Abstract:
:Parallel excitation using multiple transmit channels has emerged as an effective method to shorten multidimensional spatially selective radiofrequency (RF) pulses, which have a number of important applications, including B1 field inhomogeneity correction in high-field MRI. The specific absorption rate (SAR) is a primary concern in high-field MRI, where wavelength effects can lead to local peaks in SAR. In parallel excitation, the subjects are exposed to RF pulses from multiple coils, which makes the SAR problem more complex to analyze, yet potentially enables greater freedom in designing RF pulses with lower SAR. Parallel-excitation techniques typically employ either Cartesian or constant-density (CD) spiral trajectories. In this article, variable-density (VD) spiral trajectories are explored as a means for SAR reduction in parallel-excitation pulse design. Numerical simulations were conducted to study the effects of CD and VD spirals on parallel excitation. Specifically, the electromagnetic fields of a four-channel transmit head coil with a three-dimensional head model at 4.7 T were simulated using a finite-difference time domain method. The parallel RF pulses were designed and the resulting excitation patterns were generated using a Bloch simulator. The SAR distributions due to CD and VD spirals were evaluated quantitatively. The simulation results show that, for the same pulse duration, parallel excitation with VD spirals can achieve a lower SAR compared to CD spirals for parallel excitation. VD spirals also resulted in reduced artifact power in the excitation patterns. This gain came with slight, but noticeable, degrading of the spatial resolution of the resulting excitation patterns.
journal_name
Magn Reson Imagingjournal_title
Magnetic resonance imagingauthors
Liu Y,Feng K,McDougall MP,Wright SM,Ji Jdoi
10.1016/j.mri.2008.02.003subject
Has Abstractpub_date
2008-10-01 00:00:00pages
1122-32issue
8eissn
0730-725Xissn
1873-5894pii
S0730-725X(08)00035-0journal_volume
26pub_type
杂志文章abstract:OBJECTIVE:The pathological changes in Parkinson disease begin in the brainstem; reach the limbic system and ultimately spread to the cerebral cortex. In Parkinson disease (PD) patients, we evaluated the alteration of cingulate fibers, which comprise part of the limbic system, by using diffusional kurtosis imaging (DKI)...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2013.06.009
更新日期:2013-11-01 00:00:00
abstract::Localized high-resolution diffusion tensor images (DTI) from the midbrain were obtained using reduced field-of-view (rFOV) methods combined with SENSE parallel imaging and single-shot echo planar (EPI) acquisitions at 7T. This combination aimed to diminish sensitivities of DTI to motion, susceptibility variations, and...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2013.01.013
更新日期:2013-07-01 00:00:00
abstract::Manganese-dipyridoxal diphosphate (Mn-DPDP) is a liver-selective contrast agent selectively taken up by the hepatocytes. Because of the analogy of structure with pyridoxine (vitamin B6), it was previously suggested that this compound can be selectively taken up by the facilitated transport of vitamers B6. To understan...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/s0730-725x(96)00140-3
更新日期:1996-01-01 00:00:00
abstract:PURPOSE:To evaluate whether semi-quantitative analysis of high temporal resolution dynamic contrast-enhanced MRI (DCE-MRI) acquired early in treatment can predict the response of locally advanced breast cancer (LABC) to neoadjuvant chemotherapy (NAC). MATERIALS AND METHODS:As part of an IRB-approved prospective study,...
