successfully employed to extract information about brain tumor metabolism, such as cell membrane breakdown, cellular energetics, and neuronal integrity, through its ability to differentiate signals coming from choline (Cho), creatine (Cr), and N-acetyl aspartate (NAA) molecules. The additional presence of lipids within subregions of the tumor may indicate cellular membrane breakdown due to cell death. Another potential source of lipids is subcutaneous fat, which may be excited with point-resolved spectroscopy (PRESS) volume selection and aliased into the spectral field of view (FOV) due to the chemical shift artifact and the low bandwidth of the selection pulses. The purpose of our study was to employ a postprocessing method for unaliasing lipid resonances originating from in-slice subcutaneous lipids from the 3D MRSI of gliomas at 3T, using an eight-channel phased-array coil and sensitivity encoding (SENSE). 相似文献
20.
Charles H Cunningham Daniel B Vigneron Malgorzata Marjanska Albert P Chen Duan Xu Ralph E Hurd John Kurhanewicz Michael Garwood John M Pauly 《Magnetic resonance in medicine》2005,53(5):1033-1039
Magnetic resonance spectroscopic imaging (MRSI) has proven to be a powerful tool for the metabolic characterization of prostate cancer in patients before and following therapy. The metabolites that are of particular interest are citrate and choline because an increased choline-to-citrate ratio can be used as a marker for cancer. High-field systems offer the advantage of improved spectral resolution as well as increased magnetization. Initial attempts at extending MRSI methods to 3 T have been confounded by the J-modulation of the citrate resonances. A new pulse sequence is presented that controls the J-modulation of citrate at 3 T such that citrate is upright, with high amplitude, at a practical echo time. The design of short (14 ms) spectral-spatial refocusing pulses and trains of nonselective refocusing pulses are described. Phantom studies and simulations showed that upright citrate with negligible sidebands is observed at an echo time of 85 ms. Studies in a human subject verified that this behavior is reproduced in vivo and demonstrated that the water and lipid suppression of the new pulse sequence are sufficient for application in prostate cancer patients. 相似文献