journal_title:Magnetic resonance imaging
pub_type: 临床试验,杂志文章
doi:10.1016/j.mri.2013.07.002
更新日期:2013-11-01 00:00:00
abstract::In this manuscript, fast and clinically feasible model-based bootstrapping algorithms using a geometrically constrained two-tensor diffusion model are employed for estimating uncertainty in fiber orientation. A Monte-Carlo-based tensor morphology voxel classification algorithm is initially applied using single-tensor ...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2012.07.004
更新日期:2013-02-01 00:00:00
abstract:OBJECTIVE:To characterize capillary perfusion and tissue diffusion changes in transplant renal artery stenosis (TRAS) with diffusion-weighted imaging (DWI). MATERIALS & METHODS:We retrospectively identified 30 patients with non-contrast enhanced magnetic resonance angiography-proven TRAS. Another 20 kidney transplant ...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2019.05.007
更新日期:2019-07-01 00:00:00
abstract::Using both quantitative computer-assisted analysis and visual estimation the MR imaging response of brain metastases to whole-brain radiotherapy (WBRT) was prospectively studied in 49 patients. Compared to the computer-assisted analysis, the precision of the visual estimation (by two readers in conference) of tumor re...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/s0730-725x(96)00024-0
更新日期:1997-01-01 00:00:00
abstract::Open-configuration magnetic resonance imaging (MRI) systems are becoming increasingly desirable for musculoskeletal imaging and image-guided radiotherapy because of their non-claustrophobic configuration. However, geometric image distortion in large fields-of-view (FOV) due to field inhomogeneity and gradient nonlinea...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2014.02.007
更新日期:2014-07-01 00:00:00
abstract::Various analogs of NMR and MRI are now technically possible in optics; specifically, high-resolution laser-pulse shaping and complex pulse sequence generation with well-defined phase shifts has been demonstrated. Here we summarize this technology and discuss the potential for these methods to enhance optical functiona...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2003.08.024
更新日期:2003-12-01 00:00:00
abstract::In the longitudinal study of multiple sclerosis (MS) lesions, varying position of the patient inside the MRI scanner is one of the major sources of assessment errors. We propose to use analytical indices that are invariant to spatial orientation to describe the lesions, rather than focus on patient repositioning or im...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2004.01.053
更新日期:2004-07-01 00:00:00
abstract::Combining electrical stimulation with fMRI (esfMRI) has proven to be an important tool to study the global effects of electrical stimulation on neural networks in the brain. Here we extend our previous studies to stimulating the upper superior temporal sulcus (STS) in the anesthetized monkey. Our results show that sti...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2011.04.005
更新日期:2011-12-01 00:00:00
abstract::Magnetic field inhomogeneities like eddy current-related gradient fields cause geometric distortions in echo-planar imaging (EPI). This in particular affects diffusion-weighted imaging where these distortions vary with the direction of the diffusion weighting and hamper the accurate determination of diffusion paramete...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2009.12.004
更新日期:2010-04-01 00:00:00
abstract::The general aims of functional brain magnetic resonance imaging (fMRI) studies are to ascertain which areas of the brain are activated during a specific task, the extent of this activation, whether different groups of subjects demonstrate different patterns of activation, and how these groups behave in different tasks...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/s0730-725x(97)00278-6
更新日期:1998-04-01 00:00:00
abstract::The effects of varying the inversion or excitation RF pulse flip angles on image contrast and imaging time have been investigated in IR imaging theoretically, with phantoms and with normal volunteers. Signal intensity in an IR pulse sequence as a function of excitation, inversion and refocusing pulse flip angles was c...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/0730-725x(92)90481-e
更新日期:1992-01-01 00:00:00
abstract:BACKGROUND AND PURPOSE:Diffusion MRI characteristics have been used as biomarkers to guide prognosis in cerebral pathologies including brain metastases. The measurement of ADC is often described poorly in clinical and research studies with little detail given to the practical considerations of where to place ROIs, whic...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2013.12.010
更新日期:2014-04-01 00:00:00
abstract:OBJECTIVE:Our purpose was to evaluate imaging findings of breast cancers according to the dominant stroma type by using kinetic curve analysis and model-based perfusion parameters from dynamic contrast-enhanced magnetic resonance imaging. METHODS:From March 2011 to September 2011, 64 cancers in 64 patients were includ...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2015.07.010
更新日期:2016-01-01 00:00:00
abstract::Conditions for generation of polarized RF fields in cylindrical symmetry by high order coils are presented. Whole body NMR transmitters utilizing this principle would require a current control on a certain number of loops. In the present design this is obtained by feeding each loop by an appropriate linear combination...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/0730-725x(88)90398-0
更新日期:1988-05-01 00:00:00
abstract:PURPOSE:To develop a free-running framework for 3D isotropic simultaneous myocardial T1/T2 mapping and cine imaging. METHODS:Continuous data acquisition with 3D golden angle radial trajectory is used in conjunction with T2 preparation of varying echo times and inversion recovery (IR) pulses to enable simultaneous myoc...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2019.08.008
更新日期:2019-11-01 00:00:00
abstract:PURPOSE:To investigate the alterations in water-fat (W-F) ratio of the normal breast tissue of female volunteers as a function of the histological phases of the menstrual cycle. METHODS:Image-guided volume localized in vivo proton ((1)H) magnetic resonance spectroscopy (MRS) at 1.5 T was carried out in the para-areola...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2009.01.004
更新日期:2009-07-01 00:00:00
abstract::The purpose of the study was to determine whether diffusion-weighted magnetic resonance imaging (DWI) could identify focal lesions that develop in ischemia-sensitive cerebral tissues during reperfusion following global brain ischemia. Localized 1H-Magnetic Resonance Spectroscopy (1H-MRS) measurements were also obtaine...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/0730-725x(96)00094-x
更新日期:1996-01-01 00:00:00
abstract::We retrospectively compared the diagnostic accuracy of abdominal ultrasound (US), computed tomography (CT), and magnetic resonance imaging (MRI) studies performed on the same individual to determine the relative performance of these modalities in the evaluation of disease processes, arising from different intra-abdomi...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2003.01.001
更新日期:2004-01-01 00:00:00
abstract::We used magnetic resonance imaging (MRI) and water-suppressed proton MR spectroscopic imaging (1H MRSI) to study the effects of human immunodeficiency virus (HIV) infection on the brain. Our recent in vivo finding of lower N-acetylaspartate (NAA), a putative marker of neurons, in the supraventricular brain of cognitiv...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/0730-725x(94)92460-0
更新日期:1994-01-01 00:00:00
abstract::Rhizomelic chondrodysplasia punctata is a member of genetic peroxisomal disorders. Delayed myelination, which is probably related to the inadequacy of plasmalogens biosynthesis, is an important feature of this disorder. Direct assessment of neuropathologic aspects of RCDP syndrome such as neuronal degeneration and del...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/s0730-725x(02)00625-2
更新日期:2003-01-01 00:00:00
abstract:PURPOSE:This study aims to develop and evaluate a robust conductivity imaging method that combines total variation and wavelet regularization to enhance the accuracy of conductivity maps. THEORY AND METHODS:The proposed approach is based on a gradient-based method. The central equation is derived from Maxwell's equati...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2020.02.015
更新日期:2020-06-01 00:00:00
abstract::More than a dozen Nuclear Magnetic Resonance (NMR) imaging methods have been described using different radio-frequency pulse sequences, magnetic field gradient variations, and data processing. In order to have a theoretical understanding in the most general case, we have conceived a computer program for the simulation...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/0730-725x(84)90065-1
更新日期:1984-01-01 00:00:00
abstract: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...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2018.08.018
更新日期:2019-01-01 00:00:00
abstract::The aim of this study was to establish a rapid method for in vivo quantification of a large range of flow velocities using phase information. A basic gradient-echo sequence was constructed, in which flow was encoded along the slice selection direction by variation of the amplitude of a bipolar gradient without changes...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/0730-725x(89)90535-3
更新日期:1989-11-01 00:00:00
abstract:PURPOSE:Visual review of individual spectra in magnetic resonance spectroscopic imaging (MRSI) data benefits from the application of spectral smoothing; however, if this processing step is applied prior to spectral analysis this can impact the accuracy of the quantitation. This study aims to analyze the effect of spect...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2020.04.013
更新日期:2020-07-01 00:00:00
abstract::Myelin water fraction (MWF) images in brain tend to be spatially noisy with unknown or no apparent spatial patterns structure, so values are therefore typically averaged over large white matter (WM) volumes. We investigated the existence of an inherent spatial structure in MWF maps and explored the benefits of examini...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2019.09.012
更新日期:2020-04-01 00:00:00
abstract::Functional MR imaging of the alert, behaving monkey is being used more and more often to detect activation patterns and guide electrophysiological research investigating the neural basis of behavior. Several labs have reported fMRI data from the awake monkey, but none of them has studied and systematically corrected t...
journal_title:Magnetic resonance imaging
pub_type: 杂志文章
doi:10.1016/j.mri.2007.03.002
更新日期:2007-07-01 00:00:00